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Tolerance-enhanced SU(1,1) interferometers using asymmetric gain

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Chinese Physics B 2023年第1期32卷 190-195页

作者：张建东王帅 School of Mathematics and Physics Jiangsu University of TechnologyChangzhou 213001China

SU(1,1) interferometers play an important role in quantum metrology. Previous studies focus on various inputs and detection strategies with symmetric gain. In this paper, we analyze a modified SU(1,1) interferometer using asymmetric gain. Two vacuum states are used as the input and on–off detection is performed at the output. In a lossless scenario,symmetric gain is the optimal selection and the corresponding phase sensitivity can achieve the heisenberg limit as well as the quantum Cramer–Rao bound. In addition, we analyze the phase sensitivity with symmetric gain in the lossy *** phase sensitivity is sensitive to internal losses but extremely robust against external losses. We address the optimal asymmetric gain and the results suggest that this method can improve the tolerance to internal losses. Our work may contribute to the practical development of quantum metrology.

关键词： SU(1 1)interferometer asymmetric gain heisenberg limit quantum Cramer–Rao bound

Feedback control and quantum error correction assisted quantum multi-parameter estimation

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Chinese Physics B 2023年第4期32卷 260-267页

作者：洪海源鲁秀娟匡森 Department of Automation University of Science and Technology of ChinaHefei 230027China Department of Mechanical Engineering The University of Hong KongHong Kong 999077China

Quantum metrology provides a fundamental limit on the precision of multi-parameter estimation,called the heisenberg limit,which has been achieved in noiseless quantum ***,for systems subject to noises,it is hard to achieve this limit since noises are inclined to destroy quantum coherence and *** this paper,a combined control scheme with feedback and quantum error correction(QEC)is proposed to achieve the heisenberg limit in the presence of spontaneous emission,where the feedback control is used to protect a stabilizer code space containing an optimal probe state and an additional control is applied to eliminate the measurement incompatibility among three *** an ancilla system is necessary for the preparation of the optimal probe state,our scheme does not require the ancilla system to be *** addition,the control scheme in this paper has a low-dimensional code *** the three components of a magnetic field,it can achieve the highest estimation precision with only a 2-dimensional code space,while at least a4-dimensional code space is required in the common optimal error correction protocols.

关键词： quantum multi-parameter estimation feedback control quantum error correction heisenberg limit

Persistent and enhanced spin-nematic squeezing in a spinor Bose–Einstein condensate

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Communications in Theoretical Physics 2022年第2期74卷 44-50页

作者： Xinfang Li Jianning Liu Osei Seth Heng-Na Xiong Qing-Shou Tan Yixiao Huang School of Science Zhejiang University of Science and TechnologyHangzhou 310023China School of Mechanical and Electrical Engineering University of Electronic Science and Technology of ChinaChengdu 611731China Department of Applied Physics Zhejiang University of TechnologyHangzhou 310023China School of Physics&Electronic Science Hunan Institute of Science and TechnologyYueyang 414006China

We propose a simple scheme to realize the persistent spin-nematic squeezing in a spinor Bose–Einstein condensate by rapidly turning-off the external magnetic field at a time that maximal spinnematic squeezing *** observe that the optimal spin-nematic squeezing can be maintained in a nearly fixed *** a proper initial magnetic field,the optimal squeezing can be obviously *** further construct a spin-mixing interferometer,where the quantum correlation of the squeezed state(generated by our scheme)is fully utilized in the phase measurement,and show the phase sensitivity of the interferometer has a significant enhancement.

关键词： quantum metrology heisenberg limit interferometry

Two-parameter estimation in a matter-wave Sagnac interferometer

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Communications in Theoretical Physics 2020年第9期72卷 39-48页

作者： Xu Yu Hong-Bin Liang Xiao-Guang Wang Zhejiang Institute of Modem Physics Department of PhysicsZhejiang UniversityHangzhou 310027China Graduate School of China Academy of Engineering Physics Beijing 100193China

We explore the general characteristics of a matter-wave Sagnac interferometer in a two-parameter estimation scheme. We find that the measurement precisions of both parameters cannot reach the heisenberg limit(HL) simultaneously when the input state is maximally entangled. Only one of the parameters' uncertainties can approach the HL while the other is scaled by the standard quantum *** provide the conditions with which the measurement precision of the specific parameter can reach the HL. We also discuss and figure out the concrete expressions of the constraint conditions for saturating the quantum Cramér–Rao bound. To satisfy these constraint conditions, the evolution time has to be a series of discrete values. Additionally, we calculate the variances of the parameters through some examples under these constraint conditions. The results provided in our work show some intrinsic features of the matter-wave Sagnac interferometer for the two-parameter estimation, which can be valuable in actual experiments.

关键词： multi-parameter estimation matter wave Sagnac interferometer heisenberg limit

Quantum-enhanced interferometry with asymmetric beam splitters

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中国科学：物理学、力学、天文学英文版 2020年第6期63卷 22-32页

作者： Wei Zhong Fan Wang Lan Zhou Peng Xu YuBo Sheng Institute of Quantum Information and Technology Nanjing University of Posts and TelecommunicationsNanjing 210003China National Laboratory of Solid State Microstructures Nanjing UniversityNanjing 210093China School of Science Nanjing University of Posts and TelecommunicationsNanjing 210003China Key Lab of Broadband Wireless Communication and Sensor Network Technology Ministry of EducationNanjing University of Posts and TelecommunicationsNanjing 210003China

In this paper,we investigate the phase sensitivities in two-path optical interferometry with asymmetric beam ***,we present the optimal conditions for the transmission ratio and the phase of the beam splitter to gain the highest sensitivities for a general class of non-classical states with parity ***,we address the controversial question of whether the scheme with a combination of coherent state and photon-added or photon-subtracted squeezed vacuum state is better or worse than the most celebrated one using a combination of coherent state and squeezed vacuum state.

关键词： quantum metrology quantum Fisher information heisenberg limit optical interferometry

Toward Constructing a Continuous Logical Operator for Error-Corrected Quantum Sensing

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Journal of Quantum Information Science 2023年第2期13卷 45-55页

作者： Cameron Cianci Physics Department University of Connecticut Storrs CT USA

Error correction has long been suggested to extend the sensitivity of quantum sensors into the heisenberg limit. However, operations on logical qubits are only performed through universal gate sets consisting of finite-sized gates such as Clifford + T. Although these logical gate sets allow for universal quantum computation, the finite gate sizes present a problem for quantum sensing, since in sensing protocols, such as the Ramsey measurement protocol, the signal must act continuously. The difficulty in constructing a continuous logical op-erator comes from the Eastin-Knill theorem, which prevents a continuous sig-nal from being both fault-tolerant to local errors and transverse. Since error correction is needed to approach the heisenberg limit in a noisy environment, it is important to explore how to construct fault-tolerant continuous operators. In this paper, a protocol to design continuous logical z-rotations is proposed and applied to the Steane Code. The fault tolerance of the designed operator is investigated using the Knill-Laflamme conditions. The Knill-Laflamme condi-tions indicate that the diagonal unitary operator constructed cannot be fault tolerant solely due to the possibilities of X errors on the middle qubit. The ap-proach demonstrated throughout this paper may, however, find success in codes with more qubits such as the Shor code, distance 3 surface code, [15, 1, 3] code, or codes with a larger distance such as the [11, 1, 5] code.

关键词： Quantum Sensing Quantum Error Correction Steane Code heisenberg limit