Abstract We explore the impact of channel correlations, resulting from consecutive uses of the channel, on the estimation of channel parameters. Specifically, we analyze the dynamics of quantum Fisher information (QFI) for correlation strength and coupling strength in a two-qubit system subjected to either a Random Telegraph (RT) noise channel or an Amplitude Damping (AD) noise channel. Our findings indicate that the correlation in the RT noise channel enhances the estimation precision of correlation strength but detracts from the precision of coupling strength estimation. However, the correlation in the AD noise channel exhibits a similar effect to that of the RT noise channel only in the initial stage of system’s evolution. In the long-term evolution, the correlation of the AD noise channel reduces the estimation precision of correlation strength but has no monotonic relationship with the estimation precision of coupling strength. Our study provides new insights into the effects of channel correlations on channel parameter estimation and has potential implications for controlling the precision of parameter estimation in quantum information processing.
Abstract We explore the impact of channel correlations, resulting from consecutive uses of the channel, on the estimation of channel parameters. Specifically, we analyze the dynamics of quantum Fisher information (QFI) for correlation strength and coupling strength in a two-qubit system subjected to either a Random Telegraph (RT) noise channel or an Amplitude Damping (AD) noise channel. Our findings indicate that the correlation in the RT noise channel enhances the estimation precision of correlation strength but detracts from the precision of coupling strength estimation. However, the correlation in the AD noise channel exhibits a similar effect to that of the RT noise channel only in the initial stage of system’s evolution. In the long-term evolution, the correlation of the AD noise channel reduces the estimation precision of correlation strength but has no monotonic relationship with the estimation precision of coupling strength. Our study provides new insights into the effects of channel correlations on channel parameter estimation and has potential implications for controlling the precision of parameter estimation in quantum information processing.
Abstract The inherent association between real quantum systems and their surrounding environment invariably results in decoherence, leading to the loss of entanglement. This diminution in entanglement coincides with a decline in the fidelity of transmitted information using the entangled quantum resource. This study scrutinizes the impact of the squeezed generalized amplitude damping (SGAD) channel on quantum Fisher information (QFI) parameters. The SGAD channel model, a versatile framework, is also employed to simulate other dissipative channels, including amplitude damping (AD) and generalized amplitude damping (GAD). Kraus operators facilitate the modeling of noisy channels. The results reveal that, within the SGAD channel, the QFI remains impervious to the squeezing variables (r and Φ Φ ). In the GAD channel, FθGAD F θ GAD undergoes enhancement to a constant value with an upswing in temperature (T), while the ϕ ϕ parameter in the GAD channel, FϕGAD F ϕ GAD , akin to the SGAD channel, surges around T = 2 before complete loss ensues. Concerning the AD channel, the θ θ component of the QFI initially experiences decoherence with an augmentation in the AD noise parameter ( λ λ ). Subsequently, it is restored to its initial value with a further escalation in λ λ . Conversely, the ϕ ϕ component of the QFI in the AD channel experiences decoherence with an elevation in the AD noise parameter ( λ λ ).
Abstract The impact of nonequilibrium environment effects on the accuracy of quantum parameter estimation is investigated, and it is found that these effects can significantly affect estimation accuracy. Using an individual estimation strategy reveals that the nonequilibrium effects consistently enhance accuracy, regardless of the coupling strength between the probe and its environment. In contrast, weak memory effects undermine estimation accuracy. When employing a multi‐parameter simultaneous estimation strategy, it is observed that the nonequilibrium effects consistently improve the advantages of simultaneous estimation, as analyzed by the ratio of total variances between the two estimation scenarios. However, the memory effects on these advantages depend on the coupling strength between the qubit and the environment. These findings suggest that appropriate parameters of a nonequilibrium environment can increase the quantum Fisher information (QFI), thereby enhancing the accuracy of quantum parameter estimation. These significant results are essential for improving parameter estimation accuracy in quantum systems interacting with nonequilibrium environments.
This work explores the dynamics of quantum Fisher information (QFI) in open quantum systems coupled to squeezed reservoirs, providing a mathematical framework for analyzing parameter estimation precision under decoherence. We analyze QFI in two-qubit systems undergoing pure dephasing, considering the effects of squeezing parameter, phase difference, and coupling strength within an Ohmic spectral density model. The decoherence factor shows how reservoir engineering influences coherence loss. Numerical results demonstrate that optimal squeezing and local bath configurations enhance QFI preservation, while collective couplings accelerate decay. We also examine the interplay with von Neumann entropy, highlighting their inverse correlation, where increased mixedness reduces metrological sensitivity.
Quantum Fisher information (QFI) quantifies the sensitivity of a quantum state to a parameter change and plays a key role in quantum metrology. Meanwhile, quantum coherence is a crucial resource for quantum information processing. However, despite extensive studies on various aspects of quantum metrology, the interplay between the dynamics of the QFI and quantum coherence remains unexplored. Here, we explore the factorization relationship between the QFI and quantum coherence, both theoretically and experimentally. We prepare pure states in qubit and qutrit systems and apply unitary evolution to investigate this relationship. Our results confirm the factorization law, offering strong evidence for this relationship. Furthermore, we establish a lower bound on the variance of the estimated parameter that does not require the final state information. This approach reveals a deep connection between the QFI and quantum coherence, providing insights into quantum parameter estimation. These findings have potential applications in quantum sensing and quantum metrology.
Quantum fisher information of a parameter characterizing the sensitivity of a state with respect to parameter changes. In this paper, we study the quantum fisher information of the W state for four, five, six and seven particles in decoherence channels, such as amplitude damping, phase damping and depolarizing channel. Using Krauss operators for decoherence channels components, we investigate the quantum fisher information quite analytically. We observe that for the W state, the amount of the quantum fisher information and consequently, the amount of entanglement are reduced by applying the quantum noises, which affect each particle in the same way. In some cases, a relative increase appears in the quantum fisher information for certain values of the decay strength p. We also show that the phase damping channel vanishes the value of the quantum fisher information for the W state.
Abstract Quantum Fisher information (QFI) has potential applications in quantum metrology tasks. QFI is investigated when the consecutive actions of a quantum channel on the sequence of qubits have partial classical correlations. The results showed that while the decoherence effect is detrimental to QFI, effects of such classical correlations on QFI are channel‐dependent. For the Bell‐type probe states, the classical correlations on consecutive actions of the depolarizing and phase flip channels can be harnessed to improve QFI, while the classical correlations in the bit flip and bit‐phase flip channels induce a slight decrease of QFI. For a more general parameterization form of the probe states, the advantage of using the initial correlated system on improving QFI can also remain in a wide regime of the correlated quantum channels.