Young-Tak Chough

Cavity-Q-driven spectral shift in a cylindrical whispering-gallery-mode microcavity laser

Cavity-Q-driven spectral shift of lasing was observed in a cylindrical microcavity formed by rhodamine6G-doped quinoline in a capillary. The envelope of lasing spectrum showed a blueshift induced by the decreasing cavity Q of whispering gallery modes as the pump fluence increases. The thermally induced refractive index changes were measured from the shifts of individual lasing modes. The observed cavity-Q-driven spectral shift was well described by a simple dye laser model, which accounts for the dependence of cavity Q on the thermally induced refractive index change.

Coherent and dynamic beam splitting based on light storage in cold atoms.

We demonstrate a coherent and dynamic beam splitter based on light storage in cold atoms. An input weak laser pulse is first stored in a cold atom ensemble via electromagnetically-induced transparency (EIT). A set of counter-propagating control fields, applied at a later time, retrieves the stored pulse into two output spatial modes. The high visibility interference between the two output pulses clearly demonstrates that the beam splitting process is coherent. Furthermore, by manipulating the control lasers, it is possible to dynamically control the storage time, the power splitting ratio, the relative phase, and the optical frequencies of the output pulses. With further improvements, the active beam splitter demonstrated in this work might have applications in photonic photonic quantum information and in all-optical information processing.

Atomic Solc filter: multi-resonant photoemission via periodic poling of atom-cavity coupling constant.

This paper describes a novel atom-cavity interaction induced by periodically poled atom-cavity coupling constant which leads to multiple narrow photoemission bands for an initially inverted two-level atom under the strong coupling condition. The emission bandpass narrowing has a close analogy with the folded Solc filter in the context of quasi-phase matching by periodic poling. We present a closed form solution of the emission probability at the end of interaction and deduce the multiple phase matching condition for this system which is programmable by the interaction time. The Bloch sphere analysis provides a clear understanding of the underlying atomic dynamics associated with the multiple resonances in the semiclassical limit. Furthermore, we show that this interaction can be applied to generation of nonclassical fields with sub-Poisson photon statistics.

Squeezing Enhancement by Damping in a Driven Atom-Cavity System

We investigate a coupled atom-cavity system in which a two-level atom is driven by a classical field. It is shown that the cavity mode, which is in a coherent state in the absence of its reservoir, can be squeezed via coupling to the reservoir. The squeezing effect is enhanced to some extent as the cavity damping rate is increased. In particular, we obtain an unusual optimal condition for the squeezing in which the pumping field is inversely proportional to the damping rate.

Self-Consistency of Thermal Jump Trajectories

It is problematic to interpret the quantum jumps of an atom interacting with thermal light in terms of counts at detectors monitoring the atoms inputs and outputs. As an alternative, we develop an interpretation based on a self-consistency argument. We include one mode of the thermal field in the system Hamiltonian and describe its interaction with the atom by an entangled quantum state while assuming that the other modes induce quantum jumps in the usual fashion. In the weak-coupling limit, the photon number expectation of the selected mode is also seen to execute quantum jumps, although more generally, for stronger coupling, Rabi oscillations are observed; the equilibrium photon number distribution is a Bose-Einstein distribution. Each mode may be viewed in isolation in a similar fashion, and summing over their weak-coupling jump rates returns the net jump rates for the atom assumed at the outset.

Compatibility of Continuous Rabi Oscillation and Discontinuous Quantum Jumps

The connection between the continuousness of Rabi oscillation and the discontinuity of quantum jumps has long remained one of the conceptual difficulties since the discovery of the quantum physical paradigm. In this study, however, we demonstrate that the behavior of the atom-field composite system gradually changes from the continuous Rabi interaction to the discontinuous quantum jumps as the atom-field coupling strength is reduced. The reduction occurs through enlarging the quantization volume of the mode so that the mode approaches one of the infinitely many modes of the thermal background.

“Trapping states” — Revisited

We revisit the “trapping states” of the micromaser from a quantum trajectory point of view, treating many simultaneously interacting atoms and a random atomic beam. Previous studies of trapping states are severely restricted by simplifying assumptions. We show that sub-Poissonian maser fields are generated still after the principal restrictions are lifted.

A Microlaser Pumped by Atoms in Polarized States

A microlaser pumped by atoms in various initial states is studied in the unsaturated gain limit. It turns out that the greatest gain is achieved not by the inverted atoms but by the polarized atoms. Also the photon number fluctuation is smallest in case of the polarized state pumping.

Motion of an Atomic Wave Packet in a Standing-Wave Cavity Field

We present an in-depth study on the behavior of an atomic wave packet which is placed in a standing wave cavity prepared in various states of light. We extract a simple classical oscillator model out of the dynamics of the quantum system. We quantitatively resolve the states of the spatially reorganized wave packet by the dressed state spatial probability distribution functions we developed. We also report a novel type of the “quantum collapse and revival” behavior of the Rabi nutation which is originated from the effect of the quantized atomic center-of-mass motion on the atomic internal motion.

Atomic deflection by the two dimensional traveling-wave and standing-wave vacuum modes

We analyze the interaction of an two-state atom with two dimensional cavity modes in the strong coupling regime, with the quantized atomic center of mass motion taken into account. By choosing proper initial condition for the atomic transverse momentum and the cavity detuning, we can control the atomic transverse momentum distribution in two dimensions. We have analyzed the two-dimensional momentum distribution of the excited atom fully quantum mechanically, which interacts with two independent pairs of counterpropagating traveling-wave modes, one pair of folded traveling-wave modes, two independent crossed standing-wave modes and one folded standing-wave mode, respectively.