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Quantum
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New method for putting quantum correlations to the test
https://www.sciencedaily.com/releases/2021/04/210413121005.htm
Quantum Computers News  ScienceDaily
urn:uuid:902bb03c78ac0a525adb228fcf8f0ec9
Tue, 13 Apr 2021 16:10:05 +0000
An international team of physicists has identified a new technique for testing the quality of quantum correlations. Quantum computers run their algorithms on large quantum systems by creating quantum correlations across all of them. It is important to verify the quantum correlations achieved are of the desired quality. However, carrying out checks is resourceintensive so the team has proposed a new technique that significantly reduces the number of measurements while increasing the resilience against noise.

A molecule that responds to light
https://www.sciencedaily.com/releases/2021/04/210413110623.htm
Quantum Computers News  ScienceDaily
urn:uuid:7734d9ccf184e664c402fa957cddc3b7
Tue, 13 Apr 2021 15:06:23 +0000
Light can be used to operate quantum information processing systems, e.g. quantum computers, quickly and efficiently. Researchers have now significantly advanced the development of moleculebased materials suitable for use as lightaddressable fundamental quantum units. They have demonstrated for the first time the possibility of addressing nuclear spin levels of a molecular complex of europium(III) rareearth ions with light.

NVIDIA Announces SDK for Quantum Simulation on GPUs
https://quantumcomputingreport.com/nvidiaannouncessdkforquantumsimulationongpus/
Quantum Computing Report
urn:uuid:d6ccc396b205929da24d3123a5717585
Mon, 12 Apr 2021 18:56:13 +0000
<p>One very useful tools for those wishing to develop quantum programs is a classical computing based simulator that can demonstrate how a quantum computer would process the program. Although the drawback of this approach is that it is limited to the number of qubits the classical computer can simulate, but it has the advantage is [...]</p>
<p>The post <a rel="nofollow" href="https://quantumcomputingreport.com/nvidiaannouncessdkforquantumsimulationongpus/">NVIDIA Announces SDK for Quantum Simulation on GPUs</a> appeared first on <a rel="nofollow" href="https://quantumcomputingreport.com">Quantum Computing Report</a>.</p>
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dougfinke

Keysight Technologies Partners with Women in Quantum to Create a Mentoring Program and also Provides Support for Quantum Education
https://quantumcomputingreport.com/keysighttechnologiespartnerswithwomeninquantumtocreateamentoringprogramandprovidessupportforquantumeducation/
Quantum Computing Report
urn:uuid:380d3ca9bd38c2be28db9b94e36fe280
Sat, 10 Apr 2021 22:59:57 +0000
<p>You may not recognize the name Keysight Technologies as a participant in the quantum industry. But perhaps you would recognize them if we told you they are a direct descendent of the original HewlettPackard (HP) company that was founded in a garage in Palo Alto, California in 1939. The original HewlettPackage product line consisted of [...]</p>
<p>The post <a rel="nofollow" href="https://quantumcomputingreport.com/keysighttechnologiespartnerswithwomeninquantumtocreateamentoringprogramandprovidessupportforquantumeducation/">Keysight Technologies Partners with Women in Quantum to Create a Mentoring Program and also Provides Support for Quantum Education</a> appeared first on <a rel="nofollow" href="https://quantumcomputingreport.com">Quantum Computing Report</a>.</p>
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dougfinke

IBM Releases New Version of Qiskit; Adds Additional Libraries for Natural Sciences and Machine Learning
https://quantumcomputingreport.com/ibmreleasesnewversionofqiskitaddsadditionallibrariesfornaturalsciencesandmachinelearning/
Quantum Computing Report
urn:uuid:0abfe0429170a0810beabcf738fe1f90
Sat, 10 Apr 2021 18:12:06 +0000
<p>IBM has released version 0.25 of its Qiskit quantum programming platform with the biggest changes related to a restructuring and extension of their application libraries. Previously they had introduced a package called Qiskit Aqua that included application modules for chemistry, AI, optimization and finance. Qiskit Aqua was a separate package independent of the core Qiskit [...]</p>
<p>The post <a rel="nofollow" href="https://quantumcomputingreport.com/ibmreleasesnewversionofqiskitaddsadditionallibrariesfornaturalsciencesandmachinelearning/">IBM Releases New Version of Qiskit; Adds Additional Libraries for Natural Sciences and Machine Learning</a> appeared first on <a rel="nofollow" href="https://quantumcomputingreport.com">Quantum Computing Report</a>.</p>
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dougfinke

U.S. Air Force and NSF Award $1 Million in Grants to University of Massachusetts Lowell Professor
https://quantumcomputingreport.com/usairforceandnsfaward1millioningrantstouniversityofmassachusettslowellprofessor/
Quantum Computing Report
urn:uuid:fd1d830ce8d931c844abd692dbdd5321
Fri, 09 Apr 2021 23:45:50 +0000
<p>The grants were made in two separate early career awards to Professor Archana Kamal at the University of Massachusetts Lowell (UMASS Lowell). The first award from the Air Force Office of Scientific Research is for $450,000 over three years to study tunable quantum dissipation. The goal of this research is to correct quantum errors by [...]</p>
<p>The post <a rel="nofollow" href="https://quantumcomputingreport.com/usairforceandnsfaward1millioningrantstouniversityofmassachusettslowellprofessor/">U.S. Air Force and NSF Award $1 Million in Grants to University of Massachusetts Lowell Professor</a> appeared first on <a rel="nofollow" href="https://quantumcomputingreport.com">Quantum Computing Report</a>.</p>
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dougfinke

The Netherlands has Awarded €615 Million ($732M USD) to Quantum Delta NL for Quantum R&D
https://quantumcomputingreport.com/thenetherlandshasawardede615million732musdtoquantumdeltanlforquantumrd/
Quantum Computing Report
urn:uuid:8249541e274b9ab2bb682169b9523056
Fri, 09 Apr 2021 21:30:49 +0000
<p>The award was provided by the Dutch Ministry of Economic Affairs and Climate Policy's National Growth Fund to Quantum Delta NL, a publicprivate partnership of tech companies, government agencies, and all major quantum research centers in the Netherlands. The goals for this award will be to train 2,000 researchers and engineers in quantum technology, scale [...]</p>
<p>The post <a rel="nofollow" href="https://quantumcomputingreport.com/thenetherlandshasawardede615million732musdtoquantumdeltanlforquantumrd/">The Netherlands has Awarded €615 Million ($732M USD) to Quantum Delta NL for Quantum R&D</a> appeared first on <a rel="nofollow" href="https://quantumcomputingreport.com">Quantum Computing Report</a>.</p>
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dougfinke

Just some prizes
https://www.scottaaronson.com/blog/?p=5437
ShtetlOptimized
urn:uuid:51f64cb1a3a69c032e5e273ed5a96437
Fri, 09 Apr 2021 18:15:33 +0000
Oded Goldreich is a theoretical computer scientist at the Weizmann Institute in Rehovot, Israel. He’s best known for helping to lay the rigorous foundations of cryptography in the 1980s, through seminal results like the GoldreichLevin Theorem (every oneway function can be modified to have a hardcore predicate), the GoldreichGoldwasserMicali Theorem (every pseudorandom generator can be […]
<p><a href="https://en.wikipedia.org/wiki/Oded_Goldreich">Oded Goldreich</a> is a theoretical computer scientist at the Weizmann Institute in Rehovot, Israel. He’s best known for helping to lay the rigorous foundations of cryptography in the 1980s, through seminal results like the <a href="https://en.wikipedia.org/wiki/Hardcore_predicate">GoldreichLevin Theorem</a> (every oneway function can be modified to have a hardcore predicate), the <a href="https://people.csail.mit.edu/silvio/Selected%20Scientific%20Papers/Pseudo%20Randomness/How%20To%20Construct%20Random%20Functions.pdf">GoldreichGoldwasserMicali Theorem</a> (every pseudorandom generator can be made into a pseudorandom function), and the <a href="https://www.cs.purdue.edu/homes/hmaji/teaching/Fall%202017/lectures/39.pdf">GoldreichMicaliWigderson protocol</a> for secure multiparty computation. I first met Oded more than 20 years ago, when he lectured at a summer school at the Institute for Advanced Study in Princeton, barefoot and wearing a tank top and what looked like pajama pants. It was a bracing introduction to complexitytheoretic cryptography. Since then, I’ve interacted with Oded from time to time, partly around his <a href="http://www.wisdom.weizmann.ac.il/~oded/onqc.html">firm belief</a> that quantum computing is impossible.</p>
<p>Last month a committee in Israel voted to award Goldreich the <a href="https://en.wikipedia.org/wiki/Israel_Prize">Israel Prize</a> (roughly analogous to the US National Medal of Science), for which I’d say Goldreich had been a plausible candidate for decades. But alas, Yoav Gallant, Netanyahu’s Education Minister, then rather <a href="https://www.jpost.com/israelnews/highcourtrevokesisraelprizeinmathtoprobdsprofessor664538">nongallantly blocked the award</a>, solely because he objected to Goldreich’s farleft political views (and apparently because of various statements Goldreich signed, including in support of a boycott of Ariel University, which is in the West Bank). The case went all the way to the Israeli Supreme Court (!), which <a href="https://www.washingtonpost.com/world/middle_east/israeliacademicwontreceiveprizeaftersigningpetition/2021/04/08/d1e987ca987b11eb8f0a3384cf4fb399_story.html">ruled two days ago</a> in Gallant’s favor: he gets to “delay” the award to investigate the matter further, and in the meantime has apparently sent out invitations for an award ceremony next week that doesn’t include Goldreich. Some are now calling for the other winners to boycott the prize in solidarity until this is righted.</p>
<p>I doubt readers of this blog need convincing that this is a travesty and an embarrassment, a <em><a href="https://en.wiktionary.org/wiki/shanda#:~:text=shanda%20(uncountable),(Jewish)%20shame%3B%20disgrace.">shanda</a></em>, for the Netanyahu government itself. That I disagree with Goldreich’s farleft views (or <em>might</em> disagree, if I knew in any detail what they were) is totally immaterial to that judgment. In my opinion, not even Goldreich’s belief in the impossibility of quantum computers should affect his eligibility for the prize. <img src="https://s.w.org/images/core/emoji/13.0.1/72x72/1f642.png" alt="
Announcements
Complexity
Scott

Engineering researchers visualize the motion of vortices in superfluid turbulence
https://www.sciencedaily.com/releases/2021/04/210408163441.htm
Quantum Computers News  ScienceDaily
urn:uuid:5d5d011071ff01d0dd800aefcb1ffb95
Thu, 08 Apr 2021 20:34:41 +0000
Researchers have managed to visualize the vortex tubes in a quantum fluid, findings that could help researchers better understand turbulence in quantum fluids and beyond.

A breakthrough that enables practical semiconductor spintronics
https://www.sciencedaily.com/releases/2021/04/210408112352.htm
Quantum Computers News  ScienceDaily
urn:uuid:fadae7e9497a84bf55fff6d7d85aff77
Thu, 08 Apr 2021 15:23:52 +0000
It may be possible in the future to use information technology where electron spin is used to store, process and transfer information in quantum computers. It has long been the goal of scientists to be able to use spinbased quantum information technology at room temperature. Researchers have now constructed a semiconductor component in which information can be efficiently exchanged between electron spin and light at room temperature and above.

