Entangled State Representation Research Articles

Infinite Operator-Sum Representation of Density Operator for a Dissipative Cavity with Kerr Medium Derived by Virtue of Entangled State Representation

By using the thermo entangled state representation we solve the master equation for a dissipative cavity with Kerr medium to obtain density operators' infinite operator-sum representation}$\rho (t) =\sum_{m,n,l=0}^{\infty}M_{m,n,l}\rho_{0}\mathcal{M}_{m,n,l}^{\dagger}.$ It is noticeable that}$M_{m,n,l}$ is not hermite conjugate to $\mathcal{M}_{m,n,l}^{\dagger}$, nevertheless the normalization}$\sum_{m,n,l=0}^{\infty}\mathcal{M}_{nm,,l}^{\dagger}M_{m,n,l}=1$ still holds}, i.e., they are trace-preserving in a general sense. This example may stimulate further studying if general superoperator theory needs modification.

Husimi Functions of Excited Squeezed Vacuum States

Based on the Husimi operator in pure state form introduced by Fan et al., which is a squeezed coherent state projector, and the technique of integration within an ordered product (IWOP) of operators, as well as the entangled state representations, we obtain the Husimi functions of the excited squeezed vacuum states (ESVS) and two marginal distributions of the Husimi functions of the ESVS.

Some Properties of Two-mode Displaced Excited Squeezed Vacuum States

In this paper, two-mode displaced excited squeezed vacuum states (TDESVS) are constructed and their normalization and completeness are investigated. Using the entangled state representation and Weyl ordering form of the Wigner operator, the Wigner functions of TDESVS are obtained and the variations of Wigner functions with the parameters m, n and r are investigated. Besides, two marginal distributions of Wigner functions of TDESVS are obtained, which exhibit some entangled properties of the two-particle's system in TDESVS.

Quantum theory of a mutual-inductance-coupled [formula omitted] circuit including Josephson junctions studied via the entangled state representation

Based on the entangled state representation and Feynman’s idea that “electron pairs are bosons, … , a bound pair acts as a Bose particle”, we present a quantization scheme for a mutual-inductance-coupled L C circuit including Josephson junctions. Then we use the Heisenberg equation of motion to obtain the modified operator Josephson equations, which may be useful for quantum control. The variation of the phase-difference operator of the junction with time is also investigated.

Time evolution of Wigner function in laser process derived by entangled state representation

Evaluating the Wigner function of quantum states in the entangled state representation is introduced, based on which we present a new approach for deriving time evolution formula of Wigner function in laser process. Application of this formula to photon number measurement in laser process is also presented, as an example, the case when the initial state is a photon-added coherent state is discussed.

Production of genuine entangled states of four atomic qubits

We propose an optical scheme to generate genuine entangled states of four atomic qubits in optical cavities using a single-photon source, beam splitters and single-photon detectors. We demonstrate how to generate deterministically 16 orthonormal and independent genuine entangled states of four atomic qubits. It is found that the 16 genuine entangled states form a new type of representation of the four-atomic-qubit system, i.e. the genuine entangled-state representation. This representation brings a new interesting insight into better understanding of multipartite entanglement.

New Operator Realization of Superoperators and Its Application in Quantum Information Theory

By exposing deficiency of the usual superoperators that have no explicit operator-expression in quantum information theory we introduce thermo entangled state representation to endow each of these superoperators a definite operator-expression in an enlarged space in which one mode is a fictitious. This helps us to directly derive the role of exponential of superoperators and the solutions of some master equations.

MODIFIED JOSEPHSON EQUATION AND MEASUREMENT DYNAMICS FOR THE JOSEPHSON TRANSMISSION LINE DETECTOR

By introducing the entangled state representation and following Feynman's assumption that "electron pairs are bosons … A bound pair acts as a Bose particle", we construct a Hamiltonian operator for the Josephson transmission line (JTL) detector, then we use the Heisenberg equation of motion to derive the modified Josephson equation. Based on the modified Josephson equation, the measurement dynamics of JTL detector is investigated, which will be helpful for us to analyze the quantum measurement of JTL detector.

MULTIPARTITE COHERENT ENTANGLED STATE OF CONTINUOUS VARIABLES: STRUCTURE AND GENERATION

Motivated by the new approach to finding multipartite entangled state representation [Int. J. Mod. Phys. A22, 4481 (2007)], we construct the multipartite coherent entangled state (MCES) of continuous variables which exhibits both coherent state's and entangled state's properties. A protocol of generating such an MCES is proposed by using beam splitters in a sequence. Applications of MCES in studying generalized Wigner function, squeezing and quantum teleportation are discussed.

