Probing Two-Dimensional Quantum Fluids with Cavity Optomechanics by Yauhen Sachkou

Author:Yauhen Sachkou
Language: eng
Format: epub
ISBN: 9783030527662
Publisher: Springer International Publishing

We next investigate the effect of the heat generated due to optical absorption on the microtoroid temperature. To do so, we determine the temperature of the microtoroid mechanical mode as a function of the laser power. The temperature is obtained through integrating the power spectral density of the flexural mode and is observed to grow with rising laser power. Increasing optical heat results in thermal effects that degrade the system above certain threshold. In the case of our superfluid —based system this thermal degradation corresponds to boil-off of the superfluid film, as shown in Fig. 3.4b. First, while the laser power is increased over two orders of magnitude from 10 nW to 2.1 W, the microtoroid mode temperature grows only modestly from 510 to 730 mK. However, when the laser power is further increased above 2.2 W, the mechanical mode temperature exhibits an abrupt jump to about 3 K, which is indicated by the shaded area in Fig. 3.4b. This threshold is a consequence of the upper limit on the superfluid flow rate through the narrowest point of the pedestal which is dependent upon the optical heat power (see Sect. 3.2.2). The maximal flow rate through the junction between the pedestal and the microtoroid dictates the maximal optical thermal load which can be balanced out by the superfluid film. Plugging in the boil-off power of W into Eq. (3.15) for the flow velocity through the constriction point of the pedestal, yields 30 m/s, that is in the vicinity of the superfluid critical velocity beyond which superfluidity breaks down and the superfluid flow ceases to be dissipationless. This causes a thermal run-away process, whereby the superfluid at the outer boundary of the resonator can no longer be replenished at the same rate as it evaporates and, hence, boils off entirely. As a result, thermalization of the microtoroid breaks and the resonator is no longer thermally anchored to the cryostat through the efficient superfluid link, but rather through the thermal conductance of its silicon pedestal, with its final temperature dominated by the optically generated heat.

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