Measurement of transverse spin-relaxation rates in a rubidium vapor by use of spin-noise spectroscopy

Abstract

Spin noise sets fundamental limits to the attainable precision of measurements using spin-polarized atomic vapors and therefore merits a careful study. On the other hand, it has been recently shown that spin noise contains useful physical information about the atomic system, otherwise accessible via magnetic-resonancetype experiments. We here show in yet another manifestation of the fluctuation-dissipation theorem, that spin noise reveals information on the spin-coherence dissipation properties of the atomic system, described by 1 / T 2 , the transverse spin-relaxation rate. We present the high-resolution measurements of spin noise at a low magnetic field, leading to an accurate comparison of the extracted relaxation rates with the ones inferred from traditional magnetic-resonance-type measurements in optical pumping experiments.

Squeezed-light spin noise spectroscopy

“…At higher values, light scattering and atomic collisions broaden the spin noise resonances, and thus introduce systematic errors in measurements, e.g. of relaxation rates, that are derived from the SNS linewidth [5][6][7]. This trade-off between statistical sensitivity and line broadening is a fundamental limitation of the technique, with its origin in quantum noise properties of the atomic and optical parts of the system.…”

“…of relaxation rates, that are derived from the SNS linewidth [5][6][7]. This trade-off between statistical sensitivity and line broadening is a fundamental limitation of the technique, with its origin in quantum noise properties of the atomic and optical parts of the system.Here we work in a high-density regime, with atomic number densities up to n ∼ 10 13 cm −3 , covering the range of recent experiments with optimized atomic instruments [5,6,18,27]. Earlier studies in this regime have observed non-trivial interactions between optical quantum noise and nonlinear magneto-optical rotation (NMOR) of a on-resonance probe [30] including increased measurement noise as a result of input squeezing for densities above n ≈ 2 × 10 11 cm −3 [31].…”

“…SNS has allowed measurement of g-factors, nuclear spin, isotope abundance ratios and relaxation rates of alkali atoms [5,6], g-factors, relaxation times and doping concentration of electrons in semiconductors [7][8][9][10][11] and localized holes in quantum dot ensembles [12,13] including single hole spin detection [14]. Recently, SNS has been used to study complex optical transitions and broadening processes [15,16], coherent phenomena beyond linear response [17] and cross-correlations of heterogeneous spin systems [18,19].Spin noise has been measured with nuclear magnetic resonance [20,21] and magnetic force microscopy [22][23][24], but the most sensitive and widely used detection technique is Faraday rotation (FR) [2,5,6], in which the spin noise is mapped onto the polarization of an off-resonant probe. In FR-SNS, spin noise near the Larmor frequency competes with quantum noise [25] of the detected photons, i.e., the optical shot noise.…”

Sensitivity, quantum limits, and quantum enhancement of noise spectroscopies

“…, and quantum information processing [12][13][14][15][16]. By the fluctuation-dissipation theorem, the noise spectrum under thermal equilibrium gives the same information as do driven spectroscopies, with the advantage of characterizing the system in its natural, undisturbed state [17]. Understanding the statistical sensitivity of noise spectroscopy is essential for rigorous use of the technique in any of these fields.…”

“…Non-optical SNS based on resonance force microscopy [19,20] and NV-center magnetometry [21][22][23] have recently emerged, but still the most widely used technique is optical Faraday rotation (FR) to detect spin orientation [24]. This FR-SNS is used to study spin physics in atomic gases [1,17] as well as conduction electrons [25] and localized states in semiconductors [26,27]. Extensions of SNS include measurements of cross-correlations of heterogeneous spin systems [28,29], spin dynamics beyond thermal equilibrium [30] and multidimensional SNS [31,32], see [33] for a review.…”