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A new ellipse fitting method of the minimum differential-mode noise in the atom interference gravimeter

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Chinese Physics B 2018年第7期27卷 190-195页

作者：许翱鹏王兆英孔德龙付志杰林强 Institute of Optics Department of Physics Zhejiang University Center for Optics and Optoelectronics research College of Science Zhejiang University of Technology

Ellipse fitting is a useful tool to obtain the differential signal of two atom interference gravimeters. The quality standard of ellipse fitting should be the deviation between the true phase and the fitting phase of the interference fringe. In this paper, we present a new algorithm to fit the ellipse. The algorithm is to minimize the differential noise of two interference gravimeters and obtain a more accurate value of the gravity gradient. We have theoretically derived the expression of the differential-mode noise and implemented the ellipse fitting in the program. This new algorithm is also compared with the classical methods.

关键词： ellipse fitting atom interference gravity measurement

Enhancement of Sensitivity by Initial Phase Matching in SU(1,1) Interferometers

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Communications in Theoretical Physics 2019年第1期71卷 37-42页

作者：肖骁梁宏宾李国龙王晓光 Zhejiang Institute of Modern Physics Department of Physics Zhejiang University

We derive a general phase-matching condition(PMC) for enhancement of sensitivity in SU(1,1) interferometers. under this condition, the quantum Fisher information(QFI) of two-mode SU(1,1) interferometry becomes maximal with respect to the relative phase of two modes, for the case of an arbitrary state in one input port and an even(odd) state in the other port, and the phase sensitivity is enhanced. We also find that optimal parameters can let the QFI in some areas achieve the Heisenberg limit for both pure and mixed initial states. As examples, we consider several input states: coherent and even coherent states, squeezed vacuum and even coherent states, squeezed thermal and even coherent states. Furthermore, in the realistic scenario of the photon loss channel, we investigate the effect of photon losses on QFI with numerical studies. We find the PMC remains unchanged and is not affected by the transmission coefficients for the above input states. Our results suggest that the PMC can exist in various kinds of interferometers and the phase-matching is robust to even strong photon losses.

关键词： quantum Fisher information SU(1,1) parameter estimation phase-matching condition

Majorana stellar representation for mixed-spin (s, 1/2) systems

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Chinese Physics B 2021年第3期30卷 168-175页

作者：苏玉国姚飞梁宏宾车彦明傅立斌王晓光 Zhejiang Province Key Laboratory of Quantum Technology and Device Department of PhysicsZhejiang UniversityHangzhou 310027China National Laboratory of Science and Technology on Computational Physics Institute of Applied Physics and Computational MathematicsBeijing 100088China

By describing the evolution of a quantum state with the trajectories of the Majorana stars on a Bloch sphere,Majorana’s stellar representation provides an intuitive geometric perspective to comprehend the quantum system with highdimensional Hilbert ***,the representation of a two-spin coupling system on a Bloch sphere has not been solved satisfactorily ***,a practical method is presented to resolve the problem for the mixed-spin(s,1/2)system and describe the entanglement of the *** system can be decomposed into two spins:spin-(s+1/2)and spin-(s−1/2)at the coupling bases,which can be regarded as independent ***,any pure state may be written as a superposition of two orthonormal states with one spin-(s+1/2)state and the other spin-(s−1/2)***,the whole initial state can be regarded as a state of a pseudo spin-1/*** this way,the mixed spin decomposes into three ***,the state can be represented by(2s+1)+(2s−1)+1=4s+1 sets of stars on a Bloch ***,some examples are given to show symmetric patterns on the Bloch sphere and unveil the properties of the high-spin system by analyzing the trajectories of the Majorana stars on the Bloch sphere.

关键词： Majorana’s stellar representation Bloch sphere high-dimensional projective Hilbert space mixedspin

Enhancing Phase Sensitivity in Mach–Zehnder Interferometers for Arbitrary Input States

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Chinese Physics Letters 2020年第7期37卷 1-4页

作者：梁宏宾裴健成王晓光 Zhejiang Institute of Modern Physics and Department of Physics Zhejiang UniversityHangzhou 310027China Graduate School of China Academy of Engineering Physics Beijing 100193China

To enhance the phase sensitivity of Mach–Zehnder interferometers,we use a tunable phase shift before the light beams are injected into the *** analytical result of the optimal phase shift is obtained,which only depends on the initial input *** a non-zero optimal phase shift,the phase sensitivity of the interferometers in the output ports is always *** can achieve this enhancement for most states,including entangled and mixed *** optimal phase shift is exhibited in three *** to previous methods,this scheme provides a general way to improve phase sensitivity and could find wide applications in optical phase estimations.

