We investigate the time evolution and asymptotic behavior of a system of two two-level atoms (qubits) interacting off-resonance with a single mode radiation field. The two atoms are coupled to each other through dipole-dipole as well as Ising interactions. An exact analytic solution for the system dynamics that spans the entire phase space is provided. We focus on initial states that cause the system to evolve to entanglement sudden death (ESD) between the two atoms. We find that combining the Ising and dipole-dipole interactions is very powerful in controlling the entanglement dynamics and ESD compared with either one of them separately. Their effects on eliminating ESD may add up constructively or destructively depending on the type of Ising interaction (Ferromagnetic or anti-Ferromagnetic), the detuning parameter value, and the initial state of the system. The asymptotic behavior of the ESD is found to depend substantially on the initial state of the system, where ESD can be entirely eliminated by tuning the system parameters except in the case of an initial correlated Bell state. Interestingly, the entanglement, atomic population and quantum correlation between the two atoms and the field synchronize and reach asymptotically quasi-steady dynamic states. Each one of them ends up as a continuous irregular oscillation, where the collapse periods vanish, with a limited amplitude and an approximately constant mean value that depend on the initial state and the system parameters choice. This indicates an asymptotic continuous exchange of energy (and strong quantum correlation) between the atoms and the field takes place, accompanied by diminished ESD for these chosen setups of the system. This system can be realized in spin states of quantum dots or Rydberg atoms in optical cavities, and superconducting or hybrid qubits in linear resonators.
We investigate the time evolution and asymptotic behavior of a system of two two-level atoms (qubits) interacting off-resonance with a single mode radiation field. The two atoms are coupled to each other through dipole-dipole as well as Ising interactions. An exact analytic solution for the system dynamics that spans the entire phase space is provided. We focus on initial states that cause the system to evolve to entanglement sudden death (ESD) between the two atoms. We find that combining the Ising and dipole-dipole interactions is very powerful in controlling the entanglement dynamics and ESD compared with either one of them separately. Their effects on eliminating ESD may add up constructively or destructively depending on the type of Ising interaction (Ferromagnetic or anti-Ferromagnetic), the detuning parameter value, and the initial state of the system. The asymptotic behavior of the ESD is found to depend substantially on the initial state of the system, where ESD can be entirely eliminated by tuning the system parameters except in the case of an initial correlated Bell state. Interestingly, the entanglement, atomic population and quantum correlation between the two atoms and the field synchronize and reach asymptotically quasi-steady dynamic states. Each one of them ends up as a continuous irregular oscillation, where the collapse periods vanish, with a limited amplitude and an approximately constant mean value that depend on the initial state and the system parameters choice. This indicates an asymptotic continuous exchange of energy (and strong quantum correlation) between the atoms and the field takes place, accompanied by diminished ESD for these chosen setups of the system. This system can be realized in spin states of quantum dots or Rydberg atoms in optical cavities, and superconducting or hybrid qubits in linear resonators.
We study a model of two coupled two-level atoms (qubits) interacting off-resonance (at non-zero detuning) with a single mode radiation field. This system is of special interest in the field of quantum information processing (QIP) and can be realized in electron spin states in quantum dots or Rydberg atoms in optical cavities and superconducting qubits in linear resonators. We present an exact analytical solution for the time evolution of the system starting from any initial state. Utilizing this solution, we show how the entanglement sudden death (ESD), which represents a major threat to QIP, can be efficiently controlled by tuning atom-atom coupling and non-zero detuning. We demonstrate that while one of these two system parameters may not separately affect the ESD, combining the two can be very effective, as in the case of an initial correlated Bell state. However in other cases, such as a W-like initial state, they may have a competing impacts on ESD. Moreover, their combined effect can be used to create ESD in the system, as in the case of an anti-correlated initial Bell state. A clear synchronization between the population inversion collapse-revival pattern and the entanglement dynamics is observed at all system parameter combinations. Nevertheless, only for initial states that may evolve to ESD, the population inversion revival oscillations, where exchange of energy between the atoms and the field takes place, temporally coincide with the entanglement revival peaks, whereas the population collapse periods match the ESD intervals. The variation of the radiation field intensity has a clear impact on the duration of the ESD at any combination of the other system parameters.
The rapid advancement in the field of quantum information processing sparked great interest in developing what are believed to be new promising qubits made of artificial atoms as well as customized natural ones. Those qubits enjoy mutual interaction with other qubits of the same type or different one in what is known as the hybrid quantum systems. In this work, an asymmetrical generalized version of the famous Tavis-Cummings model is used to prototype the behavior of such hybrid systems. The problem is explored in its full generality by analytically solving the model while upholding realistic conditions, namely two mutually interacting non-identical qubits coupled off-resonance to a radiation field, with non-linearity in both the cavity medium and the qubit-field interaction. The work focuses on studying the entanglement dynamics of the system and its asymptotic behavior, with special emphasis on entanglement sudden death (ESD) and birth (ESB). The system is found to exhibit typical death-revival pattern, which asymptotically approaches a pseudo-steady state that is considerably sensitive to the degree of asymmetry between the qubits, the initial state, and other system parameters. We show that for certain initial entangled states, the system parameters can be tuned to provide maximized persistent terminal entanglement values that are steady and free of any collapse-revival patterns or ESD. In contrary, the disentangled initial states asymptotically attain scattered entanglement maxima that lack any systematic behavior. This terminal entanglement behavior can be attained more rapidly by strengthening the mutual interaction between the qubits, a process that is now experimentally accessible with contemporary artificial qubit systems. These results pave the road for preparing strongly entangled qubits in long-life steady states that are crucially needed for performing efficient quantum information algorithms. These systems can be realized using typical qubits such as quantum dots, trapped ions, superconductors, and Rydberg atoms, in either cavity or circuit QED structures.
