 Subjects -> SCIENCES: COMPREHENSIVE WORKS (Total: 374 journals)
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- Single-particle versus many-body phase coherence in an interacting Fermi
gas-
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Authors: Giovanni Pecci; Piero Naldesi, Anna Minguzzi Luigi Amico
First page: 01LT03
Abstract: In quantum mechanics, each particle is described by a complex valued wave-function characterized by amplitude and phase. When many particles interact each other, cooperative phenomena give rise to a quantum many-body state with a specific quantum coherence. What is the interplay between single-particle’s phase coherence and many-body quantum coherence' Over the years, such question has been object of profound analysis in quantum physics. Here, we demonstrate how the time-dependent interference formed by releasing an interacting degenerate Fermi gas from a specific matter-wave circuit in an effective magnetic field can tell apart the two notions. Single-particle phase coherence, indicated by the first-order correlator, and many-body quantum coherence, indicated by the density–density correlator, are displayed as distinct features of the interferogram. Single particle phase coherence produces spiral interference of the Fermi orbitals at intermediate times. Many-body quantum coherence emerges as long times interference. The interplay between single-particle coherence and many-body coherence is reflected in a stepwise dependence of the interference pattern on the effective magnetic field.
Citation: Quantum Science and Technology
PubDate: 2022-12-06T00:00:00Z
DOI: 10.1088/2058-9565/aca712
Issue No: Vol. 8, No. 1 (2022)
- Optical atomic clock aboard an Earth-orbiting space station (OACESS):
enhancing searches for physics beyond the standard model in space-
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Authors: Vladimir Schkolnik; Dmitry Budker, Oliver Fartmann, Victor Flambaum, Leo Hollberg, Tigran Kalaydzhyan, Shimon Kolkowitz, Markus Krutzik, Andrew Ludlow, Nathan Newbury, Christoph Pyrlik, Laura Sinclair, Yevgeny Stadnik, Ingmari Tietje, Jun Ye Jason Williams
First page: 014003
Abstract: We present a concept for a high-precision optical atomic clock (OAC) operating on an Earth-orbiting space station. This pathfinder science mission will compare the space-based OAC with one or more ultra-stable terrestrial OACs to search for space-time-dependent signatures of dark scalar fields that manifest as anomalies in the relative frequencies of station-based and ground-based clocks. This opens the possibility of probing models of new physics that are inaccessible to purely ground-based OAC experiments where a dark scalar field may potentially be strongly screened near Earth’s surface. This unique enhancement of sensitivity to potential dark matter candidates harnesses the potential of space-based OACs.
Citation: Quantum Science and Technology
PubDate: 2022-11-18T00:00:00Z
DOI: 10.1088/2058-9565/ac9f2b
Issue No: Vol. 8, No. 1 (2022)
- Exploring the quantum world with a third generation ultra-cold atom
facility-
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Authors: R J Thompson; D Aveline, S W Chiow, E R Elliott, J R Kellogg, J m Kohel, M S Sbroscia, L Phillips, C Schneider, J R Williams, N Bigelow, P Engels, N Lundblad, C A Sackett L Woerner
First page: 014007
Abstract: We briefly describe a ‘third generation’ follow-on to the Cold Atom Lab mission, currently operating aboard the ISS and the Bose–Einstein Condensate and Cold Atom Lab mission, which is expected to launch in 2026. This mission would feature a modular design that would allow critical hardware to be optimized for specific investigations while allowing easy exchange with other hardware to enable a multi-user facility.
Citation: Quantum Science and Technology
PubDate: 2022-12-05T00:00:00Z
DOI: 10.1088/2058-9565/aca34f
Issue No: Vol. 8, No. 1 (2022)
- Verification of colorable hypergraph states with stabilizer test
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Authors: Hong Tao; Xiaoqian Zhang, Lei Shao Xiaoqing Tan
First page: 015012
Abstract: Many-body quantum states, as a matter of fact, are extremely essential to solve certain mathematical problems or simulate quantum systems in measurement-based quantum computation. However, how to verify large-scale quantum states, such as hypergraph states, is an exceedingly hard task for many-body quantum systems. Here, we propose a novel fault-tolerant solution for the verification of colorable hypergraph states by using the stabilizer test. Furthermore, our protocol is dramatically facilitated by making only Pauli-X and Pauli-Z measurements. For geometric structure hypergraph states, the computational complexity of our protocol is polynomial. As to appliance, it will be also applied to blind quantum computing based on the no-signaling principle.
