Coherent Population Trapping Effect Research Articles

Study of coherent population trapping and AC Stark effect in ensembles of NV-centers in diamond at room temperature in microwave range

We study coherent population trapping and AC Stark effect using microwave transitions between the sublevels of the ground state of the NV-center. Sublevels with different projections of the nuclear spin of the nitrogen atom are used to implement the -scheme. Dependence of the characteristics of the coherent population trapping dip on the control field frequency and intensity is studied. Various schemes for observing the AC Stark effect are considered. Keywords: NV-center, coherent population trapping, AC Stark.

Исследование когерентного пленения населенности и динамического эффекта Штарка в ансамблях NV-центров в алмазе при комнатной температуре в микроволновом диапазоне

We study coherent population trapping and AC Stark effect using microwave transitions between the sublevels of the ground state of the NV-center. Sublevels with different projections of the nuclear spin of the nitrogen atom are used to implement the Lambda-scheme. Dependence of the characteristics of the coherent population trapping dip on the control field frequency and intensity is studied. Various schemes for observing the AC Stark effect are considered.

Control of the VCSEL spectrum by dual microwave frequency modulation.

We propose and investigate a method for controlling the spectrum of the vertical-cavity surface-emitting laser by simultaneous modulation of the injection current at single and doubled frequencies. We experimentally demonstrate the ability to control the power asymmetry of the first-order sidebands and to suppress the carrier by the proposed method. These possibilities are beneficial to improve frequency stability of atomic clocks based on the effect of coherent population trapping.

Frequency shift compensation for single and dual laser beam pass sensors of a coherent population trapping resonance based coupled dark state magnetometer

The Coupled Dark State Magnetometer is an atomic magnetometer designed for magnetic field measurements in space. Its measurement principle is based on the excitation of coupled dark state resonances prepared via the coherent population trapping effect. The coupled dark state resonances enable the compensation of disturbing frequency shifts which degrade the measurement accuracy. Results with a sensor design based on a single laser beam pass through the sensor unit reveal a reduced ability to compensate these disturbing effects compared to theoretical predictions. Therefore, a new sensor design is presented which enables a dual laser beam pass through the sensor unit. For almost all angles between the external magnetic field and the light propagation direction, the dual pass sensor design enables a better compensation of disturbing frequency shifts than the single pass sensor design - up to a factor of nine.

Spin-squeezing-induced enhancement of the sensitivity of an atomic clock using coherent population trapping

The coherent population trapping (CPT) effect is used for making compact atomic clocks. There are two types of CPT clocks: the one in which the Raman beams are applied continuously and the one in which two CPT pulses separated by a dark period are applied (Ramsey scheme). It is obvious that the technique of spin squeezing can only be applied to the Ramsey CPT clock to enhance the sensitivity. However, it is not apparent how to adapt to the CPT clock the protocols for the microwave clock using one-axis-twist squeezing (OATS), since the Ramsey CPT clock is not trivially equivalent to the Ramsey microwave clock. In this paper, we show explicitly how to adapt two protocols using OATS, namely, the Schr\"odinger cat state protocol (SCSP) and the generalization thereof, and the echo squeezing protocol (ESP), to the CPT clock. The ESP magnifies the phase shift by a factor of $\sqrt{N/e}$, while the SCSP magnifies the phase shift by a factor of $N/2$, making it able to achieve a higher sensitivity in the presence of excess noise.

Vector magnetometer based on the effect of coherent population trapping.

The method is presented for converting a coherent population trapping (CPT) atomic clock into a CPT vector (compass-) magnetometer without mechanically moving parts through a relatively simple add-on. The system of 3D Helmholtz coils was used for compensation of the external magnetic field, allowing measurement of both strength and direction of a magnetic field at the sensitivity level of sub-nT/Hz1/2 within a 10-Hz bandwidth. Angular resolution of the developed vector magnetometer amounts to about 10-2 degrees.

Comparison of field shifts in an atomic clock based on the effect of coherent population trapping in 87Rb atoms under modulation of laser pump current at frequencies of 3.4 and 6.8 GHz

Experimental parameters of the resonance of coherent population trapping (CTP) on D1 line in 87Rb and light shifts are compared under modulation of the laser pump current at frequencies of 3.4 and 6.8 GHz. Reproducibility of the parameters of a laser with a vertical cavity needed for long-term stability of an atomic clock is considered. The instabilities of atomic CPT-clock obtained for 1 s are 1.2 × 10−11 and 3 × 10−12 for frequencies of 3.4 GHz and 6.8 GHz, respectively.