Duality, a Quantum Startup Accelerator, Launched in Chicago
https://quantumcomputingreport.com/dualityaquantumstartupacceleratorlaunchedinchicago/
Quantum Computing Report
urn:uuid:22978301fd4963ad50ad381d64e79bc2
Thu, 08 Apr 2021 00:16:45 +0000
<p>Duality is a startup accelerator designed to bridge the gap from laboratory to the marketplace. They will offer 12 month programs to selected teams within each yearly cohort that provides entrepreneurial training, business expertise and mentorship, technical expertise, access to stateoftheart facilities, industry exposure and $50,000 in unrestricted funding. It is the first such accelerator [...]</p>
<p>The post <a rel="nofollow" href="https://quantumcomputingreport.com/dualityaquantumstartupacceleratorlaunchedinchicago/">Duality, a Quantum Startup Accelerator, Launched in Chicago</a> appeared first on <a rel="nofollow" href="https://quantumcomputingreport.com">Quantum Computing Report</a>.</p>
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dougfinke

Quantum Xchange Expands their QuantumSafe Encryption Product Line with Phio TXD
https://quantumcomputingreport.com/quantumxchangeexpandstheirquantumsafeencryptionproductlinewithphiotxd/
Quantum Computing Report
urn:uuid:94bf9921501a676bab73b8e41ad49889
Tue, 06 Apr 2021 15:22:26 +0000
<p>We first reported on Quantum Xchange' flagship Phio TX product in October 2019 when they introduced the concept of providing extra security for encryption keys with a separate outofband symmetric key distribution system that is separate from the main data channel. This system can be compatible with other encryption technologies including physicsbased QKD (Quantum Key [...]</p>
<p>The post <a rel="nofollow" href="https://quantumcomputingreport.com/quantumxchangeexpandstheirquantumsafeencryptionproductlinewithphiotxd/">Quantum Xchange Expands their QuantumSafe Encryption Product Line with Phio TXD</a> appeared first on <a rel="nofollow" href="https://quantumcomputingreport.com">Quantum Computing Report</a>.</p>
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dougfinke

New computing algorithms expand the boundaries of a quantum future
https://news.fnal.gov/2021/04/newcomputingalgorithmsexpandtheboundariesofaquantumfuture/
quantum computing – News
urn:uuid:a162479b8818bb1690d3273a5920b8cc
Mon, 05 Apr 2021 12:00:33 +0000
To fully realize the potential of quantum computing, scientists must start with the basics: developing stepbystep procedures, or algorithms, for quantum computers to perform simple tasks. A Fermilab scientist has done just that, announcing two new algorithms that build upon existing work in the field to further diversify the types of problems quantum computers can solve.
<p><a href="https://www.energy.gov/science/doeexplainsquantumcomputing">Quantum computing</a> promises to harness the strange properties of quantum mechanics in machines that will outperform even the most powerful supercomputers of today. But the extent of their application, it turns out, isn’t entirely clear.</p>
<p>To fully realize the potential of quantum computing, scientists must start with the basics: developing stepbystep procedures, or algorithms, for quantum computers to perform simple tasks, like the factoring of a number. These simple algorithms can then be used as building blocks for more complicated calculations.</p>
<p>Prasanth Shyamsundar, a postdoctoral research associate at the Department of Energy’s Fermilab Quantum Institute, has done just that. In a <a href="https://arxiv.org/abs/2102.04975">preprint</a> paper released in February, he announced two new algorithms that build upon existing work in the field to further diversify the types of problems quantum computers can solve.</p>
<p>“There are specific tasks that can be done faster using quantum computers, and I’m interested in understanding what those are,” Shyamsundar said. “These new algorithms perform generic tasks, and I am hoping they will inspire people to design even more algorithms around them.”</p>
<p>Shyamsundar’s quantum algorithms, in particular, are useful when searching for a specific entry in an unsorted collection of data. Consider a toy example: Suppose we have a stack of 100 vinyl records, and we task a computer with finding the one jazz album in the stack.</p>
<p>Classically, a computer would need to examine each individual record and make a yesorno decision about whether it is the album we are searching for, based on a given set of search criteria.</p>
<p>“You have a query, and the computer gives you an output,” Shyamsundar said. “In this case, the query is: Does this record satisfy my set of criteria? And the output is yes or no.”</p>
<p>Finding the record in question could take only a few queries if it is near the top of the stack, or closer to 100 queries if the record is near the bottom. On average, a classical computer would locate the correct record with 50 queries, or half the total number in the stack.</p>
<p>A quantum computer, on the other hand, would locate the jazz album much faster. This is because it has the ability to analyze all of the records at once, using a quantum effect called superposition.</p>
<p>With this property, the number of queries needed to locate the jazz album is only about 10, the square root of the number of records in the stack. This phenomenon is known as quantum speedup and is a result of the unique way quantum computers store information.</p>
<p><strong>The quantum advantage</strong></p>
<p>Classical computers use units of storage called bits to save and analyze data. A bit can be assigned one of two values: 0 or 1.</p>
<p>The quantum version of this is called a qubit. Qubits can be either 0 or 1 as well, but unlike their classical counterparts, they can also be a combination of both values at the same time. This is known as superposition, and allows quantum computers to assess multiple records, or states, simultaneously.</p>
<div id="attachment_259305" style="width: 610px" class="wpcaption aligncenter"><a href="https://news.fnal.gov/wpcontent/uploads/2021/04/quantumvsclassicalbitpinson.jpg"><img ariadescribedby="captionattachment259305" loading="lazy" class="wpimage259305" src="https://news.fnal.gov/wpcontent/uploads/2021/04/quantumvsclassicalbitpinson1024x614.jpg" alt="Qubits can be in a superposition of 0 and 1, while classical bits can be only one or the other. Image: Jerald Pinson" width="600" height="360" srcset="https://news.fnal.gov/wpcontent/uploads/2021/04/quantumvsclassicalbitpinson1024x614.jpg 1024w, https://news.fnal.gov/wpcontent/uploads/2021/04/quantumvsclassicalbitpinson300x180.jpg 300w, https://news.fnal.gov/wpcontent/uploads/2021/04/quantumvsclassicalbitpinson768x461.jpg 768w, https://news.fnal.gov/wpcontent/uploads/2021/04/quantumvsclassicalbitpinson1536x922.jpg 1536w, https://news.fnal.gov/wpcontent/uploads/2021/04/quantumvsclassicalbitpinson2048x1229.jpg 2048w, https://news.fnal.gov/wpcontent/uploads/2021/04/quantumvsclassicalbitpinson470x282.jpg 470w, https://news.fnal.gov/wpcontent/uploads/2021/04/quantumvsclassicalbitpinson640x384.jpg 640w, https://news.fnal.gov/wpcontent/uploads/2021/04/quantumvsclassicalbitpinson400x240.jpg 400w, https://news.fnal.gov/wpcontent/uploads/2021/04/quantumvsclassicalbitpinson150x90.jpg 150w, https://news.fnal.gov/wpcontent/uploads/2021/04/quantumvsclassicalbitpinson450x270.jpg 450w, https://news.fnal.gov/wpcontent/uploads/2021/04/quantumvsclassicalbitpinson180x108.jpg 180w, https://news.fnal.gov/wpcontent/uploads/2021/04/quantumvsclassicalbitpinson620x372.jpg 620w" sizes="(maxwidth: 600px) 100vw, 600px" /></a><p id="captionattachment259305" class="wpcaptiontext">Qubits can be in a superposition of 0 and 1, while classical bits can be only one or the other. Image: Jerald Pinson</p></div>
<p>“If a single qubit can be in a superposition of 0 and 1, that means two qubits can be in a superposition of four possible states,” Shyamsundar said. The number of accessible states grows exponentially with the number of qubits used.</p>
<p>Seems powerful, right? It’s a huge advantage when approaching problems that require extensive computing power. The downside, however, is that superpositions are probabilistic in nature — meaning they won’t yield definite outputs about the individual states themselves.</p>
<p>Think of it like a coin flip. When in the air, the state of the coin is indeterminate; it has a 50% probability of landing either heads or tails. Only when the coin reaches the ground does it settle into a value that can be determined precisely.</p>
<p>Quantum superpositions work in a similar way. They’re a combination of individual states, each with their own probability of showing up when measured.</p>
<p>But the process of measuring won’t necessarily collapse the superposition into the value we are looking for. That depends on the probability associated with the correct state.</p>
<p>“If we create a superposition of records and measure it, we’re not necessarily going to get the right answer,” Shyamsundar said. “It’s just going to give us one of the records.”</p>
<p>To fully capitalize on the speedup quantum computers provide, then, scientists must somehow be able to extract the correct record they are looking for. If they cannot, the advantage over classical computers is lost.</p>
<p><strong>Amplifying the probabilities of correct states</strong></p>
<p>Luckily, scientists developed an algorithm nearly 25 years ago that will perform a series of operations on a superposition to amplify the probabilities of certain individual states and suppress others, depending on a given set of search criteria. That means when it comes time to measure, the superposition will most likely collapse into the state they are searching for.</p>
<p>But the limitation of this algorithm is that it can be applied only to Boolean situations, or ones that can be queried with a yes or no output, like searching for a jazz album in a stack of several records.</p>
<div id="attachment_259164" style="width: 611px" class="wpcaption aligncenter"><a href="https://news.fnal.gov/wpcontent/uploads/2021/04/boolean_illustration.png"><img ariadescribedby="captionattachment259164" loading="lazy" class="wpimage259164" src="https://news.fnal.gov/wpcontent/uploads/2021/04/boolean_illustration1024x407.png" alt="" width="601" height="239" srcset="https://news.fnal.gov/wpcontent/uploads/2021/04/boolean_illustration1024x407.png 1024w, https://news.fnal.gov/wpcontent/uploads/2021/04/boolean_illustration300x119.png 300w, https://news.fnal.gov/wpcontent/uploads/2021/04/boolean_illustration768x305.png 768w, https://news.fnal.gov/wpcontent/uploads/2021/04/boolean_illustration1536x611.png 1536w, https://news.fnal.gov/wpcontent/uploads/2021/04/boolean_illustration2048x814.png 2048w, https://news.fnal.gov/wpcontent/uploads/2021/04/boolean_illustration470x187.png 470w, https://news.fnal.gov/wpcontent/uploads/2021/04/boolean_illustration640x255.png 640w, https://news.fnal.gov/wpcontent/uploads/2021/04/boolean_illustration400x159.png 400w, https://news.fnal.gov/wpcontent/uploads/2021/04/boolean_illustration150x60.png 150w, https://news.fnal.gov/wpcontent/uploads/2021/04/boolean_illustration450x179.png 450w, https://news.fnal.gov/wpcontent/uploads/2021/04/boolean_illustration180x72.png 180w, https://news.fnal.gov/wpcontent/uploads/2021/04/boolean_illustration620x247.png 620w" sizes="(maxwidth: 601px) 100vw, 601px" /></a><p id="captionattachment259164" class="wpcaptiontext">A quantum computer can amplify the probabilities of certain individual records and suppress others, as indicated by the size and color of the disks in the output superposition. Standard techniques are able to assess only Boolean scenarios, or ones that can be answered with a yes or no output. Illustration: Prasanth Shyamsundar</p></div>
<p>Scenarios with nonBoolean outputs present a challenge. Music genres aren’t precisely defined, so a better approach to the jazz record problem might be to ask the computer to rate the albums by how “jazzy” they are. This could look like assigning each record a score on a scale from 1 to 10.</p>
<div id="attachment_259161" style="width: 611px" class="wpcaption aligncenter"><a href="https://news.fnal.gov/wpcontent/uploads/2021/04/nonbooleanillustration.png"><img ariadescribedby="captionattachment259161" loading="lazy" class="wpimage259161" src="https://news.fnal.gov/wpcontent/uploads/2021/04/nonbooleanillustration1024x407.png" alt="New amplification algorithms expand the utility of quantum computers to handle nonBoolean scenarios, allowing for an extended range of values to characterize individual records, such as the scores assigned to each disk in the output superposition above. Illustration: Prasanth Shyamsundar" width="601" height="239" srcset="https://news.fnal.gov/wpcontent/uploads/2021/04/nonbooleanillustration1024x407.png 1024w, https://news.fnal.gov/wpcontent/uploads/2021/04/nonbooleanillustration300x119.png 300w, https://news.fnal.gov/wpcontent/uploads/2021/04/nonbooleanillustration768x305.png 768w, https://news.fnal.gov/wpcontent/uploads/2021/04/nonbooleanillustration1536x611.png 1536w, https://news.fnal.gov/wpcontent/uploads/2021/04/nonbooleanillustration2048x814.png 2048w, https://news.fnal.gov/wpcontent/uploads/2021/04/nonbooleanillustration470x187.png 470w, https://news.fnal.gov/wpcontent/uploads/2021/04/nonbooleanillustration640x255.png 640w, https://news.fnal.gov/wpcontent/uploads/2021/04/nonbooleanillustration400x159.png 400w, https://news.fnal.gov/wpcontent/uploads/2021/04/nonbooleanillustration150x60.png 150w, https://news.fnal.gov/wpcontent/uploads/2021/04/nonbooleanillustration450x179.png 450w, https://news.fnal.gov/wpcontent/uploads/2021/04/nonbooleanillustration180x72.png 180w, https://news.fnal.gov/wpcontent/uploads/2021/04/nonbooleanillustration620x247.png 620w" sizes="(maxwidth: 601px) 100vw, 601px" /></a><p id="captionattachment259161" class="wpcaptiontext">New amplification algorithms expand the utility of quantum computers to handle nonBoolean scenarios, allowing for an extended range of values to characterize individual records, such as the scores assigned to each disk in the output superposition above. Illustration: Prasanth Shyamsundar</p></div>
<p>Previously, scientists would have to convert nonBoolean problems such as this into ones with Boolean outputs.</p>
<p>“You’d set a threshold and say any state below this threshold is bad, and any state above this threshold is good,” Shyamsundar said. In our jazz record example, that would be the equivalent of saying anything rated between 1 and 5 isn’t jazz, while anything between 5 and 10 is.</p>
<p>But Shyamsundar has extended this computation such that a Boolean conversion is no longer necessary. He calls this new technique the nonBoolean quantum amplitude amplification algorithm.</p>
<p>“If a problem requires a yesorno answer, the new algorithm is identical to the previous one,” Shyamsundar said. “But this now becomes open to more tasks; there are a lot of problems that can be solved more naturally in terms of a score rather than a yesorno output.”</p>
<p>A second algorithm introduced in the paper, dubbed the quantum mean estimation algorithm, allows scientists to estimate the average rating of all the records. In other words, it can assess how “jazzy” the stack is as a whole.</p>
<p>Both algorithms do away with having to reduce scenarios into computations with only two types of output, and instead allow for a range of outputs to more accurately characterize information with a quantum speedup over classical computing methods.</p>
<p>Procedures like these may seem primitive and abstract, but they build an essential foundation for more complex and useful tasks in the quantum future. Within physics, the newly introduced algorithms may eventually allow scientists to reach target sensitivities faster in certain experiments. Shyamsundar is also planning to leverage these algorithms for use in quantum machine learning.</p>
<p>And outside the realm of science? The possibilities are yet to be discovered.</p>
<p>“We’re still in the early days of quantum computing,” Shyamsundar said, noting that curiosity often drives innovation. “These algorithms are going to have an impact on how we use quantum computers in the future.”</p>
<p><em>This work is supported by the Department of Energy’s Office of Science Office of High Energy Physics </em><em>QuantISED program</em><em>. </em></p>
<p><em>The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, visit </em><a href="http://science.energy.gov/"><em>science.energy.gov</em></a><em>.</em></p>
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lindseya

