Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Japanese Journal of Applied Physics

Light shift of Ramsey coherent population trapping resonance using drive current modulation

Masahiro Fukuoka, Shigeyoshi Goka, Masatoshi Kajita, Yuichiro Yano

Published Nov 16, 2023• 5 citations
Publisher

Abstract

Abstract We investigated the light shift of Ramsey coherent population trapping (CPT) resonance by drive current modulation (DCM), which can be realized with low power consumption in a small system, to improve the performance of a CPT atomic clock. The light shift makes the greatest contribution to the degradation of long-term frequency stability of a CPT atomic clock. We also devised digitizer-based DCM to reduce the uncertainty in the frequency of light shift due to wavelength variation at the time of observation. The results show that light shift with DCM is reduced compared with cw excitation and is consistent with theoretical calculations. The estimated frequency uncertainty of the light shift due to wavelength variation using the proposed method is 2.1 × 10−13, which is approximately 165 times better than that of the conventional method without a digitizer, thus demonstrating the effectiveness of the proposed method for future small atomic clocks.

DOI
10.35848/1347-4065/ad0d72

Related papers

Estimation of a Light Shift Using Various Atomic Resonances in Ramsey-Coherent Population Trapping Sequence

Masahiro Fukuoka, Sigeyoshi Goka

This study aimed to detect the light shift by utilizing various atomic resonances observed under pulsed excitation with drive current modulation (DCM). Light shift degrades the performance of atomic clocks, and several studies have attempted to mitigate or correct it. Pulsed excitation with DCM facilitates the observation of various Ramsey-coherent population trapping (CPT) resonances owing to wavelength variation. Further, in the Ramsey-CPT sequence, a semi-continuous wave CPT resonance (SCW-CPT resonance), which is a continuous wave CPT resonance from pulsed lasers, is also observed. As these atomic resonances exhibit different frequency sensitivities to laser intensity, the frequency shifts differ based on the changes in laser intensity. This facilitates the detection of the light shift. By simultaneously measuring the resonance frequencies of two Ramsey-CPT resonances and the SCW-CPT resonance while varying the laser intensity to induce light shifts, we measured the resulting frequency changes. Each resonance exhibited a different frequency shift in response to the light shift. Therefore, this study conformed the feasibility of detecting and estimating the light shift in an operational atomic clock.

IEEE Ultrasonics, Ferroelectrics, and Frequency Control Joint Symposium (UFFC-JS)•Sep 22, 2024•0 citations

Reducing frequency drift caused by light shift in coherent population trapping-based low-power atomic clocks

Shinya Yanagimachi, Kazuhiro Harasaka, Ryoichiro Suzuki +2 more

We propose a model to reduce the influence that the light-shift induced frequency drift has on the long-term stability of coherent population trapping (CPT)-based low-power atomic clocks. We experimentally validated the proposed model using the chip-scale atomic clock architecture. The model considers both the drift of the dc-bias current to compensate for the wavelength aging of the vertical-cavity surface-emitting laser (VCSEL) and the variation in the modulation index of the light field generated by the VCSEL. We investigated the dc-bias-current-dependency of the frequency drift in an atomic clock module both theoretically and experimentally, confirming that the frequency drift can change as a function of the VCSEL basic parameters. When the atomic clock module was operated over a period of five months at the dc-bias current affording a zero-crossing of the clock frequency drift, the Allan standard deviation and clock frequency drift for long-term stability were 8.0×10−12 for averaging times of 4×106 s and 2.4×10−13/day, respectively. Our approach is promising to improve the long-term stability of CPT-based low-power atomic clocks.

Applied Physics Letters•Mar 9, 2020•32 citations

Simultaneous observation of semi-continuous and Ramsey-coherent population trapping resonances using the Ramsey pulse sequence with drive current modulation

Masahiro Fukuoka, Shigeyoshi Goka

Abstract In this study, we proposed a method to observe the semi-cw excited coherent population trapping (SCW-CPT) and the Ramsey-CPT resonance during a Ramsey pulse sequence. By simultaneously observing the Ramsey-CPT and SCW-CPT resonances, which have distinct light shift coefficients, it is easy to detect light shift from the resonance frequency ratio of these two atomic resonances. Experimental results demonstrated the capability of the proposed method to simultaneously observe both the Ramsey-CPT and SCW-CPT resonances. The frequency difference attributable to the light shift was 308.9 Hz, indicating the successful detection of the light shift. Long-term measurements revealed that the frequency drift rates of the two atomic resonances differ by a factor of 3.5, and the variation in the frequency ratio enabled the detection of fluctuations in these two resonance frequencies.

