New features of Wehrl entropy and Wehrl PD of a single Cooper-pair box placed inside a dissipative cavity

In this paper, we discuss the coherence of a single Cooper-pair box irradiated by a single-mode quantized field in a coherent state inside a phase-damped cavity. Analytic results under certain parametric conditions are obtained, by means of which we analyze the influence of dissipation on the Wehrl entropy and Wehrl phase distribution. An interesting relation between the coherence and the dissipation effect is observed.     

Quantum Fisher information for a qubit system placed inside a dissipative cavity

We study the time evolution of the quantum Fisher information of a system whose the dynamics is described by the phase-damped model. We discuss the correlation between the Fisher information and entanglement dynamics of a qubit and single-mode quantized field in a coherent state inside phase-damped cavity. Analytic results under certain parametric conditions are obtained, by means of which we analyze the influence of dissipation on the negativity and quantum Fisher information for different values of the estimator parameter. An interesting monotonic relation between the Fisher information and nonlocal correlation behavior is observed during the time evolution.     

Preparation of optimal entropy squeezing state of atomic qubit inside the cavity via two-photon process and manipulation of atomic qubit outside the cavity

Considering two atomic qubits initially in Bell states, we send one qubit into a vacuum cavity with two-photon resonance and leave the other one outside. Using quantum information entropy squeezing theory, the time evolutions of the entropy squeezing factor of the atomic qubit inside the cavity are discussed for two cases, i.e., before and after rotation and measurement of the atomic qubit outside the cavity. It is shown that the atomic qubit inside the cavity has no entropy squeezing phenomenon and is always in a decoherent state before the operating atomic qubit outside the cavity. However,the periodical entropy squeezing phenomenon emerges and the optimal entropy squeezing state can be prepared for the atomic qubit inside the cavity by adjusting the rotation angle, choosing the interaction time between the atomic qubit and the cavity, controlling the probability amplitudes of subsystem states. Its physical essence is cutting the entanglement between the atomic qubit and its environment, causing the atomic qubit inside the cavity to change from the initial decoherent state into maximum coherent superposition state, which is a possible way of recovering the coherence of a single atomic qubit in the noise environment.     

Controlling dipole squeezing of two atoms inside a cavity via manipulating an atom outside the cavity

Considering that three two-level atoms are initially in the GHZ single state and two of the atoms are simultaneously put into a cavity initially in the coherent state, we investigate the dipole squeezing properties of the two atoms inside the cavity under the condition of resonant interaction. It is shown that dipole squeezing properties of the two atoms inside the cavity are strongly affected by rotation manipulating of the atom outside the cavity.     

Collapse and revival of a single—Cooper—pair box in a single—mode quantized field

We study the quantum dynamics of a single-Cooper-pair box biased by a classical voltage and also irradiated by a single-mode quantized field. We demonstrate that under weak damping of the quantized field, the collapse-revival phenomena can exist in this system, and the oscillations of the collapse and revival depend sensitively on the initial state of the single-mode quantized field and the damping rate κ. We also demonstrate that this system can show the beats phenomena.     

Dynamic behaviour of a single—Cooper—pair box in a single—mode quantized field with dissipation

We study the quantum dynamics of a single-Cooper-pair box biased by a classical voltage and also irradiated by a single-mode quantized field.We demonstrate that under the weak damping,the collapse-revival phenomena can exist in this system.We also demonstrate that the revivals of oscillations are sensitive to the initial coherent field and the damping rate of the single-mode quantized field.     

A simple model for maser action obtained through a magnetic tunnel junction placed inside a resonant cavity

Magnetic tunnel junctions are currently being used in magnetoresistive reading heads, magnetic field sensors and MRAMs, due to its giant magnetoresistance effect whose roots are linked to strong spin-dependent scattering mechanisms. The existence of spin-polarized currents in such devices posed us the question over the possibility to generate coherent microwave radiation in a spin inverted population medium, maintained through a spin-polarized current. In this paper we investigate the possibility of obtaining a maser effect considering a magnetic tunnel junction placed inside a resonant cavity. We put forward a simple model based on phenomenological rate equations, being the spin-polarized currents determined by the physics of the magnetic tunnel junction.     

相位阻尼腔中依赖强度Jaynes-Cummings模型的线性熵

在大失谐近似和腔场与库之间耦合假设存在相位阻尼的条件下，通过展示原子、场和原子-场系统的线性熵研究了由含任意强度耦合的Jaynes-Cummings模型描述的量子系统演化规律，讨论了相位阻尼对系统的纠缠及相干性丢失效应。     

Effect of phase-damped cavity on dynamics of tangles of a nondegenerate two-photon JC model

A two-mode cavity field coupled to a two-level atom and damped by the environment through a phase-damped process is considered. For a chosen initial state, the effects of phase damping on the purity loss of the global system and different bipartite partitions of the system (atom-two modes, mode-(atom-mode)) through the tangles are considered. In particular, the effect of phase damping on the amount of entanglement between atom and field is evaluated by the negativity.     