The Computational Expressiveness of a Model Train Set: A Paperlet
https://www.scottaaronson.com/blog/?p=5402
ShtetlOptimized
urn:uuid:0ff8dd0124d2a5f6c69a833d1db3aa63
Sun, 04 Apr 2021 18:37:49 +0000
My son Daniel had his fourth birthday a couple weeks ago. For a present, he got an electric train set. (For completeness—and since the details of the train set will be rather important to the post—it’s called “WESPREX Create a Dinosaur Track”, but this is not an ad and I’m not getting a kickback for […]
<p>My son Daniel had his fourth birthday a couple weeks ago. For a present, he got an electric train set. (For completeness—and since the details of the train set will be rather important to the post—it’s called <a href="https://www.amazon.com/DinosaurFlexibleTracksCreateChildren/dp/B07ZDLXSXK">“WESPREX Create a Dinosaur Track”</a>, but this is not an ad and I’m not getting a kickback for it.)</p>
<figure class="wpblockvideo"><video controls src="https://www.scottaaronson.com/yjunctions.MOV"></video></figure>
<p>As you can see, the main feature of this set is a Yshaped junction, which has a flap that can control which direction the train goes. The logic is as follows:</p>
<ul><li>If the train is coming up from the “bottom” of the Y, then it continues to either the left arm or the right arm, depending on where the flap is. It leaves the flap as it was.</li></ul>
<ul><li>If the train is coming down the left or right arms of the Y, then it continues to the bottom of the Y, <em>pushing the flap out of its way if it’s in the way</em>. (Thus, if the train were ever to return to this Yjunction coming up from the bottom, not having passed the junction in the interim, it would necessarily go to the same arm, left or right, that it came down from.)</li></ul>
<p>The train set also comes with bridges and tunnels; thus, there’s no restriction of planarity. Finally, the train set comes with little gadgets that can reverse the train’s direction, sending it back in the direction that it came from:</p>
<figure class="wpblockvideo"><video controls src="https://www.scottaaronson.com/train1.MOV"></video></figure>
<p>These gadgets don’t seem particularly important, though, since we could always replace them if we wanted by a Yjunction together with a loop.</p>
<p>Notice that, at each Yjunction, the position of the flap stores one bit of internal state, and that the train can both “read” and “write” these bits as it moves around. Thus, a question naturally arises: can this train set do any nontrivial computations? If there are <em>n</em> Yjunctions, then can it cycle through exp(<em>n</em>) different states? Could it even solve <strong>PSPACE</strong>complete problems, if we let it run for exponential time? (For a very different example of a modeltrainlike system that, as it turns out, <em>is</em> able to express <strong>PSPACE</strong>complete problems, see <a href="https://arxiv.org/abs/1905.00518">this recent paper</a> by Erik Demaine et al.)</p>
<p>Whatever the answers regarding Daniel’s train set, I knew immediately on watching the thing go that I’d have to write a “paperlet” on the problem and publish it on my blog (no, I don’t inflict such things on journals!). Today’s post constitutes my third “paperlet,” on the general theme of a discrete dynamical system that someone showed me in real life (e.g. in a children’s toy or in biology) having more structure and regularity than one might naïvely expect. My first such paperlet, from 2014, was <a href="https://www.scottaaronson.com/blog/?p=1902">on a 1960s toy called the DigiComp II</a>; my second, from 2016, was <a href="https://www.scottaaronson.com/blog/?p=2862">on DNA strings acted on by recombinase</a> (OK, that one <em>was</em> associated with a <a href="https://science.sciencemag.org/content/353/6297/aad8559.full?ijkey=wzroPPh1eIu9k&keytype=ref&siteid=sci">paper in <em>Science</em></a>, but my combinatorial analysis wasn’t the main point of the paper).</p>
<p>Anyway, after spending an enjoyable evening on the problem of Daniel’s train set, I was able to prove that, alas, the possible behaviors are quite limited (I classified them all), falling far short of computational universality.</p>
<p>If you feel like I’m wasting your time with trivialities (or if you simply enjoy puzzles), then before you read any further, I encourage you to stop and try to prove this for yourself!</p>
<p>Back yet? OK then…</p>
<p><hr></p>
<p><strong>Theorem:</strong> Assume a finite amount of train track. Then after a linear amount of time, the train will necessarily enter a “boring infinite loop”—i.e., an attractor state in which at most two of the flaps keep getting toggled, and the rest of the flaps are fixed in place. In more detail, the attractor must take one of four forms:</p>
<p>I. a line (with reversing gadgets on both ends),<br>II. a simple cycle,<br>III. a “lollipop” (with one reversing gadget and one flap that keeps getting toggled), or<br>IV. a “dumbbell” (with two flaps that keep getting toggled).</p>
<p>In more detail still, there are seven possible topologically distinct trajectories for the train, as shown in the figure below.</p>
<figure class="wpblockimage sizelarge"><a href="https://www.scottaaronson.com/trajectories.png"><img src="https://www.scottaaronson.com/trajectories.png" alt=""/></a></figure>
<p>Here the red paths represent the attractors, where the train loops around and around for an unlimited amount of time, while the blue paths represent “runways” where the train spends a limited amount of time on its way into the attractor. Every degree3 vertex is assumed to have a Yjunction, while every degree1 vertex is assumed to have a reversing gadget, unless (in IIb) the train starts at that vertex and never returns to it.</p>
<p>The proof of the theorem rests on two simple observations.</p>
<p><strong>Observation 1:</strong> While the Yjunctions correspond to vertices of degree 3, there are no vertices of degree 4 or higher. This means that, if the train ever revisits a vertex <em>v</em> (other than the start vertex) for a second time, then there must be some edge <em>e</em> incident to <em>v</em> that it also traverses for a second time immediately afterward.</p>
<p><strong>Observation 2:</strong> Suppose the train traverses some edge <em>e</em>, then goes around a simple cycle (meaning, one where no edges or vertices are reused), and then traverses <em>e</em> again, <em>going in the same direction as the first time</em>. Then from that point forward, the train will just continue around the same simple cycle forever.</p>
<p>The proof of Observation 2 is simply that, if there were any flap that might be in the train’s way as it continued around the simple cycle, then the train would already have pushed it out of the way its <em>first</em> time around the cycle, and nothing that happened thereafter could possibly change the flap’s position.</p>
<p>Using the two observations above, let’s now prove the theorem. Let the train start where it will, and follow it as it traces out a path. Since the graph is finite, at some point some alreadytraversed edge must be traversed a second time. Let <em>e</em> be the first such edge. By Observation 1, this will also be the first time the train’s path intersects itself at all. There are then three cases:</p>
<p><strong>Case 1:</strong> The train traverses <em>e</em> in the same direction as it did the first time. By Observation 2, the train is now stuck in a simple cycle forever after. So the only question is what the train could’ve done <em>before</em> entering the simple cycle. We claim that at most, it could’ve traversed a simple path. For otherwise, we’d contradict the assumption that <em>e</em> was the first edge that the train visited twice on its journey. So the trajectory must have type IIa, IIb, or IIc in the figure.</p>
<p><strong>Case 2:</strong> Immediately after traversing e, the train hits a reversing gadget and traverses <em>e</em> again the other way. In this case, the train will clearly retrace its entire path and then continue past its starting point; the question is what happens next. If it hits another reversing gadget, then the trajectory will have type I in the figure. If it enters a simple cycle and stays in it, then the trajectory will have type IIb in the figure. If, finally, it makes a simple cycle and then <em>exits</em> the cycle, then the trajectory will have type III in the figure. In this last case, the train’s trajectory will form a “lollipop” shape. Note that there must be a Yjunction where the “stick” of the lollipop meets the “candy” (i.e., the simple cycle), with the base of the Y aligned with the stick (since otherwise the train would’ve continued around and around the candy). From this, we deduce that every time the train goes around the candy, it does so in a different orientation (clockwise or counterclockwise) than the time before; and that the train toggles the Yjunction’s flap every time it exits the candy (although not when it enters the candy).</p>
<p><strong>Case 3:</strong> At some point after traversing <em>e</em> in the forward direction (but not <em>immediately</em> after), the train traverses <em>e</em> in the reverse direction. In this case, the broad picture is analogous to Case 2. So far, the train has made a lollipop with a Yjunction connecting the stick to the candy (i.e. cycle), the base of the Y aligned with the stick, and <em>e</em> at the very top of the stick. The question is what happens next. If the train next hits a reversing gadget, the trajectory will have type III in the figure. If it enters a new simple cycle, disjoint from the first cycle, and never leaves it, the trajectory will have type IId in the figure. If it enters a new simple cycle, disjoint from the first cycle, and <em>does</em> leave it, then the trajectory now has a “dumbbell” pattern, type IV in the figure (also shown in the first video). There’s only one last situation to worry about: namely, that the train makes a new cycle that <em>intersects</em> the first cycle, forming a “theta” (θ) shaped trajectory. In this case, there must be a Yjunction at the point where the new cycle bumps into the old cycle. Now, if the base of the Y isn’t part of the old cycle, then the train never could’ve made it all the way around the old cycle in the first place (it would’ve exited the old cycle at this Yjunction), contradiction. If the base of the Y <em>is</em> part of the old cycle, then the flap must have been initially set to let the train make it all the way around the old cycle; when the train then reenters the old cycle, the flap must be moved so that the train will never make it all the way around the old cycle again. So now the train is stuck in a new simple cycle (sharing some edges with the old cycle), and the trajectory has type IIc in the figure.</p>
<p>This completes the proof of the theorem.</p>
<p><hr></p>
<p>We might wonder: <em>why</em> isn’t this model train set capable of universal computation, of AND, OR, and NOT gates—or at any rate, of <em>some</em> computation more interesting than repeatedly toggling one or two flaps? My answer might sound tautological: it’s simply that the logic of the Yjunctions is too limited. Yes, the flaps can get pushed out of the way—that’s a “bit flip”—but every time such a flip happens, it helps to set up a “groove” in which the train just wants to continue around and around forever, not flipping any additional bits, with only the minor complications of the lollipop and dumbbell structures to deal with. Even though my proof of the theorem might’ve seemed like a tedious case analysis, it had this as its unifying message.</p>
<p>It’s interesting to think about what gadgets would need to be added to the train set to <em>make</em> it computationally universal, or at least expressively richer—able, as <a href="https://www.scottaaronson.com/blog/?p=1902">turned out</a> to be the case for the DigiComp II, to express some nontrivial complexity class falling short of <strong>P</strong>. So for example, what if we had degree4 vertices, with little turnstile gadgets? Or multiple trains, which could be synchronized to the millisecond to control how they interacted with each other via the flaps, or which could even crash into each other? I look forward to reading your ideas in the comment section!</p>
<p>For the truth is this: quantum complexity classes, BosonSampling, closed timelike curves, circuit complexity in black holes and AdS/CFT, etc. etc.—all these topics are great, but the same models and problems do get stale after a while. I aspire for my research agenda to chug forward, full steam ahead, into new computational domains.</p>
<p>PS. Happy Easter to those who celebrate!</p>
Complexity
Embarrassing Myself
Procrastination
Scott