Japanese Journal of Applied Physics•Dec 15, 2023•4 citations

Continuous light-shift correction in modulated coherent population trapping clocks

Vishal Shah, Vladislav P. Gerginov, Peter D. D. Schwindt +3 more

The authors demonstrate a simple technique to significantly improve the long-term frequency stability of atomic clocks based on coherent population trapping (CPT). In this technique, the CPT fields are created by a modulated diode laser and a slow servo is used to actively tune the laser modulation index to a value where the light shift vanishes. The observed clock frequency at this modulation index is given by the rubidium hyperfine frequency when no light fields are present, and this makes the clock frequency largely insensitive to variations in laser properties. In addition to reducing stringent requirements on the long-term stabilities of laser temperature, laser frequency, and rf modulation power, this technique may also significantly reduce frequency drifts related to laser aging. In the experiment, they demonstrate improvement by over one order of magnitude in the stability of a clock that is limited by light-shift-induced frequency drifts.

Applied Physics Letters•Oct 9, 2006•72 citations

Operation of a Ramsey-CPT microcell atomic clock with driving current-based power modulation of a VCSEL

C. M. Rivera-Aguilar, Martin Callejo, Andrei Mursa +6 more

We report on the operation of a coherent population trapping (CPT) microcell atomic clock using a pulsed Ramsey-like interrogation. The Ramsey-CPT sequence, defined by two-step optical pulses separated by a free-evolution dark time, is produced by switching on and off the output power of a low-power vertical-cavity surface-emitting laser, through direct modulation of its driving current. High-contrast and narrow Ramsey-CPT fringes are detected without the use of any external optical modulator stage. We demonstrate closed-loop operation of the clock based on high-speed digital signal processing implemented in a field programmable gate array board. The clock's short-term fractional frequency stability is 1.3 × 10−10τ−1/2 until 2000 s. A power light-shift coefficient of 8 × 10−11/μW, in relative value, is obtained for a dark time of 150 μs. This value is about ten times lower than in the continuous regime. These results show the feasibility of fully integrated atomic clocks based on Ramsey spectroscopy, which could provide enhanced long-term stability.

Applied Physics Letters•Mar 11, 2024•9 citations

Frequency Stability of Atomic Clocks Based on Coherent Population Trapping Resonance in 85 Rb

Lu Liu, Guo Tao, Ke Deng +3 more

An atomic clock system based on coherent population trapping (CPT) resonance in 85 Rb is reported, while most past works about the CPT clock are in 87 Rb. A new modulation method (full-hyperfine-frequency-splitting modulation) is presented to reduce the effect of light shift to improve the frequency stability of the CPT clock in 85 Rb. The experimental results show that the short-term frequency stability of the CPT clock in 85 Rb is in the order of 10 −10 /s and the long-term frequency stability can achieve 1.5 × 10 −11 /80000 s, which performs as well as 87 Rb in CPT resonance. This very good frequency stability performance associated with the low-cost and low-power properties of 85 Rb indicates that an atomic clock based on CPT in 85 Rb should be a promising candidate for making the chip scale atomic clock.

