Parametric Amplification and Noise Squeezing in Room Temperature Atomic Vapors.

We report on the use of parametric excitation to coherently manipulate the collective spin state of an atomic vapor at room temperature. Signatures of the parametric excitation are detected in the ground-state spin evolution. These include the excitation spectrum of the atomic coherences, which contains resonances at frequencies characteristic of the parametric process. The amplitudes of the signal quadratures show amplification and attenuation, and their noise distribution is characterized by a strong asymmetry, similar to those observed in mechanical oscillators. The parametric excitation is produced by periodic modulation of the pumping beam, exploiting a Bell-Bloom-like technique widely used in atomic magnetometry. Notably, we find that the noise squeezing obtained by this technique enhances the signal-to-noise ratio of the measurements up to a factor of 10, and improves the performance of a Bell-Bloom magnetometer by a factor of 3.

Alkali-Metal Spin Maser.

Quantum measurement is a combination of a read-out and a perturbation of the quantum system. We explore the nonlinear spin dynamics generated by a linearly polarized probe beam in a continuous measurement of the collective spin state in a thermal alkali-metal atomic sample. We demonstrate that the probe-beam-driven perturbation leads, in the presence of indirect pumping, to complete polarization of the sample and macroscopic coherent spin oscillations. As a consequence of the former we report observation of spectral profiles free from collisional broadening. Nonlinear dynamics is studied through exploring its effect on radio frequency as well as spin noise spectra.

Identification of object composition with magnetic inductive tomography.

The inductive response of an object to an oscillating magnetic field reveals information about its electrical conductivity and magnetic permeability. Here, we introduce a technique that uses measurements of the angular, frequency, and spatial dependence of the inductive signal to determine the object composition. Identification is performed by referencing an object's inductive response to that of materials with mutually exclusive properties such as copper (high electrical conductivity and negligible magnetic permeability) and ferrite (negligible electrical conductivity and high magnetic permeability). The technique uses a sensor with anisotropic sensitivity to discriminate between the different characters of the eddy current and magnetization driven object responses. Experimental validation of the method is performed using magnetic induction tomography measurement with a radio-frequency atomic magnetometer. Possible applications of the technique in security screening devices are discussed.

Object surveillance with radio-frequency atomic magnetometers.

The capabilities of a radio-frequency atomic magnetometer for object detection based on magnetic induction tomography are explored. The determination of object orientation is demonstrated by utilizing the measurement geometry. The self-compensation configuration of the atomic magnetometer is implemented to address the issue of saturation of the sensor response by the radio-frequency primary field that generates the object signature. Three methods of "covert" detection are investigated as a testbed for exploring the functionalities of this sensor, where (1) the operational frequency of the sensor is continuously changed, (2) the primary field has non-monochromatic frequency distribution, and (3) the sensor operates in the so-called spin maser mode. The results of the measurements are also discussed in terms of possible magnetic field communication.

Imaging of material defects with a radio-frequency atomic magnetometer.

Non-destructive inductive testing of defects in metal plates using the magnetic resonance signal of a radio-frequency atomic magnetometer is demonstrated. The shape and amplitude of the spatial profile of the signal features, which represent structural defects, are explored. By comparing numerical and experimental results on a series of benchmark aluminium plates, we show correspondence between the properties of the secondary field and those of the magnetometer signal. In particular, we show that two components of the secondary field are mapped onto the amplitude and phase of the atomic magnetometer signal. Hence, a magnetic field measurement with the atomic magnetometer, although scalar in its nature, provides semi-vectorial information on the secondary field. Moreover, we demonstrate a robust process for determining defect dimensions, which is not limited by the size of the sensor. We prove that the amplitude and phase contrast of the observed profiles enables us to reliably measure defect depth.

Apparent power-dependent frequency shift due to collisions in a cesium fountain.

We describe a situation where a varying collisional frequency shift in cesium fountain primary frequency standards can be misinterpreted as a power-dependent shift. This misinterpretation may affect analyses of fountains test-operated at multiple pi/2 microwave pulse areas. Such tests are typically performed in the search for microwave- and cavity-related systematic frequency biases.

Cancellation of the collisional frequency shift in caesium fountain clocks.

We have observed that the collisional frequency shift in primary caesium fountain clocks varies with the clock state population composition and, in particular, is zero for a given fraction of the |F=4,mF=0) atoms, depending on the initial cloud parameters. We present a theoretical model explaining our observations. The possibility of the collisional shift cancellation implies an improvement in the performance of caesium fountain standards and a simplification in their operation.