Dissipative Quantum Systems: Reservoir‐Mediated Enhancement of Quantum Fisher Information and Non‐Classical Correlations

In this study, we apply quantum master equations beyond secular approximation and investigate the nonequilibrium thermodynamic cost of enhanced quantum metrology and quantum correlations. We find that the nonequilibrium conditions enhance quantum Fisher information (QFI) and quantum correlations predominantly for weak tunneling scenarios. The enhancement is assisted by a corresponding increase in the thermodynamic cost characterized by the entropy production rate (EPR). For the strong tunneling regimes, the QFI and quantum correlations cannot be unceasingly boosted by higher thermodynamic costs and decay once the system is overburdened with extremely large energy currents. The result indicates that for open systems with weak tunneling rates, thermodynamic cost can be potentially exploited to improve the quantum metrology and quantum correlations.

In this work, we investigate quantum Fisher information (QFI) and quantum coherence (QC) of an atom in a dissipative cavity. In a zero-temperature reservoir and with one excitation number, we obtain the analytical solutions of QFI and QC as well as their relationship for Ohmic and Lorentzian reservoirs, respectively. The results show that both the atom–cavity coupling and the cavity–reservoir coupling can effectively protect QFI and QC. In particular, QFI and QC will tend to their stable values when the atom–cavity coupling or cavity–reservoir coupling is larger than a certain value. QC can augment QFI and can effectively improve the quantum metrology. In addition, we give a physical explanation of the dynamic behavior of QFI and QC using the decoherence rate.

This research delves into the dynamical behavior of quantum correlations and coherence within a mixed Heisenberg dimer system under the intrinsic decoherence. Our approach involves the application of logarithmic negativity, local quantum uncertainty, and the ℓ 1 norm-based coherence as quantifiers for entanglement, skew information correlations, and quantum coherence in this qubit-qutrit model. Our primary objective is to explore the impact of various factors on the dynamics of quantum correlations and quantum coherence. These factors encompass the initial density matrix and its mixing parameter, the intrinsic decoherence rate (γ), the external magnetic field, as well as intrinsic system parameters, notably the XXZ and uniaxial single-ion anisotropies. Our results demonstrate that the introduction of intrinsic decoherence (ID) significantly erodes quantum resources. Particularly, for high values of the ID rate (γ), excessive damping occurs, leading to the absence of oscillations or a rapid decay of quantum resources, ultimately stabilizing in steady states. Furthermore, the presence of an external homogeneous magnetic field further diminishes quantum resources within the system. However, despite the degradation induced by the combined influence of intrinsic decoherence and high external magnetic field intensities, the judicious selection of the initial density matrix and precise adjustment of the uniaxial single-ion anisotropy enable the preservation of quantum resources within the mixed spin-(1/2, 1) Heisenberg dimer.

This paper investigates the evolution of global quantum discord (GQD) and quantum Fisher information (QFI) of the interaction of multiple two-level atomic systems (TLS) with a single thermal field mode and a non-linear Kerr medium (NLKM) considering the cases of intrinsic decoherence and its absence. Results indicate that increasing the number of atomic systems (N) while maintaining the NLKM parameter constant ? leads to higher GQD and QFI values for both intrinsic intrinsic decoherence cases. With rising ?, the GQD values decrease but the oscillation rate of the GQD increases. The presence of intrinsic decoherence does not significantly reduce the GQD quasi-static value compared to the no-decoherence scenario for certain ? values. At the same time, a different trend is observed for higher ? values. The average QFI value rises with reduced oscillation amplitudes for higher ? values and larger N subsystems. Unlike the GQD, higher ? values aid in maintaining average QFI in the presence of intrinsic decoherence. For moving TLS, changing ? does not alter the oscillation periods of the GQD and QFI. The GQD values decrease with increased ? in the moving system case, while the QFI improves with higher ? values. Additionally, higher average thermal photons within the system suppress the GQD and QFI values and decrease oscillation amplitudes for both quantifiers.

