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Chinese Optics Letters

Experimental realization of strong coupling between a cold atomic ensemble and an optical fiber microcavity

Li Li, Yuhao Pan, Yi-Jia Liu, Xiao-Long Zhou, Dong-Yu Huang, Ze-Min Shen, Jian Wang, Chuan‐Feng Li, Guang‐Can Guo

Published Jan 1, 2023• 6 citations
Publisher

Abstract

The cavity quantum electrodynamics (QED) system is a promising platform for quantum optics and quantum information experiments.Its core is the strong coupling between atoms and optical cavity, which causes difficulty in the overlap between the atoms and the antinode of optical cavity mode.Here, we use a programmable movable optical dipole trap to load a cold atomic ensemble into an optical fiber microcavity and realize the strong coupling between the atoms and the optical cavity in which the coupling strength can be improved by polarization gradient cooling and adiabatic loading.By the measurement of vacuum Rabi splitting, the coupling strength can be as high as g N = 2π × 400 MHz, which means the effective atom number is N eff = 16 and the collective cooperativity is C N = 1466.These results show that this experimental system can be used for cold atomic ensemble and cold molecule based cavity QED research.

DOI
10.3788/col202321.092702

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The cavity quantum electrodynamics (QED) system is a promising platform for quantum optics and quantum information experiments.Its core is the strong coupling between atoms and optical cavity, which causes difficulty in the overlap between the atoms and the antinode of optical cavity mode.Here, we use a programmable movable optical dipole trap to load a cold atomic ensemble into an optical fiber microcavity and realize the strong coupling between the atoms and the optical cavity in which the coupling strength can be improved by polarization gradient cooling and adiabatic loading.By the measurement of vacuum Rabi splitting, the coupling strength can be as high as g N = 2π × 400 MHz, which means the effective atom number is N eff = 16 and the collective cooperativity is C N = 1466.These results show that this experimental system can be used for cold atomic ensemble and cold molecule based cavity QED research.
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The ultracold molecule is a promising candidate for versatile quantum tasks due to its long-range interaction and rich internal rovibrational states.With the help of the cavity quantum electrodynamics (QED) effects, an optical cavity can be employed to increase the efficiency of the formation of the photoassociated molecules and offers a non-demolition detection of the internal states of molecules.Here, we demonstrate the production of the high-finesse optical fiber microcavity for the Rb 2 molecule cavity QED experiment, which includes the fabrication of fiber-based cavity mirrors, testing, and the assembly of ultra-high vacuum-compatible optical fiber microcavity.The optical fiber microcavity offers high cooperativity between cavity mode and ultracold molecule and paves the way for the study of molecule cavity QED experimental research.
Abstract We experimentally realize a new cavity quantum electrodynamics (QED) platform with defect-free single-atom array strongly coupled to an optical cavity. The defect-free single-atom array is obtained by rearranging a probabilistically loaded one-dimensional (1D) optical tweezer array with dimensions of 1×401 \times 401×40 1 × 40 . The atom array is enclosed with two cavity mirrors, which compose a miniature optical Fabry-Pérot cavity with cavity length of 1.15 mm. By precisely controlling the position of the atom array, we demonstrate uniform and strong coupling of all atoms in the array with the optical cavity. The average coupling strength between the single atom and the cavity is 2.62 MHz. The vacuum Rabi splitting spectra for single-atom arrays with atom number N changing from 3 to 26 are measured. Thus, the collective enhancement of the coupling strength with N{\sqrt {N}}N​ N -dependence for multiple atoms is validated at the single atom level. Our system holds significant potential for establishing the foundation of distributed quantum computing and advancing fundamental research in many-body physics.
Generating and manipulating multiparticle quantum entangled states is an exciting challenge of modern physics. Along this line, we have built a platform where cold rubidium atoms are strongly coupled to a fiber-based microcavity, under a quantum gas microscope. The atoms are trapped in a lattice at 1560nm, which allows strong and homogeneous coupling to the commensurate probe lattice at 780nm. First, we observe a coherent interaction between the cavity and the atoms, in the strong coupling regime, in spite of a large frequency inhomogeneity induced by the trap. It is the first report of such cavity protection effect with less than 200 emitters. We measure the growing coupling of the dark states to the cavity as the disorder takes over the collective coupling. In the protected regime we engineer frequency-modulated polaritons through a modulation of the atomic frequency. Then, we setup optical tweezers in the microcavity to obtain and manipulate several single atoms. The cavity enables fast and non demolition detection of a single atom in a tweezer. We measure the vacuum Rabi splitting of this atom, demonstrating its strong coupling with an effective cooperativity of 30. Finally, we obtain single atoms in a chain of 9 tweezers. This work opens to way to manipulating many individual atoms strongly coupled to the cavity, with applications in multiparameter quantum metrology, using spatially distributed and locally measurable entanglement as a resource, and quantum simulation of a chain of addressable spins with cavity-mediated infinite range interactions.
A major focus in modern experimental quantum physics is to create many-particle entangled states with single-particle control. In this Thesis we present a new platform that aims at achieving this purpose by combining two main ingredients: the collective coupling of cold rubidium atoms to an optical cavity and the individual control of the particles via a highresolution microscope. At the heart of our experimental system is a miniaturized fiber Fabry-Perot cavity that allows accessing the strong coupling regime of Cavity Quantum Electrodynamics (CQED). In addition to the CQED probe, a second cavity mode with twice the wavelength creates a lattice potential for identically and maximally coupling the atoms to the cavity. The spatial overlap between the two intra-cavity standing waves plays an essential role and we present methods to characterize and optimize it. We also report a technique for integrating the fiber cavity with a high-numerical aperture objective in a compact and stable setup. For transporting cold atoms from the capture region to the fiber resonator, we developed a system based on a movable optical dipole trap, driven by an acousto-optical deflector, which realizes a fast and efficient loading of the intracavity lattice. The combination of these elements allowed the observation of strong coupling between the cavity mode and the atoms in the 1D lattice via vacuum-Rabi-splitting measurements. This constitutes an important step towards generating many-body entanglement in our system, where the interplay between collective operations (performed via the cavity) and local control on the atomic qubits (provided by the microscope) is a promising approach for new entanglement schemes.
Optical traps, including those used in atomic physics, cold chemistry, and quantum science, are widely used in the research on cold atoms and molecules. Owing to their microscopic structure and excellent operational capability, optical traps have been proposed for cold atom experiments involving complex physical systems, which generally induce violent background scattering. In this study, using a background-free imaging scheme in cavity quantum electrodynamics systems, a cold atomic ensemble was accurately prepared below a fiber cavity and loaded into an optical trap for transfer into the cavity. By satisfying the demanding requirements for the background-free imaging scheme in optical traps, cold atoms in an optical trap were detected with a high signal-to-noise ratio while maintaining atomic loading. The cold atoms were then transferred into the fiber cavity using an optical trap, and the vacuum Rabi splitting was measured, facilitating relevant research on cavity quantum electrodynamics. This method can be extended to related experiments involving cold atoms and molecules in complex physical systems using optical traps.