1
|
Lieu S, Liu YJ, Gorshkov AV. Candidate for a Passively Protected Quantum Memory in Two Dimensions. PHYSICAL REVIEW LETTERS 2024; 133:030601. [PMID: 39094134 DOI: 10.1103/physrevlett.133.030601] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2022] [Accepted: 06/03/2024] [Indexed: 08/04/2024]
Abstract
An interesting problem in the field of quantum error correction involves finding a physical system that hosts a "passively protected quantum memory," defined as an encoded qubit coupled to an environment that naturally wants to correct errors. To date, a quantum memory stable against finite-temperature effects is known only in four spatial dimensions or higher. Here, we take a different approach to realize a stable quantum memory by relying on a driven-dissipative environment. We propose a new model, the photonic-Ising model, which appears to passively correct against both bit-flip and phase-flip errors in two dimensions: a square lattice composed of photonic "cat qubits" coupled via dissipative terms which tend to fix errors locally. Inspired by the presence of two distinct Z_{2}-symmetry-broken phases, our scheme relies on Ising-like dissipators to protect against bit flips and on a driven-dissipative photonic environment to protect against phase flips. We also discuss possible ways to realize the photonic-Ising model.
Collapse
|
2
|
van Mourik MW, Zapusek E, Hrmo P, Gerster L, Blatt R, Monz T, Schindler P, Reiter F. Experimental Realization of Nonunitary Multiqubit Operations. PHYSICAL REVIEW LETTERS 2024; 132:040602. [PMID: 38335353 DOI: 10.1103/physrevlett.132.040602] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/07/2023] [Accepted: 11/13/2023] [Indexed: 02/12/2024]
Abstract
We demonstrate a novel experimental tool set that enables irreversible multiqubit operations on a quantum platform. To exemplify our approach, we realize two elementary nonunitary operations: the or and nor gates. The electronic states of two trapped ^{40}Ca^{+} ions encode the logical information, and a cotrapped ^{88}Sr^{+} ion provides the irreversibility of the gate by a dissipation channel through sideband cooling. We measure 87% and 81% success rates for the or and nor gates, respectively. The presented methods are a stepping stone toward other nonunitary operations such as in quantum error correction and quantum machine learning.
Collapse
Affiliation(s)
- M W van Mourik
- Institut für Experimentalphysik, Universität Innsbruck, Technikerstraße 25/4, 6020 Innsbruck, Austria
| | - E Zapusek
- Institute for Quantum Electronics, ETH Zürich, Otto-Stern-Weg 1, 8093 Zürich, Switzerland
| | - P Hrmo
- Institut für Experimentalphysik, Universität Innsbruck, Technikerstraße 25/4, 6020 Innsbruck, Austria
| | - L Gerster
- Institut für Experimentalphysik, Universität Innsbruck, Technikerstraße 25/4, 6020 Innsbruck, Austria
| | - R Blatt
- Institut für Experimentalphysik, Universität Innsbruck, Technikerstraße 25/4, 6020 Innsbruck, Austria
| | - T Monz
- Institut für Experimentalphysik, Universität Innsbruck, Technikerstraße 25/4, 6020 Innsbruck, Austria
- AQT, Technikerstraße 17, 6020 Innsbruck, Austria
| | - P Schindler
- Institut für Experimentalphysik, Universität Innsbruck, Technikerstraße 25/4, 6020 Innsbruck, Austria
| | - F Reiter
- Institute for Quantum Electronics, ETH Zürich, Otto-Stern-Weg 1, 8093 Zürich, Switzerland
| |
Collapse
|
3
|
Zeng Y, Zhou ZY, Rinaldi E, Gneiting C, Nori F. Approximate Autonomous Quantum Error Correction with Reinforcement Learning. PHYSICAL REVIEW LETTERS 2023; 131:050601. [PMID: 37595216 DOI: 10.1103/physrevlett.131.050601] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/22/2022] [Accepted: 06/22/2023] [Indexed: 08/20/2023]
Abstract
Autonomous quantum error correction (AQEC) protects logical qubits by engineered dissipation and thus circumvents the necessity of frequent, error-prone measurement-feedback loops. Bosonic code spaces, where single-photon loss represents the dominant source of error, are promising candidates for AQEC due to their flexibility and controllability. While existing proposals have demonstrated the in-principle feasibility of AQEC with bosonic code spaces, these schemes are typically based on the exact implementation of the Knill-Laflamme conditions and thus require the realization of Hamiltonian distances d≥2. Implementing such Hamiltonian distances requires multiple nonlinear interactions and control fields, rendering these schemes experimentally challenging. Here, we propose a bosonic code for approximate AQEC by relaxing the Knill-Laflamme conditions. Using reinforcement learning (RL), we identify the optimal bosonic set of code words (denoted here by RL code), which, surprisingly, is composed of the Fock states |2⟩ and |4⟩. As we show, the RL code, despite its approximate nature, successfully suppresses single-photon loss, reducing it to an effective dephasing process that well surpasses the break-even threshold. It may thus provide a valuable building block toward full error protection. The error-correcting Hamiltonian, which includes ancilla systems that emulate the engineered dissipation, is entirely based on the Hamiltonian distance d=1, significantly reducing model complexity. Single-qubit gates are implemented in the RL code with a maximum distance d_{g}=2.
