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Optics Express

Characterization of isotropic laser cooling for application in quantum sensing

Xin Wang, Yuan Sun, Liang Liu

Published Nov 26, 2021• 7 citations
Publisher

Abstract

Quantum sensing with cold atoms is attracting more and more attention in the research frontier of quantum technologies. Isotropic laser cooling serves as a promising platform for this area and its many advantages include compactness, robustness, and not requiring fine-tuning of the optical alignment or magnetic field, which are particularly suitable for field and space applications. We have designed and demonstrated a special form of isotropic laser cooling system that is specifically tailored for the purpose of quantum sensing. In particular, the diffused cooling optical field is generated by hollow laser beam injection and the quality of detection process is improved. Moreover, the effective strength of diffused cooling laser is quantitatively deduced. We have carefully characterized the properties of our system, including the laser cooling performances with respect to different parameter settings, the influences of cooling laser polarization and repumping laser power, and radial atom density distribution. We anticipate that our progress will contribute to the future development of isotropic laser cooling for quantum sensing and quantum precision measurements.

DOI
10.1364/oe.445877

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Quantum sensing with cold atoms is attracting more and more attention in the research frontier of quantum technologies. Isotropic laser cooling serves as a promising platform for this area and its many advantages include compactness, robustness, and not requiring fine-tuning of the optical alignment or magnetic field, which are particularly suitable for field and space applications. We have designed and demonstrated a special form of isotropic laser cooling system that is specifically tailored for the purpose of quantum sensing. In particular, the diffused cooling optical field is generated by hollow laser beam injection and the quality of detection process is improved. Moreover, the effective strength of diffused cooling laser is quantitatively deduced. We have carefully characterized the properties of our system, including the laser cooling performances with respect to different parameter settings, the influences of cooling laser polarization and repumping laser power, and radial atom density distribution. We anticipate that our progress will contribute to the future development of isotropic laser cooling for quantum sensing and quantum precision measurements.
Abstract Isotropic laser cooling (ILC) is widely recognized for its distinct advantages and demonstrates significant potential in quantum precision measurements and quantum sensing technologies. The morphology and density distribution of the cold atomic cloud generated by ILC are strongly influenced by the distribution of cooling light and the structural geometry of the cavity, making precise characterization and optimization of cold atom distribution essential for practical applications. In this paper, we present an innovative flat diffuse cavity design with the dimensions approximating a quasi-two-dimensional configuration, which generates a sheet-like isotropic laser field inside the cavity through diffuse reflections. We thoroughly characterized the system’s performance under different optical parameter settings. A two-dimensional (2D) movable detection system was employed to detect the quasi-two-dimensional distribution of cold atoms. These results demonstrate the ability of ILC to produce diverse morphological and density distributions of cold atoms, which we anticipate will be suitable for quantum sensing.
We develop a form of nondestructive optical thermometry to deterministically measure the temperature of the selected segment of a cold-atom ensemble. The essence is to monitor the thermal expansion of the targeted cold atoms after their labeling through manipulation of the internal states, and the nondestructive property relies on nearly lossless detection via the driving of a cycling transition. The temperature information is extracted from the change of densities via a bucket detector without the necessity of a complicated imaging setup. We also focus on the application of this method to isotropic laser cooling, and it has the capability of addressing only the atoms on the optical detection axis within the enclosure, which is readily compatible with typical configurations of atomic clocks or quantum sensing. Our results confirm the sub-Doppler-cooling features of isotropic laser cooling, and we further investigate the relevant cooling properties. Furthermore, we demonstrate the recently developed optical configuration with injection of cooling-laser light in the form of hollow beams, which helps to enhance the cooling performance and accumulate more cold atoms in the central regions.
Abstract We demonstrate an integrating sphere to cool 87Rb atoms and measure the recoil-induced resonance and electromagnetically induced absorption spectrum. We measure the relationship between their linewidth and light shift with variation of the detuning and power of the cooling laser and study the performance of the diffuse laser cooling mechanism by the absorption linewidth radio Δν E/Δν R and light shift |Δ R–Δ E| using nonlinear spectroscopy. Specifically, when Δν E/Δν R reaches a value of 1.57, the temperature and number of cold atoms achieve the optimal cooling effect. This characterization of absorption linewidth and light shift will provide a method to estimate whether diffuse light cooling achieves the best cooling effect, contributing to the future development of isotropic laser cooling for application in quantum sensing.
We demonstrate experimentally the generation of one-dimensional cold gases of 87Rb^{87}\mathrm{Rb}87Rb atoms by diffuse laser cooling. A horizontal slender vacuum glass tube with a length of 105 cm and diameter of 2 cm is used in our experiment. The diffuse laser light inside the tube, which is generated by multireflection of injected lasers, cools the background vapor atoms. With 250 mW of cooling light and 50 mW of repumping light, an evenly distributed 1-m-long profile of cold atom cloud is obtained. We observe a factor 4 improvement in the atomic optical density for a typical cooling duration of 170 ms and a sub-Doppler atomic temperature of 25 $\ensuremath{\mu}\mathrm{K}$. The central number of detected cold atoms remains constant for a free-fall duration of 30 ms. Such samples are ideal for many quantum optical experiments involving electromagnetically induced transparency, electronically highly excited (Rydberg) atoms, and quantum precision measurements.
The invention of laser cooling has fundamentally influenced the research frontier of atomic physics and quantum physics, and recently an intense focus has been on the studies of cold atom physics in microgravity environments. Herein, we report the results of our laser cooling experiment in TianGong-2 space lab, which operated for 34 consecutive months in orbit. Over such an extended operation time, the quality of laser cooling did not experience any significant decline, while the properties of laser cooling in orbital microgravity were systematically studied. In particular, we demonstrate magneto-optical trapping and polarization-gradient cooling in orbit and carefully examine their performances. A comparison of the in-orbit and on-ground results indicates that a higher cooling efficiency exists in microgravity, including a smaller loss rate during the trapping and cooling process and lower ultimate temperature of laser-cooled atoms. Our progress has laid the technical foundations for future applications of cold atoms in space missions with operation times of the order of years.
Laser cooling is an important emerging technology in such areas as the cooling of semiconductors. The book examines and suggests solutions for a range of problems in the development of miniature solid-state laser refrigerators, self-cooling solid-state lasers and optical echo-processors. It begins by looking at the basic theory of laser cooling before considering such topics as self-cooling of active elements of solid-state lasers, laser cooling of solid-state information media of optical echo-processors, and problems of cooling solid-state quantum processors. Laser Cooling of Solids is an important contribution to the development of compact laser-powered cryogenic refrigerators, both for the academic community and those in the microelectronics and other industries. Provides a timely review of this promising field of research and discusses the fundamentals and theory of laser cooling Particular attention is given to the physics of cooling processes and the mathematical description of these processes Reviews previous experimental investigations in laser cooling and presents progress towards key potential applications.