Hu Li-Yun

Photon-subtracted squeezed thermal state: Nonclassicality and decoherence

We investigate nonclassical properties of the field states generated by subtracting any number of photons from the squeezed thermal state (STS). It is found that the normalization factor of photon-subtracted STS (PSSTS) is a Legendre polynomial of squeezing parameter r and average photon number n-bar of the thermal state. Expressions of several quasiprobability distributions of PSSTS are derived analytically. Furthermore, the nonclassicality is discussed in terms of the negativity of the Wigner function (WF). It is shown that the WF of single PSSTS always has negative values if n-bar<sinh{sup 2}r at the phase space center. The decoherence effect on PSSTS is then included by analytically deriving the time evolution of WF. The results show that the WF of single PSSTS has negative value if 2{kappa}t<ln{l_brace}1-(2n-bar+1)(n-bar-sinh{sup 2}r)/[(2N+1)(n-barcosh2r+sinh{sup 2}r)]{r_brace}, which is dependent not only on average number N of thermal photons in the environment, but also on n-bar and r.

Photon Distribution of a Squeezed Chaotic State

We investigate the photon number distribution of squeezed chaotic field (SCF) (a mixed state), by converting the density operator of SCF into its normally ordered bivariate distribution form we find that it is a Legendre distribution. This is a remarkable result.

Inversion formula and Parseval theorem for complex continuous wavelet transforms studied by entangled state representation

In a preceding letter (2007 Opt. Lett. 32 554) we propose complex continuous wavelet transforms and found Laguerre-Gaussian mother wavelets family. In this work we present the inversion formula and Parseval theorem for complex continuous wavelet transform by virtue of the entangled state representation, which makes the complex continuous wavelet transform theory complete. A new orthogonal property of mother wavelet in parameter space is revealed.In a preceding Letter (Opt. Lett. 32, 554 (2007)) we have proposed complex continuous wavelet transforms (CCWTs) and found Laguerre--Gaussian mother wavelets family. In this work we present the inversion formula and Parsval theorem for CCWT by virtue of the entangled state representation, which makes the CCWT theory complete. A new orthogonal property of mother wavelet in parameter space is revealed.

Damping Law of Photocount Distribution in a Dissipative Channel

For a dissipative channel governed by the master equation of the density operator describing the photon loss, we find that the photocount distribution formula at time t can be related to the initial photocount distribution by replacing the efficiency of the detector ξ with ξe−2κt, as if the quantum efficiency ξ of the detector becomes ξe−2κt. This law greatly simplifies the theoretical study of the photocount distribution for quantum optical fields.

The s -parameterized Weyl－Wigner correspondence in the entangled form and its applications

Based on the theory of integration within s-ordering of operators and the bipartite entangled state representation we introduce s-parameterized Weyl–Wigner correspondence in the entangled form. Some of its applications in quantum optics theory are presented as well.

Entropy-variation with resistance in a quantized RLC circuit derived by the generalized Hellmann–Feynman theorem

By virtue of the generalized Hellmann-Feynman theorem for ensemble average, we obtain internal energy and average energy consumed by the resistance R in a quantized RLC electric circuit. We also calculate entropy-variation with respect to R. The relation between entropy and R is also derived. By depicting figures we indeed see that the entropy increases with the increment of R.By virtue of the generalized Hellmann–Feynman theorem for the ensemble average, we obtain the internal energy and average energy consumed by the resistance R in a quantized resistance–inductance–capacitance (RLC) electric circuit. We also calculate the entropy-variation with R. The relation between entropy and R is also derived. By the use of figures we indeed see that the entropy increases with the increment of R.

Statistical properties of coherent photon-subtracted two-mode squeezed vacuum and its application in quantum teleportation

We introduce a kind of non-Gaussian entangled state, which can be obtained by operating a non-local coherent photon-subtraction operation on a two-mode squeezed vacuum. It is found that its normalization factor is only related to the Legendre polynomials, which is a compact expression. Its statistical properties are discussed by the negative region Wigner function with the analytical expression. As an application, the quantum teleportation for coherent states is considered by using the non-Gaussian state as an entangled channel. It is found that the teleportation fidelity can be enhanced by this non-Gaussian operation.

Thermal vacuum state for the two-coupled-oscillator model at finite temperature: Derivation and application

Following the spirit of thermo field dynamics initiated by Takahashi and Umezawa, we employ the technique of integration within an ordered product of operators to derive the thermal vacuum state (TVS) for the Hamiltonian H of the two-coupled-oscillator model. The ensemble averages of the system are derived conveniently by using the TVS. In addition, the entropy for this system is discussed based on the relation between the generalized Hellmann—Feynman theorem and the entroy variation in the context of the TVS.