Collapse
Affiliation(s)
- Yexiong Zeng
- Theoretical Quantum Physics Laboratory, Cluster for Pioneering Research, RIKEN, Wakoshi, Saitama 351-0198, Japan
- Quantum Computing Center, RIKEN, Wakoshi, Saitama 351-0198, Japan
| | - Zheng-Yang Zhou
- Theoretical Quantum Physics Laboratory, Cluster for Pioneering Research, RIKEN, Wakoshi, Saitama 351-0198, Japan
| | - Enrico Rinaldi
- Theoretical Quantum Physics Laboratory, Cluster for Pioneering Research, RIKEN, Wakoshi, Saitama 351-0198, Japan
- Quantum Computing Center, RIKEN, Wakoshi, Saitama 351-0198, Japan
- Quantinuum K.K., Otemachi Financial City Grand Cube 3F, 1-9-2 Otemachi, Chiyoda-ku, Tokyo, Japan
- Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-1040, USA
- Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS), RIKEN, Wakoshi, Saitama 351-0198, Japan
| | - Clemens Gneiting
- Theoretical Quantum Physics Laboratory, Cluster for Pioneering Research, RIKEN, Wakoshi, Saitama 351-0198, Japan
- Quantum Computing Center, RIKEN, Wakoshi, Saitama 351-0198, Japan
| | - Franco Nori
- Theoretical Quantum Physics Laboratory, Cluster for Pioneering Research, RIKEN, Wakoshi, Saitama 351-0198, Japan
- Quantum Computing Center, RIKEN, Wakoshi, Saitama 351-0198, Japan
- Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-1040, USA
| |
Collapse
|
4
|
Bai SY, An JH. Floquet Engineering to Overcome No-Go Theorem of Noisy Quantum Metrology. PHYSICAL REVIEW LETTERS 2023; 131:050801. [PMID: 37595225 DOI: 10.1103/physrevlett.131.050801] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/06/2023] [Accepted: 07/17/2023] [Indexed: 08/20/2023]
Abstract
Permitting a more precise measurement to physical quantities than the classical limit by using quantum resources, quantum metrology holds a promise in developing many revolutionary technologies. However, the noise-induced decoherence forces its superiority to disappear, which is called no-go theorem of noisy quantum metrology and constrains its application. We propose a scheme to overcome the no-go theorem by Floquet engineering. It is found that, by applying a periodic driving on the atoms of the Ramsey spectroscopy, the ultimate sensitivity to measure their frequency characterized by quantum Fisher information returns to the ideal t^{2} scaling with the encoding time whenever a Floquet bound state is formed by the system consisting of each driven atom and its local noise. Combining with the optimal control, this mechanism also allows us to retrieve the ideal Heisenberg-limit scaling with the atom number N. Our result gives an efficient way to avoid the no-go theorem of noisy quantum metrology and to realize high-precision measurements.
