AVS Quantum Science Current Issue
https://pubs.aip.org/aqs
en-usMon, 11 Sep 2023 00:00:00 GMTMon, 11 Sep 2023 22:46:08 GMTSilverchaireditor@pubs.aip.org/aqswebmaster@pubs.aip.org/aqsQuantum double structure in cold atom superfluids
https://pubs.aip.org/avs/aqs/article/5/3/033201/2910702/Quantum-double-structure-in-cold-atom-superfluids
Mon, 11 Sep 2023 00:00:00 GMT<span class="paragraphSection">The theory of topological quantum computation is underpinned by two important classes of models. One is based on non-abelian Chern–Simons theory, which yields the so-called SU ( 2 ) k anyon models that often appear in the context of electrically charged quantum fluids. The physics of the other is captured by symmetry broken Yang–Mills theory in the absence of a Chern–Simons term and results in the so-called quantum double models. Extensive resources have been invested into the search for SU ( 2 ) k anyon quasi-particles, in particular, the so-called Ising anyons (<span style="font-style:italic;">k</span> = 2) of which Majorana zero modes are believed to be an incarnation. In contrast to the SU ( 2 ) k models, quantum doubles have attracted little attention in experiments despite their pivotal role in the theory of error correction. Beyond topological error correcting codes, the appearance of quantum doubles has been limited to contexts primarily within mathematical physics, and as such, they are of seemingly little relevance for the study of experimentally tangible systems. However, recent works suggest that quantum double anyons may be found in spinor Bose–Einstein condensates. In light of this, the core purpose of this article is to provide a self-contained exposition of the quantum double structure, framed in the context of spinor condensates, by constructing explicitly the quantum doubles for various ground state symmetry groups and discuss their experimental realisability. We also derive analytically an equation for the quantum double Clebsch–Gordan coefficients from which the relevant braid matrices can be worked out. Finally, the existence of a particle-vortex duality is exposed and illuminated upon in this context.</span>5303320110.1116/5.0155096https://pubs.aip.org/avs/aqs/article/5/3/033201/2910702/Quantum-double-structure-in-cold-atom-superfluidsNondestructively probing the thermodynamics of quantum systems with qumodes
https://pubs.aip.org/avs/aqs/article/5/3/034402/2909937/Nondestructively-probing-the-thermodynamics-of
Thu, 07 Sep 2023 00:00:00 GMT<span class="paragraphSection">Quantum systems are by their very nature fragile. The fundamental backaction on a state due to quantum measurement notwithstanding, there is also in practice often a destruction of the system itself due to the means of measurement. This becomes acutely problematic when we wish to make measurements of the same system at multiple times, or generate a large quantity of measurement statistics. One approach to circumventing this is the use of ancillary probes that couple to the system under investigation, and through their interaction, enable properties of the primary system to be imprinted onto and inferred from the ancillae. Here we highlight means by which continuous variable quantum modes (qumodes) can be employed to probe the thermodynamics of quantum systems in and out of equilibrium, including thermometry, reconstruction of the partition function, and reversible and irreversible work. We illustrate application of our results with the example of a spin-1/2 system in a transverse field.</span>5303440210.1116/5.0139099https://pubs.aip.org/avs/aqs/article/5/3/034402/2909937/Nondestructively-probing-the-thermodynamics-ofDynamic phases induced by two-level system defects on driven qubits
https://pubs.aip.org/avs/aqs/article/5/3/036201/2909874/Dynamic-phases-induced-by-two-level-system-defects
