Cooling by measurement


Observing a physical quantity without disturbing it is a key capability for the control of individual quantum systems. Such back-action-evading or quantum non-demolition measurements were first introduced in the 1970s for gravitational wave detection, and now such techniques are an indispensable tool throughout quantum science.

Researchers of the University of Vienna have now implemented a back-action-evading interaction for measuring the position of a micromechanical oscillator. Following a scheme that they had suggested two years ago [PNAS USA 108, 16182 (2011)] Michael Vanner and colleagues use pulses of light with a duration much shorter than a period of mechanical motion, which allows state preparation and full state tomography of the mechanical motional state. They have reconstructed mechanical states with a position uncertainty reduced to 19 pm, limited by the quantum fluctuations of the optical pulse, and they have performed ‘cooling-by-measurement’ to reduce the mechanical mode temperature from an initial 1,100 K to 16 K. Future improvements to this technique will allow for quantum squeezing of mechanical motion, even from room temperature, and reconstruction of non-classical states exhibiting negative phase-space quasi-probability.




Cooling-by-measurement and mechanical state tomography via pulsed optomechanics; M. R. Vanner, J. Hofer, G. D. Cole, M. Aspelmeyer; Nature Communications 4, 2295 (2013)