Mirror quiescence and high-sensitivity position measurements with feedback

Abstract

We present a detailed study of how phase-sensitive feedback schemes can be used to improve the performance of optomechanical devices. Considering the case of a cavity mode coupled to an oscillating mirror by the radiation pressure, we show how feedback can be used to reduce the position noise spectrum of the mirror, cool it to its quantum ground state, or achieve position squeezing. Then, we show that even though feedback is not able to improve the sensitivity of stationary position spectral measurements, it is possible to design a nonstationary strategy able to increase this sensitivity.

Relaxation and decoherence in a resonantly driven qubit

“…Thus the relaxation and decoherence can not be suppressed simultaneously with a single resonant driving field. [42,43,44,45,46,47] Nevertheless, as will be demonstrated below, for a special class of initial states, a properly chosen resonant driving field could slow down the decoherence. [64] Since in general the population and coherence of a driven qubit decay with more than one rates, it is necessary to introduce multiple relaxation and decoherence times to describe the system's behavior properly.…”

“…[2,13,14,15,16] The environment-induced decoherence of superconducting qubits has been extensively studied both theoretically [15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33] and experimentally [2,8,13,21,25,34,35,36,37,38,39,40] in the absence of ac driving fields (free decay). Quite a few proposals, such as dynamical decoupling, [41,42,43,44,45,46,47,48] decoherence free subspaces, [49,50,51,52] spin echoes, [2,7,…”

Nonclassical States of Light and Mechanics

“…Such a state would also be useful in ultrahigh precision measurements or detection of gravitational waves and has been experimentally proven in only one instance for a nonlinear Duffing resonator [7]. Numerous proposals exist and can be categorized as i) direct: modulated drive in optomechanical settings with or without feedback loop [8,9,10,11], and ii) indirect: mapping a squeezed state of light or atoms onto the resonator, coupling to a cavity with atomic medium within [12], coupling to a Cooper pair box [13] or a superconducting quantum interference loop [14,15]. In the following we take the example of state transfer in a pure optomechanical setup where laser cooling of a mirror/membrane via a strong laser is accompanied by squeezing transfer from a squeezed vacuum second input light field [16].…”

Overcoming quantum noise in optical fibers

“…Recall that T = X/v, τ = (∆/v) and we assumed τ ∼ ε. The coupling strength α is typically of order unity [7,23]; we shall set α = 1. We take v = c/1.6, the speed of light in a typical fiber, and δ(T ) = 10 −4 .…”