title: 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.
authors.affiliation: Department of Physics, Technical University of Denmark, Fysikvej 309, 2800 Kgs Lyngby, Denmark.
authors.forename: Clemens
authors.initials: C
authors.lastname: Schäfermeier
authors.affiliation: Department of Physics, Technical University of Denmark, Fysikvej 309, 2800 Kgs Lyngby, Denmark.
authors.forename: Hugo
authors.initials: H
authors.lastname: Kerdoncuff
authors.affiliation: Department of Physics, Technical University of Denmark, Fysikvej 309, 2800 Kgs Lyngby, Denmark.
authors.forename: Ulrich B
authors.identifier: 0000-0002-7122-8577
authors.initials: UB
authors.lastname: Hoff
authors.affiliation: Department of Physics, Technical University of Denmark, Fysikvej 309, 2800 Kgs Lyngby, Denmark.
authors.forename: Hao
authors.initials: H
authors.lastname: Fu
authors.affiliation: Department of Physics, Technical University of Denmark, Fysikvej 309, 2800 Kgs Lyngby, Denmark.
authors.forename: Alexander
authors.initials: A
authors.lastname: Huck
authors.affiliation: Department of Physics, Technical University of Denmark, Fysikvej 309, 2800 Kgs Lyngby, Denmark.
authors.forename: Jan
authors.initials: J
authors.lastname: Bilek
authors.affiliation: Australian Centre of Excellence for Engineered Quantum Systems, University of Queensland, St Lucia, Queensland 4072, Australia.
authors.forename: Glen I
authors.initials: GI
authors.lastname: Harris
authors.affiliation: Australian Centre of Excellence for Engineered Quantum Systems, University of Queensland, St Lucia, Queensland 4072, Australia.
authors.forename: Warwick P
authors.initials: WP
authors.lastname: Bowen
authors.affiliation: Department of Physics, Technical University of Denmark, Fysikvej 309, 2800 Kgs Lyngby, Denmark.
authors.forename: Tobias
authors.initials: T
authors.lastname: Gehring
authors.affiliation: Department of Physics, Technical University of Denmark, Fysikvej 309, 2800 Kgs Lyngby, Denmark.
authors.forename: Ulrik L
authors.initials: UL
authors.lastname: Andersen