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Laser Physics Letters

Enhancing precision of phase estimation by homodyne-mediated feedback and classical driving

Yaohua Hu, Leiming Cao, Haifeng Yang, Yong-Gang Tan, Qin mu Wu

Published Feb 20, 2020• 4 citations
Publisher

Abstract

Abstract A two-level atom interacting with a single-mode cavity is considered. The atom-cavity system is driven by a classical field with the homodyne-mediated feedback. The influences of the driving field and two types of the feedback on the precision of the phase estimation are investigated. The results show the quantum Fisher information (QFI) can be preserved by the homodyne-mediated feedback and the classical driving when the system parameters are suitable. In addition, the initial value of the relative phase greatly effects the QFI. Therefore, the phase estimation precision of the two-level atom can be enhanced, and the extent of the enhancement is decided by not only the driving frequency and the type of quantum feedback, but also the initial parameters of the two-level system.

DOI
10.1088/1612-202x/ab7301

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Abstract A two-level atom interacting with a single-mode cavity is considered. The atom-cavity system is driven by a classical field with the homodyne-mediated feedback. The influences of the driving field and two types of the feedback on the precision of the phase estimation are investigated. The results show the quantum Fisher information (QFI) can be preserved by the homodyne-mediated feedback and the classical driving when the system parameters are suitable. In addition, the initial value of the relative phase greatly effects the QFI. Therefore, the phase estimation precision of the two-level atom can be enhanced, and the extent of the enhancement is decided by not only the driving frequency and the type of quantum feedback, but also the initial parameters of the two-level system.
We investigate the quantum Fisher information (QFI) dynamics of a dissipative two-level system in homodyne-mediated quantum feedback control. The analytical results demonstrate that the maximum values and stable values of the QFI can be greatly enhanced via feedback control. The quantum feedback plays a more evident role in the improvement of classical Fisher information. The classical part can reach a high stable value, while the quantum part eventually decays to zero whatever the feedback parameter is .
The dynamics of quantum Fisher information (QFI) of the phase parameter in a driven two-state system is studied within the framework of the non-Markovian dissipative process. The influences of memory effects, classical driving, and detunings on the parameter-estimation precision are demonstrated by exactly solving the Hamiltonian under rotating-wave approximation. In sharp contrast with the results obtained in the presence of Markovian dissipation, we find that classical driving can drastically enhance the QFI, namely, the precision of parameter estimation in the non-Markovian regime. Moreover, the parameter-estimation precision may even be preserved from the influence of surrounding non-Markovian dissipation with the assistance of classical driving. Remarkably, we reveal that the enhancement and preservation of QFI highly depend on the combination of classical driving and non-Markovian effects. Finally, a phenomenological explanation of the underlying mechanism is presented in detail via the quasimode theory.
Abstract Quantum metrology enables measurement sensitivities beyond classical limits by exploiting quantum resources. Among promising platforms, hybrid cavity–magnon systems—where microwave photons interact with collective spin excitations in magnetic materials—offer a versatile testbed for emerging quantum technologies. However, their performance hinges on precise knowledge of the cavity–magnon coupling strength. Here, we propose an experimentally feasible scheme to enhance the quantum estimation of this parameter by leveraging coherent feedback and parametric amplification. Using the Heisenberg–Langevin formalism, we linearize the system dynamics and compute both quantum (QFI) and classical Fisher information. Our analysis shows that optimal detuning, strong driving, and cryogenic temperatures below 0.1 K significantly improve estimation precision, while magnon dissipation and thermal noise degrade the QFI. Parametric amplification enhances precision when the gain and phase are optimally tuned, and coherent feedback yields even greater sensitivity at tailored phase shifts and reflectivities. Notably, their combination achieves the lowest estimation error and the highest robustness against thermal noise. Finally, we identify the cavity mode as the optimal probe, with homodyne detection nearly saturating the quantum limit under ideal conditions. These findings establish a robust pathway for high-precision, noise-resilient cavity–magnon coupling estimation.
Entangled systems with large quantum Fisher information (QFI) can be used to outperform the standard quantum limit of the separable systems in quantum metrology. However, the interaction between the system and the environments inevitably leads to decoherence and decrease of the QFI, and it is not clear whether the entanglement systems can be a better resource than separable systems in the realistic physical condition. In this work, we study the steady QFI of two driven and collectively damped qubits with homodyne-mediated feedback. We show that the steady QFI can be significantly enhanced both in the cases of symmetric feedback and nonsymmetric feedback, and the shot-noise limit of separable states can be surpassed in both cases. The QFI can even achieve the Heisenberg limit for appropriate feedback parameters and initial conditions in the case of symmetric feedback. We also show that an initial-condition-independent steady QFI can be obtained by using nonsymmetric feedback.
In the present manuscript, we demonstrate the potential to control and enhance the accuracy of parameter estimation (P-E) in a two-level atom (TLA) immersed in a cavity field that interacts with another cavity. We investigate the dynamics of quantum Fisher information (FI), considering the influence of coupling strength between the two cavities and the detuning parameter. Our findings reveal that, in the case of a perfect cavity, a high quantum FI value can be maintained during the dynamics concerning the detuning and coupling strength parameters. The results indicate that with a proper choice of quantum model parameters, long-term protection of the FI can be achieved without being affected by decoherence.
For two two-level atoms coupled to a single Bosonic mode that is driven and heavily damped, the steady state can be entangled by resonantly driving the system [S. Schneider and G. J. Milburn, Phys. Rev. A 65, 042107 (2002)]. We present a scheme to significantly increase the steady-state entanglement by using homodyne-mediated feedback, in which the Bosonic mode is that of an electromagnetic cavity, the output of which is measured and the resulting homodyne photocurrent is used to modulate the field driving the qubits. Such feedback can increase the nonlinear response to both the decoherence process of the two-qubit system and the coherent evolution of individual qubits. We present the properties of the entangled states using the SO(3) QQQ function.