We describe measurements of the motional sidebands produced by a mechanical oscillator (with effective mass 43 ng and resonant frequency 705 kHz) placed in an optical cavity and cooled close to its quantum ground state. The red and blue sidebands (corresponding to Stokes and anti-Stokes scattering) from a single laser beam are recorded simultaneously via a heterodyne measurement. The oscillator’s mean phonon number is inferred from the ratio of the sidebands and reaches a minimum value of 0.84 ± 0.22, corresponding to a mode temperature of T = 28 ± 7 μK. We also infer the mean phonon number from the calibrated area of each sideband and from the oscillator’s total damping. The values inferred from these four methods are in close agreement. The behavior of the sidebands as a function of the oscillator’s temperature agrees well with theory that includes the quantum fluctuations of both the cavity field and the mechanical oscillator.
Multimode optomechanical dynamics in a cavity with avoided crossings
D. Lee,
M. Underwood,
D. Mason,
A.B. Shkarin,
S.W. Hoch,
J.G.E. Harris
Cavity optomechanics offers powerful methods for controlling optical fields and mechanical motion. A number of proposals have predicted that this control can be extended considerably in devices where multiple cavity modes couple to each other via the motion of a single mechanical oscillator. Here we study the dynamic properties of such a multimode optomechanical device, in which the coupling between cavity modes results from mechanically induced avoided crossings in the cavity’s spectrum. Near the avoided crossings we find that the optical spring shows distinct features that arise from the interaction between cavity modes. Precisely at an avoided crossing, we show that the particular form of the optical spring provides a classical analogue of a quantum non-demolition measurement of the intracavity photon number. The mechanical oscillator’s Brownian motion, an important source of noise in these measurements, is minimized by operating the device at cryogenic temperature (500 mK).
Max-Planck-Zentren und -Schulen
Datenerfassung
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