Collapse
Affiliation(s)
- Si-Yuan Bai
- Key Laboratory of Quantum Theory and Applications of MoE, Lanzhou Center for Theoretical Physics, and Key Laboratory of Theoretical Physics of Gansu Province, Lanzhou University, Lanzhou 730000, China
| | - Jun-Hong An
- Key Laboratory of Quantum Theory and Applications of MoE, Lanzhou Center for Theoretical Physics, and Key Laboratory of Theoretical Physics of Gansu Province, Lanzhou University, Lanzhou 730000, China
| |
Collapse
|
5
|
Quantum-enhanced radiometry via approximate quantum error correction. Nat Commun 2022; 13:3214. [PMID: 35680786 PMCID: PMC9184621 DOI: 10.1038/s41467-022-30410-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2021] [Accepted: 04/29/2022] [Indexed: 11/08/2022] Open
Abstract
Quantum sensing based on exotic quantum states is appealing for practical metrology applications and fundamental studies. However, these quantum states are vulnerable to noise and the resulting quantum enhancement is weakened in practice. Here, we experimentally demonstrate a quantum-enhanced sensing scheme with a bosonic probe, by exploring the large Hilbert space of the bosonic mode and developing both the approximate quantum error correction and the quantum jump tracking approaches. In a practical radiometry scenario, we attain a 5.3 dB enhancement of sensitivity, which reaches 9.1 × 10−4 Hz−1/2 when measuring the excitation population of a receiver mode. Our results demonstrate the potential of quantum sensing with near-term quantum technologies, not only shedding new light on the quantum advantage of sensing, but also stimulating further efforts on bosonic quantum technologies. Exotic quantum states can be advantageous for sensing, but are very fragile, so that some form of quantum error correction is needed. Here, the authors show how approximate QEC helps overcoming decoherence due to noise when measuring the excitation population of a receiver mode in a superconducting circuit.
Collapse
|
6
|
Rojkov I, Layden D, Cappellaro P, Home J, Reiter F. Bias in Error-Corrected Quantum Sensing. PHYSICAL REVIEW LETTERS 2022; 128:140503. [PMID: 35476469 DOI: 10.1103/physrevlett.128.140503] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/22/2021] [Revised: 12/21/2021] [Accepted: 01/28/2022] [Indexed: 06/14/2023]
Abstract
The sensitivity afforded by quantum sensors is limited by decoherence. Quantum error correction (QEC) can enhance sensitivity by suppressing decoherence, but it has a side effect: it biases a sensor's output in realistic settings. If unaccounted for, this bias can systematically reduce a sensor's performance in experiment, and also give misleading values for the minimum detectable signal in theory. We analyze this effect in the experimentally motivated setting of continuous-time QEC, showing both how one can remedy it, and how incorrect results can arise when one does not.
Collapse
Affiliation(s)
- Ivan Rojkov
- Institute for Quantum Electronics, ETH Zürich, 8093 Zürich, Switzerland
| | - David Layden
- Research Laboratory of Electronics and Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Paola Cappellaro
- Research Laboratory of Electronics and Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Jonathan Home
- Institute for Quantum Electronics, ETH Zürich, 8093 Zürich, Switzerland
| | - Florentin Reiter
- Institute for Quantum Electronics, ETH Zürich, 8093 Zürich, Switzerland
| |
Collapse
|
7
|
Temporal Quantum Memory and Non-Locality of Two Trapped Ions under the Effect of the Intrinsic Decoherence: Entropic Uncertainty, Trace Norm Nonlocality and Entanglement. Symmetry (Basel) 2022. [DOI: 10.3390/sym14040648] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The engineering properties of trapped ions and their capacity to engender numerous quantum information resources determine many aspects of quantum information processing. We devise a setup of coherent and even coherent fields acting on two trapped ions to generate quantum memory, non-locality, and entanglement. Various effects, such as intrinsic decoherence, Lamb–Dicke regime, and dipole–dipole interaction are investigated. The inter-coupling of trapped ions, as well as the generation and dynamics of correlations between them, are analyzed. Using quantum memory assisted entropic uncertainty, trace-norm measurement induced non-locality, and concurrence, we find that the coherent and even coherent fields successfully generate non-local correlations in trapped-ions, with the latter being more resourceful for the dynamics and preservation of the non-local correlations. Furthermore, we observe that the entropic uncertainty and the trace norm induced non-locality present symmetrical dynamics. The dipole–dipole interaction improves correlation’s generation, robustness, and entropic uncertainty suppression.