Line shape and light shift of coherent population trapping resonance under Ramsey interrogation in ‘hot’ atoms in an optically dense medium

A theory is developed for the effect of coherent population trapping (CPT) in ‘hot’ atoms under pulsed pumping in an optically dense medium with a buffer gas. The case is considered when the excited level is not degenerate. Based on an analysis of the shape of Ramsey resonances, we show that with increasing optical density of the medium, the dependence of the light shifts of the CPT resonance becomes more and more nontrivial. The dependence of the light shifts of the CPT resonance on the magnitude of the hyperfine splitting of the excited level, concentration of active atoms, temperature, and duration of the dark pause is constructed.

Method of characterizing the multicomponent spectrum of a VCSEL in devices based on the CPT effect

We propose and experimentally demonstrate a method of spectral measurement of multicomponent radiation emitted by a modulated vertical cavity surface-emitting laser (VCSEL) relying on peculiarities of absorption in alkali metal vapor. The method consists in determination of the radiation spectrum (which is formed due to RF modulation of the injection current of a diode laser) from the dependence of transmittance of rubidium vapor upon the radiation wavelength. We show that the proposed method allows fairly precise measurement of the spectrum of multicomponent radiation used in devices based on the coherent population trapping (CPT) effect when the frequency difference between the radiation components matches that between absorption lines of an alkali metal.

Laser frequency stabilization via bichromatic Doppler-free spectroscopy of an 87Rb D1 line.

We demonstrate a bichromatic Doppler-free spectroscopy of an 87RbD1 line by using a dual-frequency, counterpropagating laser field with orthogonal linear polarizations. A reversed Doppler-free resonance dip is observed in the dual-frequency scheme, and a significant improvement of frequency discrimination curve is acquired due to the coherent population trapping (CPT) effect. The influence of the static magnetic field and laser intensity on the spectroscopy is studied in both single- and dual-frequency schemes. After locking the laser frequency to the 87RbD1 line in the dual-frequency stabilization scheme, the beat note fractional frequency stability is at the level of 7×10-12 at 1 s integration time. This technique can be used in various applications, such as CPT atomic clocks, laser spectroscopy, quantum optics, and laser-cooling experiments.

Generalised Ramsey methods for suppressing light shifts in atomic clocks based on the coherent population trapping effect

We study the possibility of suppressing light shifts in Ramsey spectroscopy of coherent population trapping (CPT) using generalised autobalanced Ramsey spectroscopy (GABRS) and combined error signal in Ramsey spectroscopy (CESRS). We consider CPT resonances excited by a coherent bichromatic field in an open Λ-system with a ‘trap’ state. Using a rigorous mathematical proof and numerical calculations, these methods are shown to lead to complete suppression of the light shift and its fluctuations. Implementation of GABRS and CESRS in CPT clocks can markedly improve accuracy and long-term stability of these devices. These methods can also be applied in atomic CPT magnetometers and interferometers.

Control Algorithms in Quantum Frequency Standards Based on the Effect of Coherent Population Trapping

Control Algorithms in Quantum Frequency Standards Based on the Effect of Coherent Population Trapping

Control algorithms in quantum frequency standards based on the effect of coherent population trapping

The problem of developing control algorithms in quantum frequency standards based on the effect of coherent population trapping is considered. The development of such algorithms will make it possible to create frequency standards with metrological characteristics that are not inferior to the characteristics of rubidium frequency standards, with reduced power consumption and overall dimensions. A method for studying the dependence of the actual value and frequency instability of quantum frequency standards based on the effect of coherent population trapping on the operating modes of individual parts of the standards is presented. As a criterion for optimizing the laser injection current, the output power of the microwave generator, and the cell temperature, we chose to minimize the effect on the shift of the actual frequency of the standard. A comparative analysis of methods for changing the radiation intensity of a surface-emitting laser with a vertical resonator has been carried out and control algorithms have been developed that take into account the features of these methods. Based on these algorithms, software and tuning methods have been developed in quantum frequency standards based on the effect of coherent population trapping. For the prototype standard, the results of measuring the frequency instability are shown. It is shown that control algorithms and tuning methods can qualitatively change the metrological characteristics of quantum frequency standards based on the effect of coherent population trapping.