Citation: Quantum Science and Technology
PubDate: 2022-11-21T00:00:00Z
DOI: 10.1088/2058-9565/aca1d8
Issue No: Vol. 8, No. 1 (2022)
- Benchmarking quantum error-correcting codes on quasi-linear and
central-spin processors-
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Authors: Regina Finsterhoelzl; Guido Burkard
First page: 015013
Abstract: We evaluate the performance of small error-correcting codes, which we tailor to hardware platforms of very different connectivity and coherence: on a superconducting processor based on transmon qubits and a spintronic quantum register consisting of a nitrogen-vacancy center in diamond. Taking the hardware-specific errors and connectivity into account, we investigate the dependence of the resulting logical error rate on the platform features such as the native gates, native connectivity, gate times, and coherence times. Using a standard error model parameterized for the given hardware, we simulate the performance and benchmark these predictions with experimental results when running the code on the superconducting quantum device. The results indicate that for small codes, the quasi-linear layout of the superconducting device is advantageous. Yet, for codes involving multi-qubit controlled operations, the central-spin connectivity of the color centers enables lower error rates.
Citation: Quantum Science and Technology
PubDate: 2022-11-25T00:00:00Z
DOI: 10.1088/2058-9565/aca21f
Issue No: Vol. 8, No. 1 (2022)
- Stationary optomagnonic entanglement and magnon-to-optics quantum state
transfer via opto-magnomechanics-
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Authors: Zhi-Yuan Fan; Hang Qian Jie Li
First page: 015014
Abstract: We show how to prepare a steady-state entangled state between magnons and optical photons in an opto-magnomechanical configuration, where a mechanical vibration mode couples to a magnon mode in a ferrimagnet by the dispersive magnetostrictive interaction, and to an optical cavity by the radiation pressure. We find that, by appropriately driving the magnon mode and the cavity to simultaneously activate the magnomechanical Stokes and the optomechanical anti-Stokes scattering, a stationary optomagnonic entangled state can be created. We further show that, by activating the magnomechanical state–swap interaction and subsequently sending a weak red-detuned optical pulse to drive the cavity, the magnonic state can be read out in the cavity output field of the pulse via the mechanical transduction. The demonstrated entanglement and state-readout protocols in such a novel opto-magnomechanical configuration allow us to optically control, prepare, and read out quantum states of collective spin excitations in solids, and provide promising opportunities for the study of quantum magnonics, macroscopic quantum states, and magnonic quantum information processing.
Citation: Quantum Science and Technology
PubDate: 2022-11-25T00:00:00Z
DOI: 10.1088/2058-9565/aca3cf
Issue No: Vol. 8, No. 1 (2022)
- Quantum correlations in molecules: from quantum resourcing to chemical
bonding-
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Authors: Lexin Ding; Stefan Knecht, Zoltán Zimborás Christian Schilling
First page: 015015
Abstract: The second quantum revolution is all about exploiting the quantum nature of atoms and molecules to execute quantum information processing tasks. To boost this growing endeavor and by anticipating the key role of quantum chemistry therein, our work establishes a framework for systematically exploring, quantifying and dissecting correlation effects in molecules. By utilizing the geometric picture of quantum states we compare—on a unified basis and in an operationally meaningful way—total, quantum and classical correlation and entanglement in molecular ground states. To unlock and maximize the quantum informational resourcefulness of molecules an orbital optimization scheme is developed, leading to a paradigm-shifting insight: a single covalent bond equates to the entanglement . This novel and more versatile perspective on electronic structure suggests a generalization of valence bond theory, overcoming deficiencies of modern chemical bonding theories.
