We present spectroscopic observation of an exceptional point or the transition point between mode crossing and avoided mode crossing of neighboring quasieigenmodes in a chaotic optical microcavity of a large size parameter. The transition to the avoided mode crossing was impeded until the degree of deformation exceeded a threshold deformation owing to the system's openness also enhanced by the shape deformation. As a result, a singular topology was observed around the exceptional point on the eigenfrequency surfaces, resulting in fundamental inconsistency in mode labeling.
A high performance distillation system to remove krypton from xenon was constructed, and a purity level of Kr/Xe = ∼ 3 × 10 −12 was achieved. This development is crucial in facilitating high sensitivity low background experiments such as the search for dark matter in the universe.
Pump-induced dynamical tunneling has been observed in free-space resonant optical pumping of a deformed microcavity by employing excitation spectroscopy. A focused-pump beam was injected into the cavity by refraction and then coupled to a high-Q cavity mode via dynamical tunneling. Pump-coupling efficiency as high as 50% and an effective coupling constant responsible for the tunneling were obtained from the observed pumping efficiency with a mode-mode coupling model. DOI: 10.1103/PhysRevLett.104.243601 PACS numbers: 42.55.Sa, 03.65.Xp, 05.45.Mt, 42.50.Àp Efficient optical pumping of high-Q cavity modes is of primary concern in microcavity applications such as microlasers and optoelectronic components and devices [1]. Prism and tapered-fiber couplings are commonly used for ultrahigh-Q whispering gallery modes [2,3]. However, simple free-space coupling without near-field couplers is often needed for practical reasons such as experimental limitations or implementation cost. Microcavities deformed from rotational symmetry can provide directional emission of high-Q modes, and, moreover, allow one to excite them by a free-space pump beam. Recently, cryogenic cooling of an optomechanical resonator assisted by free-space evanescent coupling has been reported in a slightly deformed microsphere [4]. Efficient nonresonant optical pumping based on ray chaos has also been demonstrated in deformed microcavities [5,6], suggesting further enhancements by resonant optical pumping.In a significantly deformed microcavity, the ray dynamics typically exhibits both regular and chaotic trajectories [7], resulting in a mixed phase space: high-Q modes are usually localized on regular regions such as invariant tori and regular islands surrounded by a chaotic sea. It is known that light in high-Q modes localized on those regular regions can be transferred to the nearest chaotic sea by a dynamical process and then transported by ray chaos resulting in a directional refractive output. The dynamical process is called dynamical tunneling [8] since the transport from a regular region to the chaotic sea is strictly forbidden classically.The dynamical tunneling is thus an essential link between high-Q modes and directional output, important assets for the aforementioned photonic applications. In fact, dynamical tunneling is of great current interest and has been studied theoretically in various physical systems [9][10][11][12][13][14]. Experimental signatures of dynamical tunneling were reported in a microwave billiard in energy splitting [15,16], in an acoustical resonator through spectral statistics [17], and in a cold atomic sample in atomic momentum distribution [18,19]. In microcavities, although it has been studied theoretically [20][21][22][23], there is no direct experimental evidence for dynamical tunneling.How can then the dynamical tunneling be used to improve the optical pumping? The answer lies in the reverse of the aforementioned output process. If we inject a pump beam in a time reversed way, the pump light might be transferre...
Experimental investigation of the characteristics of quasi-bound states of a quadrupole deformed microcavity has revealed five distinct mode groups in cavity emission spectra with cavity quality factors different by orders of magnitude and consistently with much different intracavity mode distributions but with almost universal far-field emission patterns. These universal directionality of high Q modes are explained by a subtle manifestation of unstable manifolds of classical chaos in the formation of quasi-bound states.
We experimentally studied evolution of quasi-eigenmodes as classical dynamics undergoing a transition from being regular to chaotic in open quantum billiards. In a deformation-variable microcavity we traced all high-Q cavity modes in a wide range of frequency as the cavity deformation increased. By employing an internal parameter we were able to obtain a mode-dynamics diagram at a given deformation, showing avoided crossings between different mode groups, and could directly observe the coupling strengths induced by ray chaos among encountering modes. We also show that the observed mode-dynamics diagrams reflect the underlying classical ray dynamics in the phase space. PACS numbers: 42.55.Sa,42.65.Sf, 05.45.Mt Quantum manifestation in a classically chaotic system has become an important issue in atomic, nano, mesoscopic physics, etc., due to its fundamental importance in quantum mechanics and applications to practical quantum/wave systems [1]. Most of early works have focused on statistical analysis of eigenvalues and eigenfunctions and comparison with the random matrix theory, e.g., the transition from Poisson to Wigner distribution of level spacings during a transition to chaos, providing an averaged view on mode dynamics [1]. Experimental verifications of the statistics have been performed mainly in closed microwave cavities [2]. Dynamical tunneling or coupling between regular and chaotic modes has recently been observed for a mixed phase space specially tailored for this purpose [3].In open quantum systems, each quasi-eigenmode has a linewidth, and thereby changes the mode dynamics significantly. Trapped modes were observed showing high Q even with increasing coupling strength to open channels in microwave cavities [4], and crossing and avoided crossing (AC) of cavity modes were reported near an exceptional point formed by two coupled microwave cavities [5]. We note, however, that the previous experimental works in microwave cavities and other systems neither realized an optimal system showing a continuous chaotic transition from being regular to chaotic nor provide observations direct enough to tell the variation of statistics.In this paper, we have experimentally observed, for the first time, the evolution of quasi-eigenmode dynamics in a generic open nonintegrable system when classical dynamics undergoes a transition from being regular to fully chaotic. In a dielectric deformation-variable chaotic optical microcavity (COM) we traced all high-Q cavity modes in a wide range of frequency as the cavity deformation increases. By introducing an additional parameter orthogonal to the cavity deformation, we could explicitly observe mode-mode dynamics under the chaotic transi-tion and measure various mode-mode coupling constants which can be associated with the underlying classical ray dynamics in phase space. We believe our data would be a valuable asset for future formulation of a currentlynonexisting semiclassical theory for coupling strengths between modes in a mixed phase space.Our experiment was performed i...
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