In this work, we investigate the non-Markovianity, quantum Fisher information (QFI) and quantum coherence of a qubit in a nonequilibrium environment and have obtained the expressions of QFI and quantum coherence as well as their relationship. We have also discussed in detail the influences of the different environment parameters on these quantum effects. The results show that the suitable parameters of the nonequilibrium environment can retard the QFI and quantum coherence in both Markovian and non-Markovian regions. In addition, the smaller memory effects and the larger the jumping rate, the greater the QFI and quantum coherence. And a larger QFI naturally corresponds to a larger quantum coherence, which indicates that the quantum coherence can enlarge the QFI and can effectively enhance the quantum metrology.

In this paper, we investigate the quantum Fisher information (QFI), quantum entanglement, quantum correlation and quantum phase transition (QPT) within the one-dimensional transverse Ising model by exploiting quantum renormalization-group method. The results show that quantum Fisher information, quantum entanglement, quantum correlation can evolve to two saturated values which exhibit QPT at the critical point after several iterations of the renormalization. Meanwhile, we find quantum entanglement or correlation can be detected perfectly by means of quantum Fisher information. Besides, it cannot capture any information about the system in the paramagnetic phase in view of quantum entanglement and correlation. Contrarily, it is evident the QFI is always nonzero even if the system is in the paramagnetic phase, i.e., the QFI can also be utilized as a highly favorable measure of quantum information in a broad of quantum spin systems. Furthermore, we disclose the nonanalytic and scaling behaviors of quantum Fisher information, which can be taken as a representation of quantum critical characterism.

Quantum coherence is a fundamental common trait of quantum phenomena, from the interference of matter waves to quantum degeneracy of identical particles. Despite its importance, estimating and measuring quantum coherence in generic, mixed many-body quantum states remains a formidable challenge, with fundamental implications in areas as broad as quantum condensed matter, quantum information, quantum metrology and quantum biology. Here we provide a quantitative definition of the variance of quantum coherent fluctuations (the quantum variance) of any observable on generic quantum states. The quantum variance generalizes the concept of thermal de Broglie wavelength (for the position of a free quantum particle) to the space of eigenvalues of any observable, quantifying the degree of coherent delocalization in that space. The quantum variance is generically measurable and computable as the difference between the static fluctuations and the static susceptibility of the observable; despite its simplicity, it is found to provide a tight lower bound to most widely accepted estimators of "quantumness" of observables (both as a feature as well as a resource), such as the Wigner-Yanase skew information and the quantum Fisher information. When considering bipartite fluctuations in an extended quantum system, the quantum variance expresses genuine quantum correlations (of discord type) among the two parts. In the case of many-body systems it is found to obey an area law at finite temperature, extending therefore area laws of entanglement and quantum fluctuations of pure states to the mixed-state context. Hence the quantum variance paves the way to the measurement of macroscopic quantum coherence and quantum correlations in most complex quantum systems.

Our research focuses on the interplay between thermal noise and decoherence channels on quantum coherence and nonclassical correlations in a hybrid ( 1 / 2 , 1 ) Heisenberg model. This hybrid system integrates the Dzyaloshinsky–Moriya interaction (DMI) and operates under the influence of an external magnetic field. We use local quantum Fisher information (LQFI) for correlation estimation and relative entropy of coherence for coherence measurement in the considered system. Our investigation encompasses various parameters of the hybrid system, the strength of the DMI and the intensity of the external magnetic field. Our findings underscore that elevated temperature compromises both nonclassical correlations and coherence. On the other hand, the robustness of the DMI mitigates the impact of thermal noise on quantum Fisher information correlations and relative entropy of coherence in the hybrid system. Additionally, we inspect the impact of decohering channels-specifically, dephasing, phase flip, and bit- and trit-flip channels-on thermal coherence and quantum correlations. The introduction of various decoherence processes into the hybrid qubit-qutrit system leads to a competition with thermal fluctuations, thereby giving rise to out-of-equilibrium states. Our results indicate that as the decoherence strength parameter (p) increases, both LQFI and relative entropy of coherence exhibit similar behaviors in the dephasing and phase flip channels. These resources gradually diminish, eventually disappearing entirely at p = 1. In the context of the bit- and trit-flip channels, quantum coherence displays notable distinctions compared to what is observed under dephasing and phase flip channels, revealing that coherence can be preserved if the DMI is strong and the intensity of the external magnetic field is reduced. These findings are important since it is crucial to first understand the decoherence process, arising from the interaction with the environment, and then to find ways to hinder this decoherence in order to avoid the complete loss of the quantum resources necessary to quantum information processing.

