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Joint Conference of the European Frequency and Time Forum and IEEE International Frequency Control Symposium (EFTF/IFCS)

A Novel Scheme for Noise Suppression of CPT Resonance

Qinglin Li, Tenghui Yang, Peter Yun

Published May 15, 2023• 0 citations
Publisher

Abstract

We proposed and demonstrated a continuous wave (CW) version of constructive, destructive & differential detection (CDD) of coherent population trapping resonance (CPT), in which we simultaneously observed electromagnetically induced transparency (EIT) and absorption (EIA) resonances with counterpropagating pump and probe bichromatic light beams. A differential CPT signal is also obtained with doubled amplitude and suppressed common-mode noise. The enhanced signal-to-noise ratio (SNR) of CPT resonance with one order of magnitude in this novel scheme could beneficial to implement high-performance CPT atomic clocks, as well as atomic sensors, and high-resolution spectroscopy.

DOI
10.1109/eftf/ifcs57587.2023.10272053

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IEEE Transactions on Instrumentation and Measurement•May 29, 2008•20 citations
We proposed and demonstrated a continuous wave (CW) version of constructive, destructive & differential detection (CDD) of coherent population trapping resonance (CPT), in which we simultaneously observed electromagnetically induced transparency (EIT) and absorption (EIA) resonances with counterpropagating pump and probe bichromatic light beams. A differential CPT signal is also obtained with doubled amplitude and suppressed common-mode noise. The enhanced signal-to-noise ratio (SNR) of CPT resonance with one order of magnitude in this novel scheme could beneficial to implement high-performance CPT atomic clocks, as well as atomic sensors, and high-resolution spectroscopy.
Abstract Well-established electromagnetically induced transparency (EIT) and absorption (EIA) have been applied to various applications including quantum computing, light storage, and precision measurement. Here, we propose and implement a differential detection scheme based on coexisting EIT and EIA signals in a double-Λ system with counterpropagating bichromatic laser fields, in which a differential coherent population trapping (diff-CPT) signal is extracted with a desired enhanced amplitude and highly suppressed common-mode noise. Compared to that of either EIT or EIA, the observed signal-to-noise ratio of the proposed method’s diff-CPT signal improved by one order of magnitude, which would benefit the implementation of high-performance CPT clocks. This technique may also be applied to magnetometers and precision spectroscopy.
SummaryWe propose and demonstrate constructive, destructive and differential detection of coherent population trapping resonance (CDD CPT), in which a CPT dark state is constructively and destructively detected by a bi-chromatic light field with proper polarization and timing setting. Electromagnetically induced transparency (EIT) and electromagnetically induced absorption (EIA) resonances are simultaneously observed in a vapor cell. A differential-CPT (diff-CPT) signal, with doubled amplitude and suppression of common-mode noise of light and of the atomic ensemble, is then obtained by subtracting EIT and EIA resonances. This approach might be of great interest for the development of high-performance atomic clocks, sensors, or high-resolution spectroscopy.
Coherent manipulation of atomic states is highly desirable in numerous applications spanning from fundamental physics to metrology. In this study, we propose and demonstrate, theoretically and experimentally, the simultaneous observation in a vapor cell of dark and bright resonances that provide, through a differential-detection stage, an output coherent-population-trapping atomic resonance that benefits from a doubled amplitude and high common-mode noise rejection. This advanced spectroscopic scheme might be of interest for the development of high-performance vapor-cell atomic clocks, sensors, or high-resolution spectroscopy experiments.
We present a digital differential detection scheme using a single photodiode to suppress the diode laser frequency noise and improve the short-term stability in atomic clocks based on coherent population trapping (CPT) resonance. One laser light is divided into two beams via modulation of an acousto-optic modulator. One beam induces CPT resonance with circularly polarized light, and the other beam induces only absorption with linearly polarized light. A differential algorithm counteracts common-mode noise from the two beams. A stability of 6.86×10−12 at 100 s and 2.26×10−12 at 1000 s has been demonstrated. The short-term stability is improved by a factor of 2.4 at 100 s. The scheme promises to eliminate laser-related noise and explore potential applications in chip-scale atomic clocks.
Traditional coherent population trapping (CPT) atomic clocks use single circularly polarized coherent multichromatic light to interact with atoms for preparing CPT dark states. While this configuration is simple, it suffers from the trap states and involves only the ±1st-order sidebands in the CPT resonance, excluding the carrier and other sidebands. This results in a lower CPT signal amplitude and higher laser noise, limiting the frequency stability of CPT atomic clocks. To address this issue, we developed and experimentally validated a scheme utilizing left- and right-circularly polarized light based on multiple coherent superpositions. This scheme significantly enhances the amplitude of the CPT resonance. Furthermore, by incorporating a Michelson interferometer, the polarization direction of the ±1st-order sidebands in the coherent multichromatic light is adjusted from parallel to perpendicular, enabling the filtering of one sideband to be detected while eliminating other unwanted sidebands and effectively suppressing laser noise. The results show that, under identical conditions, the short-term frequency stability of this method is theoretically improved by a factor of seven compared to the traditional circularly polarized light scheme, providing an effective pathway for the development of high-performance CPT atomic clocks.
We demonstrate a new technique for the suppression of noise associated with the laser source in atomic clocks based on coherent population trapping (CPT). The technique uses differential detection of the transmission of linearly and circularly polarized beams that propagate through different parts of a single rubidium vapor cell filled with a buffer gas mixture. The common-mode noise associated with the laser frequency and amplitude noise is suppressed by the differential detection of the two laser beams. The CPT signal, which is present only in the circularly polarized laser beam, is unaffected. The implementation of the technique requires only a change of the polarization of part of the laser beam and an additional photodiode. The technique is simple and applicable to CPT frequency references where a major source of noise is the laser, such as compact and chip-scale devices.