In this paper, we study the dynamics of a system consisting of two identical qubits interacting non-resonantly with a single-mode field of an ideal resonator in the presence of direct dipole-dipole and Ising interactions between the qubits. In the representation of "dressed" states, we find an exact solution of the quantum time Liouville equation for the full density matrix of the system under consideration for the initial separable and entangled states of the qubits and the thermal initial state of the resonator field. Based on the exact solution, the criterion for qubit entanglement, negativity, is calculated. The results of numerical modeling of negativity show that the inclusion of dipole-dipole and Ising coupling in the case of separable initial states of qubits can lead to a significant increase in the maximum degree of their entanglement, and in the case of entangled initial states of qubits, to stabilization of the initial entanglement. For the model with resonant interaction of qubits and the resonator field, direct interaction of qubits can also lead to the disappearance of the sudden death of entanglement effect.
In this paper, the non-resonant interaction of two two-level atoms with two quantized cavity fields is studied by considering the dipole–dipole interaction between the two atoms. The correlation between the fields has been taken into account and the parametric down conversion is considered. Under certain initial conditions which is determined for the atoms and the fields, the analytical solution for the time-dependent Schrödinger equation is obtained. Employing this solution, we are able to discuss about some physical properties such as atomic population inversion and entanglement between various subsystems, i.e. “atoms–fields” and “atom–atom” by using respectively von Neumann entropy and negativity. It is deduced from the numerical results that, the mentioned quantities can be controlled by the atomic dipole–dipole interaction and detuning parameter, appropriately. The results show that the degree of entanglement between the two atoms is increased due to the presence of dipole–dipole coupling of the atoms at the beginning of atom–field interaction. Furthermore, it is found that, in the non-resonance condition, the so-called entanglement sudden death occurs in the presence of dipole–dipole interaction.
Recalling that counter rotating terms (CRTs) in atom–field interaction are not always ignorable, particularly in the strong coupling regimes of atom–field systems, in this paper we are going to study the interaction between two qubits (two-level atoms) with a two-mode field in a high quality cavity by considering CRTs while the dipole–dipole (D–D) interaction is also taken into account. Indeed, by performing an appropriate dynamical Hamiltonian associated with the Jaynes–Cummings and anti-Jaynes–Cummings terms, as well as the D–D interaction for the system, we solve the corresponding time-dependent Schrödinger equation with specific initial conditions for atoms and field. In the continuation, concurrence, as an appropriate measure of the degree of entanglement of the two qubits, and atomic population inversion of the qubits, as the rate of energy exchange between atoms and field, are evaluated. Meanwhile, we investigate the influence of CRTs and D–D interaction (as well as other involved parameters in the model interaction) on the mentioned quantities. Our numerical results indicate that collapse-revival phenomenon can be observed in the absence of D–D interaction with or without rotating wave approximation, however, CRTs cause an increase or decrease in the number of collapse-revivals in a finite interval of time, depending on the chosen parameters. In fact, by entering the D–D interaction term, this phenomenon is destroyed and the time behaviour of the quantities experiences irregular oscillations. Noticing that the initial field is considered in the vacuum state, the occurrence of collapse-revival in the population inversion of the two qubits is an interesting feature of this work. As is shown, the degree of entanglement and atomic population inversion of the qubits can generally be tuned, and the death of entanglement can be prevented, both by adjusting the evolved parameters in the model.
The possibility of exploiting heterogeneous quantum systems to high precision, for storing, processing, and transmitting information, makes them ideal candidates for multitasking purposes in quantum communication. Appropriate quantum systems involving a judicious choice of interactions that augment each other are potentially useful for probing deep into quantum regimes. Here, we use one such hybrid bipartite quantum model, with one subsystem made of a pair of qubits and another comprising a pair of oscillators, to study the entanglement dynamics and the entanglement transfer between discrete and continuous variables. The basic model is the standard double Jaynes–Cummings model, which, under suitable conditions, is known to support both entanglement transfer and entanglement sudden death. In this work, we generalize this model to include further experimentally relevant interactions, such as the beamsplitter-type exchange interaction between the oscillators, and dipole–dipole and Ising-type interactions between the qubits. The way various interactions and initial oscillator states affect the entanglement dynamics is examined theoretically for generic experimental conditions. Using exact analytical solutions, we show that, compared to the beamsplitter or dipole–dipole interaction, the Ising interaction can have a significant positive impact on entanglement sudden death and birth, and the postponement of the onset of these phenomena, apart from producing a substantial reduction in the time duration of the death.