How to Make Money with Quantum? Create Art with It!
https://quantumcomputingreport.com/howtomakemoneywithquantumcreateartwithit/
Quantum Computing Report
urn:uuid:0dc322e8eb936dbdfb590591fe554828
Sat, 03 Apr 2021 23:19:30 +0000
<p>Are you using a quantum computer for computational chemistry, finance applications, or optimizations? That's so 2020! Here's an example of a real avantgarde use of quantum technology that combines Quantum Computers, Quantum Neural Nets (QNN), Blockchains and NonFungible Tokens (NFT). A piece of artwork titled "Everettian vibrations" was created using this technology and this is [...]</p>
<p>The post <a rel="nofollow" href="https://quantumcomputingreport.com/howtomakemoneywithquantumcreateartwithit/">How to Make Money with Quantum? Create Art with It!</a> appeared first on <a rel="nofollow" href="https://quantumcomputingreport.com">Quantum Computing Report</a>.</p>
Uncategorized
dougfinke

DARPA Announces Funding Opportunity for Quantum Benchmarking
https://quantumcomputingreport.com/darpaannouncesfundingopportunityforquantumbenchmarking/
Quantum Computing Report
urn:uuid:30fadb9a413cb63bf1e7b0a1395528e7
Sat, 03 Apr 2021 20:38:17 +0000
<p>The U.S. Defense Advanced Research Projects Agency (DARPA) has issued a Broad Agency Announcement (BAA) calling for proposals for research in the area of quantum benchmarking. Proposed research should quantify the longterm utility of quantum computers. In particular, proposed research should center around either (1) the creation of applicationspecific, hardwareagnostic benchmarks for quantum computer utility [...]</p>
<p>The post <a rel="nofollow" href="https://quantumcomputingreport.com/darpaannouncesfundingopportunityforquantumbenchmarking/">DARPA Announces Funding Opportunity for Quantum Benchmarking</a> appeared first on <a rel="nofollow" href="https://quantumcomputingreport.com">Quantum Computing Report</a>.</p>
Uncategorized
dougfinke

Riken, Fujitsu Partner to Develop a Superconducting Quantum Computer
https://quantumcomputingreport.com/rikenfujitsupartnertodevelopasuperconductingquantumcomputer/
Quantum Computing Report
urn:uuid:d7de11c7c72edb1449f137b7a585c7fc
Sat, 03 Apr 2021 19:37:58 +0000
<p>We previously reported on Fujitsu's intent to partner with Riken to research superconducting quantum computers and this week they have announced the formal launch of the project. The project is now called the RIKEN RQC  Fujitsu Collaboration Center and is located within the RIKEN Center for Quantum Computing in Wako, Saitama, Japan. The project [...]</p>
<p>The post <a rel="nofollow" href="https://quantumcomputingreport.com/rikenfujitsupartnertodevelopasuperconductingquantumcomputer/">Riken, Fujitsu Partner to Develop a Superconducting Quantum Computer</a> appeared first on <a rel="nofollow" href="https://quantumcomputingreport.com">Quantum Computing Report</a>.</p>
News Brief
dougfinke

Qubits composed of holes could be the trick to build faster, larger quantum computers
https://www.sciencedaily.com/releases/2021/04/210402095946.htm
Quantum Computers News  ScienceDaily
urn:uuid:8ab14fcd489f943501b30113bb17489c
Fri, 02 Apr 2021 13:59:46 +0000
A new study demonstrates a path towards scaling individual qubits to a miniquantum computer, using holes. The study identifies a 'sweet spot' where the qubit is least sensitive to noise (ensuring longer retention of information) and simultaneously can be operated the fastest.

Study shows promise of quantum computing using factorymade silicon chips
https://www.sciencedaily.com/releases/2021/03/210331130905.htm
Quantum Computers News  ScienceDaily
urn:uuid:30a233c43c5e56294109aa69845f836d
Wed, 31 Mar 2021 17:09:05 +0000
For the study, researchers were able to isolate and measure the quantum state of a single electron (the qubit) in a silicon transistor manufactured using a 'CMOS' technology similar to that used to make chips in computer processors.

Discovery of a mechanism for making superconductors more resistant to magnetic fields
https://www.sciencedaily.com/releases/2021/03/210330092446.htm
Quantum Computers News  ScienceDaily
urn:uuid:0f758178dcd9a1563a3d780bdd4c531e
Tue, 30 Mar 2021 13:24:46 +0000
Superconductivity is known to be easily destroyed by strong magnetic fields. Researchers have discovered that a superconductor with atomicscale thickness can retain its superconductivity even when a strong magnetic field is applied to it. The team has also identified a new mechanism behind this phenomenon. These results may facilitate the development of superconducting materials resistant to magnetic fields and topological superconductors composed of superconducting and magnetic materials.

Topological protection of entangled twophoton light in photonic topological insulators
https://www.sciencedaily.com/releases/2021/03/210330081254.htm
Quantum Computers News  ScienceDaily
urn:uuid:76b5d11369cf272b8a5f5dc4c50adfd7
Tue, 30 Mar 2021 12:12:54 +0000
Researchers have revealed the necessary conditions for the robust transport of entangled states of twophoton light in photonic topological insulators, paving the way the towards noiseresistant transport of quantum information.

Optical fiber could boost power of superconducting quantum computers
https://www.sciencedaily.com/releases/2021/03/210324135438.htm
Quantum Computers News  ScienceDaily
urn:uuid:158b41ad113650d5d4baa71098011b9e
Wed, 24 Mar 2021 17:54:38 +0000
The secret to building superconducting quantum computers with massive processing power may be an ordinary telecommunications technology  optical fiber. Physicists have measured and controlled a superconducting quantum bit (qubit) using lightconducting fiber instead of metal electrical wires, paving the way to packing a million qubits into a quantum computer rather than just a few thousand.

Semiconductor qubits scale in two dimensions
https://www.sciencedaily.com/releases/2021/03/210324135435.htm
Quantum Computers News  ScienceDaily
urn:uuid:e3a30b00dd511eea2eb7775803fb8c8b
Wed, 24 Mar 2021 17:54:35 +0000
The heart of any computer, its central processing unit, is built using semiconductor technology, which is capable of putting billions of transistors onto a single chip. Now, researchers have shown that this technology can be used to build a twodimensional array of qubits to function as a quantum processor. Their work is a crucial milestone for scalable quantum technology.

Novel thermometer can accelerate quantum computer development
https://www.sciencedaily.com/releases/2021/03/210323084726.htm
Quantum Computers News  ScienceDaily
urn:uuid:5b3abca5e3ecdaad0744c62ec33d01c1
Tue, 23 Mar 2021 12:47:26 +0000
Researchers have developed a novel type of thermometer that can simply and quickly measure temperatures during quantum calculations with extremely high accuracy. The breakthrough provides a benchmarking tool for quantum computing of great value  and opens up for experiments in the exciting field of quantum thermodynamics.

