Alexandros Tavernarakis

Backaction amplification and quantum limits in optomechanical measurements.

Optical interferometry is by far the most sensitive displacement measurement technique available, with sensitivities at the 10(-20) m/square root(Hz) level in the large-scale gravitational-wave interferometers currently in operation. Second-generation interferometers will experience a tenfold improvement in sensitivity and be mainly limited by quantum noise, close to the standard quantum limit (SQL), once considered as the ultimate displacement sensitivity achievable by interferometry. In this Letter, we experimentally demonstrate one of the techniques envisioned to go beyond the SQL: amplification of a signal by radiation-pressure backaction in a detuned cavity.

Atomic Monolayer Deposition on the Surface of Nanotube Mechanical Resonators

We study monolayers of noble gas atoms (Xe, Kr, Ar, and Ne) deposited on individual ultraclean suspended nanotubes. For this, we record the resonance frequency of the mechanical motion of the nanotube, since it provides a direct measure of the coverage. The latter is the number of adsorbed atoms divided by the number of the carbon atoms of the suspended nanotube. Monolayers form when the temperature is lowered in a constant pressure of noble gas atoms. The coverage of Xe monolayers remains constant at 1/6 over a large temperature range. This finding reveals that Xe monolayers are solid phases with a triangular atomic arrangement, and are commensurate with the underlying carbon nanotube. By comparing our measurements to theoretical calculations, we identify the phases of Ar and Ne monolayers as fluids, and we tentatively describe Kr monolayers as solid phases. These results underscore that mechanical resonators made from single nanotubes are excellent probes for surface science.

Quantum optomechanical correlations induced by radiation pressure between light and mirrors

Radiation pressure exerted by light in interferometric measurements is responsible for displacements of mirrors which appear as an additional back-action noise and limit the sensitivity of the measurement. We experimentally study these effects by monitoring in a very high-finesse optical cavity the displacements of a mirror with a sensitivity at the 10-20m/√Hz level. This unique sensitivity is a step towards the first observation of the fundamental quantum effects of radiation pressure and the resulting standard quantum limit in interferometric measurements. Our experiment may become a powerful facility to test quantum noise reduction schemes, and we already have demonstrated radiation-pressure induced correlations between two optical beams sent into the same moving mirror cavity. Our scheme can be extended down to the quantum level and has applications both in high-sensitivity measurements and in quantum optics.

Improving the read-out of the resonance frequency of nanotube mechanical resonators

We report on an electrical detection method of ultrasensitive carbon nanotube mechanical resonators. The noise floor of the detection method is reduced using a RLC resonator and an amplifier based on a high electron mobility transistor cooled at 4.2 K. This allows us to resolve the resonance frequency of nanotube resonators with an unprecedented quality. We show that the noise of the resonance frequency measured at 4.2 K is limited by the resonator itself, and not by the imprecision of the measurement. The Allan deviation reaches ~10^-5 at 125 ms integration time. When comparing the integration time dependence of the Allan deviation to a power law, the exponent approaches ~1/4. The Allan deviation might be limited by the diffusion of particles over the surface of the nanotube. Our work holds promise for mass spectrometry and surface science experiments based on mechanical nano-resonators.

Brownian fluctuations of carbon nanotube resonators

Carbon nanotube mechanical resonators hold an exceptional sensing potential, relying on their extremely low mass. As a consequence, the fundamental thermal forces are transduced into very large motion fluctuations. However, the most basic properties of these fluctuations remain poorly understood. Here we couple the motion of nanotube-based resonators to a free propagating electron beam to demonstrate that singly-clamped nanotube resonators undergo thermally-driven Brownian motion.

Optomecanical correlations and sensitivity improvement by backaction amplification

We present our experiments devoted to the observation of quantum radiation-pressure effects and to quantum-noise reduction schemes. We have demonstrated optomechanical correlations between two independent laser beams, and a backaction amplification scheme.