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Acta Physica Sinica

Construction of a strongly coupled cavity quantum electrodynamics system with easy accessibility of single or multiple intra-cavity atoms

Ruijuan Wen, Jinjin Du, LI Wen-fang, Gang Li, Tiancai Zhang

Published Jan 1, 2014• 1 citation
Publisher

Abstract

The long-time trap and control of neutral atoms in an optical micro-cavity is a crucial problem in cavity quantum electrodynamics (QED), which greatly restricts the coherent manipulation of the interaction process between single atom and light. In this paper, we design a strongly coupled cavity QED system based on the traditional Fabry-Perot cavity. The parameters of the cavity are 3.5 millimeters in length, about 57000 in fineness, (g0,,)=2 (1.48, 0.375, 2.61) MHz, 1.54 and 0.89 in critical photon and atom number, respectively. The system allows building the magneto-optical trap (MOT) and optical lattice directly inside the cavity, which provides the possibility of long-time trapping deterministic single neutral atom or a number of neutral atoms in the cavity. By setting up a dipole trap and atomic imaging system, the capture, detection and imaging of single atom or several atoms in the cavity can be realized. The system overcomes some difficulties in transferring atoms in the usual cavity QED and has potential applications in robust intracavity atom control for quantum information processing.

DOI
10.7498/aps.63.244203

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The long-time trap and control of neutral atoms in an optical micro-cavity is a crucial problem in cavity quantum electrodynamics (QED), which greatly restricts the coherent manipulation of the interaction process between single atom and light. In this paper, we design a strongly coupled cavity QED system based on the traditional Fabry-Perot cavity. The parameters of the cavity are 3.5 millimeters in length, about 57000 in fineness, (g0,,)=2 (1.48, 0.375, 2.61) MHz, 1.54 and 0.89 in critical photon and atom number, respectively. The system allows building the magneto-optical trap (MOT) and optical lattice directly inside the cavity, which provides the possibility of long-time trapping deterministic single neutral atom or a number of neutral atoms in the cavity. By setting up a dipole trap and atomic imaging system, the capture, detection and imaging of single atom or several atoms in the cavity can be realized. The system overcomes some difficulties in transferring atoms in the usual cavity QED and has potential applications in robust intracavity atom control for quantum information processing.
Cavity quantum electrodynamic system with strongly coupled single atoms provides a good platform for studying quantum information processing, quantum simulation, quantum network, and distributed quantum computing. Cooling and trapping single atoms is a crucial technique in the quantum technology. At present, in a high-finesse cavity with finite space, cooling and trapping single atoms is a big challenge, even though it is a mature technique for free space. Great efforts have been made to cool and trap single atoms inside a cavity, and for a trapped atom its lifetime has reached as long as tens of seconds. Developing a more flexible method of cooling and trapping single atoms in a cavity is still essential for a strongly coupled cavity quantum electrodynamic system. In this work, we demonstrate experimentally that a single cesium atom in a cavity can be trapped by utilizing a single optical tweezer settled in cavity mode, and its lifetime is (2.60 ± 0.18) s. The experiment is carried out in a Fabry-Perot cavity, which is assembled by two concave mirrors each with a curvature radius of 100 mm, and cavity length of 335 μm. The concave surfaces are highly reflective, and the cavity has a finesse of 6.1 × 104. The 1080 nm optical tweezer with a waist of 2 μm is formed by an achromatic lens group with a numerical aperture of 0.4. At first, the precooled atomic assemble released from the magneto-optical trap (MOT) is transferred into cavity mode by an optical dipole trap with a waist of 36 μm. Then, one of the successfully transferred atoms is captured by the optical tweezer with the aid of cavity cooling mechanism. A blue detuned cavity locking laser is used as a standing-wave optical trap along the cavity axis. The signal of successfully trapped one atom is obtained by recording transmission of the cavity that will decrease owing to the strong coupling induced vacuum Rabi splitting. Finally, we demonstrate the precise manipulation of the atom-cavity coupling strength, which is achieved by scanning the position of the trapped atom step by step by using a high-precision translation stage. The system realized in this work can be used to study the dynamics of single atom-photon interactions with adjustable coupling strength. In addition, the mechanism adopted in this work is compatible with constructing tweezer arrays inside cavity mode, and thus possesses more flexibility and great potentials in cavity-based quantum entanglement and quantum simulation.