Quantum coherence(QC) and quantum Fisher information(QFI) are investigated for the atom in Jaynes-Cummings model coupling with the Ohmic reservoir at zero temperature when the total excitation number N = 1. We discuss in detail the influence of the atom-cavity coupling and the reservoir parameters on QC and QFI. The results show that QC and QFI of the atom can be effectively controlled by the atom-cavity coupling and the reservoir parameters. Namely, the larger atom-cavity coupling and the appropriate reservoir parameters can effectively protect QC and QFI. Moreover, QC can improve QFI. Last, we provide a physical explanation using the decoherence rate.

Quantum coherence and quantum Fisher information in the XXZ system

We address the teleportation of single- and two-qubit quantum states, parametrized by weight θ and phase ϕ parameters, in the presence of the Unruh effect experienced by a mode of a free Dirac field. We investigate the effects of the partial measurement (PM) and partial measurement reversal (PMR) on the quantum resources and quantum Fisher information (QFI) of the teleported states. In particular, we discuss the optimal behaviour of the QFI, quantum coherence (QC) as well as fidelity with respect to the PM and PMR strength and examine the effect of the Unruh noise on optimal estimation. It is found that, in the single-qubit scenario, the PM (PMR) strength at which the optimal estimation of the phase parameter occurs is the same as the PM (PMR) strength with which the teleportation fidelity and the QC of the teleported single-qubit state reaches its maximum value. On the other hand, generalizing the results to two-qubit teleportation, we find that the encoded information in the weight parameter is better protected against the Unruh noise in two-qubit teleportation than in the one-qubit scenario. However, extraction of information encoded in the phase parameter is more efficient in single-qubit teleportation than in the two-qubit version.

We investigate quantum phase transitions in XY spin models using Dzyaloshinsky-Moriya (DM) interactions. We identify the quantum critical points via quantum Fisher information and quantum coherence, finding that higher DM couplings suppress quantum phase transitions. However, quantum coherence (characterized by the l1-norm and relative entropy) decreases as the DM coupling increases. Herein, we present both analytical and numerical results.

The quantum entanglement, discord, and coherence dynamics of two spins in the model of a spin coupled to a spin bath through an intermediate spin are studied. The effects of the important physical parameters including the coupling strength of two spins, the interaction strength between the intermediate spin and the spin bath, the number of bath spins and the temperature of the system on quantum coherence and correlation dynamics are discussed in different cases. The frozen quantum discord can be observed whereas coherence does not when the initial state is the Bell-diagonal state. At finite temperature, we find that coherence is more robust than quantum discord, which is better than entanglement, in terms of resisting the influence of environment. Therefore, quantum coherence is more tenacious than quantum correlation as an important resource.

Both coherence and entanglement stem from the superposition principle,\ncapture quantumness of a physical system, and play a central role in quantum\nphysics. In a multipartite quantum system, coherence and quantum correlations\nare closely connected. In particular, it has been established that quantum\ncoherence of a bipartite state is an important resource for its conversion to\nentanglement [A. Streltsov {\\it et al.}, Phys. Rev. Lett. {\\bf 115}, 020403\n(2015)] and to quantum discord [J. Ma {\\it et al}., Phys. Rev. Lett. {\\bf 116},\n160407 (2016)]. We show here that there is a very close association between\npartial coherence introduced by Luo and Sun [S. Luo and Y. Sun, Phys. Rev. A\n{\\bf 96}, 022136 (2017)] and quantum correlations (quantified by quantum\ndiscord) in both directions. Furthermore, we propose families of coherence\nmeasures in terms of quantum correlations and quantum Fisher information.\n

We investigate the dynamics of quantum coherence and quantum correlation of two qubits mediated by a one-dimensional plasmonic waveguide. The analytical expression of the dissipative dynamics of the two qubits is obtained for the initial X state. The dynamical behaviors of the quantum coherence and quantum correlation are shown to be largely dependent on the parameters of the initial state. Starting from a product state, quantum coherence and quantum correlation can be induced by the plasmonic waveguide. Under continuous drivings, steady quantum correlation can be obtained at specific distance larger than the operating wavelength and large values of steady quantum coherence are attainable at arbitrary distance. The detuning effect on the dissipation-driven generation of steady quantum coherence and quantum correlation is also explored.