title: Quantum Backaction Evading Measurement of Collective Mechanical Modes.
abstract: The standard quantum limit constrains the precision of an oscillator position measurement. It arises from a balance between the imprecision and the quantum backaction of the measurement. However, a measurement of only a single quadrature of the oscillator can evade the backaction and be made with arbitrary precision. Here we demonstrate quantum backaction evading measurements of a collective quadrature of two mechanical oscillators, both coupled to a common microwave cavity. The work allows for quantum state tomography of two mechanical oscillators, and provides a foundation for macroscopic mechanical entanglement and force sensing beyond conventional quantum limits.
authors.affiliation: Department of Applied Physics, Aalto University, P.O. Box 15100, FI-00076 AALTO, Finland.
authors.forename: C F
authors.initials: CF
authors.lastname: Ockeloen-Korppi
authors.affiliation: Department of Applied Physics, Aalto University, P.O. Box 15100, FI-00076 AALTO, Finland.
authors.forename: E
authors.initials: E
authors.lastname: Damskägg
authors.affiliation: Department of Applied Physics, Aalto University, P.O. Box 15100, FI-00076 AALTO, Finland.
authors.forename: J-M
authors.initials: JM
authors.lastname: Pirkkalainen
authors.affiliation: Department of Physics, McGill University, 3600 rue University, Montréal, Quebec H3A 2T8, Canada.
authors.forename: A A
authors.initials: AA
authors.lastname: Clerk
authors.affiliation: School of Engineering and Information Technology, UNSW Canberra, Australian Capital Territory 2600, Australia.
authors.forename: M J
authors.initials: MJ
authors.lastname: Woolley
authors.affiliation: Department of Applied Physics, Aalto University, P.O. Box 15100, FI-00076 AALTO, Finland.
authors.forename: M A
authors.initials: MA
authors.lastname: Sillanpää