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Laser Physics

Improving the capacity of quantum dense coding from decoherence of finite temperature using parity-time symmetric operations

Fei Chen, Yang Leng

Published Jul 1, 2025• 1 citation
Publisher

Abstract

Abstract This paper explores enhancing quantum dense coding capacity in finite-temperature decoherence environments via parity-time ( PT ) symmetric operations. We derive the master equation for a two-qubit system in a thermal bath, analyzing dense coding dynamics with and without PT symmetry operations. Without PT operations, the quantum dense coding capacity is highly sensitive to temperature parameter and decoherence rate, losing its advantage at high temperatures. Introducing a local PT symmetric operation on one qubit restores and surpasses the noiseless capacity. Additionally, numerical analysis demonstrates that by adjusting the non-Hermiticity, the optimal protection rate can always exceed 1. Our findings demonstrate PT symmetric operations as a novel tool to protect quantum correlations and enhance information transmission in realistic thermal settings, offering insights for robust quantum communication protocols.

DOI
10.1088/1555-6611/adebf0

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Abstract This paper explores enhancing quantum dense coding capacity in finite-temperature decoherence environments via parity-time ( PT ) symmetric operations. We derive the master equation for a two-qubit system in a thermal bath, analyzing dense coding dynamics with and without PT symmetry operations. Without PT operations, the quantum dense coding capacity is highly sensitive to temperature parameter and decoherence rate, losing its advantage at high temperatures. Introducing a local PT symmetric operation on one qubit restores and surpasses the noiseless capacity. Additionally, numerical analysis demonstrates that by adjusting the non-Hermiticity, the optimal protection rate can always exceed 1. Our findings demonstrate PT symmetric operations as a novel tool to protect quantum correlations and enhance information transmission in realistic thermal settings, offering insights for robust quantum communication protocols.
Abstract In this work, we investigate the effect of a parity-time ( PT ) symmetric operation on the dynamic behavior of quantum dense coding for a two-qubit system in non-Markovian environments. First, we derive the explicit expressions of quantum dense coding for an exactly solving model consisting of two qubits interacting with an independent structured reservoir. Then, we give two cases, i.e. resonant and off-resonant regimes, to demonstrate the performance of the PT symmetric operation on quantum dense coding dynamics. By investigation, we find that the capacity of quantum dense coding can be obviously enhanced with the assistance of the PT symmetric operation in different regimes. In addition, we show that the optimal local PT symmetric operation can completely protect quantum dense coding. The obtained results imply that the PT symmetric operation method may have potential applications in quantum decoherence control.
Abstract Using a non-Hermitian operation approach, we propose a scheme to improve quantum dense coding of a qubit-qubit system interacting with a zero-temperature reservoir with both spontaneous emission and dephasing. By solving the master equation of the two-qubit system, we numerically obtain the final capacity of quantum dense coding. The numerical results show explicitly that the non-Hermitian operation indeed helps to improve the non-Hermitian operation from amplitude-phase decoherence. In particular, non-Hermitian operations can protect quantum dense coding more efficiently in the case of strong decay rates than those with small decay rates.
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We investigate the dephasing dynamics of a qubit as an effective mechanism for estimating the temperature of its surrounding environment for different symmetries. Our approach is fundamentally quantum, leveraging the qubit’s susceptibility to decoherence without necessitating thermal equilibrium with the system under study. We also examine how symmetry properties affect the accuracy of information retrieval and the robustness of quantum information storage in such systems, highlighting their potential advantages in mitigating decoherence effects. The optimization of quantum Fisher information is performed with respect to both the interaction duration and the environmental temperature, focusing on Ohmic-like spectral density environments. Furthermore, we explicitly identify the optimal qubit measurement that attains the quantum Cramér–Rao bound for precision. Our findings reveal that optimal estimation arises from a complex interplay between the qubit’s dephasing dynamics and the Ohmic characteristics of the environment, with a particular focus on non-Hermitian systems that exhibit enhanced resilience to decoherence. We examine the decoherence dynamics of a two-level spin system governed by an anti-parity-time-symmetric Hamiltonian. The obtained results are systematically compared with those corresponding to both PT-symmetric and conventional Hermitian qubit models. To this end, we first employ a time-dependent Dyson transformation to derive the exact analytical evolution of a generic non-Hermitian qubit interacting with an external environment. The formalism is then applied to the particular case of an anti-PT-symmetric qubit. Our analysis reveals that the coherence of the non-Hermitian-symmetric qubit is preserved over significantly longer times, as evidenced by the slower decay of its decoherence function relative to its Hermitian counterparts. Furthermore, the generation of entanglement entropy is found to proceed at a reduced rate, indicating a more gradual buildup of system–environment correlations. In addition, the anti-PT-symmetric configuration exhibits substantially enhanced quantum Fisher information together with a smaller variance than those observed in the corresponding PT-symmetric and Hermitian systems. These findings highlight the remarkable robustness of anti-PT-symmetric qubits against environmental decoherence and suggest that they constitute a promising platform for the implementation of quantum information processing and quantum computing protocols.
Abstract In this letter, we explore the dynamics and protection of nonlocal advantage of quantum coherence (NAQC) for an entangled two-qubit system subjected to a noisy environment by performing parity-time ( PT ) symmetric operations on one of the two particles. For comparison, we investigate the protection of Bell nonlocality, quantum coherence, and entanglement by local PT- symmetric operations. Here, we show that the NAQC, Bell nonlocality, quantum coherence, and entanglement of a bipartite entangled state can be improved effectively by the local PT -symmetric operation and verify that the protection effect is better with the increase of PT- symmetric operation strength.
Abstract We examine the validity of the parity-time ( P T )-symmetric operation in protecting quantum state and entanglement in the non-zero temperature environment. Special attention is paid to the dependence of quantum fidelity and entanglement on the temperature. In particular, by solving the master equation, we get the exact analytical or numerical simulation expressions of the explicit formulas of protection, showing explicitly that P T -symmetric operation does indeed help in protecting quantum state from finite temperature decoherence.