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arXiv:2305.12435 · Results in Physics

Quantum estimation of tripartite coupling in spin-magnon-mechanical hybrid systems

Dong Xie, Chunling Xu

Published May 8, 2024• 1 citation
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Abstract

Tripartite interactions play a fundamental role in the quantum information processing and quantum technology. However, it is generally difficult to realize strong tripartite coupling. We investigate the estimation of a tripartite coupling strength in a hybrid setup composed of a single nitrogen-vacancy (NV) center and a micromagnet. A time-independent parametric drive can be utilized to increase the estimation precision of the tripartite coupling strength. By calculating the quantum Fisher information (QFI), we can obtain the optimal estimation precision by measuring the eigenstate of the tripartite system. At the critical position, the QFI is divergent due to that the preparation time of the eigenstate is divergent. When the system is subjected to a dissipation, the QFI near the critical point of the driven-dissipation phase transition is analytically obtained. The direct intensity measurement is the optimal measurement near the dissipation phase transition point. In addition, we quantify the robustness of an imperfect measurement operator by the measurement noise susceptibility based on the error propagation formula. We find that the direct intensity measurement is robust enough against small measurement disturbance from a coherent drive. But it can be disturbed by the nonlinear anti-harmonic measurement noise, especially near the critical point.

DOI
10.1016/j.rinp.2024.107735

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Tripartite interactions play a fundamental role in the quantum information processing and quantum technology. However, it is generally difficult to realize strong tripartite coupling. We investigate the estimation of a tripartite coupling strength in a hybrid setup composed of a single nitrogen-vacancy (NV) center and a micromagnet. A time-independent parametric drive can be utilized to increase the estimation precision of the tripartite coupling strength. By calculating the quantum Fisher information (QFI), we can obtain the optimal estimation precision by measuring the eigenstate of the tripartite system. At the critical position, the QFI is divergent due to that the preparation time of the eigenstate is divergent. When the system is subjected to a dissipation, the QFI near the critical point of the driven-dissipation phase transition is analytically obtained. The direct intensity measurement is the optimal measurement near the dissipation phase transition point. In addition, we quantify the robustness of an imperfect measurement operator by the measurement noise susceptibility based on the error propagation formula. We find that the direct intensity measurement is robust enough against small measurement disturbance from a coherent drive. But it can be disturbed by the nonlinear anti-harmonic measurement noise, especially near the critical point.
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.
Strong and controllable tripartite interactions play a pivotal role in quantum information and nonlinear quantum optics, yet challenging to realize. In this work, we propose a hybrid system consisting of a nitrogen-vacancy (NV) center coupled to Kerr magnons (magnons with Kerr nonlinearity) in two yttrium-iron-garnet spheres. By adiabatically eliminating the ground state of the NV qutrit in the dispersive regime, an effective tripartite interaction among magnons and an NV qubit encoded in its excited states is obtained. In the strong driving limit, Kerr magnons can be linearized and give rise to degenerate parametric amplification for squeezing magnons. As a result, both the tripartite interaction and cooperativity are exponentially enhanced twice, which is about exp⁡(ξ)\exp(ξ)exp(ξ) times than schemes only involving single-squeezing. Hence, our proposal is more experimentally feasible because modest squeezing parameter is sufficient. With this amplified tripartite coupling strength, the system dynamics are greatly accelerated, leading to fast generation of tripartite entanglement. In addition, noise-resilient perfect magnon blockade can be achieved, well predicted by both the analytical approach and numerical simulation with quantum master equation. Our results suggest that the NV center represents a promising interface for engineering many-body interactions in quantum magnonics, offering a versatile platform for exploring fundamental quantum phenomena such as entanglement and correlations.
