Thermal-Noise Induced Radio Frequency Superradiance in Resonator

Abstract

This paper deals with a theoretical interpretation of the experiments on detection of radio frequency superradiation in a system of nuclear spins, conducted by the authors previously.1–3 The model Hamiltonian in the pseudospin representation is used for consideration. Dynamic equations are obtained for pseudospin and photon operators with allowance for oscillators of losses and thermal noise. The radiation generating process is shown to go on as follows: thermal noise initiates maser generation that results in a superradiation pulse. The importance of taking account of thermal noise is stressed by numerical estimations.

Nonlinear spin dynamics in nuclear magnets

“…Moreover, the Bloch equations themselves may be inappropriate for explaining some kinds of relaxation processes. This concerns, for example, the interpretation of the recent series of experiments [10][11][12][13][14][15] observing nuclear spin superradiance. In these experiments a nonequilibrium system of polarized nuclear spins is placed inside a coil of a resonance electric circuit.…”

Origin of Pure Spin Superradiance

“…The nuclear spin superradiance has been recently observed in a series of experiments [6][7][8][9][10][11] with different substances: from Al nuclear spins in ruby ( Al 2 O 3 ) and from proton spins in propanediol ( C 3 H 8 O 2 ), butanol ( C 4 H 9 OH ), and ammonia ( NH 3 ). The interpretation of the pure spin superradiance in these experiments was based on the following picture.…”

“…To consider the case of pure spin superradiance, the initial conditions for the system of equations (9) and (13) are to be taken as…”

“…Let us accept the values of parameters characteristic of experiments [7][8][9][10][11] with proton spins: ω 0 ∼ ω ∼ 10 8 sec −1 , γ 1 ∼ 10 −5 sec −1 , γ 2 ∼ 10 5 sec −1 , γ 3 ∼ 10 6 sec −1 , T ∼ 0.1K , and N ∼ 10 23 . Then f 0 ∼ 10 −10 and the thermal attenuation (18) is γ f ∼ 10 −16 sec −1 .…”

“…From here it is evident that t 0 → ∞ as ε * → 0 . For the parameters typical of experiments [7][8][9][10][11] we have t 0 ∼ 10 −6 − 10 −5 sec . So, this is the local random fields that are responsible for starting the process of self-organization leading to the pure spin superradiance.…”