Thermal compensation in quantum frequency standards based on the effect of coherent population trapping

The problem of developing a thermal compensation system in quantum frequency standards based on the effect of coherent population trapping is considered. The development of such a system significantly reduces the temperature coefficient of frequency, the value of which is an order of magnitude higher than in rubidium frequency standards. One of the ways to reduce the temperature coefficient of frequency is temperature compensation. A method of thermal compensation based on the Zeeman effect for the shift of the actual frequency is proposed. A method for determining the minimum value of the magnetic field at which there is no influence of magnetosensitive resonances on the reference resonance is considered. The results of the operation of the quantum frequency standard before and after switching on the thermal compensation system are presented.

Study of factors affecting the light shift of the CPT resonance

Motivated by recent developments in atomic frequency standards employing the effect of coherent population trapping (CPT), we propose a theoretical framework for describing the CPT resonances. Our extended model includes several realistic experimental factors not accounted for in the standard approaches, namely, the FM-based technique for generating the error signal, skewed laser spectrum, etc. We provide a simple yet non-trivial analytical solution revealing the magnitude and structure of the light shift. The performance of the model is checked against numerical simulations, the agreement is good to perfect.

Effect of collisions on the shape of the coherent population trapping resonance detected by the Ramsey method

We report on a theoretical model of the effect of coherent population trapping in alkali atoms in an optically thin gas cell with a buffer gas at a nonzero temperature in a pulsed laser field. The shape of the Ramsey resonance is analysed for two different temperature ranges, i. e. for a ‘cold’ atomic ensemble and for an ensemble of ‘hot’ atoms in a cell with a buffer gas. The influence of the hyperfine structure of the excited level on the shift of the central Ramsey resonance is investigated.

Features of non-classical light during its interaction with atoms and semiconductor nano-systems

The interactions of a three-level atomic system with a single mode of quantized field is investigated analytically. The effect of coherent population trapping is demonstrated for an arbitrary initial quantum field state and the peculiarities of this regime in squeezed vacuum light are found. Mutual influence between atomic and field subsystems and their entanglement arising during the interaction is demonstrated. A significant change of the field state during the interaction is shown. The possibility of photon bunching and anti-bunching and the formation of a quantum field with non-Gaussian properties is found.

Geometric phase for “dark” subspaces in coherent population trapping

The concept of geometric phase acquired by a quantum state during its evolution is generalized to the subspace of states of evolving quantum system. Physical motivation of this generalization comes from the effect of coherent population trapping. Under certain conditions, there exists a two-dimensional “dark” subspace of atomic ground states that does not interact with the external radiation. The structure of this “dark” subspace depends on the local field amplitude. We show that certain mathematical difficulties in finding the geometric phase for “dark” subspaces can be circumvented with the help of the orthogonal “bright” subspace.

In-orbit results of the Coupled Dark State Magnetometer aboard the China Seismo-Electromagnetic Satellite

Abstract. The China Seismo-Electromagnetic Satellite (CSES) was launched in February 2018 into a polar, sun-synchronous, low Earth orbit. It provides the first demonstration of the Coupled Dark State Magnetometer (CDSM) measurement principle in space. The CDSM is an optical scalar magnetometer based on the coherent population trapping (CPT) effect and measures the scalar field with the lowest absolute error aboard CSES. Therefore, it serves as the reference instrument for the measurements done by the fluxgate sensors within the High Precision Magnetometer instrument package. In this paper several correction steps are discussed in order to improve the accuracy of the CDSM data. This includes the extraction of valid 1 Hz data, the application of the sensor heading characteristic, the handling of discontinuities, which occur when switching between the CPT resonance superpositions, and the removal of fluxgate and satellite interferences. The in-orbit performance is compared to the Absolute Scalar Magnetometer aboard the Swarm satellite Bravo via the CHAOS magnetic field model. Additionally, an uncertainty of the magnetic field measurement is derived from unexpected parametric changes of the CDSM in orbit in combination with performance measurements on the ground.

Phase-sensitive excitation of atomic systems and semiconductor quantum wells by non-classical light

The interaction of 3-level atom with two resonant quantum fields is investigated and an analytical solution is obtained. The effect of coherent population trapping and formation of a ‘dark’ state is analyzed. The atomic and field dynamics is found to be very sensitive to the photon statistics and relative phases of the initial quantum field states. The effect of quantum ‘death’ and ‘birth’ of atomic transitions and mean photon number evolution is demonstrated. Strong entanglement between atomic and field subsystems arising during the interaction is found and studied in details.