Pound-locking for characterization of superconducting microresonators.

We present a new application and implementation of the Pound-locking technique for the interrogation of superconducting microresonators. We discuss how by comparing against stable frequency sources this technique can be used to characterize properties of resonators that cannot be accessed using traditional methods. Specifically, by analyzing the noise spectra and the Allan deviation, we obtain valuable information about the nature of the noise in superconducting planar resonators. This technique also greatly improves the read-out accuracy and measurement throughput compared to conventional methods.

Splitting and lasing of whispering gallery modes in quantum dot micropillars.

We have studied the whispering gallery mode (WGM) resonances of GaAs/AlGaAs microcavity pillars containing InAs quantum dots. High quality factor WGMs are observed from a wide range of pillars with diameters from 1.2 to 50 µm. Multimode lasing with sub-milliwatt thresholds and high beta-factors approaching unity is observed under optical pumping in a 4 µm diameter pillar. Mode splitting is observed in WGMs from pillars with diameters of 5 µm, 20 µm and 50 µm.We develop a model in which the mode splitting in the larger pillars is caused by resonant scattering from the quantum dots themselves. The model explains why splittings are observed in all of the larger pillars and that the splitting decreases with increasing wavelength. Numerical simulations by COMSOL confirm that the model is plausible. This mechanism of splitting should be general for all circular resonant structures containing quantum dots such as microdisks, rings, toroids, and microspheres.

Observation of periodic orbits on curved two-dimensional geometries.

We measure elastomechanical spectra for a family of thin shells. We show that these spectra can be described by a "semiclassical" trace formula comprising periodic orbits on geodesics, with the periods of these orbits consistent with those extracted from experiment. The influence of periodic orbits on spectra in the case of two-dimensional curved geometries is thereby demonstrated, where the parameter corresponding to Planck's constant in quantum systems involves the wave number and the curvature radius. We use these findings to explain the marked clustering of levels when the shell is hemispherical.

ELISA: a cryocooled 10 GHz oscillator with 10(-15) frequency stability.

This article reports the design, the breadboarding, and the validation of an ultrastable cryogenic sapphire oscillator operated in an autonomous cryocooler. The objective of this project was to demonstrate the feasibility of a frequency stability of 3x10(-15) between 1 and 1000 s for the European Space Agency deep space stations. This represents the lowest fractional frequency instability ever achieved with cryocoolers. The preliminary results presented in this paper validate the design we adopted for the sapphire resonator, the cold source, and the oscillator loop.

Experiments on elastomechanical wave functions in chaotic plates and their statistical features.

We measure the amplitude of the elastomechanical displacement at a fine grid of points on a free plate having the shape of a Sinai stadium. The obtained displacement field formally corresponds to a wave function in a quantum system. While the distribution of the squared amplitudes agrees with the prediction of random matrix theory (RMT), there is a strong deviation of the spatial correlator from the standard prediction for quantum chaotic systems. We show that this is due to the presence of two modes, leading to a beating phenomenon. We construct a proper extension of the spatial correlator within the framework of RMT.