Wed, 06 Sep 2023 00:00:00 GMT<span class="paragraphSection">Recent experimental evidences point to two-level defects, located in the oxides and on the interfaces of the Josephson junctions, as the major constituents of decoherence in superconducting qubits. How these defects affect the qubit evolution with the presence of external driving is less well understood since the semiclassical qubit-field coupling renders the Jaynes–Cummings model for qubit-defect coupling undiagonalizable. We analyze the decoherence dynamics in the continuous coherent state space induced by the driving and solve the master equation endowed with an extra decay-cladded driving term via a Fokker–Planck equation. The solutions for diffusion propagators as Gaussian distributions show four distinct dynamic phases: four types of convergence paths to limit cycles of varying radius by the distribution mean, which are determined by the competing external driving and the defect decays. The qubit trajectory resulted from these solutions is a super-Poissonian over displaced Fock states, which reduces to a Gibbs state of effective temperature decided by the defect at zero driving limit. Furthermore, the Poincare map shows the dependence of the rate of convergence on the initial state. In other words, the qubit evolution can serve as an indicator of the defect coupling strength through the variation of the driving strength as a parameter.</span>5303620110.1116/5.0159488https://pubs.aip.org/avs/aqs/article/5/3/036201/2909874/Dynamic-phases-induced-by-two-level-system-defectsQuantum thermodynamics
https://pubs.aip.org/avs/aqs/article/5/3/030401/2906516/Quantum-thermodynamics
Fri, 11 Aug 2023 00:00:00 GMT<span class="paragraphSection">Are concepts of heat and efficiency applicable to atom-size machines or to nanoelectronics components? Can we rebuild thermodynamics from laws of quantum mechanics?</span>5303040110.1116/5.0160436https://pubs.aip.org/avs/aqs/article/5/3/030401/2906516/Quantum-thermodynamicsManQala: Game-inspired strategies for quantum state engineering
https://pubs.aip.org/avs/aqs/article/5/3/032002/2906390/ManQala-Game-inspired-strategies-for-quantum-state
Wed, 09 Aug 2023 00:00:00 GMT<span class="paragraphSection">The ability to prepare systems in specific target states through quantum engineering is essential for realizing the new technologies promised by a second quantum revolution. Here, we recast the fundamental problem of state preparation in high-dimensional Hilbert spaces as ManQala, a quantum game inspired by the West African sowing game mancala. Motivated by optimal gameplay in solitaire mancala, where nested nearest-neighbor permutations and actions evolve the state of the game board to its target configuration, ManQala acts as a pre-processing approach for deterministically arranging particles in a quantum control problem. Once pre-processing with ManQala is complete, existing quantum control methods are applied, but now with a reduced search space. We find that ManQala-type strategies match, or outperform, competing approaches in terms of final state variance even in small-scale quantum state engineering problems where we expect the slightest advantage, since the relative reduction in search space is the least. These results suggest that ManQala provides a rich platform for designing control protocols relevant to quantum technologies.</span>5303200210.1116/5.0148240https://pubs.aip.org/avs/aqs/article/5/3/032002/2906390/ManQala-Game-inspired-strategies-for-quantum-stateSequential minimum optimization algorithm with small sample size estimators
https://pubs.aip.org/avs/aqs/article/5/3/033801/2905708/Sequential-minimum-optimization-algorithm-with
Mon, 07 Aug 2023 00:00:00 GMT<span class="paragraphSection">Sequential minimum optimization is a machine learning global search training algorithm. It is applicable when the functional dependence of the cost function on a tunable parameter given the other parameters can be cheaply determined. This assumption is satisfied by quantum circuits built of known gates. We apply it to photonic circuits where the additional challenge appears: low frequency of coincidence events lowers the speed of the algorithm. We propose to modify the algorithm such that small sample size estimators are enough to successfully run the machine learning task. We demonstrate the effectiveness of the modified algorithm applying it to a photonic classifier with data reuploading.</span>5303380110.1116/5.0148369https://pubs.aip.org/avs/aqs/article/5/3/033801/2905708/Sequential-minimum-optimization-algorithm-withAccurate measurement of the loss rate of cold atoms due to background gas collisions for the quantum-based cold atom vacuum standard
https://pubs.aip.org/avs/aqs/article/5/3/035001/2905161/Accurate-measurement-of-the-loss-rate-of-cold