Machine learning shows potential to enhance quantum information transfer
https://www.sciencedaily.com/releases/2021/03/210322112937.htm
Quantum Computers News  ScienceDaily
urn:uuid:e6a9d6ebf80a3c2bba92942eb90e7472
Mon, 22 Mar 2021 15:29:37 +0000
New researchers demonstrated a machine learning approach that corrects quantum information in systems composed of photons, improving the outlook for deploying quantum sensing and quantum communications technologies on the battlefield.

Institute for Quantum Computing joins 50 – 30 challenge
https://uwaterloo.ca/instituteforquantumcomputing/news/institutequantumcomputingjoins5030challenge
Institute for Quantum Computing
urn:uuid:60ce2430dd7232271287d318546d3d32
Mon, 22 Mar 2021 00:00:00 +0000
<p>Monday, March 22, 2021</p>
<p>The Institute for Quantum Computing (IQC) at the University of Waterloo is proud to announce our membership in the Innovation, Science and Economic Development Canada <a href="https://www.ic.gc.ca/eic/site/icgc.nsf/eng/07706.html">50 – 30 Challenge</a>. The 50 – 30 Challenge is a program between the Government of Canada, businesses and diversity organizations with a goal to achieve both gender parity and increased presence of underrepresented groups on boards and in senior levels of management.</p>
12011

QC ethics and hype: the call is coming from inside the house
https://www.scottaaronson.com/blog/?p=5387
ShtetlOptimized
urn:uuid:adf383a4b645d9731be3f0ed014dc286
Sun, 21 Mar 2021 01:18:54 +0000
For years, I’d sometimes hear discussions about the ethics of quantum computing research. Quantum ethics! When the debates weren’t purely semantic, over the propriety of terms like “quantum supremacy” or “ancilla qubit,” they were always about chinstrokers like “but what if cracking RSA encryption gives governments more power to surveil their citizens? or what if […]
<p>For years, I’d sometimes hear discussions about the <em>ethics</em> of quantum computing research. Quantum ethics!</p>
<p>When the debates weren’t purely semantic, over the <a href="https://www.scottaaronson.com/blog/?p=4450">propriety</a> of terms like “quantum supremacy” or “ancilla qubit,” they were always about chinstrokers like “but what if cracking RSA encryption gives governments more power to surveil their citizens? or what if only a few big countries or companies get quantum computers, thereby widening the divide between haves and havenots?” Which, OK, conceivably these will someday be issues. But, besides barely depending on any specific facts about quantum computing, these debates always struck me as oddly <em>safe</em>, because the moral dilemmas were so hypothetical and far removed from us in time.</p>
<p>I confess I may have even occasionally poked fun when asked to expound on quantum ethics. I may have commented that quantum computers probably won’t kill anyone unless a dilution refrigerator tips over onto their head. I may have asked forgiveness for feeding customdesigned oracles to <a href="https://en.wikipedia.org/wiki/BQP">BQP</a> and <a href="https://en.wikipedia.org/wiki/QMA">QMA</a>, without first consulting an ethics committee about the longterm effects on those complexity classes.</p>
<p>Now fate has punished me for my flippancy. These days, I really <em>do</em> feel like quantum computing research has become an ethical minefield—but not for any of the reasons mentioned previously. What’s new is that millions of dollars are now potentially available to quantum computing researchers, along with equity, stock options, and whatever else causes “kaching” sound effects and bulging eyes with dollar signs. And in many cases, to have a shot at such riches, all an expert needs to do is profess optimism that quantum computing will have revolutionary, worldchanging applications and have them <em>soon</em>. Or at least, not object too strongly when others say that.</p>
<p>Some of today’s rhetoric will of course remind people of the DWave saga, which first brought this blog to prominence when it began in earnest in 2007. Quantum computers, we hear now as then, will soon leave the Earth’s fastest supercomputers in the dust. They’re going to harness superposition to try all the exponentially many possible solutions at once. They’ll crack the Traveling Salesman Problem, and will transform machine learning and AI beyond recognition. Meanwhile, simulations of quantum systems will be key to solving global warming and cancer.</p>
<p>Despite the parallels, though, this new gold rush <em>doesn’t</em> feel to me like the DWave one, which seems in retrospect like just a little dry run. If I had to articulate what’s new in one sentence, it’s that this time “the call is coming from inside the house.” Many of the companies making wildly overhyped claims are recognized leaders of the field. They have brilliant quantum computing theorists and experimentalists on their staff with impeccable research records. Some of those researchers are among my best friends. And even when I wince at the claims of nearterm applications, in many cases (especially with quantum simulation) the claims aren’t <em>obviously</em> false—we won’t know for certain until we try it and see! It’s genuinely gotten harder to draw the line between defensible optimism and exaggerations verging on fraud.</p>
<p>Indeed, this time around virtually <em>everyone</em> in QC is “complicit” to a greater or lesser degree. I, too, have accepted compensation to consult on quantum computing topics, to give talks at hedge funds, and in a few cases to serve as a scientific adviser to quantum computing startups. I tell myself that, by 2021 standards, this stuff is all trivial chump change—a few thousands of dollars here or there, to expound on the same themes that I already discuss free of charge on this blog. I actually get paid to <em>dispel</em> hype, rather than propagate it! I tell myself that I’ve turned my back on the orders of magnitude more money available to those willing to hitch their scientific reputations to the aspirations of this or that specific QC company. (Yes, this blog, and my desire to preserve its intellectual independence and credibility, might well be costing me millions!)</p>
<p>But, OK, some would argue that accepting <em>any</em> money from QC companies or QC investors just puts you at the top of a slope with unabashed snakeoil salesmen at the bottom. With the commercialization of our field that started around 2015, there’s no bright line anymore marking the boundary between pure scientific curiosity and the pursuit of filthy lucre; it’s all just points along a continuum. I’m not sure that these people are wrong.</p>
<p>As some of you might’ve seen already, IonQ, the trappedion QC startup that originated from the University of Maryland, is poised to have the <a href="https://www.reuters.com/article/usionqmadmytechnology/quantumcomputingproviderionqtogopublicvia2billionspacdealidUSKBN2B013Z">firstever quantum computing IPO</a>—a socalled “SPAC IPO,” which while I’m a financial ignoramus, apparently involves merging with a shell company and thereby bypassing the SEC’s normal IPO rules. Supposedly they’re seeking $650 million in new funding and a $2 billion market cap. If you want to see what IonQ is saying about QC to prospective investors, <a href="https://static1.squarespace.com/static/5e33152a051d2e7588f7571c/t/60459578b8c075444a656357/1615173012167/IonQ+Investor+Presentation+030721+vFF.pdf">click here</a>. Lacking any choice in the matter, I’ll probably say more about these developments in a future post.</p>
<p>Meanwhile, <a href="https://psiquantum.com/">PsiQuantum</a>, the PaloAltobased optical QC startup, has <a href="https://www.ft.com/content/a5af3039abbf4b2592e2c40e5957c8cd">said</a> that it’s soon going to leave “stealth mode.” And Amazon, Microsoft, Google, IBM, Honeywell, and other big players continue making large investments in QC—treating it, at least rhetorically, not at all like bluesky basic research, but like a central part of their future business plans.</p>
<p>All of these companies have produced or funded excellent QC research. And of course, they’re all heterogeneous, composed of individuals who might vehemently disagree with each other about the near or longterm prospects of QC. And yet all of them have, at various times, inspired reflections in me like the ones in this post.</p>
<p>I regret that this post has no clear conclusion. I’m still hashing things out, solicing thoughts from my readers and friends. Speaking of which: this coming Monday, March 22, at 810pm US Eastern time, I’ve decided to hold a discussion around these issues on <a href="https://www.joinclubhouse.com/">Clubhouse</a>—my “grand debut” on that app, and an opportunity to see whether I like it or not! My friend Adam Brown will moderate the discussion; other likely participants will be John Horgan, George Musser, Michael Nielsen, and Matjaž Leonardis. If you’re on Clubhouse, I hope to see you there!</p>
Quantum
Speaking Truth to Parallelism
Scott

Better batteries start with basics  and a big computer
https://www.sciencedaily.com/releases/2021/03/210319183945.htm
Quantum Computers News  ScienceDaily
urn:uuid:d9bddbdba73d5a3885d390b97eb095ff
Fri, 19 Mar 2021 22:39:45 +0000
Researchers ran quantum simulations to understand glycerol carbonate, a compound used in biodiesel and as a common solvent.

The girls in STEM: this is how we bridge the gender gap
https://www.vanityfair.it/news/approfondimenti/2021/03/18/leragazzenellestemcosicolmiamoilgendergap
quantum computing – News
urn:uuid:b069ee08e749af85557af61aea7dbe3e
Fri, 19 Mar 2021 21:15:13 +0000
From Vanity Fair, March 18, 2021: April is national STEM month in Italy. and Fermilab's Anna Grasselino is highlighted as a role model for young women in pursuit of a career in STEM.
From Vanity Fair, March 18, 2021: April is national STEM month in Italy. and Fermilab's Anna Grasselino is highlighted as a role model for young women in pursuit of a career in STEM.
In the news
tracym

Solving 'barren plateaus' is the key to quantum machine learning
https://www.sciencedaily.com/releases/2021/03/210319125414.htm
Quantum Computers News  ScienceDaily
urn:uuid:fddb8e650adddf12be993ad281323953
Fri, 19 Mar 2021 16:54:14 +0000
Many machine learning algorithms on quantum computers suffer from the dreaded 'barren plateau' of unsolvability, where they run into dead ends on optimization problems.

Abel to win
https://www.scottaaronson.com/blog/?p=5388
ShtetlOptimized
urn:uuid:89bf53877a5e82973774da52b8b079a9
Thu, 18 Mar 2021 03:19:46 +0000
Many of you will have seen the happy news today that Avi Wigderson and László Lovász share this year’s Abel Prize (which now contends with the Fields Medal for the highest award in pure math). This is only the second time that the Abel Prize has been given wholly or partly for work in theoretical […]
<p>Many of you will have seen the happy news today that Avi Wigderson and László Lovász <a href="https://www.abelprize.no/c76389/seksjon/vis.html?tid=76390&strukt_tid=76389">share this year’s Abel Prize</a> (which now contends with the Fields Medal for the highest award in pure math). This is only the second time that the Abel Prize has been given wholly or partly for work in theoretical computer science, after <a href="https://www.abelprize.no/c54147/seksjon/vis.html?tid=54148">Szemerédi</a> in 2012. See also the articles in <em><a href="https://www.quantamagazine.org/aviwigdersonandlaszlolovaszwinabelprize20210317/">Quanta</a></em> or the <a href="https://www.nytimes.com/2021/03/17/science/abelprizemathematics.html">NYT</a>, which actually say most of what I would’ve said for a lay audience about Wigderson’s and Lovász’s most famous research results and their importance (except, no, Avi hasn’t <em>yet</em> proved P=BPP, just taken some major steps toward it…).</p>
<p>On a personal note, Avi was both my and my wife Dana’s postdoctoral advisor at the Institute for Advanced Study in Princeton. He’s been an <em>unbelievably</em> important mentor to both of us, as he’s been for dozens of others in the CS theory community. Back in 2007, I also had the privilege of working closely with Avi for months on our <a href="https://www.scottaaronson.com/papers/alg.pdf">Algebrization</a> paper. Now would be a fine time to revisit <a href="https://www.scottaaronson.com/blog/?p=2925">Avi’s Permanent Impact on Me</a> (or <a href="https://www.youtube.com/watch?v=BLxC3rGeWBI">watch the YouTube video</a>), which is the talk I gave at IAS in 2016 on the occasion of Avi’s 60th birthday.</p>
<p>Huge congratulations to both Avi and László!</p>
Announcements
Complexity
Scott

New quantum algorithm surpasses the QPE norm
https://www.sciencedaily.com/releases/2021/03/210317094558.htm
Quantum Computers News  ScienceDaily
urn:uuid:44cbb847ef17a63bd5ac34e6bf0c7a30
Wed, 17 Mar 2021 13:45:58 +0000
Researchers refine quantum computerready algorithm to measure the vertical ionization energies of atoms and molecules within 0.1 eV of precision.