关键词： states. optimal phase

Majorana's stellar representation for the quantum geometric tensor of symmetric states

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Communications in Theoretical Physics 2022年第6期74卷 31-38页

作者： Xingyu Zhang Jiancheng Pei Libin Fu Xiaoguang Wang Zhejiang Institute of Modern Physics Department of PhysicsZhejiang UniversityHangzhou 310027China National Laboratory of Science and Technology on Computational Physics Institute of Applied Physics and Computational MathematicsBeijing 100088China Graduate School of China Academy of Engineering Physics Beijing 100193China

Majorana's stellar representation provides an intuitive picture in which quantum states in highdimensional Hilbert space can be observed using the trajectory of Majorana *** consider the Majorana's stellar representation of the quantum geometric tensor for a spin state up to spin-3/*** real and imaginary parts of the quantum geometric tensor,corresponding to the quantum metric tensor and Berry curvature,are therefore obtained in terms of the Majorana ***,we work out the expressions of quantum geometric tensor for arbitrary spin in some important *** results will benefit the comprehension of the quantum geometric tensor and provide interesting relations between the quantum geometric tensor and Majorana's stars.

关键词： quantum geometric tensor Berry curvature quantum metric tensor Majorana's stellar representation

Quantum Fisher Information Gap for Systems with Nonlinear Hamiltonians

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Communications in Theoretical Physics 2019年第1期71卷 43-48页

作者：刘博黄奕筱王晓光 Zhejiang Institute of Modern Physics Department of Physics Zhejiang University School of Physics Changchun Normal University School of Science Zhejiang University of Science and Technology

Quantum Fisher information(QFI) gap characterizes the stability of QFI to space directions. We study the QFI distributions and QFI gap for quantum states generated from nonlinear Hamiltonians for both spin and bosonic systems. We find that the same spin-squeezing parameter(or principle squeezing parameter) corresponds to two different values QFI gap, and the locations of all extreme points of the QFI are explicitly given.

关键词： quantum Fisher information metrology nonlinear Hamiltonians

Quantum Fisher information width in quantum metrology

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Science China(Physics,Mechanics & Astronomy) 2019年第4期62卷 29-37页

作者： Bo Liu GuoLong Li YanMing Che Jie Chen XiaoGuang Wang Department of Physics Zhejiang University School of Physics Changchun Normal University School of Sciences Hangzhou Dianzi University

In scenarios of quantum metrology, the unitary parametrization process often depends on space directions. How to characterize the sensitivity of parameter estimation to space directions is a natural question. We propose the concept of the quantum Fisher information(QFI) width, which is the difference between the maximum and minimum values of the QFI, to quantitatively study the sensitivity. We find that Fock states, the bosonic coherent states, and the displaced Fock states all have zero widths, indicating that QFI is completely inert over all directions, while the width for the spin state with all spins down or up is equal to the number of particles, so this concept will enable us to choose appropriate directions to make unitary transformation to obtain larger *** QFI width of the displaced quantum states is found to be independent of the magnitude of the displacement for both spin and bosonic systems. We also find some relations between the QFI width and squeezing parameters.

关键词： quantum metrology quantum Fisher information quantum Fisher information width

Coherent-State Approach for Majorana Representation

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Communications in Theoretical Physics 2017年第6期67卷 611-618页

作者：刘昊迪傅立斌王晓光 Beijing Computational Science research Center Center for Quantum Sciences and School of Physics Northeast Normal University National Laboratory of Science and Technology on Computational Physics Institute of Applied Physics and Computational Mathematics Zhejiang Institute of Modern Physics Department of PhysicsZhejiang University

By representing a quantum state and its evolution with the Majorana stars on the Bloch sphere, the Majorana representation provides us an intuitive way to study a physical system with SU(2) symmetry. In this work,based on coherent states, we propose a method to establish the generalization of Majorana representation for a general symmetry. By choosing a generalized coherent state as a reference state, we give a more general Majorana representation for both finite and infinite systems and the corresponding star equations are given. Using this method, we study the squeezed vacuum states for three different symmetries, Heisenberg–Weyl, SU(2) and SU(1,1), and express the effect of squeezing parameter on the distribution of stars. Furthermore, we also study the dynamical evolution of stars for an initial coherent state driven by a nonlinear Hamiltonian, and find that at a special time point, the stars are distributed on two orthogonal large circles.

关键词： majorana representation coherent state squeezed states SU(1,1) symmetry

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