Abstract
We demonstrate the excitation and low-noise differential detection of a coherent population trapping (CPT) resonance with two modulated optical fields with orthogonal circular polarizations. When a microwave phase delay of lambda/4 is introduced in the optical path of one of the fields, the difference in the power transmitted through the cell in each polarization shows a narrow, dispersive resonance. The differential detection allows a high degree of suppression of laser-induced noise and will enable nearly shot-noise-limited operation of atomic frequency references and magnetometers based on CPT.
Highlights
Coherent population trapping (CPT) [1], like the associated phenomenon of electromagnetically induced transparency (EIT) [2], is based on the creation of coherences in an atomic medium with optical fields and the resulting modification of the medium’s optical susceptibility
The simplest demonstration of coherent population trapping between hyperfinesplit levels of atoms was described in Refs. [3,4]
We report the observation of a CPT resonance using differential detection of two co-propagating excitation beams with orthogonal polarizations
Summary
Coherent population trapping (CPT) [1], like the associated phenomenon of electromagnetically induced transparency (EIT) [2], is based on the creation of coherences in an atomic medium with optical fields and the resulting modification of the medium’s optical susceptibility. The noise processes that affect the measurement of CPT resonances have been studied in detail [20,21] These include photon and atom shot noise, frequency and excess amplitude noise on the excitation laser [22,23], and electronic noise. These noise processes put practical and fundamental limits on the performance of devices based on CPT resonances, such as atomic clocks [21,24] and magnetometers [25,26], in the case of compact systems using diode lasers. Here we gain the additional benefit that most noise processes are strongly suppressed by the differential nature of the resonance detection; we observe a reduction of the noise power spectral density at low frequencies by two orders of magnitude under optimal conditions to within a factor of two of the fundamental shot noise limit
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