Researchers enhance quantum machine learning algorithms
https://www.sciencedaily.com/releases/2021/03/210316112244.htm
Quantum Computers News  ScienceDaily
urn:uuid:78bc0eca1a375be758d42bc475bd4e77
Tue, 16 Mar 2021 15:22:44 +0000
Researchers found a way to automatically infer parameters used in an important quantum Boltzmann machine algorithm for machine learning applications.

Smart quantum technologies for secure communication
https://www.sciencedaily.com/releases/2021/03/210316093442.htm
Quantum Computers News  ScienceDaily
urn:uuid:31af9fbc1ce3a1576361e09e155d3c63
Tue, 16 Mar 2021 13:34:42 +0000
Researchers have introduced a smart quantum technology for the spatial mode correction of single photons. The authors exploit the selflearning and selfevolving features of artificial neural networks to correct the distorted spatial profile of single photons.

Professor De Francesco participates in SQMS at Fermi National Accelerator Laboratory
https://www.lanazione.it/pisa/cronaca/laprofessoressadefrancesconelsqmsalfermiacceleratorlaboratory1.6134854
quantum computing – News
urn:uuid:6bd55e45a9826db182f20f4cbcbb151f
Mon, 15 Mar 2021 21:05:56 +0000
From La Nazione Pisa, March 15, 2021: The center directed by Fermilab’s Anna Grassellino has the task of developing a stateoftheart quantum computer with unprecedented performances based on superconducting technologies.
From La Nazione Pisa, March 15, 2021: The center directed by Fermilab’s Anna Grassellino has the task of developing a stateoftheart quantum computer with unprecedented performances based on superconducting technologies.
In the news
tracym

Remote control for quantum emitters
https://www.sciencedaily.com/releases/2021/03/210312095755.htm
Quantum Computers News  ScienceDaily
urn:uuid:6e9912dd705707fed527403dd34285ed
Fri, 12 Mar 2021 14:57:55 +0000
Quantum technologies are enabled by precise control of the state and interactions of individual quantum objects. Physicists have now proposed a way to remotely control the state of individual quantum emitters. The underlying idea is based on chirped light pulses.

Longdelayed UT Austin Quantum Complexity Theory Student Project Showcase!
https://www.scottaaronson.com/blog/?p=5382
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Thu, 11 Mar 2021 20:31:03 +0000
Back at MIT, whenever I taught my graduate course on Quantum Complexity Theory (see here for lecture notes), I had a tradition of showcasing the student projects on this blog: see here (Fall 2010), here (Fall 2012), here (Fall 2014). I was incredibly proud that, each time I taught, at least some of the projects […]
<p>Back at MIT, whenever I taught my graduate course on Quantum Complexity Theory (<a href="https://ocw.mit.edu/courses/electricalengineeringandcomputerscience/6845quantumcomplexitytheoryfall2010/lecturenotes/">see here</a> for lecture notes), I had a tradition of showcasing the student projects on this blog: see <a href="https://www.scottaaronson.com/blog/?p=515">here (Fall 2010)</a>, <a href="https://www.scottaaronson.com/blog/?p=1181">here (Fall 2012)</a>, <a href="https://www.scottaaronson.com/blog/?p=2109">here (Fall 2014)</a>. I was incredibly proud that, each time I taught, at least some of the projects led to publishable original research—sometimes highly significant research, like Paul Christiano’s work on quantum money (which led to my later <a href="https://arxiv.org/abs/1203.4740">paper with him</a>), Shelby Kimmel’s <a href="https://arxiv.org/abs/1101.0797">work</a> on quantum query complexity, Jenny Barry’s <a href="https://arxiv.org/abs/1406.2858">work</a> on quantum partially observable Markov decision processes (“QOMDPs”), or Matt Coudron and Henry Yuen’s work on randomness expansion (which led to their later <a href="https://arxiv.org/abs/1310.6755">breakthrough</a> in the subject).</p>
<p>Alas, after I moved to UT Austin, for some reason I discontinued the tradition of these blogshowcases—and inexcusably, I did this even though the wonderful new research results continued! Now that I’m teaching Quantum Complexity Theory at UT for the third time (via Zoom, of course), I decided that it was finally time to remedy this. To keep things manageable, this time I’m going to limit myself to research projects that began their lives in my course <em>and that are already public on the arXiv</em> (or in one case, that will soon be).</p>
<p>So please enjoy the following smorgasbord, from 2016 and 2019 iterations of my course! And if you have any questions about any of the projects—well, I’ll try to get the students to answer in the comments section! Thanks so much and congratulations to the students for their work.</p>
<h2>From the Fall 2016 iteration of the course</h2>
<p>William Hoza (project turned into a joint paper with Cole Graham), <strong><a href="https://arxiv.org/abs/1612.05680">Universal Bell Correlations Do Not Exist</a></strong>.</p>
<blockquote class="wpblockquote"><p>We prove that there is no finitealphabet nonlocal box that generates exactly those correlations that can be generated using a maximally entangled pair of qubits. More generally, we prove that if some finitealphabet nonlocal box is strong enough to simulate arbitrary local projective measurements of a maximally entangled pair of qubits, then that nonlocal box cannot itself be simulated using any finite amount of entanglement. We also give a quantitative version of this theorem for approximate simulations, along with a corresponding upper bound.</p></blockquote>
<p>Patrick Rall, <strong><a href="https://arxiv.org/abs/1702.06990">Signed quantum weight enumerators characterize qubit magic state distillation</a></strong>.</p>
<blockquote class="wpblockquote"><p>Many proposals for faulttolerant quantum computation require injection of ‘magic states’ to achieve a universal set of operations. Some qubit states are above a threshold fidelity, allowing them to be converted into magic states via ‘magic state distillation’, a process based on stabilizer codes from quantum error correction.<br>We define quantum weight enumerators that take into account the sign of the stabilizer operators. These enumerators completely describe the magic state distillation behavior when distilling Ttype magic states. While it is straightforward to calculate them directly by counting exponentially many operator weights, it is also an NPhard problem to compute them in general. This suggests that finding a family of distillation schemes with desired threshold properties is at least as hard as finding the weight distributions of a family of classical codes.<br>Additionally, we develop search algorithms fast enough to analyze all useful 5 qubit codes and some 7 qubit codes, finding no codes that surpass the best known threshold.</p></blockquote>
<h2>From the Spring 2019 iteration of the course</h2>
<p>YingHao Chen, <strong><a href="https://arxiv.org/abs/1909.03787">2Local Hamiltonian with Low Complexity is QCMAcomplete</a></strong>.</p>
<blockquote class="wpblockquote"><p>We prove that 2Local Hamiltonian (2LH) with Low Complexity problem is QCMAcomplete by combining the results from the QMAcompleteness of 2LH and QCMAcompleteness of 3LH with Low Complexity. The idea is straightforward. It has been known that 2LH is QMAcomplete. By putting a low complexity constraint on the input state, we make the problem QCMA. Finally, we use similar arguments as in [Kempe, Kitaev, Regev] to show that all QCMA problems can be reduced to our proposed problem.</p></blockquote>
<p>Jeremy Cook, <strong><a href="https://arxiv.org/abs/1907.11368">On the relationships between Z, C, and Hlocal unitaries</a></strong>.</p>
<blockquote class="wpblockquote"><p>Quantum walk algorithms can speed up search of physical regions of space in both the discretetime [<a href="https://arxiv.org/abs/quantph/0402107">arXiv:quantph/0402107</a>] and continuoustime setting [<a href="https://arxiv.org/abs/quantph/0306054">arXiv:quantph/0306054</a>], where the physical region of space being searched is modeled as a connected graph. In such a model, Aaronson and Ambainis [<a href="https://arxiv.org/abs/quantph/0303041">arXiv:quantph/0303041</a>] provide three different criteria for a unitary matrix to act locally with respect to a graph, called <em>Z</em>local, <em>C</em>local, and <em>H</em>local unitaries, and left the open question of relating these three locality criteria. Using a correspondence between continuous and discretetime quantum walks by Childs [<a href="https://arxiv.org/abs/0810.0312">arXiv:0810.0312</a>], we provide a way to approximate <em>N</em>×<em>N H</em>local unitaries with error <em>δ</em> using <em>O</em>(1/<em>√δ,√N</em>) <em>C</em>local unitaries, where the comma denotes the maximum of the two terms.</p></blockquote>
<p>Joshua A. Cook, <strong><a href="https://arxiv.org/abs/1906.10495">Approximating Unitary Preparations of Orthogonal Black Box States</a></strong>.</p>
<blockquote class="wpblockquote"><p>In this paper, I take a step toward answering the following question: for m different small circuits that compute m orthogonal n qubit states, is there a small circuit that will map m computational basis states to these m states without any input leaving any auxiliary bits changed. While this may seem simple, the constraint that auxiliary bits always be returned to 0 on any input (even ones besides the m we care about) led me to use sophisticated techniques. I give an approximation of such a unitary in the m = 2 case that has size polynomial in the approximation error, and the number of qubits n.</p></blockquote>
<p>Sabee Grewal (project turned into a joint paper with me), <strong><a href="https://arxiv.org/abs/2102.10458">Efficient Learning of NonInteracting Fermion Distributions</a></strong>.</p>
<blockquote class="wpblockquote"><p>We give an efficient classical algorithm that recovers the distribution of a noninteracting fermion state over the computational basis. For a system of <em>n</em> noninteracting fermions and <em>m</em> modes, we show that <em>O</em>(<em>m</em><sup>2</sup><em>n</em><sup>4</sup>log(<em>m</em>/<em>δ</em>)/<em>ε</em><sup>4</sup>) samples and <em>O</em>(<em>m</em><sup>4</sup><em>n</em><sup>4</sup>log(<em>m</em>/<em>δ</em>)/<em>ε</em><sup>4</sup>) time are sufficient to learn the original distribution to total variation distance <em>ε</em> with probability 1−<em>δ</em>. Our algorithm empirically estimates the one and twomode correlations and uses them to reconstruct a succinct description of the entire distribution efficiently.</p></blockquote>
<p>Sam Gunn and Niels Kornerup, <strong><a href="https://arxiv.org/abs/1906.07673">Review of a Quantum Algorithm for Betti Numbers</a></strong>.</p>
<blockquote class="wpblockquote"><p>We looked into the algorithm for calculating Betti numbers presented by Lloyd, Garnerone, and Zanardi (LGZ). We present a new algorithm in the same spirit as LGZ with the intent of clarifying quantum algorithms for computing Betti numbers. Our algorithm is simpler and slightly more efficient than that presented by LGZ. We present a thorough analysis of our algorithm, pointing out reasons that both our algorithm and that presented by LGZ do not run in polynomial time for most inputs. However, the algorithms do run in polynomial time for calculating an approximation of the Betti number to polynomial multiplicative error, when applied to some class of graphs for which the Betti number is exponentially large.</p></blockquote>
<p>William Kretschmer, <strong><a href="https://arxiv.org/abs/1907.06731">Lower Bounding the ANDOR Tree via Symmetrization</a></strong>.</p>
<blockquote class="wpblockquote"><p>We prove a simple, nearly tight lower bound on the approximate degree of the twolevel ANDOR tree using symmetrization arguments. Specifically, we show that ~deg(AND<em>m</em>∘OR<em>n</em>)=Ω(~<em>√</em>(<em>mn</em>)). To our knowledge, this is the first proof of this fact that relies on symmetrization exclusively; most other proofs involve the more complicated formulation of approximate degree as a linear program [BT13, She13, BDBGK18]. Our proof also demonstrates the power of a symmetrization technique involving Laurent polynomials (polynomials with negative exponents) that was previously introduced by Aaronson, Kothari, Kretschmer, and Thaler [AKKT19].</p></blockquote>
<p>Jiahui Liu and Ruizhe Zhang (project turned into a joint paper with me, Mark Zhandry, and Qipeng Liu), <br><strong><a href="https://arxiv.org/abs/2004.09674">New Approaches for Quantum CopyProtection</a></strong>.</p>
<blockquote class="wpblockquote"><p>Quantum copy protection uses the unclonability of quantum states to construct quantum software that provably cannot be pirated. Copy protection would be immensely useful, but unfortunately little is known about how to achieve it in general. In this work, we make progress on this goal, by giving the following results:<br>– We show how to copy protect any program that cannot be learned from its input/output behavior, relative to a classical oracle. This improves on Aaronson [CCC’09], which achieves the same relative to a quantum oracle. By instantiating the oracle with postquantum candidate obfuscation schemes, we obtain a heuristic construction of copy protection.<br>– We show, roughly, that any program which can be watermarked can be copy detected, a weaker version of copy protection that does not prevent copying, but guarantees that any copying can be detected. Our scheme relies on the security of the assumed watermarking, plus the assumed existence of public key quantum money. Our construction is general, applicable to many recent watermarking schemes.</p></blockquote>
<p>John Kallaugher, <strong>Triangle Counting in the Quantum Streaming Model</strong>. Not yet available but coming soon to an arXiv near you!</p>
<blockquote class="wpblockquote"><p>We give a quantum algorithm for counting triangles in graph streams that uses less space than the best possible classical algorithm.</p></blockquote>
Complexity
Quantum
Scott