Tue, 01 Aug 2023 00:00:00 GMT<span class="paragraphSection">We present the measurements of thermalized collisional rate coefficients for ultra-cold <sup>7</sup>Li and <sup>87</sup>Rb colliding with room-temperature He, Ne, N<sub>2</sub>, Ar, Kr, and Xe. In our experiments, a combined flowmeter and dynamic expansion system, a vacuum metrology standard, is used to set a known number density for the room-temperature background gas in the vicinity of the magnetically trapped <sup>7</sup>Li or <sup>87</sup>Rb clouds. Each collision with a background atom or molecule removes a <sup>7</sup>Li or <sup>87</sup>Rb atom from its trap, and the change in the atom loss rate with background gas density is used to determine the thermalized loss rate coefficients with fractional standard uncertainties better than 1.6% for <sup>7</sup>Li and 2.7% for <sup>87</sup>Rb. We find consistency—a degree of equivalence of less than one—between the measurements and recent quantum-scattering calculations of the loss rate coefficients [Kłos and Tiesinga, J. Chem. Phys. <strong>158</strong>, 014308 (2023)], with the exception of the loss rate coefficient for both <sup>7</sup>Li and <sup>87</sup>Rb colliding with Ar. Nevertheless, the agreement between theory and experiment for all other studied systems provides validation that a quantum-based measurement of vacuum pressure using cold atoms also serves as a primary standard for vacuum pressure, which we refer to as the cold-atom vacuum standard.</span>5303500110.1116/5.0147686https://pubs.aip.org/avs/aqs/article/5/3/035001/2905161/Accurate-measurement-of-the-loss-rate-of-coldExchange fluctuation theorems for strongly interacting quantum pumps
https://pubs.aip.org/avs/aqs/article/5/3/032001/2901961/Exchange-fluctuation-theorems-for-strongly
Tue, 11 Jul 2023 00:00:00 GMT<span class="paragraphSection">We derive a general quantum exchange fluctuation theorem for multipartite systems with arbitrary coupling strengths by taking into account the informational contribution of the back-action of the quantum measurements, which contributes to the increase in the von-Neumann entropy of the quantum system. The resulting second law of thermodynamics is tighter than the conventional Clausius inequality. The derived bound is the quantum mutual information of the conditional thermal state, which is a thermal state conditioned on the initial energy measurement. These results elucidate the role of quantum correlations in the heat exchange between multiple subsystems.</span>5303200110.1116/5.0152186https://pubs.aip.org/avs/aqs/article/5/3/032001/2901961/Exchange-fluctuation-theorems-for-stronglyRevisiting wave–particle duality in Bohr–Einstein debate
https://pubs.aip.org/avs/aqs/article/5/3/031401/2900860/Revisiting-wave-particle-duality-in-Bohr-Einstein
Wed, 05 Jul 2023 00:00:00 GMT<span class="paragraphSection">The notion of wave–particle duality remains one of the most debated subjects in the history of quantum physics. The most famous debate on the subject occurred between Bohr and Einstein. In this work, we revisit the wave–particle duality in the Bohr–Einstein debate from the viewpoint of the recently established duality-entanglement relation. We show that the duality-entanglement relation can provide a valuable framework for quantitative analysis of the Einstein's gedanken double-slit experiment and clarify some of its fundamental aspects.</span>5303140110.1116/5.0148225https://pubs.aip.org/avs/aqs/article/5/3/031401/2900860/Revisiting-wave-particle-duality-in-Bohr-EinsteinOptimizing the phase sensitivity of Michelson interferometer with two-mode squeezed coherent input in the presence of loss and noise
https://pubs.aip.org/avs/aqs/article/5/3/034401/2900859/Optimizing-the-phase-sensitivity-of-Michelson
Wed, 05 Jul 2023 00:00:00 GMT<span class="paragraphSection">A Michelson-type interferometer with two-mode squeezed coherent state input is considered. Such an interferometer has a better phase sensitivity over the shot-noise limit by a factor of e 2 r, where <span style="font-style:italic;">r</span> is the squeezing parameter [Phys. Rev. A <strong>102</strong>, 022614 (2020)]. We show that when photon loss and noise in the two arms are asymmetric, an optimal choice of the squeezing angle can allow improvement in phase sensitivity without any increase in input or pump power. In particular, when loss occurs only in one arm of the interferometer, we can have improvement in phase sensitivity for photon loss up to 80%. Hence, a significant improvement can be made in several applications such as LiDAR, gyroscopes, and measuring refractive indices of highly absorptive/reflective materials.</span>5303440110.1116/5.0148632https://pubs.aip.org/avs/aqs/article/5/3/034401/2900859/Optimizing-the-phase-sensitivity-of-Michelson