High-gain resonant nonlinear Raman scattering on trapped cold atoms within a high-fineness ring optical cavity is simply explained under a nonlinear opto-mechanical mechanism, and a proposal using it to detect frequency of micro-trap on atom chip is presented. The enhancement of scattering spectrum is due to a coherent Raman conversion between two different cavity modes mediated by collective vibrations of atoms through nonlinear opto-mechanical couplings. The physical conditions of this technique are roughly estimated on Rubidium atoms, and a simple quantum analysis as well as a multi-body semiclassical simulation on this nonlinear Raman process is conducted.
High-gain resonant nonlinear Raman scattering on trapped cold atoms within a high-fineness ring optical cavity is simply explained under a nonlinear opto-mechanical mechanism, and a proposal using it to detect frequency of micro-trap on atom chip is presented. The enhancement of scattering spectrum is due to a coherent Raman conversion between two different cavity modes mediated by collective vibrations of atoms through nonlinear opto-mechanical couplings. The physical conditions of this technique are roughly estimated on Rubidium atoms, and a simple quantum analysis as well as a multi-body semiclassical simulation on this nonlinear Raman process is conducted.
In this paper, the Raman scattering spectra of cold atomic gas in different environments are closely calculated. Comparing the spectra from the atoms in free and trapped environments, the calculation result gives a right spectrum structure for the free atoms and reveals a distinct high-gain spectrum exhibiting a comb-like structure for the harmonic trapped atoms. The spectral peaks of the trapped spectrum are uniformly distributed and the distance between adjacent spectral peaks exactly equals the frequency of the trap. The nonlinear gain scheme and the gain conditions of the Raman scattering process are clearly given in this paper.
Summary form only given. The strong atom-photon coupling generated inside high-finesse optical micro cavity lets us detect a single atom trajectory in real time. Such a strong coupling is a candidate for trapping a single atom with a single photon. Dynamics of trapped atoms can be observed in situ and in real time by detecting intensity change on the transmission of a blue-shifted laser beam. We cooled down and trapped rubidium atoms by using conventional cell magneto optical trap (MOT) and launched them into the micro optical cavity which locates 35 mm above the MOT. By using this signal as trigger and changing the laser frequency, it is, in principle, possible to trap the atom in the cavity.
Summary form only given. We observe the quantized motion of single atoms strongly coupled to a high-finesse optical cavity and investigate dynamics of cavity-assisted atom cooling. Single caesium atoms are trapped in a blue-detuned standing-wave intracavity dipole trap, formed by a lock laser which is used to stabilize the cavity resonance frequency. A probe laser is coupled into the cavity mode and its transmission spectrum is monitored by means of photon-counting heterodyne spectroscopy [2].Measured heterodyne spectra of single atoms in the cavity are shown in Fig. 1 for two different lock-laser intensities and compared with theoretical models. The motional Raman sidebands are offset from the carrier beat signal at 1 MHz by the atomic vibrational frequency (±ν). They show asymmetric lineshapes due to the anharmonicity of the dipole potential.We investigate the dependence of the positions and lineshapes of the motional Raman sidebands on experimantal parameters such as the cavity-atom detuning, and lock-laser intensity. Information on the atomic temperature, cooling and heating rates, as well as the atomic position in the cavity with respect to an antinode of the cavity probe field are found by comparing the observed spectra with theoretical predictions [1]. In addition, this technique can also be used to analyze the cooling dynamics of a cavity-assisted EIT cooling scheme which has been recently studied and demonstrated in [3,4].