The Purcell-Dicke effect in the emission from a coated small sphere of resonant atoms placed inside a matrix cavity

I investigate a system where both the Purcell effect and Dicke’s superradiance are present. I compute the frequency eigenmode for an ensemble of identical two-level atoms enclosed in a coated nanosphere that is embedded in a matrix. I show that, in a number of configurations, the rate of superradiant emission from the atomic system can be increased many folds from that of a similar cloud of atoms in free space.     

Entropy and entanglement in the mixed state for a dispersive JC model in a phase-damped cavity

Temporal evolution is studied for total entropy, the entropy difference and the sum of negative eigenvalues of the partially transposed density matrix as quantitative entanglement measurements for JC model in a phase-damped cavity in the dispersive approximation. The cavity field is assumed to be coupled to a reservoir with a phase-damping coupling. The case of a statistical mixture (SM) of coherent states is considered as initial field state. The effects of cavity phase damping on the entanglement between the field and the atom are studied.     

Holographic entropy packing inside a black hole

If general relativity is spontaneously induced, the black hole limit is governed by a phase transition which occurs precisely at the would-have-been horizon. The exterior Schwarzschild solution then connects with a novel core of vanishing spatial volume. The Kruskal structure, admitting the exact Hawking imaginary time periodicity, is recovered, with the conic defect defused at the origin, rather than at the horizon. The entropy stored inside any interior sphere is universal, equal to a quarter of its surface area, thus locally saturating the 't Hooft-Susskind holographic bound. The associated Komar mass and material energy functions are nonsingular.     

Entropy squeezing of multi-photon field interacting with a single Cooper-pair box

We investigate the entropy squeezing and entanglement of the Cooper-pair box interacting with multi-photon cavity field. The field is prepared initially in the coherent state, while the Cooper-pair box is assumed to start from a mixed state. We find that the number of photons and the detuning parameters play an important role in the entropy squeezing and entanglement. We observe that the entropy squeezing can be used as a good indicator of the entanglement. This study opens promising perspectives for creating remote quantum information processing networks.     

Qubit-assisted squeezing of mirror motion in a dissipative cavity optomechanical system

In this study, we investigate a hybrid system consisting of an atomic ensemble trapped inside a dissipative optomechanical cavity assisted with perturbative oscillator-qubit coupling. Such a system is generally very suitable for generating stationary squeezing of the mirror motion in the long-time limit under the unresolved sideband regime. Based on the master equation and covariance matrix approaches, we discuss in detail the respective squeezing effects. We also determine that in both approaches, simplifying the system dynamics with adiabatic elimination of the highly dissipative cavity mode is very effective. In the master equation approach, we find that the squeezing is a resulting effect of the cooling process and is robust against thermal fluctuations of the mechanical mode. In the covariance matrix approach, we can approximately obtain the analytical result of the steady-state mechanical position variance from the reduced dynamical equation. Finally, we compare the two approaches and observe that they are completely equivalent for the stationary dynamics. Moreover, the scheme may be useful for possible ultraprecise quantum measurement that involves mechanical squeezing.     

Von Neumann entropy and entropy squeezing of a two-level atom and the superposition of squeezed displaced fock states

The work presents some aspects of studying the two-level atom in a Kerr media interacting with a single-mode electromagnetic field, which is the superposition of squeezed displaced Fock states. We discuss the effect of the new field on quantum entropy and the entanglement of the atom-field system in the two-photon process. The exact results are employed to perform a careful investigation of the temporal entropy evolution. The position and momentum entropy squeezing of the optical field are investigated. The general conclusions obtained are illustrated by numerical results.     

Generation of sustained optimal entropy squeezing of a two-level atom via non-Hermitian operation

We investigate the entropy squeezing of a two-level atom in the Jaynes–Cummings model, and provide a scheme to generate the sustained optimal entropy squeezing of the atom via non-Hermitian operation. Our results show that the squeezing degree and the persistence time of entropy squeezing of atomic polarization components greatly depend on the non-Hermiticity intensity in non-Hermitian operation. Especially, under a proper choice of non-Hermiticity parameters, the sustained optimal entropy squeezing of the atom can be generated even though the atom is initially prepared in a no entropy squeezing state.     

Broadband resonant cavity inside a two-dimensional sonic crystal

A rectangular cavity inside a two-dimensional sonic crystal was theoretically and experimentally characterized by examining its response to a cylindrical source emitting narrow-band filtered noise bursts with central frequencies ranging from 2 to 12 kHz. A broadband intensity resonance was observed for frequencies within the full band-gap region of the sonic crystal (5.5–6.5 kHz). Unlike ordinary resonances, this broadband resonance depends on the reflection properties of the sonic crystal forming the surrounding walls rather than on the geometry of the cavity.     

Deterministic generation of squeezing for a cavity field with a collection of driven atoms

We propose an efficient scheme for realizing squeezing for a cavity mode. In the scheme, a collection of ladder-type three-level atoms are trapped in a cavity and driven by two classical fields. Under certain conditions, the cavity field deterministically evolves to a squeezed state. The scheme can also be used for conditional generation of superpositions of different squeezed vacuum states.