Cavity-magnon systems are emerging as a fruitful architecture for the integration of quantum technologies and spintronic technologies, where magnons are coupled to microwave photons via the magnetic-dipole interaction. Controllable, the photon-magnon (P-M) couplings provide a powerful means of accessing and manipulating quantum states in such hybrid systems. Thus, determining the relevant P-M couplings is a fundamental task. Here we address the quantum estimation problem for the P-M coupling strength in a double-cavity-magnon system with drive and dissipation. The effects of various physical factors on the estimation precision are investigated and the underlying physical mechanisms are discussed in detail. Considering that in practical experiments it is almost infeasible to perform measurements on the global quantum state of this composite system, we identify the optimal subsystem for performing measurements and estimations. Further, we evaluate the performance of different Gaussian measurements, indicating that optimal Gaussian measurement almost saturates the ultimate theoretical bound on the estimation precision given by the quantum Fisher information.
Coherent nonlinear tripartite interactions are critical for quantum simulation and information processing in hybrid quantum systems, yet remain experimentally challenging and still evade comprehensive exploration. Here, we predict a nonlinear tripartite coupling mechanism in a hybrid setup comprising a single trapped electron and a nearby micromagnet. The tripartite coupling here leverages the electron’s motional and spin degrees of freedom interacting with the magnon modes of the micromagnet. Thanks to the large spatial extent of the electron zero-point motion, a tunable and strong spin-magnon-motion coupling can be obtained, with two phonons simultaneously interacting with a single spin and magnon excitation. This enables magnons to mediate coupling among distinct degrees of freedom of two electrons, allowing rapid preparation of few-body entangled states. This protocol is compatible with well-developed techniques in electron traps and quantum magnonics, and may open avenues for quantum simulations and hybrid quantum information processing by introducing a versatile platform for exploring multipartite interactions and nonclassical state generation. Coherent many-body interactions bring the quantum nature that is key to exploring quantum applications with multipartite entanglement. This work studies a nonlinear tripartite coupling mechanism in a hybrid quantum system, which provides an experimentally promising and reliable platform for manipulating few-body entangled quantum states.
Improving multiparameter quantum estimation in magnonic systems via quantum noise suppression is a well-established and critical research objective. In this work, we propose an experimentally realistic scheme to improve the precision of simultaneously estimating different parameters in a cavity-magnon system by utilizing a degenerate optical parametric amplifier (OPA). The OPA enhances the estimation precision by decreasing the most informative quantum Cramér-Rao bound, calculated employing the symmetric logarithmic derivative (SLD) and the right logarithmic derivative (RLD). We show that when nonlinearity is introduced into the system, quantum noise is significantly suppressed. Our results show how different physical parameters influence multiparameter estimation precision and provide a detailed discussion of the associated physical mechanisms in the steady state. Our results focus on exploring practical Gaussian measurement schemes that can be realized experimentally. Besides, we further analyze the system's dynamics, comparing both the SLD quantum Fisher information (QFI) and the classical Fisher information (CFI) for both homodyne and heterodyne detection. This approach provides a robust foundation for multiparameter quantum estimation, offering significant potential for application in hybrid magnomechanical and optomechanical systems.
We investigate quantum metrology in a degenerate down-conversion system composed of a pump mode and two degenerate signal modes. In the conventional parametric approximation, the pump mode is assumed to be constant, not a quantum operator. We obtain the measurement precision of the coupling strength between the pump mode and two degenerate signal modes beyond the parametric approximation. Without a dissipation, the super-Heisenberg limit can be obtained when the initial state is the direct product of classical state and quantum state. This does not require the use of entanglement resources which are not easy to prepare. When the pump mode suffers from a single-photon dissipation, the measurement uncertainty of the coupling strength is close to 0 as the coupling strength approaches 0 with a coherent driving. The direct photon detection is proved to be the optimal measurement. This result has not been changed when the signal modes suffer from the two-photon dissipation. When the signal modes also suffer from the single-mode dissipation, the information of the coupling strength can still be obtained in the steady state. In addition, the measurement uncertainty of the coupling strength can also be close to 0 and become independent of noise temperature as the critical point between the normal and superradiance phase approaches. Finally, we show that a driven-dissipation down-conversion system can be used as a precise quantum sensor to measure the driving strength.