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arXiv:cond-mat/9710311

Relaxation Regimes of Spin Maser

Vyacheslav I. Yukalov

Published Oct 29, 1997• 0 citations
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Abstract

Spin relaxation in a microscopic model of spin maser is studied theoretically. Seven qualitatively different regimes are found: free induction, collective induction, free relaxation, collective relaxation, weak superradiance, pure superradiance, and triggered superradiance. The initiation of relaxation can be originated either by an imposed initial coherence or by local spin fluctuations due to nonsecular dipole interactions. The Nyquist noise of resonator does not influence processes in macroscopic samples. The relaxation regimes not initiated by an imposed coherence cannot be described by the standard Bloch equations.

DOI
10.48550/arxiv.cond-mat/9710311

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Abstract In the superradiance phenomenon, a collection of non-interacting atoms exhibits collective dissipation due to interaction with a common radiation field, resulting in a non-monotonic decay profile. This work shows that the dissipative dipolar-coupled systems exhibit an identical collective dissipation aided by the nonsecular part of the dipolar coupling. We consider a simplified dipolar network where the dipolar interaction between the spin-pairs is assumed to be identical. For a suitable choice of the initial condition, the resulting dynamics requires dealing with a smaller subspace that helps extend the analysis to a larger spin network. To include the nonsecular dipolar relaxation, we use a fluctuation-regulated quantum master equation. Moreover, we find that for an ensemble of N spins, the maximum intensity of the radiation exhibits a nearly quadratic scaling (N 2), and the dipolar relaxation time follows an inverse square proportionality ( 1 / N 2 ); these two observations help characterize the emergence of superradiance. Our results agree well with the standard results of pure spin superradiance observed experimentally in various systems.
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