Chinese Physics Letters•Jun 28, 2007•9 citations
Abstract We investigated the light shift of Ramsey coherent population trapping (CPT) resonance by drive current modulation (DCM), which can be realized with low power consumption in a small system, to improve the performance of a CPT atomic clock. The light shift makes the greatest contribution to the degradation of long-term frequency stability of a CPT atomic clock. We also devised digitizer-based DCM to reduce the uncertainty in the frequency of light shift due to wavelength variation at the time of observation. The results show that light shift with DCM is reduced compared with cw excitation and is consistent with theoretical calculations. The estimated frequency uncertainty of the light shift due to wavelength variation using the proposed method is 2.1 × 10−13, which is approximately 165 times better than that of the conventional method without a digitizer, thus demonstrating the effectiveness of the proposed method for future small atomic clocks.
This study aimed to detect the light shift by utilizing various atomic resonances observed under pulsed excitation with drive current modulation (DCM). Light shift degrades the performance of atomic clocks, and several studies have attempted to mitigate or correct it. Pulsed excitation with DCM facilitates the observation of various Ramsey-coherent population trapping (CPT) resonances owing to wavelength variation. Further, in the Ramsey-CPT sequence, a semi-continuous wave CPT resonance (SCW-CPT resonance), which is a continuous wave CPT resonance from pulsed lasers, is also observed. As these atomic resonances exhibit different frequency sensitivities to laser intensity, the frequency shifts differ based on the changes in laser intensity. This facilitates the detection of the light shift. By simultaneously measuring the resonance frequencies of two Ramsey-CPT resonances and the SCW-CPT resonance while varying the laser intensity to induce light shifts, we measured the resulting frequency changes. Each resonance exhibited a different frequency shift in response to the light shift. Therefore, this study conformed the feasibility of detecting and estimating the light shift in an operational atomic clock.
We propose a model to reduce the influence that the light-shift induced frequency drift has on the long-term stability of coherent population trapping (CPT)-based low-power atomic clocks. We experimentally validated the proposed model using the chip-scale atomic clock architecture. The model considers both the drift of the dc-bias current to compensate for the wavelength aging of the vertical-cavity surface-emitting laser (VCSEL) and the variation in the modulation index of the light field generated by the VCSEL. We investigated the dc-bias-current-dependency of the frequency drift in an atomic clock module both theoretically and experimentally, confirming that the frequency drift can change as a function of the VCSEL basic parameters. When the atomic clock module was operated over a period of five months at the dc-bias current affording a zero-crossing of the clock frequency drift, the Allan standard deviation and clock frequency drift for long-term stability were 8.0×10−12 for averaging times of 4×106 s and 2.4×10−13/day, respectively. Our approach is promising to improve the long-term stability of CPT-based low-power atomic clocks.
Abstract In this study, we proposed a method to observe the semi-cw excited coherent population trapping (SCW-CPT) and the Ramsey-CPT resonance during a Ramsey pulse sequence. By simultaneously observing the Ramsey-CPT and SCW-CPT resonances, which have distinct light shift coefficients, it is easy to detect light shift from the resonance frequency ratio of these two atomic resonances. Experimental results demonstrated the capability of the proposed method to simultaneously observe both the Ramsey-CPT and SCW-CPT resonances. The frequency difference attributable to the light shift was 308.9 Hz, indicating the successful detection of the light shift. Long-term measurements revealed that the frequency drift rates of the two atomic resonances differ by a factor of 3.5, and the variation in the frequency ratio enabled the detection of fluctuations in these two resonance frequencies.
The authors demonstrate a simple technique to significantly improve the long-term frequency stability of atomic clocks based on coherent population trapping (CPT). In this technique, the CPT fields are created by a modulated diode laser and a slow servo is used to actively tune the laser modulation index to a value where the light shift vanishes. The observed clock frequency at this modulation index is given by the rubidium hyperfine frequency when no light fields are present, and this makes the clock frequency largely insensitive to variations in laser properties. In addition to reducing stringent requirements on the long-term stabilities of laser temperature, laser frequency, and rf modulation power, this technique may also significantly reduce frequency drifts related to laser aging. In the experiment, they demonstrate improvement by over one order of magnitude in the stability of a clock that is limited by light-shift-induced frequency drifts.
We report on the operation of a coherent population trapping (CPT) microcell atomic clock using a pulsed Ramsey-like interrogation. The Ramsey-CPT sequence, defined by two-step optical pulses separated by a free-evolution dark time, is produced by switching on and off the output power of a low-power vertical-cavity surface-emitting laser, through direct modulation of its driving current. High-contrast and narrow Ramsey-CPT fringes are detected without the use of any external optical modulator stage. We demonstrate closed-loop operation of the clock based on high-speed digital signal processing implemented in a field programmable gate array board. The clock's short-term fractional frequency stability is 1.3 × 10−10τ−1/2 until 2000 s. A power light-shift coefficient of 8 × 10−11/μW, in relative value, is obtained for a dark time of 150 μs. This value is about ten times lower than in the continuous regime. These results show the feasibility of fully integrated atomic clocks based on Ramsey spectroscopy, which could provide enhanced long-term stability.
An atomic clock system based on coherent population trapping (CPT) resonance in 85 Rb is reported, while most past works about the CPT clock are in 87 Rb. A new modulation method (full-hyperfine-frequency-splitting modulation) is presented to reduce the effect of light shift to improve the frequency stability of the CPT clock in 85 Rb. The experimental results show that the short-term frequency stability of the CPT clock in 85 Rb is in the order of 10 −10 /s and the long-term frequency stability can achieve 1.5 × 10 −11 /80000 s, which performs as well as 87 Rb in CPT resonance. This very good frequency stability performance associated with the low-cost and low-power properties of 85 Rb indicates that an atomic clock based on CPT in 85 Rb should be a promising candidate for making the chip scale atomic clock.