Nuclear-spin noise and spontaneous emission

Tycho Sleator, Erwin L. Hahn, Claude Hilbert, John Clarke

    Research output: Contribution to journalArticlepeer-review


    The spontaneous emission from nuclear spins has been observed at liquid-4He temperatures. The spins, Cl35 nuclei, are placed in the inductor of a tuned LCR circuit coupled to a dc superconducting quantum interference device used as a radio-frequency amplifier. When the spins are saturated and have zero polarization, the emission is observed at the nuclear quadrupole Larmor frequency as a bump in the spectral density of the Nyquist noise current in the tuned circuit. This bump arises from the temperature-independent fluctuations in the transverse component of the nuclear magnetization. When the spins are in thermal equilibrium, on the other hand, a dip in the spectral density of the current noise is observed, arising from an induced absorption of noise power from the circuit at the Larmor frequency. The standard circuit-coupled Blochs equation, modified to take into account radiation damping and transverse spin fluctuations, is consistent with the predictions of the Nyquist theorem and the Einstein equation for spontaneous emission. A spin-pendulum model for spin noise is described. The signal-to-noise ratio obtainable in a spin-noise measurement is discussed.

    Original languageEnglish (US)
    Pages (from-to)1969-1980
    Number of pages12
    JournalPhysical Review B
    Issue number4
    StatePublished - 1987

    ASJC Scopus subject areas

    • Condensed Matter Physics


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