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In this paper, the decoherence features of the photon-added displaced thermal state (PADTS) in the amplitude decay channel were studied by analytically and numerically investigating the time evolution of the Wigner function. The normal product representation of density for the PADTS is presented. The results indicate that the nonclassicality of PADTS can revive after disappearing with time. This kind of revival can maintain for a period of time and inevitably disappear eventually. However, we find that the operation of adding photons has the effect of reducing the decoherence rate of PADTS in the amplitude decay channel, although it also can decrease the PADTS’s nonclassicality markedly.

The quantization scheme between double enhanced charge phase-slip (ECPS) qubits is given. In this system, there exist quantum entanglement phenomenona. The entanglement characteristic is discussed by employing the concurrence. An interesting conclusion is obtained, i.e., if one desire to change the entanglement between two ECPS qubits, the mutual inductance should be considered first, but it is also a good choice to tune symmetric and asymmetric combination of two gate voltages.

A new kind of nonlinear coherent states, i.e. the k eigenstates of the powers B^k (k ≥ 3) of the generalized annihilation operator B^=a^†-1f(N^) 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.

Extending the recent work completed by Fan et al. [Front. Phys. 9(1), 74 (2014)] to a two-mode case, we investigate how a two-mode squeezed vacuum evolves when it undergoes a two-mode amplitude dissipative channel, with the same decay rate κ, using the continuous-variable entangled state approach. Our analytical results show that the initial pure-squeezed vacuum state evolves into a definite mixed state with entanglement and squeezing, decaying over time as a result of amplitude decay. We also investigate the time evolutions of the photon number distribution, the Wigner function, and the optical tomogram in this channel. Our results indicate that the evolved photon number distribution is related to Jacobi polynomials, the Wigner function has a standard Gaussian distribution (corresponding to the vacuum) at long periods, losing its nonclassicality due to amplitude decay, and a larger squeezing leads to a longer decay time.

We theoretically analyze the nonclassicality and entanglement of two new non-Gaussian entangled states generated by applying multiple-photon addition and subtraction to a two-mode binomial state. The nonclassical properties are investigated in terms of the partial negativity of the Wigner functions, whose results show that their nonclassicality can be enhanced via one-mode even-number photon operations and two-mode symmetrical operations for the initial two-mode binomial state. We also find that there exists some enhancement in the entanglement properties in certain parameter ranges via one-mode photon-addition and two-mode symmetrical operations.

A new bipartite coherent-entangled state (CES) is found which exhibits both coherent state and entangled state properties. The set of CESs constitute a complete and partly nonorthogonal representation. Using an asymmetric beamsplitter a experimental scheme to produce the CES is proposed. Applications of CESs in quantum optics are also presented.

A new kind of bipartite coherent-entangled state (CES) is introduced in the two-mode Fock space which exhibits the properties of both coherent state and entangled state. The set of CESs make up a complete and partly nonorthogonal representation. A simple experimental scheme to produce the CES is proposed by using a beam splitter. Some applications of the CES are also presented in quantum optics.

The generalized continuous variable two-mode entangled state is proposed by using the technique of integration within an ordered product (IWOP) of operators. The characteristics of this new entangled representation and its application in quantum teleportation are analyzed in detail. These results indicate that such real parameters indeed make up a new entangled representation owing to its completeness and orthogonal relation. By employing the as quantum transmission channel, the teleportation of any single-mode quantum state can be realized by a unitary transformation.

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.

The coherent-entangled state |α, x; λ> with real parameters λ is proposed in the two-mode Fock space, which exhibits the properties of both the coherent and entangled states. The completeness relation of |α, x; λ> is proved by virtue of the technique of integral within an ordered product of operators. The corresponding squeezing operator is derived, with its own squeezing properties. Furthermore, generalized P-representation in the coherent-entangled state is constructed. Finally, it is revealed that superposition of the coherent-entangled states may produce the EPR entangled state.

Using the entangled state representation of Wigner operator and some formulae related to the two-variable Hermite polynomials, the Wigner function of the squeezed pair coherent state (SPCS) and its two marginal distributions are derived. Based on the entangled Husimi operator introduced by Fan et al. (Phys. Lett. A 358:203, 2006) and the Weyl ordering invariance under similar transformations, we also obtain the Husimi function of the SPCS and its marginal distribution functions. The comparison between the two quasibability functions shows that, for the same amount of information included in two functions, the solving process of the Husimi function is simpler than that of the Wigner function.

Using the Pegg-Barnett formalism of phase operator, we obtain phase probability distributions of new even and odd nonlinear coherent states. It is shown that the distributions for the states are rather different, and unlike the case of ordinary even and odd coherent states the Pegg-Barnett distribution clearly reflects the different character of quantum interference in the case of the new even and odd coherent states.

In this paper we shall introduce two q-analogues of the squeezed states in terms of the technique of integration within an ordered product of operators and the properties of the inverses of q-deformed annihilation and creation operators, and some nonclassical properties of the states are examined. Furthermore, we obtain some new completeness relations composed of the bra and ket which are not mutually Hermitian conjugate.

The excited squeezed light (ESL) can be the outcome of interaction between squeezed light probe and excited atom, which can explore the status and the structure of the atom. We calculate the Wigner function and tomogram of ESL that may be comparable to the experimental measurement of quadrature-amplitude distribution for the light field obtained using balanced homodyne detection. The method of calculation seems new.

