Opto-Mechanics of deformable Fabry-Perot Cavities

We investigated the opto-mechanical properties of a Fabry-Perot cavity with a mirror mounted on a spring. Such a structure allows the cavity length to change elastically under the effect of light induced forces. This opto-mechanical coupling is exploited to control the amplitude of mechanical fluctuation of the mirror. We present a model developed in the classical limit and discuss data obtained in the particular case for which photo-thermal forces are dominant.Comment: 26 pages, 7 figure

Opto-Mechanics of deformable Fabry-Perot Cavities

We investigated the opto-mechanical properties of a Fabry-Perot cavity with a mirror mounted on a spring. Such a structure allows the cavity length to change elastically under the effect of light induced forces. This opto-mechanical coupling is exploited to control the amplitude of mechanical fluctuation of the mirror. We present a model developed in the classical limit and discuss data obtained in the particular case for which photo-thermal forces are dominant.Comment: 26 pages, 7 figure

Self-induced oscillations in an optomechanical system

We have explored the nonlinear dynamics of an optomechanical system consisting of an illuminated Fabry-Perot cavity, one of whose end-mirrors is attached to a vibrating cantilever. Such a system can experience negative light-induced damping and enter a regime of self-induced oscillations. We present a systematic experimental and theoretical study of the ensuing attractor diagram describing the nonlinear dynamics, in an experimental setup where the oscillation amplitude becomes large, and the mirror motion is influenced by several optical modes. A theory has been developed that yields detailed quantitative agreement with experimental results. This includes the observation of a regime where two mechanical modes of the cantilever are excited simultaneously.Comment: 4.5 pages, 3 figures (v2: corrected few typos

Voltage-Controlled Optics of a Quantum Dot

We show how the optical properties of a single semiconductor quantum dot can be controlled with a small dc voltage applied to a gate electrode. We find that the transmission spectrum of the neutral exciton exhibits two narrow lines with $\sim 2$ $\mu$eV linewidth. The splitting into two linearly polarized components arises through an exchange interaction within the exciton. The exchange interaction can be turned off by choosing a gate voltage where the dot is occupied with an additional electron. Saturation spectroscopy demonstrates that the neutral exciton behaves as a two-level system. Our experiments show that the remaining problem for manipulating excitonic quantum states in this system is spectral fluctuation on a $\mu$eV energy scale.Comment: 4 pages, 4 figures; content as publishe

Optical detection of single electron spin resonance in a quantum dot

We demonstrate optically detected spin resonance of a single electron confined to a self-assembled quantum dot. The dot is rendered dark by resonant optical pumping of the spin with a coherent laser. Contrast is restored by applying a radio frequency (rf) magnetic field at the spin resonance. The scheme is sensitive even to rf fields of just a few micro-T. In one case, the spin resonance behaves exactly as a driven 3-level quantum system (a lambda-system) with weak damping. In another, the dot exhibits remarkably strong (67% signal recovery) and narrow (0.34 MHz) spin resonances with fluctuating resonant positions, evidence of unusual dynamic processes of non-Markovian character.Comment: 4 pages, 5 figure

The minimum model for the iron-based superconductors

A single band $t$-$U$-$J_1$-$J_2$ model is proposed as the minimum model to describe the superconductivity of the newly discovered iron-based superconductors $R(O_{1-x}F_x)FeAs$ and $RO_{1-x}FeAs$ ($R=La, Ce, Sm, Pr, Nd,Gd$). With the mean-field approach, it is found that the pairing occurs in the d-wave channel. In the likely parameter region of the real materials, by lowering temperature, the system enters firstly the $d_{xy}$ superconducting phase with $D_{4h}$-symmetry and then enters the time-reversal-symmetry-broken $d_{xy}+id_{x^2-y^2}$ superconducting phase with $C_{4h}$-symmetry.Comment: 3 pages, 3 figure

Network protocol scalability via a topological Kadanoff transformation

A natural hierarchical framework for network topology abstraction is presented based on an analogy with the Kadanoff transformation and renormalisation group in theoretical physics. Some properties of the renormalisation group bear similarities to the scalability properties of network routing protocols (interactions). Central to our abstraction are two intimately connected and complementary path diversity units: simple cycles, and cycle adjacencies. A recursive network abstraction procedure is presented, together with an associated generic recursive routing protocol family that offers many desirable features.Comment: 4 pages, 5 figures, PhysComNet 2008 workshop submissio