@article {3396, title = {Data Needs and Challenges of Quantum Dot Devices Automation: Workshop Report}, year = {2023}, month = {12/21/2023}, abstract = {

Gate-defined quantum dots are a promising candidate system to realize scalable, coupled qubit systems and serve as a fundamental building block for quantum computers. However, present-day quantum dot devices suffer from imperfections that must be accounted for, which hinders the characterization, tuning, and operation process. Moreover, with an increasing number of quantum dot qubits, the relevant parameter space grows sufficiently to make heuristic control infeasible. Thus, it is imperative that reliable and scalable autonomous tuning approaches are developed. In this report, we outline current challenges in automating quantum dot device tuning and operation with a particular focus on datasets, benchmarking, and standardization. We also present ideas put forward by the quantum dot community on how to overcome them.

}, doi = {https://doi.org/10.48550/arXiv.2312.14322}, url = {https://arxiv.org/abs/2312.14322}, author = {Justyna P. Zwolak and Jacob M. Taylor and Reed Andrews and Jared Benson and Garnett Bryant and Donovan Buterakos and Anasua Chatterjee and Sankar Das Sarma and Mark A. Eriksson and Eli{\v s}ka Greplov{\'a} and Michael Gullans and Fabian Hader and Tyler J. Kovach and Pranav S. Mundada and Mick Ramsey and Torbjoern Rasmussen and Brandon Severin and Anthony Sigillito and Brennan Undseth and Brian Weber} } @article {3366, title = {Noncommuting conserved charges in quantum thermodynamics and beyond}, journal = {Nature Reviews Physics}, year = {2023}, month = {9/7/2023}, abstract = {

Thermodynamic systems typically conserve quantities (\"charges\") such as energy and particle number. The charges are often assumed implicitly to commute with each other. Yet quantum phenomena such as uncertainty relations rely on observables\&$\#$39; failure to commute. How do noncommuting charges affect thermodynamic phenomena? This question, upon arising at the intersection of quantum information theory and thermodynamics, spread recently across many-body physics. Charges\&$\#$39; noncommutation has been found to invalidate derivations of the thermal state\&$\#$39;s form, decrease entropy production, conflict with the eigenstate thermalization hypothesis, and more. This Perspective surveys key results in, opportunities for, and work adjacent to the quantum thermodynamics of noncommuting charges. Open problems include a conceptual puzzle: Evidence suggests that noncommuting charges may hinder thermalization in some ways while enhancing thermalization in others.

}, doi = {10.1038/s42254-023-00641-9}, url = {https://arxiv.org/abs/2306.00054}, author = {Shayan Majidy and William F. Braasch and Aleksander Lasek and Twesh Upadhyaya and Amir Kalev and Nicole Yunger Halpern} } @article {3289, title = {What happens to entropy production when conserved quantities fail to commute with each other}, year = {2023}, month = {5/24/2023}, abstract = {

We extend entropy production to a deeply quantum regime involving noncommuting conserved quantities. Consider a unitary transporting conserved quantities (\"charges\") between two systems initialized in thermal states. Three common formulae model the entropy produced. They respectively cast entropy as an extensive thermodynamic variable, as an information-theoretic uncertainty measure, and as a quantifier of irreversibility. Often, the charges are assumed to commute with each other (e.g., energy and particle number). Yet quantum charges can fail to commute. Noncommutation invites generalizations, which we posit and justify, of the three formulae. Charges\&$\#$39; noncommutation, we find, breaks the formulae\&$\#$39;s equivalence. Furthermore, different formulae quantify different physical effects of charges\&$\#$39; noncommutation on entropy production. For instance, entropy production can signal contextuality - true nonclassicality - by becoming nonreal. This work opens up stochastic thermodynamics to noncommuting - and so particularly quantum - charges.

}, url = {https://arxiv.org/abs/2305.15480}, author = {Twesh Upadhyaya and William F. Braasch, Jr. and Gabriel T. Landi and Nicole Yunger Halpern} } @article {2361, title = {Circuit Transformations for Quantum Architectures}, journal = {Proceedings of TQC 2019, LIPIcs}, volume = {135 }, year = {2019}, month = {02/25/2019}, chapter = {1-3:24}, abstract = {

Quantum computer architectures impose restrictions on qubit interactions. We propose efficient circuit transformations that modify a given quantum circuit to fit an architecture, allowing for any initial and final mapping of circuit qubits to architecture qubits. To achieve this, we first consider the qubit movement subproblem and use the routing via matchings framework to prove tighter bounds on parallel routing. In practice, we only need to perform partial permutations, so we generalize routing via matchings to that setting. We give new routing procedures for common architecture graphs and for the generalized hierarchical product of graphs, which produces subgraphs of the Cartesian product. Secondly, for serial routing, we consider the token swapping framework and extend a 4-approximation algorithm for general graphs to support partial permutations. We apply these routing procedures to give several circuit transformations, using various heuristic qubit placement subroutines. We implement these transformations in software and compare their performance for large quantum circuits on grid and modular architectures, identifying strategies that work well in practice.