In our preceding work, a class of k-quantum nonlinear coherent states, i.e., the k eigenstates of the powers (B) over cap (k) (k greater than or equal to 3) of the annihilation operator (B) over cap = (a) over cap1/f((N) over cap) of f-oscillators, are introduced. In this paper, we introduce a new kind of higher-order squeezing and an antibunching effect. The quantum statistical properties of the k states are studied. The result shows that the M-th order [M = (n + 1/2)k; n = 0, 1,...] squeezing effects exist in all of the k states when k is even. There is the antibunching effect in all of the k states.

A class of even and odd nonlinear coherent states are introduced. The properties of some related states, including quadrature squeezing, antibunching effect and phase probability distribution, are studied.

Using the Pegg–Barnett formalism of phase operator, we obtain phase probability distributions of new even and odd nonlinear coherent states. It is shown that the distributions for the states are rather different, and unlike the case of ordinary even and odd coherent states the Pegg–Barnett distribution clearly reflects the different character of quantum interference in the case of the new even and odd coherent states.

The completeness of the k orthonormalized eigenstates of the operator (âf())k (k≥3) is investigated. We introduce a new kind of higher-order squeezing and an antibunching. The properties of the Mth-order squeezing and the antibunching effect of the k states are studied. The result shows that these states may form a complete Hilbert space, and the Mth-order (M = (n + 1/2)k; n = 0,1,...) squeezing effects exist in all of the k states when k is even. There is an antibunching effect in all of the states. An alternative method for constructing the k states is proposed, and the result shows that all of them can be generated by linear superposition of the time-dependent nonlinear coherent states at different instants.

We found the sufficient conditions for exactly disentangling a set of triparticle entangled states into product states, 1-qubit product and 2-qubit separable states, or fully separable states. The condition for the disentanglement of 3-qubit states into fully separable states is much stricter than the one for 2-qubit entangled states. (C) 2001 Elsevier Science B.V. All rights reserved.

In this paper the N eigenstates of the Nth powers (N greater than or equal to 3) of the annihilation operator of an anharmonic oscillator are constructed and their completeness is investigated. We introduce a new kind of higher order squeezing, Mth-order SU(I, 1) squeezing. The properties of Mth-order SU(I, I) squeezing and anticorrelation of the N states are studied. The result show that these states may form a complete Hilbert space; the Mth-order [M = (n + 1/2)N; n = 0,1,...] SU(1, 1) squeezing effects exist in all of the N states when N is even. There is anticorrelation in all of them.

power squeezing properties of even and odd q-coherent states are investigated. It is found that the -power (N = 2m + 1, m = 0, 1, 2,...) squeezing effect appears for both the even and odd q-coherent states in some ranges of the parameters q and .

In this paper, the mathematical structure and properties of orthonormalized eigenstates of the higher powers of the annihilation operator of two-parameter deformed harmonic oscillator are studied. Based on the work, the antibunching properties of them are investigated. It is found that they may form a complete Hilbert space, and all of them show antibunching effect.

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.

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.

We construct a new bipartite entangled state (NBES), which describes both the squeezing and the entanglement involved in the parametric down-conversion process and can be produced using a symmetric beam splitter. Constructing asymmetric ket?bra integrations based on the NBES leads to some new squeezing operators, which clearly exhibit the relationships between squeezing and entangled state transformations. Moreover, an entangled Wigner operator with a definite physical meaning is also presented.

We investigate how the squeezed thermal state (STS) and squeezed number state (SNS) evolve undergoing decoherence in the laser process. Remarkably, the initial SNS, an example of a pure state, evolves into a mixed state, which turns out to be a Laguerre polynomial of combination of creation and annihilation operators within normal ordering; however, the STS, a mixed state, still keeps squeezed and thermal. At long times, these fields lose their nonclassical nature and decay to a highly classical thermal field. The normally ordered density operators of such states in the laser channel lead to deriving the analytical time-evolution expressions of the Wigner functions (WFs). Their nonclassicality is investigated in reference to the time-evolution WFs, which indicates that both of the WFs decay to the same thermal WF as a result of decoherence when the decay time t or the cavity loss κ of the laser is large enough.

We investigate nonclassicality and decoherence of field states generated with the non-Gaussian operation of photon addition to a two-mode squeezed thermal state (TSTS) using the normally ordered density operator of the photon-added TSTS (PTSTS). The normalization factor of the PTSTS is just a Jacobi polynomial of the squeezing parameter γ and the average photon number n¯ of the thermal field. We show that the fields in such states exhibit remarkable quantum features, such as sub-Poissonian photon statistics, the anti-bunching effect, and photon-number distribution. The nonclassicality is discussed in phase space based on the partial negativity of the Wigner function (WF) with two-variable Hermite polynomials. The results show that the non-Gaussian WF always exhibits the quantum interference structure caused by the two-mode squeezing operation and has some negative regions for any value of n¯, γ, and the photon-addition numbers m, n. In addition, the effect of decoherence on the PTSTS in the thermal channel is studied by analytically deriving the time-evolution WF. We find that the WF becomes Gaussian (corresponding to a classical thermal state) at long times, losing its nonclassicality as a result of decoherence, and a larger m (or n) leads to a longer decoherence time κt.

A new bipartite coherent-entangled state is introduced in the two-mode Fock space, which exhibits the properties of both a coherent state and an entangled state. The set of coherent-entangled states makes up a complete and partly nonorthogonal representation. A simple experimental scheme to produce the coherent-entangled state using an asymmetric beamsplitter is proposed. Some applications of the coherent-entangled state in quantum optics are also presented.

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.