Two-atom Tavis-Cummings Model Research Articles

Thermal entanglement in two-atom Tavis–Cummings model with taking into account the dipole-dipole interaction

Background. Interest in the study of entangled states of systems of natural and artificial atoms (qubits) interacting with selected modes of microwave resonators is associated with their use as logic elements of quantum computers. At the same time, the most important task of the physics of quantum computing is the choice of the most effective mechanisms for manipulating and controlling the entangled states of qubits in such devices. Aim. The dynamics of the entanglement of two dipole-coupled superconducting Josephson qubits induced by a thermal noise of a coplanar resonator is studied for various initial states of the qubits. Methods. Based on the exact solution of the quantum Liouville equation for the whole density matrix of the system under consideration, the time behavior of the qubit entanglement parameter (negativity) is found for chaotic thermal, pure separable, and entangled initial states of qubits. Results. It is shown that the entanglement of qubits induced by the thermal noise of the resonator is possible for both the chaotic thermal states and separable states of qubits, except the case when both qubits are excited. It has also been found that, for small values of the dipole–dipole interaction parameter, taking this interaction into account leads to an increase in the degree of entanglement. For values of the dipole-dipole interaction parameter greater than some limit value, the opposite effect takes place. It is found that for entangled initial states of qubits, the inclusion of direct interaction has a small effect on the entanglement dynamics. It is shown that the initial coherence of qubit states can lead to a significant increase in the degree of their entanglement in the presence of a dipole–dipole interaction. Conclusion. The dipole-dipole interaction can be used as an effective mechanism for qubits entanglement manipulation and controlling.

Entangling operations in nonlinear two-atom Tavis-Cummings models

We derive an analytical approximate solution of the time-dependent state vector in terms of material Bell states and coherent states of the field for a generalized two-atom Tavis-Cummings model with nonlinear intensity dependent matter-field interaction. Using this solution, we obtain simple expressions for the atomic concurrence and purity in order to study the entanglement in the system at specific interaction times. We show how to implement entangling atomic operations through measurement of the field. We illustrate how these operations can lead to a complete Bell measurement. Furthermore, when considering two orthogonal states of the field as levels of a third qubit, it is possible to implement a unitary three-qubit gate capable of generating authentic tripartite entangled states such as the Greenberger-Horne-Zeilinger (GHZ) state and the W-state. As an example of the generic model, we present an ion-trap setting employing the quantized mode of the center of mass motion instead of the photonic field, showing that the implementation of realistic entangling operations from intrinsic nonlinear matter-field interactions is indeed possible.

A simple model for a minimal environment: the two-atom Tavis–Cummings model revisited

ABSTRACTIndividual quantum systems may be interacting with surrounding environments having a small number of degrees of freedom. Here we discuss a simple toy model: a system constituted by a two-level atom (atom 1) interacting with a single mode cavity field which is (weakly) coupled to a small environment (atom 2). We investigate the influence of the minimal environment on the dynamics of the linear entropy and the atomic dipole squeezing of atom 1, as well as the entanglement between atom 1 and the field. We also obtain the full analytical solution of the two-atom Tavis–Cummings model for both arbitrary coupling strengths and frequency detunings, necessary to analyse the influence of the field-environment detuning on the evolution of the system’s quantum properties. For complementarity, we discuss the role of the degree of mixedness of the environment by analysing the time-averaged linear entropy of atom 1.

The dynamics of entanglement in two-atom Tavis–Cummings model with non-degenerate two-photon transitions for four-qubits initial atom-field entangled states

The influence of dipole–dipole interaction on the entanglement between two Δ-type artificial atoms interacting with two-mode field via non-degenerate two-photon transitions has been investigated. The atom-field system is assumed to be prepared in four-partite atom-field entangled state. The results show that the entanglement between two atoms can be increased by means of dipole–dipole interaction and for some initial states the entanglement sudden death effect can be weakened.

Control of quantum information flow and quantum correlations in the two-atom Tavis–Cummings model

We investigate the quantum information of the two non-interacting two-level atoms coupled to a single mode of the cavity field via selective measurements. It is found that the information of the two atoms can be protected by intensive measurements and can be enhanced by a single measurement which is demonstrated by the growth of the trace distance between two marginal states of the two atoms, as well as the positive information flow in the first instance. We also show that the single measurement is effective for enhancing the quantum information flow, which leads to the increase of quantum correlations including concurrence and quantum discord. Moreover, we explore the behaviour of total information measured by the trace distance when the total system is initially in its thermal equilibrium state and how the atom–cavity coupling and the temperature affect the total correlation for the thermal state of the entire system.

Entanglement for two-atom Tavis–Cummings model with degenerate two-photon transitions in the presence of the Stark shift

The dynamics of atom–field entanglement for two two-level atoms with degenerate two-photon transitions interacting with one-mode radiation field with taking into account the Stark shift is investigated. Asymptotic solutions for system state vectors are obtained in the approximation of large initial coherent fields. The atom–field entanglement is investigated also on the basis of the linear atomic entropy dynamics. The possibility of the system being initially in a pure disentangled state to revive into this state during the evolution process is shown. Conditions and times of disentanglement are derived.

Wehrl entropy of the state in a two-atom Tavis-Cummings model

Wehrl entropy of the state in a two-atom Tavis-Cummings model

Entanglement in the adiabatic limit of a two-atom Tavis–Cummings model

We study the adiabatic limit for the sequential passage of atoms through a high-Q cavity, in the presence of frequency chirps. Despite the fact that the adiabatic approximation might be expected to fail, we were able to show that for proper choice of Stark-pulses this is not the case. Instead, a connection to the resonant limit is established, where the robust creation of entanglement is demonstrated. Recent developments in the fabrication of high-Q cavities allow fidelities for a maximally entangled state up to 97%.

Effect of external field on the fidelity of quantum states in the two-atom Tavis-Cummings model

The fidelities of quantum states in the two-atom Tavis-Cummings model where the atoms are driven by an external classical field are derived. The influence of the external field and the dipole-dipole interaction of the atoms in a special initial state on the fidelity is discussd.

Nonclassical feature of the field in the two-atom Tavis-Cummings model with atomic motion

We study the nonclassical feature of the field in the two-atom Tavis-Cummings model with atomic motion using the quantum theory. The influence of atomic motion, the field mode structure and the field initial states on the properties of the light squeezing and the photon antibunching are discussed.

Effect of an external radiation field on the properties of the atoms and cavity field in the two-atom Tavis–Cummings model

We study the properties of atoms and cavity field in the two-atom Tavis–Cummings model where the two atoms interact with each other and are also driven by an external classical field. We consider the special case that the cavity is initially in a coherent state. The atomic inversion, the average photons number and the Mandel parameter in the driven Tavis–Cummings model are given and analysed numerically. We pay special attention to the dynamical behaviour of the atoms and the cavity field modified by the external field.

Entanglement sharing in the two-atom Tavis-Cummings model

Individual members of an ensemble of identical systems coupled to a common probe can become entangled with one another, even when they do not interact directly. We investigate how this type of multipartite entanglement is generated in the context of a system consisting of two two-level atoms resonantly coupled to a single mode of the electromagnetic field. The dynamical evolution is studied in terms of the entanglements in the different bipartite partitions of the system, as quantified by the I tangle. We also propose a generalization of the so-called residual tangle that quantifies the inherent three-body correlations in our tripartite system. This enables us to completely characterize the phenomenon of entanglement sharing in the case of the two-atom Tavis-Cummings model, a system of both theoretical and experimental interest.