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Laser Physics

Long-lived genuine entangled of Werner and Greenberger–Horn–Zeilinger states in the three-qubit Tavis–Cummings thermal model with multiphoton processes

Eugene K. Bashkirov, Alexander R. Bagrov

Published Jun 1, 2025• 2 citations
Publisher

Abstract

Abstract An exact solution for the evolution operator of the multiphoton three-qubit Tavis–Cummings model was found. On this basis, the entanglement dynamics and the phenomenon of entanglement sudden death for entangled initial W-, GHZ-, and GHZ-like qubit states and the thermal state of the resonator were studied by means of pairwise negativity and fidelity. The results of entanglement parameters calculations showed that in the nonlinear multiphoton processes, the atomic entanglement is stronger than in the linear one-photon process. We also obtained that the so-called sudden death phenomenon occurs only for some kind of initial qubit states and some thermal noise intensities, i.e. the phenomenon is sensitive to the initial conditions. The length of the time interval for the zero entanglement is dependent on not only the initial qubit states but also the photon transition multiple. We also showed that for large values of the multiple, only one W-type initial state and one GHZ-like initial state are the long-lived and maximally persistent and robust states.

DOI
10.1088/1555-6611/addd90

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Abstract An exact solution for the evolution operator of the multiphoton three-qubit Tavis–Cummings model was found. On this basis, the entanglement dynamics and the phenomenon of entanglement sudden death for entangled initial W-, GHZ-, and GHZ-like qubit states and the thermal state of the resonator were studied by means of pairwise negativity and fidelity. The results of entanglement parameters calculations showed that in the nonlinear multiphoton processes, the atomic entanglement is stronger than in the linear one-photon process. We also obtained that the so-called sudden death phenomenon occurs only for some kind of initial qubit states and some thermal noise intensities, i.e. the phenomenon is sensitive to the initial conditions. The length of the time interval for the zero entanglement is dependent on not only the initial qubit states but also the photon transition multiple. We also showed that for large values of the multiple, only one W-type initial state and one GHZ-like initial state are the long-lived and maximally persistent and robust states.
We obtained a solution of the Liouville equation for a system of three identical qubits interacting without detuning with a thermal field of a cavity with a Kerr medium, for two type of initial pure genuine W-entangled qubits states. On its basis, three entanglement parameters: fidelity, tangle and pairwise negativities were calculated. We obtained that sudden death of entanglement takes place for large intensities of the cavity thermal noise for all considered W-states. We also showed that Kerr nonlinearity prevents the destruction of the initial qubits entanglement induced by the thermal noise of the cavity and eliminates the sudden death of entanglement.
In this article, we consider the entanglement between three identical qubits resonantly interacting with a thermal field of an Q-infinite resonator. We derived the exact solution of the evolution equation for density matrix of the considered system. On it basis we calculate the negativity as a criteria of entanglement between pairs of qubits for biseparable and entangled W-type states of qubits. The results showed that for considered initial qubits states the effect of the entanglement sudden death occurs for all values of the average number of thermal photons.
In this work we study in detail the generalized Tavis — Cummings model, in which three identical qubits are trapped in a lossless single-mode resonator and interact resonantly with the quantized thermal electromagnetic field of this resonator by means of multiphoton processes. An exact solution of the unsteady Schr¨odinger equation for separable qubit states and Fock states of the resonator field was demonstrated for the model under study. The resulting expressions were used to calculate the density matrix in the case of the thermal field of the resonator and to calculate the criterion for pairwise entanglement of qubits — Wootters concurrence. The results showed that the thermal field can induce pairwise entanglement between qubits for all initial separable states for certain system parameters. The calculations also showed that the photon multiple can be considered as an effective mechanism for controlling the entanglement of qubits, since its increase leads to a significant suppression of the effect of the sudden death of entanglement and to an increase in the maximum degree of entanglement for some separable qubit states.
In this paper, we analyze in detail the dynamics of the negativity criterion, fidelity and concurrence fill for the Tavis-Cummings model in which three qubits are in a common single-mode ideal resonator and interact resonantly with the field mode via multiphoton processes. By solving the unsteady Schrödinger equation, we give analytic solutions for genuine entangled Werner- and Greenberger-Horn-Zeilinger states. It is shown that the multiplicity of photon transitions can significantly stabilize the genuine entangled states of both types. Key features in the dynamics pattern of the entanglement parameters are highlighted. We conclude that the negativity criterion is not suitable for describing the dynamics of entanglement of qubits in the case of three-qubit Greenberger-Horn-Zeilinger states. Main advantages of the concurrence fill over the negativity criterion are shown.
In this paper, a three-qubit Tavis-Cummings model with two independent lossless single-mode resonators is considered. It is assumed that the initial states of the resonator fields are thermal fields and the qubits are in genuine entangled W- and GHZ-type states. For the model under study and the specified initial states of the resonator fields and qubits, we have exactly solved the quantum Liouville equation for the full density matrix. The full density matrix was used to calculate the entanglement parameters - negativity and fidelity. The computer simulation results showed that in the investigated model, the entanglement for all initial qubit states breaks down rapidly with increasing intensity of the thermal fields of the resonators compared to the previously investigated three-qubit models. Moreover, a sudden death of entanglement is observed even for vacuum resonator fields.
In this paper, we investigated the dynamics of systems of two and three identical qubits interacting resonantly with a selected mode of a thermal field of a lossless resonator. We found solutions of the quantum time-dependent Liouville equation for various three- and two-qubit entangled states of qubits. Based on these solutions, we calculated the criterion of the qubit entanglement — fidelity. The results of numerical calculations of the fidelity showed that increasing the average number of photons in a mode leads to a decrease in the maximum degree of entanglement. It is shown that the two-qubit entangled state is more stable with respect to external noise than the three-qubit entangled Greenberger — Horne — Zeilinger states (GHZ). Moreover, a genuine entangled GHZ-state is more stable to noise than a GHZ-like entangled state.