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Long-lived entanglement with Pulsed-driven initially entangled qubit pair

NASSER METWALLY, Hanan Ali Batarfi, S. S. Hassan

Published Aug 17, 2016• 3 citations
OpenAlex

Abstract

The entanglement of different classes of initially entangled qubit pair is investigated in the presence of short laser pulses of rectangular and exponential shapes with either one or both qubits are excited. For the rectangular pulse, the detuning parameter protects the entanglement from degradation and controls its upper and lower bounds. We show that the upper bounds of entanglement decrease if both particles are excited, but the lower bounds are much better if only one particle is excited. The phenomena of entanglement degradation, sudden-death and -birth are shown for small initial time. Long-lived entanglement behavior, but with a variable degree, appears in the presence of rectangular pulse. However, in the case of the exponential pulse one obtains an invariably long-lived entanglement. For the combined case (rectangular + exponential), we show that one can generate a long-lived entanglement with small variable by increasing the strength of the rectangular pulse area and decreasing the Rabi-frequency of the exponential pulse.

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Long-lived entanglement with pulsed-driven initially entangled qubit pair

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The entanglement of different classes of initially entangled qubit pair is investigated in the presence of short laser pulses of rectangular and exponential shapes with either one or both qubits are excited. For the rectangular pulse, the detuning parameter protects the entanglement from degradation and controls its upper and lower bounds. We show that the upper bounds of entanglement decrease if both particles are excited, but the lower bounds are much better if only one particle is excited. The phenomena of entanglement degradation, sudden-death and -birth are shown for small initial time. Long-lived entanglement behavior, but with a variable degree, appears in the presence of rectangular pulse. However, in the case of the exponential pulse one obtains an invariably long-lived entanglement. For the combined case (rectangular + exponential), we show that one can generate a long-lived entanglement with small variable by increasing the strength of the rectangular pulse area and decreasing the Rabi-frequency of the exponential pulse.

