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Classical and Quantum Dynamics of a Strongly Coupled Atom-Cavity System

Markus Koch

Published Jan 1, 2011• 4 citations
OpenAlex

Abstract

We describe a new experimental apparatus strongly coupling individual rubidium atoms to the light field of a high-finesse cavity. The main focus of this work lies on the observation of the dynamics of the system. Because of the strong coupling between the atom and the light field, we can track the atomic motion in real time. This enables us to reduce the motion by means of feedback resulting in a dramatic increase of the duration of stay of the atom in the cavity. In another experiment, we study the quantum dynamics of the internal degrees of freedom. For this purpose, we analyze the temporal distribution of the photon stream that is emitted from the system. We observe the coherent exchange of energy between the atom and the cavity, as well as between the atom-cavity system and the driving laser. Moreover, we show that the fluctuations of the emitted light are asymmetric in time.

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•Jan 1, 2003•1 citation
We describe a new experimental apparatus strongly coupling individual rubidium atoms to the light field of a high-finesse cavity. The main focus of this work lies on the observation of the dynamics of the system. Because of the strong coupling between the atom and the light field, we can track the atomic motion in real time. This enables us to reduce the motion by means of feedback resulting in a dramatic increase of the duration of stay of the atom in the cavity. In another experiment, we study the quantum dynamics of the internal degrees of freedom. For this purpose, we analyze the temporal distribution of the photon stream that is emitted from the system. We observe the coherent exchange of energy between the atom and the cavity, as well as between the atom-cavity system and the driving laser. Moreover, we show that the fluctuations of the emitted light are asymmetric in time.
We report on the observation of long-range forces between ultracold rubidium atoms that are mutually coupled by the field of a driven high-finesse optical cavity. Even for much less than one photon in the cavity on average, the forces strongly influence the spatial distribution of the atoms. This manifests itself as an asymmetric normal-mode spectrum of the strongly coupled atoms-cavity system. Expressions are given for the dipole force and the diffusion coefficient for the atoms in the presence of the other atoms. The data agree well with calculated spectra, which include the full motional dynamics of the many-atom system.
The quantum dynamics of a strongly driven, strongly coupled single-atom-cavity system is studied by evaluating time-dependent second- and third-order correlations of the emitted photons. The coherent energy exchange, first, between the atom and the cavity mode, and second, between the atom-cavity system and the driving laser, is observed. Three-photon detections show an asymmetry in time, a consequence of the breakdown of detailed balance. The results are in good agreement with theory and are a first step towards the control of a quantum trajectory at larger driving strength.
Cavity quantum electrodynamics (QED) in the strong-coupling regime provides the opportunity to monitor and control the dynamics of a simple quantum system. A single Cesium atom interacts strongly with single-photon fields in the mode of a high-finesse optical cavity. When the resulting coherent coupling rate dominates dissipation in the system, strong coupling is realized and the system displays distinctively quantum behavior. The coupling between atomic internal states and the quantized cavity field allows for diverse protocols in quantum state preparation, quantum communication, and quantum logic. However, the atom's external or motional state must also be taken into account. My research develops cavity QED in the limit where the coherent atom-field coupling dominates the atomic kinetic energy and thus significantly affects the atomic center-of-mass motion. In this regime, the interaction of the atom with the cavity field provides both a means of controlling atomic motion and a signal for detecting that motion in real time with high signal-to-noise. The sensing capability of the ``atom-cavity microscope" is exploited to trap single atoms with single-photon fields and to monitor their orbits in real time as they are bound in the cavity. Such real-time position sensing is the basis for a detailed strategy and ongoing experiment to actively stabilize select aspects of an atom's motion within the cavity. As the cavity-enabled position measurement approaches the standard quantum limit, this work begins to realize a quantum servo for atomic position and to address questions of optimal state estimation and state preparation. In combination with other progress in cavity QED, it furthers the goal of controlled atom-field interactions for quantum information science.
The experiments discussed in this thesis focus on the interaction of a single trapped atom with the single mode of a high-finesse optical cavity, in the regime of strong coupling. Chapter 1 gives a brief introduction, after which Chapter 2 describes our recent measurements of the transmission spectrum of the atom-cavity system. The spectrum exhibits a clearly resolved vacuum-Rabi splitting, in good quantitative agreement with theoretical predictions. A new Raman scheme for cooling atomic motion along the cavity axis enables a complete spectrum to be recorded for an individual atom trapped within the cavity mode, in contrast to all previous measurements of this type that have required averaging over 10^3-10^5 atoms. Chapter 3 discusses our observations of photon blockade for the transmitted light in the presence of one trapped atom. Excitation of the atom-cavity system by a first photon blocks the transmission of a second one, thereby converting an incident Poissonian stream of photons into a sub-Poissonian, anti-bunched stream, as confirmed by measurements of the photon statistics of the transmitted field. The intensity correlations of the cavity transmission also reveal the energy distribution for oscillatory motion of the trapped atom. Chapter 4 details a set of simple but necessary measurements of relevant experimental parameters such as cavity geometry, linewidth, mirror properties, birefringence, and detection efficiency. The thesis concludes with Appendix A, describing the efficient laser setup we use for our magneto-optical traps.
This thesis reports on experiments with single atoms strongly coupled to a single mode of a high-finesse optical cavity. In the first part, it is shown that the motion of the atom in an intracavity dipole trap can be observed with high spatial and temporal resolution. Depending on the atom's current position, the dipole trap is switched to control the motion of the atom. The feedback acts in real time, faster than one oscillation period of the atom in the trap. In the second part the anharmonic energy level structure of the system is investigated. This anharmonicity allows one to selectively populate states containing two energy quanta in a two-photon process, resulting in a nonlinear response of the system with respect to the drive laser intensity. The photon statistics of the light transmitted through the cavity shows photon bunching and super-Poissonian fluctuations, indicating the transmission of photon pairs typical for a two-photon gateway.
An experiment is described where slow laser-cooled atoms are injected into a high-finesse optical cavity. Single atoms are trapped in the cavity light field and observed by measuring the light intensity transmitted through the cavity. Feedback-based methods are realized to extend the time the atom stays in the cavity. The influence of atoms on the cavity transmission and the light force on atoms in a cavity are also analyzed theoretically. This allows to study the motion of an atom in the cavity and to interpret the experimental transmission signals. The current limitations for the storage time are identified and a strategy to overcome them is suggested. Apart from that, a method is proposed which allows a two-dimensional position measurement of atoms in the cavity.