Collapse
|
8
|
Ma WL, Puri S, Schoelkopf RJ, Devoret MH, Girvin SM, Jiang L. Quantum control of bosonic modes with superconducting circuits. Sci Bull (Beijing) 2021; 66:1789-1805. [PMID: 36654386 DOI: 10.1016/j.scib.2021.05.024] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2021] [Revised: 05/20/2021] [Accepted: 05/24/2021] [Indexed: 01/20/2023]
Abstract
Bosonic modes have wide applications in various quantum technologies, such as optical photons for quantum communication, magnons in spin ensembles for quantum information storage and mechanical modes for reversible microwave-to-optical quantum transduction. There is emerging interest in utilizing bosonic modes for quantum information processing, with circuit quantum electrodynamics (circuit QED) as one of the leading architectures. Quantum information can be encoded into subspaces of a bosonic superconducting cavity mode with long coherence time. However, standard Gaussian operations (e.g., beam splitting and two-mode squeezing) are insufficient for universal quantum computing. The major challenge is to introduce additional nonlinear control beyond Gaussian operations without adding significant bosonic loss or decoherence. Here we review recent advances in universal control of a single bosonic code with superconducting circuits, including unitary control, quantum feedback control, driven-dissipative control and holonomic dissipative control. Various approaches to entangling different bosonic modes are also discussed.
Collapse
Affiliation(s)
- Wen-Long Ma
- State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China; Pritzker School of Molecular Engineering, University of Chicago, Illinois 60637, USA
| | - Shruti Puri
- Department of Applied Physics and Physics, Yale University, New Haven, Connecticut 06511, USA; Yale Quantum Institute, Yale University, New Haven, Connecticut 06511, USA
| | - Robert J Schoelkopf
- Department of Applied Physics and Physics, Yale University, New Haven, Connecticut 06511, USA; Yale Quantum Institute, Yale University, New Haven, Connecticut 06511, USA
| | - Michel H Devoret
- Department of Applied Physics and Physics, Yale University, New Haven, Connecticut 06511, USA; Yale Quantum Institute, Yale University, New Haven, Connecticut 06511, USA
| | - S M Girvin
- Department of Applied Physics and Physics, Yale University, New Haven, Connecticut 06511, USA; Yale Quantum Institute, Yale University, New Haven, Connecticut 06511, USA
| | - Liang Jiang
- Pritzker School of Molecular Engineering, University of Chicago, Illinois 60637, USA.
| |
Collapse
|
9
|
|
10
|
Bácsi Á, Moca CP, Zaránd G, Dóra B. Vaporization Dynamics of a Dissipative Quantum Liquid. PHYSICAL REVIEW LETTERS 2020; 125:266803. [PMID: 33449736 DOI: 10.1103/physrevlett.125.266803] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2020] [Accepted: 12/07/2020] [Indexed: 06/12/2023]
Abstract
We investigate the stability of a Luttinger liquid, upon suddenly coupling it to a dissipative environment. Within the Lindblad equation, the environment couples to local currents and heats the quantum liquid up to infinite temperatures. The single particle density matrix reveals the fractionalization of fermionic excitations in the spatial correlations by retaining the initial noninteger power law exponents, accompanied by an exponential decay in time with an interaction dependent rate. The spectrum of the time evolved density matrix is gapped, which collapses gradually as -ln(t). The von Neumann entropy crosses over from the early time -tln(t) behavior to ln(t) growth for late times. The early time dynamics is captured numerically by performing simulations on spinless interacting fermions, using several numerically exact methods. Our results could be tested experimentally in bosonic Luttinger liquids.
Collapse
Affiliation(s)
- Ádám Bácsi
- MTA-BME Lendület Topology and Correlation Research Group, Budapest University of Technology and Economics, 1521 Budapest, Hungary
- Department of Mathematics and Computational Sciences, Széchenyi István University, 9026 Győr, Hungary
| | - Cătălin Paşcu Moca
- MTA-BME Quantum Dynamics and Correlations Research Group, Budapest University of Technology and Economics, 1521 Budapest, Hungary
- Department of Physics, University of Oradea, 410087 Oradea, Romania
| | - Gergely Zaránd
- MTA-BME Quantum Dynamics and Correlations Research Group, Budapest University of Technology and Economics, 1521 Budapest, Hungary
- BME-MTA Exotic Quantum Phases Research Group, Department of Theoretical Physics, Budapest University of Technology and Economics, 1521 Budapest, Hungary
| | - Balázs Dóra
- MTA-BME Lendület Topology and Correlation Research Group, Budapest University of Technology and Economics, 1521 Budapest, Hungary
- Department of Theoretical Physics, Budapest University of Technology and Economics, 1521 Budapest, Hungary
| |
Collapse
|
11
|
Gau M, Egger R, Zazunov A, Gefen Y. Driven Dissipative Majorana Dark Spaces. PHYSICAL REVIEW LETTERS 2020; 125:147701. [PMID: 33064546 DOI: 10.1103/physrevlett.125.147701] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/30/2020] [Accepted: 09/01/2020] [Indexed: 06/11/2023]
Abstract
Pure quantum states can be stabilized in open quantum systems subject to external driving forces and dissipation by environmental modes. We show that driven dissipative (DD) Majorana devices offer key advantages for stabilizing degenerate state manifolds ("dark spaces") and for manipulating states in dark spaces, both with respect to native (non-DD) Majorana devices and to DD platforms with topologically trivial building blocks. For two tunnel-coupled Majorana boxes, using otherwise only standard hardware elements (e.g., a noisy electromagnetic environment and quantum dots with driven tunnel links), we propose a dark qubit encoding. We anticipate exceptionally high fault tolerance levels due to a conspiracy of DD-based autonomous error correction and topology.