Breakthrough lays groundwork for future quantum networks
https://www.sciencedaily.com/releases/2021/03/210311142041.htm
Quantum Computers News  ScienceDaily
urn:uuid:5985b193198a22dc09b4d1e037f95602
Thu, 11 Mar 2021 19:20:41 +0000
New research could help lay the groundwork for future quantum communication networks and largescale quantum computers.

Robots learn faster with quantum technology
https://www.sciencedaily.com/releases/2021/03/210311123432.htm
Quantum Computers News  ScienceDaily
urn:uuid:6f38cf1a8921a5b5f6e6068323ec215c
Thu, 11 Mar 2021 17:34:32 +0000
Artificial intelligence is part of our modern life. A crucial question for practical applications is how fast such intelligent machines can learn. An experiment has answered this question, showing that quantum technology enables a speedup in the learning process. The physicists have achieved this result by using a quantum processor for single photons as a robot.

Sayonara Majorana?
https://www.scottaaronson.com/blog/?p=5376
ShtetlOptimized
urn:uuid:7a82d524b9a0ee04f42c8309bd66fa24
Wed, 10 Mar 2021 22:29:51 +0000
Many of you have surely already seen the news that the Kouwenhoven group in Delft—which in 2018 published a paper in Nature claiming to have detected Majorana fermions, a type of nonabelian anyon—have retracted the paper and apologized for “insufficient scientific rigour.” This work was considered one of the linchpins of Microsoft’s experimental effort toward […]
<p>Many of you have surely <a href="https://www.wired.com/story/microsoftretractsdisputedquantumcomputingpaper/">already</a> <a href="https://www.nature.com/articles/d4158602100612z">seen</a> the news that the Kouwenhoven group in Delft—which in 2018 published a paper in <em>Nature</em> claiming to have detected <a href="https://en.wikipedia.org/wiki/Majorana_fermion">Majorana fermions</a>, a type of nonabelian <a href="https://en.wikipedia.org/wiki/Anyon">anyon</a>—have <a href="https://www.nature.com/articles/s4158602103373x?utm_medium=affiliate&utm_source=commission_junction&utm_campaign=3_nsn6445_deeplink_PID100095187&utm_content=deeplink">retracted the paper</a> and apologized for “insufficient scientific rigour.” This work was considered one of the linchpins of Microsoft’s experimental effort toward building topological quantum computers.</p>
<p>Like most quantum computing theorists, I guess, I’m thrilled if Majorana fermions can be created using existing technology, I’m sad if they can’t be, but I don’t have any special investment in or knowledge of the topic, beyond what I read in the news or hear from colleagues. Certainly Majorana fermions seem neither necessary nor sufficient for building a scalable quantum computer, although they’d be a step forward for the topological approach to QC.</p>
<p>The purpose of this post is to invite <em>informed scientific discussion</em> of the relevant issues—first and foremost so that I can learn something, and second so that my readers can! I’d be especially interested to understand:</p>
<ol><li>Weren’t there, like, several <em>other</em> claims to have produced Majorana fermions? What of those then?</li><li>If, today, no one has convincingly demonstrated the existence of Majoranas, then do people think it more likely that they were produced but not detected, or that they weren’t even produced?</li><li>How credible are the explanations as to what went wrong?</li><li>Are there any broader implications for the prospects of topological QC, or Microsoft’s path to topological QC, or was this just an isolated mistake?</li></ol>
Quantum
Scott

Finding quvigints in a quantum treasure map
https://www.sciencedaily.com/releases/2021/03/210310122524.htm
Quantum Computers News  ScienceDaily
urn:uuid:df99b9d0ff565be382b1d5a6bac5d556
Wed, 10 Mar 2021 17:25:24 +0000
Researchers have struck quantum gold  and created a new word  by enlisting machine learning to efficiently navigate a 20dimensional quantum treasure map.

Superconducting Quantum Materials and Systems Center in Chicago University, the scientist Anna Grassellino inaugurates the teaching of the second semester
https://www.lanazione.it/pisa/cronaca/scienziataannagrassellino1.6108186
quantum computing – News
urn:uuid:1407a0f844c462a85feffa00601d21eb
Tue, 09 Mar 2021 15:05:20 +0000
From La Nazione, March 8, 2021: Fermilab’s Anna Grassellino will inaugurate second semester teaching at the University of Pisa at 4 pm on Wednesday 10 March, live streaming on the social channels of the Pisa University.
From La Nazione, March 8, 2021: Fermilab’s Anna Grassellino will inaugurate second semester teaching at the University of Pisa at 4 pm on Wednesday 10 March, live streaming on the social channels of the Pisa University.
In the news
tracym

Another axe swung at the Sycamore
https://www.scottaaronson.com/blog/?p=5371
ShtetlOptimized
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Sun, 07 Mar 2021 19:15:53 +0000
So there’s an interesting new paper on the arXiv by Feng Pan and Pan Zhang, entitled “Simulating the Sycamore supremacy circuits.” It’s about a new tensor contraction strategy for classically simulating Google’s 53qubit quantum supremacy experiment from Fall 2019. Using their approach, and using just 60 GPUs running for a few days, the authors say […]
<p>So there’s an interesting new paper on the arXiv by Feng Pan and Pan Zhang, entitled <a href="https://arxiv.org/abs/2103.03074">“Simulating the Sycamore supremacy circuits.”</a> It’s about a new tensor contraction strategy for classically simulating Google’s 53qubit quantum supremacy experiment from Fall 2019. Using their approach, and using just 60 GPUs running for a few days, the authors say they managed to generate a million <em>correlated</em> 53bit strings—meaning, strings that all agree on a specific subset of 20 or so bits—that achieve a high linear crossentropy score.</p>
<p>Alas, I haven’t had time this weekend to write a “proper” blog post about this, but several people have by now emailed to ask my opinion, so I thought I’d share the brief response I sent to a journalist.</p>
<p>This does look like a significant advance on simulating Sycamorelike random quantum circuits! Since it’s based on tensor networks, you don’t need the literally largest supercomputer on the planet filling up tens of petabytes of hard disk space with amplitudes, as in the bruteforce strategy <a href="https://arxiv.org/abs/1910.09534">proposed by IBM</a>. Pan and Zhang’s strategy seems most similar to the strategy previously <a href="https://arxiv.org/pdf/2005.06787.pdf">proposed by Alibaba</a>, with the key difference being that the new approach generates millions of correlated samples rather than just one.</p>
<p>I guess my main thoughts for now are:</p>
<ol><li>Once you knew about this particular attack, you could evade it and get back to where we were before by switching to a more sophisticated verification test — namely, one where you not only computed a Linear XEB score for the observed samples, you <em>also</em> made sure that the samples didn’t share too many bits in common. (Strangely, though, the paper never mentions this point.)</li><li>The other response, of course, would just be to redo random circuit sampling with a slightly bigger quantum computer, like the ~70qubit devices that Google, IBM, and others are now building!</li></ol>
<p>Anyway, very happy for thoughts from anyone who knows more.</p>
Complexity
Quantum
Scott

New quantum theory heats up thermodynamic research
https://www.sciencedaily.com/releases/2021/03/210305080115.htm
Quantum Computers News  ScienceDaily
urn:uuid:e87041a90dad855ea094ea50c1f99300
Fri, 05 Mar 2021 13:01:15 +0000
Researchers have developed a new quantum version of a 150yearold thermodynamical thought experiment that could pave the way for the development of quantum heat engines.