}, doi = {https://doi.org/10.4230/LIPIcs.TQC.2019.3}, url = {https://arxiv.org/abs/1902.09102}, author = {Andrew M. Childs and Eddie Schoute and Cem M. Unsal} } @article {1998, title = {Electro-mechano-optical NMR detection}, journal = {Optica}, volume = {5}, year = {2018}, month = {2018/02/01}, pages = {152-158}, abstract = {

Signal reception of nuclear magnetic resonance (NMR) usually relies on electrical amplification of the electromotive force caused by nuclear induction. Here, we report up-conversion of a radio-frequency NMR signal to an optical regime using a high-stress silicon nitride membrane that interfaces the electrical detection circuit and an optical cavity through the electro-mechanical and the opto-mechanical couplings. This enables optical NMR detection without sacrificing the versatility of the traditional nuclear induction approach. While the signal-to-noise ratio is currently limited by the Brownian motion of the membrane as well as additional technical noise, we find it can exceed that of the conventional electrical schemes by increasing the electro-mechanical coupling strength. The electro-mechano-optical NMR detection presented here can even be combined with the laser cooling technique applied to nuclear spins.

}, doi = {10.1364/OPTICA.5.000152}, url = {https://www.osapublishing.org/optica/abstract.cfm?uri=optica-5-2-152}, author = {Kazuyuki Takeda and Kentaro Nagasaka and Atsushi Noguchi and Rekishu Yamazaki and Yasunobu Nakamura and Eiji Iwase and J. M. Taylor and Koji Usami} } @article {1464, title = {The Power of Quantum Fourier Sampling}, year = {2015}, month = {2015/07/20}, abstract = { A line of work initiated by Terhal and DiVincenzo and Bremner, Jozsa, and Shepherd, shows that quantum computers can efficiently sample from probability distributions that cannot be exactly sampled efficiently on a classical computer, unless the PH collapses. Aaronson and Arkhipov take this further by considering a distribution that can be sampled efficiently by linear optical quantum computation, that under two feasible conjectures, cannot even be approximately sampled classically within bounded total variation distance, unless the PH collapses. In this work we use Quantum Fourier Sampling to construct a class of distributions that can be sampled by a quantum computer. We then argue that these distributions cannot be approximately sampled classically, unless the PH collapses, under variants of the Aaronson and Arkhipov conjectures. In particular, we show a general class of quantumly sampleable distributions each of which is based on an "Efficiently Specifiable" polynomial, for which a classical approximate sampler implies an average-case approximation. This class of polynomials contains the Permanent but also includes, for example, the Hamiltonian Cycle polynomial, and many other familiar $\#$P-hard polynomials. Although our construction, unlike that proposed by Aaronson and Arkhipov, likely requires a universal quantum computer, we are able to use this additional power to weaken the conjectures needed to prove approximate sampling hardness results. }, url = {http://arxiv.org/abs/1507.05592v1}, author = {Bill Fefferman and Chris Umans} } @article {1342, title = {Optical detection of radio waves through a nanomechanical transducer}, journal = {Nature}, volume = {507}, year = {2014}, month = {2014/3/5}, pages = {81 - 85}, abstract = {Low-loss transmission and sensitive recovery of weak radio-frequency (rf) and microwave signals is an ubiquitous technological challenge, crucial in fields as diverse as radio astronomy, medical imaging, navigation and communication, including those of quantum states. Efficient upconversion of rf-signals to an optical carrier would allow transmitting them via optical fibers dramatically reducing losses, and give access to the mature toolbox of quantum optical techniques, routinely enabling quantum-limited signal detection. Research in the field of cavity optomechanics has shown that nanomechanical oscillators can couple very strongly to either microwave or optical fields. An oscillator accommodating both functionalities would bear great promise as the intermediate platform in a radio-to-optical transduction cascade. Here, we demonstrate such an opto-electro-mechanical transducer utilizing a high-Q nanomembrane. A moderate voltage bias (<10V) is sufficient to induce strong coupling between the voltage fluctuations in a rf resonance circuit and the membrane{\textquoteright}s displacement, which is simultaneously coupled to light reflected off its metallized surface. The circuit acts as an antenna; the voltage signals it induces are detected as an optical phase shift with quantum-limited sensitivity. The half-wave voltage is in the microvolt range, orders of magnitude below that of standard optical modulators. The noise added by the membrane is suppressed by the electro-mechanical cooperativity C~6800 and has a temperature of 40mK, far below 300K where the entire device is operated. This corresponds to a sensitivity limit as low as 5 pV/Hz^1/2, or -210dBm/Hz in a narrow band around 1 MHz. Our work introduces an entirely new approach to