arXiv subjects

Li-Yun Hu

Publications and source records attributed to Li-Yun Hu.

12 recordsLinked to original sources

arXiv2015

Laguerre polynomial excited coherent states generated by multiphoton catalysis: Nonclassicality and Decoherence

We theoretically introduce a new kind of non-Gaussian state-----Laguerre polynomial excited coherent states by using the multiphoton catalysis which actually can be considered as a block comprising photon number operator. It is found that the normalized factor is related to the two-variable Hermite polynomials. We then investigate the nonclassical properties in terms of Mandel's Q parameter, quadrature squeezing, second correlation, and the negativity of Wigner function (WF). It is shown that all these properties are related to the amplitude of coherent state, catalysis number and unbalanced beam splitter (BS). In particular, the maximum degree of squeezing can be enhanced as catalysis number and keeps a constant for single-photon catalysis. In addition, we examine the effect of decoherence by Wigner function, which show that the negative region, characteristic time of decoherence and structure of WF are affected by catalysis number and unbalanced BS. Our work provides a general analysis about how to prepare theoretically polynomials quantum states.

quant-ph↗

arXiv2015

Optimal fidelity of teleportation with continuous-variable using three-tunable parameters in realistic environment

We introduce three tunable parameters to optimize the fidelity of quantum teleportation with continuous-variable in nonideal scheme. Using the characteristic function formalism, we present the condition that the teleportation fidelity is independent of the amplitude of input coherent states for any entangled resource. Then we investigate the effects of tunable parameters on the fidelity with or without the presence of environment and imperfect measurements, by analytically deriving the expression of fidelity for three different input coherent state distributions. It is shown that, for the linear distribution, the optimization with three tunable parameters is the best one with respect to single- and two-parameter optimization. Our results reveal the usefulness of tunable parameters for improving the fidelity of teleportation and the ability against the decoherence.

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arXiv2014

Nonclassical properties of Hermite polynomial's excitation on squeezed vacuum and its decoherence in phase-sensitive reservoirs

We introduce Hermite polynomial excitation squeezed vacuum (SV) H_{n}(O)S(r)|0> with O=u a+v a^{{+}}. We investigate analytically the nonclassical properties according to Mandel's Q parameter, second correlation function, squeezing effect and the negativity of Wigner function (WF). It is found that all these nonclassicalities can be enhanced by H_{n}(O)operation and adjustable parameters u and v. In particular, the optimal negative volume delta_{opt}of WF can be achieved by modulating u and v for n>=2,while delta is kept unchanged for n=1. Furthermore, the decoherence effect of phase-sensitive enviornment on this state is examined. It is shown that delta with bigger ndiminishes more quickly than that with lower n, which indicates that single-photon subtraction SV presents more roboustness. Parameter Mof reservoirs can be effectively used to improve the nonclassicality.

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arXiv2014

Improving entanglement of even entangled coherent states by a coherent superposition of photon subtraction and addition

A new entangled quantum state is introduced by applying local coherent superposition (ra^+ +ta) of photon subtraction and addition to each mode of even entangled coherent state (EECS) and the properties of entanglement are investigated. It is found that the Shchukin-Vogel inseparability, the degree of entanglement and the average fidelity of quantum teleportation of the EECS can be improved due to the coherent superposition operation. The effects of improvement by coherent superposition operation are better than those by single (a^+) and two-photon (a^+ b^+) addition operations under a small region of amplitude.

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arXiv2014

Comments on "Asking Photons Where They Have Been"

By using the nonuniform discrete Fourier transform on the center positions of the symmetric intensity distribution of the output beam, we recover the vibration information of two mirrors, which is lost in the analysis of Danan \emph{et al.} in the work [Phys. Rev. Lett. \textbf{111}, 240402 (2013), arXiv:1304.7469]. We believe a photon always follows continuous trajectories, and a photon has to enter an interferometer at first and then leave it, if this photon has ever been inside the interferometer.

