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Register a new userSignal tracking beyond the time resolution of an atomic sensor by Kalman filtering
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Added by
Ricardo Jimenez-Martinez
Publication date
2017
fields
Physics
and research's language is
English
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We study causal waveform estimation (tracking) of time-varying signals in a paradigmatic atomic sensor, an alkali vapor monitored by Faraday rotation probing. We use Kalman filtering, which optimally tracks known linear Gaussian stochastic processes, to estimate stochastic input signals that we generate by optical pumping. Comparing the known input to the estimates, we confirm the accuracy of the atomic statistical model and the reliability of the Kalman filter, allowing recovery of waveform details far briefer than the sensors intrinsic time resolution. With proper filter choice, we obtain similar benefits when tracking partially-known and non-Gaussian signal processes, as are found in most practical sensing applications. The method evades the trade-off between sensitivity and time resolution in coherent sensing.
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The shot-noise detection limit in current high-precision atomic magnetometry is a manifestation of quantum fluctuations that scale as the square root of N in an ensemble of N particles. However, there is a general expectation that the reduced projection noise provided by conditional spin-squeezing could be exploited to surpass the conventional shot-noise limit. We show that continuous measurement coupled with quantum Kalman filtering provides an optimal procedure for magnetic detection limits that scale with 1/N, the Heisenberg squeezing limit. Our analysis demonstrates the importance of optimal estimation procedures for high bandwidth precision magnetometry.
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We have studied relative-intensity fluctuations for a variable set of orthogonal elliptic polarization components of a linearly polarized laser beam traversing a resonant $^{87}$Rb vapor cell. Significant polarization squeezing at the threshold level (-3dB) required for the implementation of several continuous variables quantum protocols was observed. The extreme simplicity of the setup, based on standard polarization components, makes it particularly convenient for quantum information applications.
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