STUDY ON QUANTUM CORRELATIONS FOR CIRCUIT QED STATES

We investigate the dynamic evolution behaviors of entanglement and geometric quantum discord of coupled superconducting qubits in circuit QED system. We carefully analyze the effect of cavity field quantum state on the quantum entanglement and quantum correlations dynamic behaviors of coupling superconducting qubits. The results show that when the cavity field is in coherent state, with the average photon number increasing, the quantum discord death (including entanglement death) would become more difficult to appear, that is to say prolonging the survival time of quantum correlations will be a benefit for keeping the quantum correlations. When the cavity field is in squeezed state, the squeezed amplitude parameters are all too big or too small to keep the system quantum correlations. However, the further study results show that with the initial relative phase of coupling superconducting increasing, qubits can also keep the quantum correlations.

NONCLASSICALITY AND DECOHERENCE OF PHOTON-ADDED THERMAL STATE

Using the normally ordered form of thermal state characteristic of average photon number nc, we introduce the photon-added thermal state (PATS) and investigate its statistical properties, such as Mandel's Q-parameter, photon number distribution (PND), and Wigner function (WF). We then study its decoherence in a thermal environment with average thermal photon number [Formula: see text] and dissipative coefficient κ by deriving analytical expressions of the WF. The nonclassicality is discussed in terms of the negativity of the WF. It is found that the WF is always positive when [Formula: see text] for any number PATS. The expression for time evolution of the PND and the tomogram of PATS are also derived analytically, which are related to hypergeometric function and single variable Hermite polynomials.

DYNAMIC PROPERTIES OF THE LARGE-DETUNING CAVITY QED SYSTEM IN THE PRESENCE OF CAVITY DECAY

We consider a physical process of two Λ-type three-level atoms interacting with a bimodal cavity including the influence of the cavity decay. We analyze the influence of cavity decay on several physical quantities of the process, such as atomic population probability, residual entanglement, concurrence of two atoms, average population inversion, average photon number, the fidelity for quantum phase gate, and the fidelity of generating atomic EPR state. It is found that all of these physical quantities decrease with the increase of cavity decay when the other relevant parameters are fixed.

Macroscopic displaced thermal field as the entanglement catalyst

We show that entanglement of multiple atoms can arise via resonant interaction with a displaced thermal field with a macroscopic photon-number. The cavity field acts as the catalyst, which is disentangled with the atomic system after the operation. Remarkably, the entanglement speed does not decrease as the average photon-number of the mixed thermal state increases. The atoms may evolve to a highly entangled state even when the photon-number of the cavity mode approaches infinity.

Exact solutions of the equation for composite scalar particles in quantized electromagnetic waves

An equation is considered for a composite scalar particle with polarizabilities in an external quantized electromagnetic plane wave. This equation is reduced to a system of equations for an infinite number of interacting oscillators. After diagonalization, we come to equations for free oscillators. As a result, exact solutions of the equation for a particle are found in a plane-quantized electromagnetic wave of arbitrary polarization. As a particular case, the solution for monochromatic electromagnetic waves is considered. The relativistic coherent states of a particle are constructed using the Poisson distribution of photon numbers. In the limit, when the average photon number [Formula: see text] and the volume V of the quantization tend to infinity (but the photon density [Formula: see text] /V remains constant), the wave function converts to the solution corresponding to the external classical electromagnetic wave. PACS Nos.: 14.40.Aq, 13.40.Ks, 13.40.-f

DYNAMICS OF A NONDEGENERATE TWO-PHOTON JAYNES–CUMMINGS MODEL

A generalized Jaynes–Cummings model including the Stark shifts is investigated where the transition is mediated by two different modes of photons. For two different types of correlated field states, the pair coherent states and two-mode SU(1, 1) coherent states, the effect of including the Stark shift on the dynamical behavior of atomic inversion, atomic squeezing parameters, second order coherence function, and photon number distribution is investigated. Our results indicate significant changes in the behavior of these quantities for large and small average photon number <n> in the presence and absence of Stark shift and depending on the type of correlated field involved.