Citation: Quantum Science and Technology
PubDate: 2022-12-05T00:00:00Z
DOI: 10.1088/2058-9565/aca4ee
Issue No: Vol. 8, No. 1 (2022)
- Quantum capsule networks
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Authors: Zidu Liu; Pei-Xin Shen, Weikang Li, L-M Duan Dong-Ling Deng
First page: 015016
Abstract: Capsule networks (CapsNets), which incorporate the paradigms of connectionism and symbolism, have brought fresh insights into artificial intelligence (AI). The capsule, as the building block of CapsNets, is a group of neurons represented by a vector to encode different features of an entity. The information is extracted hierarchically through capsule layers via routing algorithms. Here, we introduce a quantum capsule network (dubbed QCapsNet) together with an efficient quantum dynamic routing algorithm. To benchmark the performance of the QCapsNet, we carry out extensive numerical simulations on the classification of handwritten digits and symmetry-protected topological phases, and show that the QCapsNet can achieve an enhanced accuracy and outperform conventional quantum classifiers evidently. We further unpack the output capsule state and find that a particular subspace may correspond to a human-understandable feature of the input data, which indicates the potential explainability of such networks. Our work reveals an intriguing prospect of QCapsNets in quantum machine learning, which may provide a valuable guide towards explainable quantum AI.
Citation: Quantum Science and Technology
PubDate: 2022-12-05T00:00:00Z
DOI: 10.1088/2058-9565/aca55d
Issue No: Vol. 8, No. 1 (2022)
- Analytical framework for quantum alternating operator ansätze
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Authors: Stuart Hadfield; Tad Hogg Eleanor G Rieffel
First page: 015017
Abstract: We develop a framework for analyzing layered quantum algorithms such as quantum alternating operator ansätze (QAOA). In the context of combinatorial optimization, our framework relates quantum cost gradient operators, derived from the cost and mixing Hamiltonians, to classical cost difference functions that reflect cost function neighborhood structure. By considering QAOA circuits from the Heisenberg picture, we derive exact general expressions for expectation values as series expansions in the algorithm parameters, cost gradient operators, and cost difference functions. This enables novel interpretability and insight into QAOA behavior in various parameter regimes. For single-level QAOA1 we show the leading-order changes in the output probabilities and cost expectation value explicitly in terms of classical cost differences, for arbitrary cost functions. This demonstrates that, for sufficiently small positive parameters, probability flows from lower to higher cost states on average. By selecting signs of the parameters, we can control the direction of flow. We use these results to derive a classical random algorithm emulating QAOA1 in the small-parameter regime, i.e. that produces bitstring samples with the same probabilities as QAOA1 up to small error. For deeper QAOAp circuits we apply our framework to derive analogous and additional results in several settings. In particular we show QAOA always beats random guessing. We describe how our framework incorporates cost Hamiltonian locality for specific problem classes, including causal cone approaches, and applies to QAOA performance analysis with arbitrary parameters. We illuminate our results with a number of examples including applications to QUBO problems, MaxCut, and variants of MaxSAT. We illustrate the generalization of our framework to QAOA circuits using mixing unitaries beyond the transverse-field mixer through two examples of constrained optimization problems, Max Independent Set and Graph Coloring. We conclude by outlining some of the further applications we envision for the framework.
Citation: Quantum Science and Technology
PubDate: 2022-12-07T00:00:00Z
DOI: 10.1088/2058-9565/aca3ce
Issue No: Vol. 8, No. 1 (2022)
- Multi-axis control of a qubit in the presence of unknown non-Markovian
quantum noise-
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Authors: Akram Youssry; Hendra I Nurdin
First page: 015018
Abstract: In this paper, we consider the problem of open-loop control of a qubit that is coupled to an unknown fully quantum non-Markovian noise (either bosonic or fermionic). A graybox model that is empirically obtained from measurement data is employed to approximately represent the unknown quantum noise. The estimated model is then used to calculate the open-loop control pulses under constraints on the pulse amplitude and timing. For the control pulse optimization, we explore the use of gradient descent and genetic optimization methods. We consider the effect of finite sampling on estimating expectation values of observables and show results for single- and multi-axis control of a qubit.
Citation: Quantum Science and Technology
PubDate: 2022-12-13T00:00:00Z
DOI: 10.1088/2058-9565/aca711
Issue No: Vol. 8, No. 1 (2022)
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