Gapped Two-Body Hamiltonian Whose Unique Ground State Is Universal for One-Way Quantum Computation

Many-body entangled quantum states studied in condensed matter physics can be primary resources for quantum information, allowing any quantum computation to be realized using measurements alone, on the state. Such a universal state would be remarkably valuable, if only it were thermodynamically stable and experimentally accessible, by virtue of being the unique ground state of a physically reasonable Hamiltonian made of two-body, nearest-neighbor interactions. We introduce such a state, composed of six-state particles on a hexagonal lattice, and describe a general method for analyzing its properties based on its projected entangled pair state representation.

New Representation of Rotation Operator and Its Application

By employing the technique of integration within an ordered product of operators, we derive natural representations of the rotation operator, the two-mode Fourier transform operator and the two-mode parity operator in entangled state representations. As an application, it is proved that the rotation operator constructed by the entangled state representation is a useful tool to solve the exact energy spectra of the two-mode harmonic oscillators with coordinate-momentum interaction.

Optical Four-Wave Mixing Operator, Fresnel Operators and Three-Mode Entangled State Representation

We analyse the optical four-wave mixing operator S and relate it to the two-mode Fresnel operator. It is shown that the direct product of the two-mode Fresnel operator and the single-mode Fresnel operator has a natural representation on the basis of a three-mode entangled state, which is constructed by S and a beam splitter transform.

PHASE OPERATOR AND PHASE STATE IN THERMO FIELD DYNAMICS

We extend the Susskind–Glogower phase operator and phase state in quantum optics to thermo field dynamics (TFD). Based on the thermo entangled state representation, we introduce thermo excitation and de-excitation operators with which the phase operator and phase state in TFD can be constructed. The phase state treated as a limiting case of a new SU(1, 1) coherent states is also exhibited.

Quasiprobability Distribution Functions of Squeezed Pair Coherent States

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.

New Approach for Solving Master Equations in Quantum Optics and Quantum Statistics by Virtue of Thermo-Entangled State Representation

By introducing a fictitious mode to be a counterpart mode of the system mode under review we introduce the entangled state representation ⟨η|, which can arrange master equations of density operators ρ(t) in quantum statistics as state-vector evolution equations due to the elegant properties of ⟨η|. In this way many master equations (respectively describing damping oscillator, laser, phase sensitive, and phase diffusion processes with different initial density operators) can be concisely solved. Specially, for a damping process characteristic of the decay constant κ we find that the matrix element of ρ(t) at time t in ⟨η| representation is proportional to that of the initial ρ0 in the decayed entangled state ⟨ηe−κt| representation, accompanying with a Gaussian damping factor. Thus we have a new insight about the nature of the dissipative process. We also set up the so-called thermo-entangled state representation of density operators, ρ = ∫(d2η/π)⟨η|ρ⟩D(η), which is different from all the previous known representations.

Effective Approach to Constructing n-Mode Wigner Operator in the Entangled State Representation

By extending Fan-Klauder entangled state representation to multipartite case. We construct n-mode Wigner operator in the common eigenvector of the multipartite centre-of-mass coordinate and two mass-weighted relative momenta, and its canonical conjugate state, they are both more complicated entangled state of continuum variables. the technique of integration within an ordered product (IWOP) of operators is essential in our derivation.

NEW n-MODE BOSE OPERATOR REALIZATION OF SU(2) LIE ALGEBRA AND ITS APPLICATION IN ENTANGLED FRACTIONAL FOURIER TRANSFORM

We introduce a new n-mode Bose operator realization of SU(2) Lie algebra and link it to the two mutually conjugate multipartite entangled state representations. In so doing we are naturally lead to the n-mode entangle fractional Fourier transform (EFFT), which provides us with a convenient way to deriving the EFFT of quantum-mechanical wave functions.

New approach for analysing master equations of generalized phase diffusion models in the entangled state representation

By virtue of the well-behaved properties of the bipartite entangled states representation, this paper analyse and solves some master equations for generalized phase diffusion models, which seems concise and effective. This method can also be applied to solve other master equations.

Statistical properties of photon-added coherent state in a dissipative channel

We adopt a new approach (using the entangled state representation) to study time evolution of the mixed state in a dissipative channel (DC) with decay rate κ. We then investigate the statistical properties of the m-photon-added coherent state (PACS) in the DC, by deriving the analytical expressions of the Wigner function (WF), which turns out to be the Laguerre–Gaussian function. The criterion time for the definite positivity of WF: , valid for arbitrary m, is revealed. Time evolution of the photocount distribution is also derived analytically, which is related to two-variable Hermite polynomials. The tomogram of PACS is also calculated through the intermediate coordinate–momentum representation.

Wigner function of the thermo number states

Based on thermo field dynamics (TFD) and using the thermo Wigner operator in the thermo entangled state representation we derive the Wigner function of number states at finite temperature (named thermo number states). The figure of Wigner function shows that its shape gets smoothed as the temperature rises, implying that the quantum noise becomes larger.