Collapse
Affiliation(s)
- Matthias Gau
- Institut für Theoretische Physik, Heinrich-Heine-Universität, D-40225 Düsseldorf, Germany
- Department of Condensed Matter Physics, Weizmann Institute, Rehovot, Israel
| | - Reinhold Egger
- Institut für Theoretische Physik, Heinrich-Heine-Universität, D-40225 Düsseldorf, Germany
| | - Alex Zazunov
- Institut für Theoretische Physik, Heinrich-Heine-Universität, D-40225 Düsseldorf, Germany
| | - Yuval Gefen
- Department of Condensed Matter Physics, Weizmann Institute, Rehovot, Israel
| |
Collapse
|
12
|
|
13
|
Cimini V, Gianani I, Spagnolo N, Leccese F, Sciarrino F, Barbieri M. Calibration of Quantum Sensors by Neural Networks. PHYSICAL REVIEW LETTERS 2019; 123:230502. [PMID: 31868431 DOI: 10.1103/physrevlett.123.230502] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/30/2019] [Indexed: 06/10/2023]
Abstract
Introducing quantum sensors as a solution to real world problems demands reliability and controllability outside of laboratory conditions. Producers and operators ought to be assumed to have limited resources readily available for calibration, and yet, they should be able to trust the devices. Neural networks are almost ubiquitous for similar tasks for classical sensors: here we show the applications of this technique to calibrating a quantum photonic sensor. This is based on a set of training data, collected only relying on the available probe states, hence reducing overhead. We found that covering finely the parameter space is key to achieving uncertainties close to their ultimate level. This technique has the potential to become the standard approach to calibrate quantum sensors.
Collapse
Affiliation(s)
- Valeria Cimini
- Dipartimento di Scienze, Università degli Studi Roma Tre, Via della Vasca Navale 84, 00146, Rome, Italy
| | - Ilaria Gianani
- Dipartimento di Scienze, Università degli Studi Roma Tre, Via della Vasca Navale 84, 00146, Rome, Italy
- Dipartimento di Fisica, Sapienza Università di Roma, Piazzale Aldo Moro, 5, 00185, Rome, Italy
| | - Nicolò Spagnolo
- Dipartimento di Fisica, Sapienza Università di Roma, Piazzale Aldo Moro, 5, 00185, Rome, Italy
| | - Fabio Leccese
- Dipartimento di Scienze, Università degli Studi Roma Tre, Via della Vasca Navale 84, 00146, Rome, Italy
| | - Fabio Sciarrino
- Dipartimento di Fisica, Sapienza Università di Roma, Piazzale Aldo Moro, 5, 00185, Rome, Italy
- Consiglio Nazionale delle Ricerche, Istituto dei sistemi Complessi (CNR-ISC), Via dei Taurini 19, 00185, Rome, Italy
| | - Marco Barbieri
- Dipartimento di Scienze, Università degli Studi Roma Tre, Via della Vasca Navale 84, 00146, Rome, Italy
- Istituto Nazionale di Ottica-CNR, Largo Enrico Fermi 6, 50125, Florence, Italy
| |
Collapse
|
14
|
Li DX, Liao XM, Shao XQ. One-way quantum state transfer in a lossy coupled-cavity array. OPTICS EXPRESS 2019; 27:35971-35980. [PMID: 31878761 DOI: 10.1364/oe.27.035971] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/16/2019] [Accepted: 11/11/2019] [Indexed: 06/10/2023]
Abstract
Quantum state transfer plays an important role in quantum information processing, and it has been obtained many of the theoretical and experimental triumphs. But designing a dissipation-assisted scheme to transfer a quantum state is still by no means trivial. Here we put forward an easier scheme to dissipatively transfer an arbitrary quantum state from a sender to a receiver with two four-level atoms and three lasers in a lossy coupled-cavity array, and make the quantum state stable at the receiver via the photon loss of optical cavities. Owing to the assistance of the dissipation, the target state becomes the steady state of the whole process. Thus there is no requirement on external time-dependent controls. Furthermore, the atomic spontaneous emission can be significantly suppressed as the adiabatic elimination of the excited states. We also discuss the experimental feasibility of this scheme with the current experimental technologies and a high fidelity of the transferred state in the receiver can be above 98%.