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The entanglement of different classes of initially entangled qubit pair is investigated in the presence of short laser pulses of rectangular and exponential shapes with either one or both qubits are excited. For the rectangular pulse, the detuning parameter protects the entanglement from degradation and controls its upper and lower bounds. We show that the upper bounds of entanglement decrease if both particles are excited, but the lower bounds are much better if only one particle is excited. The phenomena of entanglement degradation, sudden-death and -birth are shown for small initial time. Long-lived entanglement behavior, but with a variable degree, appears in the presence of rectangular pulse. However, in the case of the exponential pulse one obtains an invariably long-lived entanglement. For the combined case (rectangular + exponential), we show that one can generate a long-lived entanglement with small variable by increasing the strength of the rectangular pulse area and decreasing the Rabi-frequency of the exponential pulse.
The entanglement of different classes of initially entangled qubit pair is investigated in the presence of short laser pulses of rectangular and exponential shapes with either one or both qubits are excited. For the rectangular pulse, the detuning parameter protects the entanglement from degradation and controls its upper and lower bounds. We show that the upper bounds of entanglement decrease if both particles are excited, but the lower bounds are much better if only one particle is excited. The phenomena of entanglement degradation, sudden-death and -birth are shown for small initial time. Long-lived entanglement behavior, but with a variable degree, appears in the presence of rectangular pulse. However, in the case of the exponential pulse one obtains an invariably long-lived entanglement. For the combined case (rectangular + exponential), we show that one can generate a long-lived entanglement with small variable by increasing the strength of the rectangular pulse area and decreasing the Rabi-frequency of the exponential pulse.
Abstract We investigate the entanglement dynamic behavior of a system with two driven coupled qubits. The effects of the Rabi frequency ratio of nearest qubits, different initial states and different thermal boson number on quantum entanglement are addressed in detail. The results show that, whether the initial state is entangled or not, the two-qubit state will be in a stable entangled state when we select an appropriate parameter for the Rabi frequency ratio. Meanwhile, quantum sudden death and quantum sudden birth can happen in these systems. Increasing the noise strength can also put the system in a stable entanglement state. Hence steady-state entanglement can be obtained by adjusting the parameter of the Rabi frequency ratio and noise strength.
Background. The study of entangled states in Jaynes–Cummings models and its multiqubit generalizations and extensions remains an important and relevant topic in modern quantum optics, quantum information science and solid state physics. This is due to the fact that such models naturally describe the dynamics of interaction of logical elements of quantum devices, such as quantum computers or quantum networks (qubits) with microwave fields of resonators used to control the states of qubits. In this regard, it is very important to search for the most efficient schemes of generation, control and monitoring of entangled qubit states within the framework of Jaynes–Cummings type models. Aim. To investigate the entanglement dynamics of a pair of qubits, each of which is locked in a single-mode resonator and interacts non-resonantly with the vacuum field mode, in the presence of detuning between frequencies of transitions in the qubits and frequencies of resonator modes and dipole-dipole interaction of the qubits. Methods. To analyze the dynamics of the considered system, the solution of the time-dependent quantum Schrödinger equation is investigated. The exact solution of the above equation in the case of entangled Bell-type initial qubits states is found. This is used to calculate the criterion of entanglement of a pair of qubits – negativity. Numerical modeling of the time dependence of negativity for different values of the parameters of the considered model has been carried out. Results. It is shown that the presence of detuning, the difference in the qubit-photon couplings and the intensity of the dipole-dipole interaction significantly affect the maximum degree of entanglement of the qubit subsystem during its evolution. It is found that for certain parameters of the model under consideration, the initial Bell entangled states of qubits can be considered as long-lived stable states. Conclusion. The possibility of realization of long-lived and robust two-qubit entangled states in the system under consideration has been established. The obtained results can be used for effective control and manipulation of the degree of entanglement of qubits interacting with microwave fields of resonators.
Preventing quantum entanglement from decoherence effect is of theoretical and practical importance in the quantum information processing technologies. In this regard, we consider the entanglement dynamics of two identical qubits where the qubits which are coupled to two independent (Markovian and/or non-Markovian) as well as a common reservoir at zero temperature are further interacted with a classical driving laser field. Then, we study the preservation of generated two-qubit entanglement in various situations using the concurrence measure. It is shown that by applying the classical driving field and so the possibility of controlling the Rabi frequency, the amount of entanglement of the two-qubit system is improved in the off-resonance condition between the qubit and the central cavity frequencies (central detuning) in both non-Markovian and Markovian reservoirs. While the central detuning has a constructive role, the detuning between the qubit and the classical field (laser detuning) affects negatively on the entanglement protection. The obtained results show that long-living entanglement in the non-Markovian reservoir is more accessible than in the Markovian reservoir. We demonstrate that, in a common reservoir non-zero stationary entanglement is achievable whenever the two-qubit system is coupled to the reservoir with appropriate values of relative coupling strengths.
The entanglement dynamics of two two-level atoms which are respectively trapped in two independent dissipative single-mode cavities and strongly driven by the classical fields is investigated analytically utilizing the super operator method.It is found that the entanglement is not related to the initial value of the cavity coherent states.The driving field enhances the entanglement sudden death for small dissipation of the cavity,while it protects the entanglement from sudden death for large dissipation in the presence of strong driving field.These results show that even in the bad cavity(with large decay rate),the entanglement can be free from sudden death with the assistance of classical driving field.
We investigate the entanglement dynamics of systems consisting of up to five qubits coupled to an optical microcavity. This is depicted by a system of excitons in strained graphene. We numerically calculate the time evolution of multiple entanglement monotones in such systems when subjected to a coherent source of photons (e.g., a laser). We propose a different way of estimating the total amount of quantum entanglement contained within a multipartite system based on the negativity which we refer to as total negativity, and to which we give clear upper and lower bounds for this quantity. We compared the results for a system of excitons in strained graphene along with two other systems which can be described by the same Hamiltonian as that for superconducting qubits coupled to a waveguide, and for trapped Rb atoms. We have shown that, depending on the physical parameters of the system, a reasonable amount of long-living entanglement can be created between the qubits. This entanglement is exempt from decay as long as the systems are being continuously pumped with coherent photons. We have reached the interesting conclusion that freely adding new qubits to the system does not, in general, increase the overall amount of entanglement created by the dynamics: there exist an optimum number of system qubits which depend on the Rabi coupling as well as the cavity decay rate for maximal entanglement. We believe that such systems are good candidates for the generation of resilient sets of long-lived partially entangled states suitable for experiments in entanglement distillation.