The process of single-atom transfer in strongly coupled cavity quantum electrodynamics (QED) with free falling atoms is investigated by experiment and Monte Carlo simulation. We conduct the simulation of the whole physical process and give the corresponding experimental results. In experiment, a high finesse optical cavity is used for real-time detection of the single-atom transits from which the interaction information between single atoms and cavity can be extracted, including the transmission spectra of the cavity strongly coupled to single atoms, the interaction duration of the single atoms in the mode, the probability distribution of atom arrival time and the atomic kinetic energy distribution when arriving at the mode. All these can be completely derived from the transmission spectra of the different initial status. An intracavity far-off resonance trap (FORT) has been established and the single-atom trapping time inside the cavity is about 5 ms which is about 30 times longer than that without FORT. This study gives the detailed analysis of the whole procedure of free-falling atom transfer in cavity QED system and is helpful for optimizing the experimental parameters and design.
We experimentally demonstrate real-time detection of individual cesium atoms by using a high-finesse optical micro-cavity in a strong coupling regime. A cloud of cesium atoms is trapped in a magneto-optical trap positioned at 5 mm above the micro-cavity center. The atoms fall down freely in gravitation after shutting off the magneto-optical trap and pass through the cavity. The cavity transmission is strongly affected by the atoms in the cavity, which enables the micro-cavity to sense the atoms individually. We detect the single atom transits either in the resonance or various detunings. The single atom vacuum-Rabi splitting is directly measured to be Ω = 2π × 23.9 MHz. The average duration of atom-cavity coupling of about 110 μs is obtained according to the probability distribution of the atom transits.
Neutral-atom array and cavity quantum electrodynamics offer complementary strengths for quantum science: scalable, reconfigurable qubit architectures and strong coherent light-matter coupling. Combining them in a single platform requires an optical cavity with simultaneously high cooperativity, sufficient mode volume to accommodate atom array, and ample side optical access for atom trapping, imaging, cooling, and rearrangement, a combination that is challenging to achieve. Here we realize an atomic array integrated with a millimeter-scale Fabry--Pérot cavity whose optically-characterized single-atom cooperativity reaches ηcav=125±13η_{\mathrm{cav}}=125\pm13ηcav​=125±13. Atom-cavity transmission spectra of trapped atoms yield an effective spectroscopic cooperativity ηspec=106±3η_{\mathrm{spec}}=106\pm 3ηspec​=106±3, providing an in-situ verification of strong coupling in the integrated platform. In this integrated system, we achieve a state-measurement fidelity of 99.925−18+15%99.925^{+15}_{-18}\%99.925−18+15​% for a single atom with a 4-μμμs readout time. We also demonstrate simultaneous coupling of up to 21 individually trapped atoms to the antinode of the cavity mode. The key technical advance is a two-step mirror-fabrication method combining precision mechanical shaping and carbon-dioxide laser polishing, which produces concave fused-silica mirrors with sub-millimeter radii of curvature and residual roughness below 2 A˚2~Å2 A˚. Our results establish a regime of cavity-integrated atomic array that simultaneously provides high cooperativity, large mode volume, and flexible manipulation of individual atoms, opening opportunities for cavity-assisted quantum state readout and long-range entanglement-engineering in atom-array platforms.
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.
A leading strategy for the creation of a scalable quantum computer is through a networked architecture. This would comprise stationary nodes for quantum information processing and photonic channels for their communication and entanglement distribution. In this scheme a coherent interface between light and matter is a critical component, facilitating the deterministic and reversible transfer of quantum information between stationary and travelling qubits. This requirement may be fulfilled by a high finesse optical cavity, whose radiation field is strongly coupled to a trapped quantised emitter. Neutral atoms are an ideal species for the development of such a device, given their inherent compatibility with dielectric mirror surfaces. However, an outstanding challenge in building an elementary network of neutral atom-cavity systems is in establishing a single atom dipole trap within each cavity mode. This thesis presents the development of an open-access cavity suitable for single atom localisation, whilst maintaining strong atom-cavity coupling, {g0,κ,γ} = {11,2.1,3} × 2πMHz, and the efficient extraction of generated photons, η=0.5. We consider cavity design methodology, deriving a connection between the physical properties of the optical resonator and its intended role in the production of single photons. An experimental platform is developed for the creation of cavity mirrors by laser ablation, with a high degree of geometrical control. This is used to produce a set of pyramidal micro-mirrors, demonstrated to represent a favourable alternative to the widespread adoption of fibre-tip cavities. These pyramidal mirrors are shown to support multi-feature resonators, allowing several atom-cavity interfaces to be formed using a pair of substrates. By developing a novel procedure for mirror alignment, a hybrid mirror cavity is fabricated and integrated into an experimental architecture tailored for atomic trapping. Suitability of the cavity for future experimentation is demonstrated by frequency stabilisation to an atomic resonance of 87Rb.