Applied Physics Seminar

Achieving non-classical states of a mesoscopic mechanical oscillator has been an important goal of the quantum physics community for several decades. With rapid progress in micro- and nano-fabrication techniques in the past ten years, this goal is now feasible in a diverse range of physical architectures[1]. Such capabilities have potential for both experimental tests of longstanding scientific problems such as quantum gravity and quantum nonlinear dynamics, and far-reaching applications in metrology and quantum information. Here, we report progress towards achieving non-classical states via real-time quantum control; where mechanical nonlinearities are used to engineer the states, and high quantum efficiency mechanical transduction and feedback control are used to stabilize the process.

Our experimental system is a hybrid opto-electromechanical device consisting of a microtoroidal resonator with ultrasensitive opto-mechanical transduction at the level of 10-18m/Hz1/2 and strong electro-mechanical actuation achievable via electrical gradient forces[2]. Applying a gradient force at twice the mechanical resonance frequency allows mechanical parametric amplification. Just below parametric threshold, a noiseless phase sensitive amplification process occurs which squeezes the mechanical motion. By including weak measurement, optimal estimation, and feedback the well known 3 dB limit for intracavity squeezing can be surpassed, and in principle arbitrarily strong squeezing achieved [3].

In efforts to demonstrate this prediction, we have experimentally achieved parametric electric gradient forces at the level of mN[4]. Although a further factor of 20 is required to achieve parametric amplification threshold, such forces are sufficient to implement strong feedback control of the mechanical motion; and thereby cool[2], heat[5], or stabilize it. We utilize this feedback control to stabilize the parametric instability in our optomechanical system. This allows the barrier placed by parametric instability on intracavity optical power to be overcome, and hence enables enhanced transduction sensitivity.

[1] Kippenberg and Vahala, Science 321 1172 (2008). [2] K. H. Lee et al, Phys. Rev. Lett. 104, 123604 (2010). [3] A. Szorkovszky, A. C. Doherty, G. I. Harris, W. P. Bowen,arXiv:1107.1294 [4] T. G. McRae et al, Phys. Rev. A, 82, 023825 (2010). [5] M. A. Taylor, et al, arXiv:1107.0779