Collapse
|
15
|
Stabilization of All Bell States in a Lossy Coupled-Cavity Array. ENTROPY 2019; 21:e21040402. [PMID: 33267116 PMCID: PMC7514889 DOI: 10.3390/e21040402] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/07/2019] [Revised: 04/13/2019] [Accepted: 04/14/2019] [Indexed: 11/17/2022]
Abstract
A scheme is proposed to generate maximally entangled states of two Λ-type atoms trapped in separate overdamped optical cavities using quantum-jump-based feedback. This proposal can stabilize not only the singlet state, but also the other three triplet states by alternating the detuning parameter and relative phase of the classical fields. Meanwhile it is convenient to manipulate atoms, and much more robust against spontaneous emission of atoms. The parameters related to the potential experiment are analyzed comprehensively and it is confirmed that the quantum feedback technology is a significant tool for entanglement production with a high fidelity.
Collapse
|
16
|
Layden D, Zhou S, Cappellaro P, Jiang L. Ancilla-Free Quantum Error Correction Codes for Quantum Metrology. PHYSICAL REVIEW LETTERS 2019; 122:040502. [PMID: 30768303 DOI: 10.1103/physrevlett.122.040502] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/05/2018] [Indexed: 06/09/2023]
Abstract
Quantum error correction has recently emerged as a tool to enhance quantum sensing under Markovian noise. It works by correcting errors in a sensor while letting a signal imprint on the logical state. This approach typically requires a specialized error-correcting code, as most existing codes correct away both the dominant errors and the signal. To date, however, few such specialized codes are known, among which most require noiseless, controllable ancillas. We show here that such ancillas are not needed when the signal Hamiltonian and the error operators commute, a common limiting type of decoherence in quantum sensors. We give a semidefinite program for finding optimal ancilla-free sensing codes in general, as well as closed-form codes for two common sensing scenarios: qubits undergoing dephasing, and a lossy bosonic mode. Finally, we analyze the sensitivity enhancement offered by the qubit code under arbitrary spatial noise correlations, beyond the ideal limit of orthogonal signal and noise operators.
Collapse
Affiliation(s)
- David Layden
- Research Laboratory of Electronics and Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Sisi Zhou
- Departments of Applied Physics and Physics, Yale University, New Haven, Connecticut 06511, USA
- Yale Quantum Institute, Yale University, New Haven, Connecticut 06511, USA
| | - Paola Cappellaro
- Research Laboratory of Electronics and Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Liang Jiang
- Departments of Applied Physics and Physics, Yale University, New Haven, Connecticut 06511, USA
- Yale Quantum Institute, Yale University, New Haven, Connecticut 06511, USA
| |
Collapse
|
17
|
Experimental repetitive quantum channel simulation. Sci Bull (Beijing) 2018; 63:1551-1557. [PMID: 36751075 DOI: 10.1016/j.scib.2018.11.010] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2018] [Revised: 11/17/2018] [Accepted: 11/19/2018] [Indexed: 11/22/2022]
Abstract
Universal control of quantum systems is a major goal to be achieved for quantum information processing, which demands thorough understanding of fundamental quantum mechanics and promises applications of quantum technologies. So far, most studies concentrate on ideally isolated quantum systems governed by unitary evolutions, while practical quantum systems are open and described by quantum channels due to their inevitable coupling to environment. Here, we experimentally simulate arbitrary quantum channels for an open quantum system, i.e. a single photonic qubit in a superconducting quantum circuit. The arbitrary channel simulation is achieved with minimum resource of only one ancilla qubit and measurement-based adaptive control. By repetitively implementing the quantum channel simulation, we realize an arbitrary Liouvillian for a continuous evolution of an open quantum system for the first time. Our experiment provides not only a testbed for understanding quantum noise and decoherence, but also a powerful tool for full control of practical open quantum systems.
Collapse
|