Xiang-Guo Meng

Nonclassicality and decoherence of photon-subtracted squeezed vacuum states

Extending the recent work completed by Biswas and Agarwal [Phys. Rev. A75, 032104 (2007)] to the case of m-photon-subtracted squeezed vacuum states (m-PSSVSs), we focus our study on nonclassicality and decoherence of the m-PSSVSs. The nonclassical properties are investigated in terms of the squeezing character, the oscillation of photon-number distribution, and the partial negativity of Wigner function (WF).We then study the effect of decoherence on the m-PSSVSs in two different channels, viz., thermal process and phase damping. In each case, the time-evolution of density operators and WFs of such states is derived analytically. After undergoing the thermal channel, the initial pure m-PSSVSs evolve into a mixed state that turns out to be a Laguerre polynomial of combination of creation and annihilation operators within normal ordering; however, they become another mixed state with the exponential decay due to phase damping. At long times, these fields decay to a highly classical thermal field as a result of thermal noise, but they still keep nonclassicality in the phase-damping channel.

A new kind of nonlinear coherent states and their properties

Abstract A new kind of nonlinear coherent states, i.e. the k eigenstates of the powers (k ≥ 3) of the generalized annihilation operator of f-oscillators, are constructed using the inverse operators of the boson annihilation and creation operators. The set of these states may form a complete quantum mechanics representation. Using newly defined higher order squeezing and an antibunching, the properties of the Mth-order squeezing and the antibunching effect of the k states are investigated. The results show that the Mth-order [M = (n + 1/2)k; n = 0, 1, 2, …] squeezing effects exist in all of the k states when k is even and the antibunching effect exists in all of the k states.

Wigner function, optical tomography of two-variable Hermite polynomial state, and its decoherence effects studied by the entangled-state representations

We analytically investigate the Wigner function (WF) and the optical tomography for the two-variable Hermite polynomial state (THPS) and the effect of decoherence on the THPS via the entangled-state representations. The nonclassicality of the THPS is investigated in terms of the partial negativity of the WF, which depends much on the polynomial orders m, n and the squeezing parameter r. We also extend recent theoretical studies of optical tomography and introduce the radon transformation between the Wigner operator and the projection operator of the entangled state |η,τ1,τ2〉 to derive the tomogram of the THPS. Furthermore, we investigate how the WF for the THPS evolves undergoing the thermal channel. The results show that quantum dissipation in the decoherence channel can thoroughly deteriorate the nonclassicality of the THPS, and thermal noise leads to much quicker decoherence than amplitude damping.

QUANTIZATION FOR THE MESOSCOPIC RLC CIRCUIT AND ITS THERMAL EFFECT BY VIRTUE OF GHFT

The mesoscopic single RLC (resistance-inductance-capacitance) circuit and the RLC circuit including complicated coupling are quantized by employing Diracs standard canonical quantization method. The thermal effects for the systems are investigated by virtue of GHFT (the generalized Hellmann–Feynman theorem). The results distinctly show the effect of temperature on the quantum fluctuation.

Kraus operator solutions to a fermionic master equation describing a thermal bath and their matrix representation

We solve the fermionic master equation for a thermal bath to obtain its explicit Kraus operator solutions via the fermionic state approach. The normalization condition of the Kraus operators is proved. The matrix representation for these solutions is obtained, which is incongruous with the result in the book completed by Nielsen and Chuang [Quantum Computation and Quantum Information, Cambridge University Press, 2000]. As especial cases, we also present the Kraus operator solutions to master equations for describing the amplitude-decay model and the diffusion process at finite temperature.

The construction, properties and applications of a new bipartite coherent-entangled state in the two-mode Fock space

Using the technique of integration within an ordered product (IWOP) of operators, we find a new kind of bipartite coherent-entangled state (CES) that exhibits both coherent state and entangled state properties. The set of CESs makes up a complete and partly nonorthogonal representation. Using an asymmetric beamsplitter we propose a simple experimental scheme for producing the CES. Finally, we present some new quantum states related to the CES and some applications of the CES to quantum optics.

QUANTUM STATISTICAL PROPERTIES OF THE EVEN AND ODD NEGATIVE BINOMIAL STATES

The properties of the even and odd negative binomial states are investigated. Mainly we concentrate on the statistical properties for such states and we consider the squeezing phenomenon by examining the variation in the quadrature variances. Using the Pegg–Barnett formalism of phase operator, the phase probability distributions of the states are discussed, and also the phase and number squeezing with different parameters are studied. The numerical computation results show that the phase probability distributions for the even and odd NBSs can clearly exhibit the different features of quantum effects.

New relationship between quantum state’s tomogram and its wave function

Abstract By searching for - and -ordering form of the coordinate-momentum intermediate representation (formed by the eigenvector of with eigenvalue being x, ), and noting that is just the Radon transformation of the Wigner operator, we find new relationship between a quantum state ’s tomogram and its wave function in coordinate (or momentum) representation, i.e. the tomogram can be split into two parts, one is ’s Gaussian integration transformation with the parameter and another is ’s Gaussian integration transformation with the parameter . In this way, the quantum tomogram of number state is conveniently deduced. We also derive Radon transform of and , which can be either viewed as - and -ordered operator correspondence of the classical function .

Nonclassical properties and decoherence of fields in photon-added squeezing-enhanced thermal states

We put forward the photon-added squeezing-enhanced thermal states (PASETS) theoretically by adding photon to the squeezed enhancing thermal states (SETS) repeatedly. Based on the normally ordered density operator of PASETS, we investigate the nonclassical behavior of the PASETS by evaluating, both analytically and numerically, Mandels Q-parameter, photon-number distribution (PND), and Wigner function (WF). It is found that smaller squeezing parameter r and thermal photon number nc can lead to more chance of the appearance of sub-Poissonian statistics. And it is shown that the PND of PASETS exhibit more remarkable oscillations than that of SETS in stronger squeezing case. The WF exhibit partial negativity in phase space and the squeezing parameter r can result in both squeezing and rotating effect. By investigating the fidelity between PASETS and SETS shows that the fidelity tender to steady values in the high value of squeezing parameter or thermal photon number. In addition, the decoherence effect on the PASETS is examined by the time-evolution of the analytical WF in thermal channel. The results show that the PASETS shall lose nonclassicality and non-Gaussianity and reduce to classical states with Gaussian distribution after sufficient time interaction with the thermal noise. And larger photon-added number or thermal photon number shall render shorter decoherence time.