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arXiv2013

A new optical field state as an output of diffusion channel when the input being number state

We theoretically propose a new optical field state which is named Laguerre-polynomial-weighted chaotic field. We show that such state can be implemented, i.e., when a number state enters into a diffusion channel, the output state is just this kind of states. We solve the master equation describing the diffusion process by using the summation method within ordered product of operators and the entangled state representaion. The solution manifestly shows how a pure state evolves into a mixed state. The physical difference between the diffusion and the amplitude damping is pointed out.

physics.optics↗

arXiv2013

Damping law of photocount distribution in a dissipative channel

For a dissipative channel governed by the master equation of density operator}$d\rho /dt=\kappa \left(2a\rho a^{\dagger}-a^{\dagger}a\rho -\rho a^{\dagger}a\right) ,${\small \ we find that photocount distribution formula at time}$t,${\small \}$p\left(n,t\right) =Tr\left\{\rho \left(t\right) \mathbf{\colon}\left(\xi a^{\dagger}a\right) ^{n}e^{-\xi a^{\dagger}a}/n!\colon \right\} ,${\small \ becomes}$p\left(n,t\right) =Tr% \left[ \rho \left(0\right) \mathbf{\colon}\left(\xi e^{-2\kappa t}a^{\dagger}a\right) ^{n}e^{-\xi e^{-2\kappa t}a^{\dagger}a}/n!\colon % \right] ,${\small \ as if the quantum efficiency}$\xi ${\small \ of the detector becomes}$\xi e^{-2\kappa t}${\ This law greatly simplifies the theoretical study of photocount distribution for quantum optical field.

quant-ph↗

arXiv2012

Separability criterion for bipartite states and its generalization to multipartite systems

A group of symmetric operators are introduced to carry out the separability criterion for bipartite and multipartite quantum states. Every symmetric operator, represented by a symmetric matrix with only two nonzero elements, and their arbitrary linear combinations are found to be entanglement witnesses. By using these symmetric operators, Wootters' separability criterion for two-qubit states can be generalized to bipartite and multipartite systems in arbitrary dimensions.

quant-ph↗

arXiv2012

Entanglement and nonclassicality of photon-added two-mode squeezed thermal state

We introduce a kind of entangled state---photon-addition two-mode squeezed thermal state (TMSTS) by adding photons to each mode of the TMSTS. Using the P-representation of thermal state, the compact expression of the normalization factor is derived, a Jacobi polynomial. The nonclassicality is investigated by exploring especially the negativity of Wigner function. The entanglement is discussed by using Shchukin-Vogel criteria. It is shown that the photon-addtion to the TMSTS may be more effective for the entanglement enhancement than the photon-subtraction from the TMSTS. In addition, the quantum teleportation is also examined, which shows that symmetrical photon-added TMSTS may be more useful for quantum teleportation than the non-symmetric case.

quant-ph↗

arXiv2011

Evolution of the single-mode squeezed vacuum state in amplitude dissipative channel

Using the way of deriving infinitive sum representation of density operator as a solution to the master equation describing the amplitude dissipative channel by virtue of the entangled state representation, we show manifestly how the initial density operator of a single-mode squeezed vacuum state evolves into a definite mixed state which turns out to be a squeezed chaotic state with decreasing-squeezing. We investigate average photon number, photon statistics distributions for this state.

quant-ph↗

arXiv2011

New approach for normalization and photon-number distributions of photon-added (-subtracted) squeezed thermal states

Using the thermal field dynamics theory to convert the thermal state to a "pure" state in doubled Fock space, it is found that the average value of e^{fa^{{\dag}}a} under squeezed thermal state (STS) is just the generating function of Legendre polynomials, a remarkable result. Based on this point, the normalization and photon-number distributions of m-photon added (or subtracted) STS are conviently obtained as the Legendre polynomials. This new concise method can be expanded to the entangled case.

quant-ph↗

arXiv2011

Nonclassicality and decoherence of photon-added squeezed thermal state in thermal environment

Theoretical analysis is given of nonclassicality and decoherence of the field states generated by adding any number of photons to the squeezed thermal state (STS). Based on the fact that the squeezed number state can be considered as a single-variable Hermite polynomial excited state, the compact expression of the normalization factor is derived, a Legendre polynomial. The nonclassicality is investigated by exploring the sub-Poissonian and negative Wigner function (WF). The results show that the WF of single photon-added STS (PASTS) always has negative values at the phase space center. The decoherence effect on PASTS is examined by the analytical expression of WF. It is found that a longer threshold value of decay time is included in single PASTS than in single-photon subtraction STS.

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