Techniques to controllably interface atoms with quantum optical fields form the basis for many applications in quantum information science. For example, photons are convenient to relay information over large quantum networks, while atoms naturally are physical systems that can process and store this information. Thus far, the available techniques to efficiently couple single photons with atomic media fall into one of the following, mostly independent, categories: i) cavity quantum electrodynamics (QED), where atomic interactions with light are enhanced via a high-finesse cavity, ii) coherent coupling with atomic ensembles exhibiting large optical depths, and iii) the use of fields tightly focused to dimensions smaller than or approaching the scattering cross-section of a single atom. Although remarkable achievements have been made with all of these approaches, a robust, scalable technique remains elusive. Recently, several groups have successfully demonstrated that cold atoms can be trapped near and interfaced with nanophotonic systems, such as hollow-core photonic crystal fibers [1] and tapered nanofibers [2–4]. The traps are well-characterized [2, 3, 5], and the nearly diffraction-limited transverse confinement of optical fields enables ∼ 10% coupling efficiency of a single atom to the fiber [2, 3]. This has already led to remarkable observations of strong light-matter interactions using relatively few atoms and low powers [1]. It has also been proposed that such techniques can be extended to highly configurable photonic crystal waveguides [6]. Together, these efforts raise the intriguing possibility for future nanophotonic systems with tremendous figures of merit, wherein atom-light interactions can be tailored nearly at will. Here, we discuss recent efforts to develop novel techniques to realize strong, controllable atom-photon and photon-photon interactions, which take full advantage of the parameter space afforded by nanophotonic interfaces and are not based upon the extension of existing techniques. As a specific example, we discuss a protocol to achieve “all-atomic” cavity QED [7], as briefly described below. First, we show that although the single-atom coupling to guided modes of a nanophotonic waveguide might be relatively weak, there exist collective modes of a trapped atomic ensemble whose coupling to light is enhanced by the square root of the atom number, √ NA. While collective effects are generally well-known, special consequences emerge in the nanofiber system when the atoms are trapped in a lattice. In particular, collective effects cause such a lattice to act as a near-perfect mirror for an incident field close to resonance. In analogy to cavity QED, we then demonstrate that two sets of atomic mirrors can form an effective cavity, which can greatly enhance the coupling of a single, specially chosen “impurity” atom (or a few impurity atoms) positioned inside. We introduce a novel quantum spin model to describe the atom-light coupling, which allows one to exactly map the atom-nanofiber interface onto the simple and elegant Jaynes-Cummings model of cavity QED [8]. A unique feature of our atomic mirrors compared to conventional cavities is that they have long relaxation times and are highly dispersive. Remarkably, even with very low mirror finesse (F ∼ 10 2 ), this property allows one to attain the “strong coupling” regime of cavity QED, where vacuum Rabi oscillations [9–12] occur between an excited impurity atom and a single “photon” stored in the cavity (or more precisely, in the atomic mirrors). Furthermore, as quantum mechanical objects, these atom mirrors can be used to store quantum information and transfer this information into propagating waveguide modes. These various features can be combined to realize all of the building blocks for scalable quantum information processing.
Molecular cavity optomechanical systems have recently emerged as a promising platform for enhancing infrared detection sensitivity, owing to their ability to up-convert low-frequency infrared (IR) photons to visible frequency range. Generally, under red-detuned pumping in such systems, the ideal conversion efficiency of the IR signal approaches 1. To overcome this efficiency constraint, we propose a scheme that incorporates gain into the infrared cavity of a molecular cavity optomechanical system comprising two cavities and an ensemble of N molecules. The upconversion process, which relies on IR absorption and Raman scattering associated with specific vibrational modes, is significantly amplified by the incorporation of gain under the red-detuned conditions. Moreover, our analysis demonstrates that the added noise is maintained near 0.5.
Superradiant Raman scattering of Rubidium atoms has been explored in the experiment [Nature 484, 78 (2012)] to prove the concept of the superradiant laser, which attracts significant attentions in quantum metrology due to the expected ultra-narrow linewidth down to millihertz. To better understand the physics involved in this experiment, we have developed a quantum master equation theory by treating the Rubidium atoms as three-level systems, and coupling them with a dressed laser and an optical cavity. Our simulations show different superradiant Raman scattering pulses for the systems within the crossover and strong coupling regime, and the shifted and broader spectrum of the steady-state Raman scattering. Thus, our studies provide a unified view on the superradiant Raman scattering pulses, and an alternative explanation to the broad spectrum of the steady-state Raman scattering, as observed in the experiment. In future, our theory can be readily applied to study other interesting phenomena relying on the superradiant Raman scattering, such as magnetic field sensing, real-time tracking of quantum phase, Dicke phase transition of non-equilibrium dynamics and so on.