T Kippenberg
​SEM figure of an nano-optomechanical system for implementing real time quantum feedback of a mechanical oscillator​​​​​

This seminar is CANCELLED: Quantum feedback of a mechanical oscillator

The colloquim by Tomas Kippenberg, Institute of Physics, scheduled on 19 March, has been cancelled due to the corona virus situation.​

In real-time quantum feedback protocols (1), the record of a continuous measurement is used to stabilize a desired quantum state. Recent years have seen spectacular advances in a variety of well-isolated micro-systems, including microwave photons(2) and superconducting qubits(3). By contrast, the ability to stabilize the quantum state of a tangibly massive object, such as a nano-mechanical oscillator, remains a difficult challenge. The main obstacle is environmental decoherence, which places stringent requirements on the timescale in which the state must be  measured. Using cavity optomechanical coupling(4, 5) we report on a position sensor that is capable of resolving the zero-point motion of a solid-state, 4.3 MHz frequency nanomechanical oscillator in the timescale of its thermal decoherence(6), a basic requirement for preparing its ground-state using feedback as well as (Markovian) quantum feedback. The sensor is based on evanescent coupling to a high-Q optical microcavity(7), and achieves an imprecision 40 dB below that at the standard quantum limit for a weak continuous position measurement(8), while maintaining an imprecision-back-action product within a factor of 5 of the Heisenberg uncertainty limit. As a demonstration of its utility, we use the measurement as an error signal with which to feedback cool the oscillator. Using radiation pressure as an actuator, the oscillator is cold-damped(9) with unprecedented efficiency: from a cryogenic bath temperature of 4.4 K to an effective value of 1.1 mK, corresponding to a mean phonon number of 5 (i.e., a ground state probability of 16%). The measurement reveals strong backaction-imprecision correlations, which we observe as quantum mechanical sideband asymmetries, as well as pondermotive squeezing of the light field(10). Our results set a new benchmark for the performance of a linear position sensor, and signal the emergence of mechanical oscillators as practical subjects for measurement-based quantum control.  We moreover demonstrate the existence of such quantum correlations due to the optomechanical interaction at room temperature (11) and demonstrate that the correlations enable quantum enhanced force sensing (termed “variational measurements”). This scheme, rather than utilizing squeezed vacuum, uses the quantum correlations produced in the interferometer for enhanced force sensing. Closing, we will describe recent progress which uses soft clamping and strain engineering, which has enabled to attain mechanical quality factor exceeding 800 million at room temperature, implying a mechanical oscillator undergoing more than hundreds of oscillations during the thermal decoherence time. These results signal the emergence of room temperature quantum feedback, and room temperature quantum control of mechanical oscillators. Time permitting, I will also show emerging hybrid optomechanical technologies, ranging from non-reciprocal photonic circuits using optomechanics, to quantum limited amplifiers based on ground state cooled mechanical oscillators.
1. H. Wiseman, Quantum theory of continuous feedback. Physical Review A 49, 2133 (1994).
2. C. Sayrin et al., Real-time quantum feedback prepares and stabilizes photon number states. Nature 477, 73 (Sep 1, 2011).
3. R. Vijay et al., Stabilizing Rabi oscillations in a superconducting qubit using quantum feedback. Nature 490, 77 (Oct 4, 2012).
4. T. Kippenberg, H. Rokhsari, T. Carmon, A. Scherer, K. Vahala, Analysis of Radiation-Pressure Induced Mechanical Oscillation of an Optical Microcavity. Physical Review Letters 95,  (2005).
5. M. Aspelmeyer, T. J. Kippenberg, F. Marquardt, Cavity optomechanics. Reviews of Modern Physics 86, 1391 (December 30, 2014, 2014).
6. D. J. Wilson et al., Measurement and control of a mechanical oscillator at its thermal decoherence rate. Nature doi:10.1038/nature14672,  (2015, 2014).
7. E. Gavartin, P. Verlot, T. J. Kippenberg, A hybrid on-chip optomechanical transducer for ultrasensitive force measurements. Nature nanotechnology 7, 509 (Aug, 2012).
8. A. A. Clerk, M. H. Devoret, S. M. Girvin, F. Marquardt, R. J. Schoelkopf, Introduction to quantum noise, measurement, and amplification. Reviews of Modern Physics 82, 1155 (2010).
9. M. Pinard, P. Cohadon, T. Briant, A. Heidmann, Full mechanical characterization of a cold damped mirror. Physical Review A 63,  (2000).
10. V. Sudhir, D. Wilson, A. Ghadimi, T. J. Kippenberg, Appearance and disappearance of quantum correlations in measurement-based feedback control of a mechanical oscillator. Phys. Rev.  X  (2017).
11. V. Sudhir, D. Wilson,  T. J. Kippenberg, Room temperature quantum correlations of a mechanical oscillator. Phys. Rev.  X  (2017).
12. A. Ghadimi et al., Elastic strain engineering for ultralow mechanical dissipation, Science (2018)

​Coff​e will be served from 15:00 followed by the colloquium at 15:15
Category Seminar; Lecture; Colloquium
Location: Kollektorn, lecture room, Kemivägen 9, MC2-huset
Starts: 19 March, 2020, 15:15
Ends: 19 March, 2020, 16:00

Published: Wed 18 Mar 2020.