Dynamics of Quantum Coherence and Non-Classical Correlations in Open Quantum System Coupled to a Squeezed Thermal Bath

We investigate the intricate dynamics of quantum coherence and non-classical correlations in a two-qubit open quantum system coupled to a squeezed thermal reservoir. By exploring the correlations between spatially separated qubits, we unravel the complex interplay between quantum correlations and decoherence induced by the reservoir. Our findings demonstrate that non-classical correlations such as quantum consonance, quantum discord, local quantum uncertainty, and quantum Fisher information are highly sensitive to the collective regime. These insights identify key parameters for optimizing quantum metrology and parameter estimation in systems exposed to environmental interactions. Furthermore, we quantify these quantum correlations in the context of practical applications such as quantum teleportation, using the two metrics viz. maximal teleportation fidelity and fidelity deviation. This work bridges theoretical advancements with real-world applications, offering a comprehensive framework for leveraging quantum resources under the influence of environmental decoherence.

💡 Research Summary

The paper investigates the time‑dependent behavior of quantum coherence and a suite of non‑classical correlations in a two‑qubit open quantum system that interacts with a squeezed thermal reservoir. By treating the qubits as spatially separated entities, the authors explore two distinct regimes: a collective decoherence regime, where the qubits are close enough to experience a common bath, and an independent decoherence regime, where each qubit couples to its own local environment. The study employs a comprehensive set of quantifiers: relative entropy of coherence (C_rel), concurrence (C_E) for entanglement, quantum discord (QD), quantum consonance (QC), local quantum uncertainty (LQU), and quantum Fisher information (QFI). For teleportation performance, average teleportation fidelity (F̄) and fidelity deviation (ΔF) are calculated, with the classical benchmark set at 2/3.

Theoretical sections define each measure and show how, for X‑states, QC reduces to a simple function of the off‑diagonal density‑matrix elements, while LQU can be obtained analytically from the maximal eigenvalue of a 3×3 matrix constructed from Pauli operators. The dynamics are obtained by solving the master equation for the reduced two‑qubit state under non‑Markovian conditions induced by the squeezed bath, with the squeezing parameter r and mean thermal photon number (\bar n) serving as key environmental knobs.

Key findings include:

1. Coherence Decay: C_rel decays faster as r or (\bar n) increase, but in the collective regime a temporary revival appears due to bath‑mediated correlations.
2. Entanglement Dynamics: Concurrence exhibits environment‑induced generation from an initially uncorrelated state in the collective regime, followed by damped oscillations characteristic of non‑Markovian memory effects. In the independent regime, entanglement generation is suppressed.
3. Discord and Consonance: Quantum discord remains non‑zero even when concurrence vanishes, highlighting correlations beyond entanglement. QC grows sharply with the squeezing strength because it directly tracks the magnitude of off‑diagonal elements |ρ_14| and |ρ_23|.
4. Local Quantum Uncertainty: LQU attains values close to unity in the collective regime, indicating that a local measurement on one qubit significantly perturbs the joint state—an indicator of strong quantum correlations even for separable states.
5. Quantum Fisher Information: QFI, evaluated for a generic parameter θ (e.g., system‑bath coupling), shows transient peaks in the presence of non‑Markovian memory, implying enhanced metrological precision during those intervals.
6. Teleportation Performance: The average teleportation fidelity surpasses the classical limit (2/3) precisely in regions where both QC and LQU are high. Moreover, the fidelity deviation ΔF is minimized in these regions, signifying robust and uniform teleportation quality across input states.

By scanning the parameter space (r, (\bar n), inter‑qubit distance d), the authors identify optimal operating points that maximize non‑classical correlations while mitigating decoherence. The results suggest that engineered squeezed reservoirs can be exploited not only to protect quantum resources but also to actively enhance them, offering practical guidance for quantum metrology, parameter estimation, and quantum communication protocols such as teleportation. The work bridges theoretical analysis with potential experimental implementations, emphasizing the constructive role of environmental squeezing and non‑Markovian effects in future quantum technologies.