The Zen AntiInterpretation of Quantum Mechanics
https://www.scottaaronson.com/blog/?p=5359
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Thu, 04 Mar 2021 23:26:29 +0000
As I lay bedridden this week, knocked out by my second dose of the Moderna vaccine, I decided I should blog some more halfbaked ideas because what the hell? It feels therapeutic, I have tenure, and anyone who doesn’t like it can close their broswer tab. So: although I’ve written tens of thousands of words, […]
<p>As I lay bedridden this week, knocked out by my second dose of the Moderna vaccine, I decided I should blog some more halfbaked ideas because what the hell? It feels therapeutic, I have tenure, and anyone who doesn’t like it can close their broswer tab.</p>
<p>So: although I’ve written tens of thousands <a href="https://www.pbs.org/wgbh/nova/article/canquantumcomputingrevealthetruemeaningofquantummechanics/">of</a> <a href="https://arxiv.org/abs/1306.0159">words</a>, <a href="https://www.scottaaronson.com/papers/philos.pdf">on</a> <a href="https://www.scottaaronson.com/blog/?p=1103">this</a> <a href="https://www.scottaaronson.com/blog/?p=3628">blog</a> <a href="https://www.scottaaronson.com/democritus/">and</a> <a href="https://www.scottaaronson.com/qclec.pdf">elsewhere</a>, about interpretations of quantum mechanics, again and again I’ve dodged the question of which interpretation (if any) I <em>really believe myself</em>. Today, at last, I’ll emerge from the shadows and tell you precisely where I stand.</p>
<p>I hold that all interpretations of QM are just crutches that are better or worse at helping you along to the Zen realization that <strong>QM is what it is and doesn’t need an interpretation</strong>. As Sidney Coleman <a href="https://arxiv.org/abs/2011.12671">famously argued</a>, what needs reinterpretation is not QM itself, but all our <em>pre</em>quantum philosophical baggage—the baggage that leads us to demand, for example, that a wavefunction ψ⟩ either be “real” like a stubbed toe or else “unreal” like a dream. Crucially, because this philosophical baggage differs somewhat from person to person, the “best” interpretation—meaning, the one that leads most quickly to the desired Zen state—can also differ from person to person. Meanwhile, though, thousands of physicists (and chemists, mathematicians, quantum computer scientists, etc.) have approached the Zen state merely by spending decades working with QM, never worrying much about interpretations at all. This is probably the truest path; it’s just that most people lack the inclination, ability, or time.</p>
<p>Greg Kuperberg, one of the smartest people I know, once told me that the problem with the ManyWorlds Interpretation is not that it says anything wrong, but only that it’s “melodramatic” and “overwritten.” Greg is far along the Zen path, probably further than me.</p>
<p>You shouldn’t confuse the Zen AntiInterpretation with “Shut Up And Calculate.” The latter phrase, mistakenly attributed to Feynman but really due to David Mermin, is something one might say at the <em>beginning</em> of the path, when one is as a baby. I’m talking here only about the <em>endpoint</em> of path, which one can approach but never reach—the endpoint where you intuitively understand exactly what a ManyWorlder, Copenhagenist, or Bohmian would say about any given issue, and also how they’d respond to each other, and how they’d respond to the responses, etc. but after years of study and effort you’ve <em>returned</em> to the situation of the baby, who just sees the thing for what it is.</p>
<p>Let no one misinterpret me as saying that the interpretations are all interchangeable, or equally good or bad. If you had to, you could call even me a “ManyWorlder,” but <em>only</em> in the following limited sense: that in fifteen years of teaching quantum information, my experience has consistently been that for <em>most</em> students, <a href="https://en.wikipedia.org/wiki/Manyworlds_interpretation">Everett’s crutch</a> is the best currently on the market. At any rate, it’s the one that’s most like a straightforward <em>picture</em> of the equations, and least like a wobbly tower of words that might collapse if you utter the wrong ones. Unlike Bohr, Everett will never make you feel stupid for asking the questions an inquisitive child would; he’ll simply tell you answers that are as clear, logical, and internally consistent as they are metaphysically extravagant. That’s a start.</p>
<p>The <a href="https://en.wikipedia.org/wiki/Copenhagen_interpretation">Copenhagen Interpretation</a> retains a place of honor as the <em>first</em> crutch, for decades the <em>only</em> crutch, and the one closest to the spirit of positivism. Unfortunately, <em>wielding</em> the Copenhagen crutch requires mad philosophical skillz—which parts of the universe should you temporarily regard as “classical”? which questions should be answered, and which deflected?—to the point where, if you’re capable of all that verbal footwork, then why do you even need a crutch in the first place? In the hands of an amateur—meaning, nearly everyone—Copenhagen can lead <em>away</em> from rather than toward the Zen state, as one sees with the generations of NewAgey bastardizations about “observations creating reality.”</p>
<p>As for <a href="https://en.wikipedia.org/wiki/De_Broglie%E2%80%93Bohm_theory">deBroglieBohm</a>—that’s a weird, interesting, baroque crutch, one whose actual details (the preferred basis and the guiding equation) are historically contingent and tied to specific physical systems. It’s probably the right crutch for <em>someone</em>—it gets eternal credit for having led Bell to discover the Bell inequality—but its quirks definitely need to be discarded along the way.</p>
<p>Note that, among those who approach the Zen state, many still call themselves ManyWorlders or Copenhagenists or Bohmians or whatever—just like those far along in spiritual enlightenment might still call themselves Buddhists or Catholics or Muslims or Jews (or atheists or agnostics)—even though, by that point, they might have more in common with each other than they do with their supposed coreligionists or coirreligionists.</p>
<p>Alright, but isn’t all this Zen stuff just a way to dodge the <em>actual, substantive</em> questions about QM, by cheaply claiming to have transcended them? If that’s your charge, then please help yourself to the following FAQ about the details of the Zen AntiInterpretation.</p>
<ol><li><strong>What is a quantum state?</strong> It’s a unit vector of complex numbers (or if we’re talking about mixed states, then a trace1, Hermitian, positive semidefinite matrix), which encodes everything there is to know about a physical system.<br></li><li><strong>OK, but are the quantum states “ontic” (really out in the world), or “epistemic” (only in our heads)?</strong> Dude. Do “basketball games” really exist, or is that just a phrase we use to summarize our knowledge about certain large agglomerations of interacting quarks and leptons? Do even the “quarks” and “leptons” exist, or are those just words for excitations of the more fundamental fields? Does “jealousy” exist? Pretty much<em> all</em> our concepts are complicated grab bags of “ontic” and “epistemic,” so it shouldn’t surprise us if quantum states are too. Bad dichotomy.<br></li><li><strong>Why are there probabilities in QM?</strong> Because QM <em>is</em> a (the?) generalization of probability theory to involve complex numbers, whose squared absolute values are probabilities. It <em>includes</em> probability as a special case.<br></li><li><strong>But why do the probabilities obey the Born rule?</strong> Because, once the unitary part of QM has picked out the 2norm as being special, for the probabilities <em>also</em> to be governed by the 2norm is pretty much the only possibility that makes mathematical sense; there are many nice theorems formalizing that intuition under reasonable assumptions.<br></li><li><strong>What is an “observer”?</strong> It’s exactly what modern decoherence theory says it is: a particular kind of quantum system that interacts with other quantum systems, becomes entangled with them, and thereby records information about them—reversibly in principle but irreversibly in practice.<br></li><li><strong>Can observers be manipulated in coherent superposition, as in the Wigner’s Friend scenario?</strong> If so, they’d be radically unlike any physical system we’ve ever had direct experience with. So, are you asking whether such “observers” would be <em>conscious</em>, or if so what they’d be conscious of? Who the hell knows?<br></li><li><strong>Do “other” branches of the wavefunction—ones, for example, where my life took a different course—exist in the same sense this one does?</strong> If you start with a quantum state for the early universe and then timeevolve it forward, then yes, you’ll get not only “our” branch but also a proliferation of other branches, in the overwhelming majority of which Donald Trump was never president and civilization didn’t grind to a halt because of a bat near Wuhan. But how could we possibly know whether anything “breathes fire” into the other branches and makes them real, when we have no idea what breathes fire into <em>this</em> branch and makes <em>it</em> real? This is not a dodge—it’s just that a simple “yes” or “no” would fail to do justice to the enormity of such a question, which is above the pay grade of physics as it currently exists. <br></li><li><strong>Is this it? Have you brought me to the end of the path of understanding QM?</strong> No, I’ve just pointed the way to the <em>beginning</em> of the path. The most fundamental tenet of the Zen AntiInterpretation is that there’s no shortcut to actually working through the Bell inequality, quantum teleportation, Shor’s algorithm, the KochenSpecker and PBR theorems, possibly even a photon or hydrogen atom, so you see quantum probability in action. I’m further along the path than I was twenty years ago, but not as far along as some of my colleagues. Even the greatest quantum Zen masters will be able to get further when new quantum phenomena and protocols are discovered in the future. All the same, though—and this is another major teaching of the Zen AntiInterpretation—there’s more to life than achieving greater and greater clarity about the foundations of QM. And on that note…</li></ol>
<p>To those who asked me about Claus Peter Schnorr’s <a href="https://eprint.iacr.org/2021/232">claim</a> to have discovered a fast <em>classical</em> factoring algorithm, thereby “destroying” (in his words) the RSA cryptosystem, see (e.g.) <a href="https://twitter.com/inf_0_/status/1367376526300172288?fbclid=IwAR19Ip7XyoPjHfm9WBzqiUkQpxUVLGfVTgLGQmmncgrkUsvcLIrkzbOPw_U">this Twitter thread by Keegan Ryan</a>, which explains what certainly <em>looks</em> like a fatal error in Schnorr’s paper.</p>
Metaphysical Spouting
Quantum
Scott

'Egg carton' quantum dot array could lead to ultralow power devices
https://www.sciencedaily.com/releases/2021/03/210304125324.htm
Quantum Computers News  ScienceDaily
urn:uuid:b391d1c32a5061601f55698c1b85cbe0
Thu, 04 Mar 2021 17:53:24 +0000
A new path toward sending and receiving information with single photons of light has been discovered by an international team of researchers.

Quantum Shorts festival announces three film winners
https://uwaterloo.ca/instituteforquantumcomputing/news/quantumshortsfestivalannouncesthreefilmwinners
Institute for Quantum Computing
urn:uuid:99727c3c29cd0cf3995972e4c04fb369
Thu, 04 Mar 2021 00:00:00 +0000
<p>Thursday, March 4, 2021</p>
<p><img alt="Stills from the three winners" class="imagebody500pxwide" height="262" src="https://uwaterloo.ca/instituteforquantumcomputing/sites/ca.instituteforquantumcomputing/files/styles/body500pxwide/public/uploads/images/fb_ad_winners.jpg?itok=K0q4RULQ" width="500" /></p>
<p>“I am Andra. Number 2342. In a few hours I will cease to exist,” opens the short film <i>Gods</i>. The futuristic fantasy film, bringing us the last message of a civilisation that deciphered the secrets of quantum physics, has taken First Prize in the Quantum Shorts festival.
12011

Heatfree optical switch would enable optical quantum computing chips
https://www.sciencedaily.com/releases/2021/03/210303142456.htm
Quantum Computers News  ScienceDaily
urn:uuid:4f674327e696d49088388813f69a9858
Wed, 03 Mar 2021 19:24:56 +0000
In a potential boost for quantum computing and communication, a European research collaboration reported a new method of controlling and manipulating single photons without generating heat. The solution makes it possible to integrate optical switches and singlephoton detectors in a single chip.

A quantum internet is closer to reality, thanks to this switch
https://www.sciencedaily.com/releases/2021/03/210302154236.htm
Quantum Computers News  ScienceDaily
urn:uuid:3030f36f6a3c305aff0eb3b43f63573b
Tue, 02 Mar 2021 20:42:36 +0000
When quantum computers become more powerful and widespread, they will need a robust quantum internet to communicate. Engineers have addressed an issue barring the development of quantum networks that are big enough to reliably support more than a handful of users.

Quantum quirk yields giant magnetic effect, where none should exist
https://www.sciencedaily.com/releases/2021/02/210226140453.htm
Quantum Computers News  ScienceDaily
urn:uuid:273a52af81e8932a2563cfc28a22fae8
Fri, 26 Feb 2021 19:04:53 +0000
In a twist befitting the strange nature of quantum mechanics, physicists have discovered the Hall effect  a characteristic change in the way electricity is conducted in the presence of a magnetic field  in a nonmagnetic quantum material to which no magnetic field was applied.