Quantum enhanced feedback cooling of a mechanical oscillator using nonclassical light

Abstract

Laser cooling is a fundamental technique used in primary atomic frequency standards, quantum computers, quantum condensed matter physics and tests of fundamental physics, among other areas. It has been known since the early 1990s that laser cooling can, in principle, be improved by using squeezed light as an electromagnetic reservoir; while quantum feedback control using a squeezed light probe is also predicted to allow improved cooling. Here we show the implementation of quantum feedback control of a micro-mechanical oscillator using squeezed probe light. This allows quantum-enhanced feedback cooling with a measurement rate greater than it is possible with classical light, and a consequent reduction in the final oscillator temperature. Our results have significance for future applications in areas ranging from quantum information networks, to quantum-enhanced force and displacement measurements and fundamental tests of macroscopic quantum mechanics.

Enhancing Sideband Cooling by Feedback-Controlled Light

“…Negative feedback has also been successfully employed in mechanical [11][12][13], and cavity optomechanical systems [4], where an electromagnetic field is used to probe a mechanical resonator, and in turn to control the feedback actuator, which acts directly on the mechanical oscillator. Engineered light fluctuations in the form of squeezed light have also been used in optomechanical systems to improve both the detection sensitivity [14][15][16][17] and the cooling efficiency [18][19][20]. In the present work we show that it is possible to manipulate, with a feedback system [see Figure 1 (a)], the fluctuations of the laser field that drives an optomechanical system to enhance optomechanical sideband cooling [21][22][23][24].…”

“…where we have neglected the second term in the expression for ζ (0) c (ω) which appears in the numerator of Eq. (18). Instead for frequencies ω ∼ −∆ we find…”

Cavity optomechanics with feedback-controlled in-loop light

“…Using the expressions for the photocurrent and for the in-loop operators in Eqs. (12) and (18), respectively, we find…”

Quantum optomechanical transducer with ultrashort pulses

“…Cooling the phonon number to this level is achievable within the sideband unresolved regime using different techniques such as active feedback cooling [58], hybrid systems [59], optomechanically induced transparency [46] or dissipative optomechanics [60]. Experimentally, feedback cooling has allowed for an occupancy of n 0 =5 of a mechanical oscillator [61,62] which can be improved to yield ground state cooling using a higher detection efficiency or using squeezed state probing [63]. These experiments on near ground state cooling have been performed in a 4 K cryostat, but with the development of new high-Q mechanical oscillators [64][65][66], ground state cooling in a room temperature environment is within reach.…”