all-optical, ultralow-noise detection of classical electronic signals, and sets the stage for coherent upconversion of low-frequency quantum signals to the optical domain. }, doi = {10.1038/nature13029}, url = {http://arxiv.org/abs/1307.3467v2}, author = {T. Bagci and A. Simonsen and S. Schmid and L. G. Villanueva and E. Zeuthen and J. Appel and J. M. Taylor and A. S{\o}rensen and K. Usami and A. Schliesser and E. S. Polzik} } @article {1549, title = {On Beating the Hybrid Argument}, journal = {Proceedings, ITCS}, volume = {9}, year = {2012}, month = {2013/11/14}, pages = {809-843}, abstract = {The hybrid argument allows one to relate the distinguishability of a distribution (from uniform) to the predictability of individual bits given a prefix. The argument incurs a loss of a factor k equal to the bit-length of the distributions: -distinguishability implies only /k-predictability. This paper studies the consequences of avoiding this loss {\textendash} what we call {\textquotedblleft}beating the hybrid argument{\textquotedblright} {\textendash} and develops new proof techniques that circumvent the loss in certain natural settings. Specifically, we obtain the following results: 1. We give an instantiation of the Nisan-Wigderson generator (JCSS {\textquoteright}94) that can be broken by quantum computers, and that is o(1)-unpredictable against AC0 . This is not enough to imply indistinguishability via the hybrid argument because of the hybrid-argument loss; nevertheless, we conjecture that this generator indeed fools AC0 , and we prove this statement for a simplified version of the problem. Our conjecture implies the existence of an oracle relative to which BQP is not in the PH, a longstanding open problem. 2. We show that the {\textquotedblleft}INW{\textquotedblright} generator by Impagliazzo, Nisan, and Wigderson (STOC {\textquoteright}94) with seed length O(log n log log n) produces a distribution that is 1/ log n-unpredictable against poly-logarithmic width (general) read-once oblivious branching programs. Thus avoiding the hybrid-argument loss would lead to a breakthrough in generators against small space. 3. We study pseudorandom generators obtained from a hard function by repeated sampling. We identify a property of functions, {\textquotedblleft}resamplability,{\textquotedblright} that allows us to beat the hybrid argument, leading to new pseudorandom generators for AC0 [p] and similar classes. Although the generators have sub-linear stretch, they represent the best-known generators for these classes. Thus we establish that {\textquotedblleft}beating{\textquotedblright} or bypassing the hybrid argument would have two significant consequences in complexity, and we take steps toward that goal by developing techniques that indeed beat the hybrid argument in related (but simpler) settings, leading to best-known PRGs for certain complexity classes. }, url = {http://users.cms.caltech.edu/~umans/papers/FSUV10.pdf}, author = {Bill Fefferman and Ronen Shaltiel and Christopher Umans and Emanuele Viola} } @article {1463, title = {Pseudorandom generators and the BQP vs. PH problem}, year = {2010}, month = {2010/07/02}, abstract = { It is a longstanding open problem to devise an oracle relative to which BQP does not lie in the Polynomial-Time Hierarchy (PH). We advance a natural conjecture about the capacity of the Nisan-Wigderson pseudorandom generator [NW94] to fool AC_0, with MAJORITY as its hard function. Our conjecture is essentially that the loss due to the hybrid argument (which is a component of the standard proof from [NW94]) can be avoided in this setting. This is a question that has been asked previously in the pseudorandomness literature [BSW03]. We then make three main contributions: (1) We show that our conjecture implies the existence of an oracle relative to which BQP is not in the PH. This entails giving an explicit construction of unitary matrices, realizable by small quantum circuits, whose row-supports are "nearly-disjoint." (2) We give a simple framework (generalizing the setting of Aaronson [A10]) in which any efficiently quantumly computable unitary gives rise to a distribution that can be distinguished from the uniform distribution by an efficient quantum algorithm. When applied to the unitaries we construct, this framework yields a problem that can be solved quantumly, and which forms the basis for the desired oracle. (3) We prove that Aaronson{\textquoteright}s "GLN conjecture" [A10] implies our conjecture; our conjecture is thus formally easier to prove. The GLN conjecture was recently proved false for depth greater than 2 [A10a], but it remains open for depth 2. If true, the depth-2 version of either conjecture would imply an oracle relative to which BQP is not in AM, which is itself an outstanding open problem. Taken together, our results have the following interesting interpretation: they give an instantiation of the Nisan-Wigderson generator that can be broken by quantum computers, but not by the relevant modes of classical computation, if our conjecture is true. }, url = {http://arxiv.org/abs/1007.0305v3}, author = {Bill Fefferman and Christopher Umans} }