Quantum instanton approach to metastable collective spins
Krzysztof Ptaszynski, Maciej Chudak, Massimiliano Esposito
TLDR
A quantum instanton approach accurately describes metastable collective spin systems, outperforming semiclassical methods by accounting for non-Gaussian fluctuations.
Key contributions
- Develops a real-time quantum instanton approach for collective spin systems using quasiprobability dynamics.
- Accurately captures stationary states and asymptotic relaxation rates in the large-spin limit.
- Demonstrates the limitations of the semiclassical Wigner approach due to its neglect of non-Gaussian fluctuations.
- Provides a more robust framework for analyzing metastable states and first-order phase transitions.
Why it matters
This paper offers a superior theoretical tool for understanding the complex dynamics of collective spin systems, which are crucial in atomic and solid-state physics. By accurately modeling metastable states and relaxation, it improves upon existing methods, enabling deeper insights into phase transitions and fundamental quantum phenomena.
Original Abstract
Collective spin systems -- spin ensembles coupled to a common reservoir and effectively described by a single macrospin -- play an important role in both atomic and solid-state physics. Their intrinsic nonlinearity gives rise to multiple long-lived metastable states that ultimately relax to a unique most probable state. This dominant state can change with a control parameter, leading to first-order phase transitions. We develop a real-time instanton approach based on quantum quasiprobability dynamics that captures the stationary state in the large-spin limit and the asymptotic scaling of relaxation rates. We further show that these features are not accurately described by the previously applied semiclassical Wigner approach due to its neglect of non-Gaussian fluctuations.
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