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Quantum Fisher information and spin squeezing in one-axis twisting model

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Chinese physics B 2014年第6期23卷 23-29页

作者：钟伟刘京马健王晓光 zhejiang institute of modern physics Zhejiang University

We investigate the dependence of the average parameter estimation precision （APEP）, which is defined by the quantum Fisher information, on the polar angle of the initial coherent spin state ｜θ0,φ0〉 in a one-axis twisting model. Jin et al. [New J. Phys. 11 （2009） 073049] found that the spin squeezing sensitively depends on the polar angle θ0 of the initial coherent spin state. We show explicitly that the APEP is robust to the initial polar angle θ0 in the vicinity of π/2 and a near- Heisenberg limit 2IN in quantum single-parameter estimation may still be achieved for states created with the nonlinear evolution of the nonideal coherent spin states θ0- π/2. Based on this model, we also consider the effects of the collective dephasing on spin squeezing and the APEE

关键词： quantum Fisher information spin squeezing one-axis twisting model

Derivation of quantum Chernoff metric with perturbation expansion method

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Chinese physics B 2014年第9期23卷 81-86页

作者：钟伟马健刘京王晓光 zhejiang institute of modern physics Zhejiang University

We investigate a measure of distinguishability defined by the quantum Chernoff bound, which naturally induces the quantum Chernoff metric over a manifold of quantum states. Based on a quantum statistical model, we alternatively derive this metric by means of perturbation expansion. Moreover, we show that the quantum Chernoff metric coincides with the infinitesimal form of the quantum Hellinger distance, and reduces to the variant version of the quantum Fisher information for the single-parameter case. We also give the exact form of the quantum Chernoff metric for a qubit system containing a single parameter.

关键词： quantum Chernoff metric Hellinger distance perturbation expansion

Entanglement and coherence of a three-level atom in Λ configuration interacting with two fields

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Chinese physics B 2009年第6期18卷 2288-2293页

作者：张建松许晶波 zhejiang institute of modern physics and Department of physics Zhejiang University

We investigate the entanglement of a three-level atom in A configuration interacting with two quantized field modes by using logarithmic negativity. Then, we study the relationship of the atomic coherence and the entanglement between two fields which are initially prepared in vacuum or thermal states. We find that if the two fields are prepared in thermal states, the atomic coherence can induce the entanglement between two thermal fields. However, there is no coherence-induced entanglement between two vacuum fields.

关键词： quantum entanglement coherence cavity QED

One-loop renormalizability of noncommutative U(1) gauge theory with scalar fields

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Chinese physics B 2010年第1期19卷 111-116页

作者：黄家辉盛正卯 zhejiang institute of modern physics Department of PhysicsZhejiang University

This paper uses the background field method to calculate one-loop divergent corrections to the gauge field propa- gators in noncommutative U（1） gauge theory with scalar fields. It shows that for a massless scalar field, the gauge field propagators are renormalizable to 02-order, but for a massive scalar field they are renormalizable only to O-order.

关键词： noncommutative geometry quantum field theory renormalization

Controlling quantum discord dynamics in cavity QED systems by applying a classical driving field with phase decoherence

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Chinese physics B 2012年第3期21卷 56-62页

作者：钱懿许晶波 institute of modern physics and physics Department Zhejiang University

We investigate a two=level atom interacting with a quantized cavity field and a classical driving field in the presence of phase decoherence and find that a stationary quantum discord can arise in the interaction of the atom and cavity field as the time turns to infinity. We also find that the stationary quantum discord can be increased by applying a classical driving field. Furthermore, we explore the quantum discord dynamics of two identical non=interacting two-level atoms independently interacting with a quantized cavity field and a classical driving field in the presence of phase decoherence. Results show that the quantum discord between two atoms is more robust than entanglement under phase decoherence and the classical driving field can help to improve the amount of quantum discord of the two atoms.

关键词： stationary quantum discord classical driving field phase decoherence

Black Hole Hair in Higher Dimensions

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Communications in Theoretical physics 2010年第2期53卷 285-290页

作者：曹超陈一新李剑龙 zhejiang institute of modern physics Zhejiang University

We study the property of matter in equilibrium with a static, spherically symmetric black hole in D- dimensional spacetime. It requires that this kind of matter has an equation of state ω≡pr/ρ = -n/（n ＋ 2k）, k, n ∈ N （where n 〉 1 corresponds to a mixture of vacuum matter and ＂hair＂ matter）, which seems to be independent of D. However, when we associate this result with specific models, we find that these hairy black holes can live only in some special dimensional spacetime：（i） D = 2 ＋ 2k/n while the black hole is surrounded by cosmic strings, which requires D is even or D ∈ N, depending on the value of n, this is consistent with some important results in superstring theory, it might reveal the relation between cosmic string and superstring in another aspect; （ii） the black hole can be surrounded by linear dilaton field only in 4-dimensional spacetime. In both cases, D = 4 is special. We also present some examples of such hairy black holes in higher dimensions, including a toy model with negative energy density.

关键词： black holes extra dimensions cosmic strings

Quantum Fisher Information of Entangled Coherent States in a Lossy Mach–Zehnder Interferometer

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Communications in Theoretical physics 2014年第1期61卷 115-120页

作者：井晓幸刘京钟伟王晓光 zhejiang institute of modern physics Department of PhysicsZhejiang University

We give an analytical result for the quantum Fisher information of entangled coherent states in a lossy Mach–Zehnder interferometer recently proposed by Joo et al.,[***.107(2011)083601].For small loss of photons,we find that the entangled coherent state can surpass the Heisenberg ***,the formalism developed here is applicable to the study of phase sensitivity of multipartite entangled coherent states.

关键词： quantum Fisher information entangled coherent state Mach–Zehnder interferometer photon loss

Quantum Fisher Information for Density Matrices with Arbitrary Ranks

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Communications in Theoretical physics 2014年第1期61卷 45-50页

作者：刘京井晓辛钟伟王晓光 zhejiang institute of modern physics Department of PhysicsZhejiang University

We provide a new expression of the quantum Fisher information(QFI) for a general *** this expression,the QFI for a non-full rank density matrix is only determined by its *** expression can bring convenience for an inf... 详细信息

关键词： quantum Fisher information quantum metrology density matrix

Spin Squeezing and Fixed-Point Bifurcation

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Communications in Theoretical physics 2012年第12期58卷 800-806页

作者：黄亦筱马健井晓幸王晓光 zhejiang institute of modern physics Department of Physics Zhejiang University

We study spin squeezing and classical bifurcation in a nonfinear bipartite system. We show that the spin squeezing can be associated with a fixed-point bifurcation in the classical dynamics, namely, it acts as an indicator of the classical bifurcation. For the ground state of a system with coupled giant spins, we find that the spin squeezing achieves its minimum value near the bifurcation point. We also study the dynamics of the spin squeezing, for an initial state corresponding to one of the fixed point, we find that in the stable regime, the spin squeezing exhibits periodic oscillation and always persists except at some fixed times, while in the unstable regime, the periodic oscillation phenomenon disappears and the spin squeezing survives for a short time. Finally, we show that the mean spin squeezing, which is defined to be averaged over time, attains its minimum value near the bifurcation point.

关键词： spin squeezing fixed point bifurcation