Thermoelastic effects at low temperatures and quantum limits in displacement measurements - art. no. 082003

The displacement fluctuations of mirrors in optomechanical devices, induced via thermal expansion by temperature fluctuations due either to thermodyna mic fluctuations or to fluctuations in the photon absorption, can be made s maller than quantum fluctuations, at the low temperatures, high reflectivit ies, and high light powers needed to readout displacements at the standard quantum limit. The result is relevant for the design of quantum-limited gra vitational-wave detectors, both "interferometers" and "bars," and for exper iments to study directly mechanical motion in the quantum regime.