Abstract
The sensitivity of laser interferometers can be pushed into regimes that enable the direct observation of the quantum behaviour of mechanical oscillators. In the past, membranes with subwavelength thickness (thin films) have been proposed to be high-mechanical-quality, low-thermal-noise oscillators. Thin films from a homogeneous material, however, generally show considerable light transmission accompanied by heating due to light absorption, which potentially limits quantum opto-mechanical experiments, in particular at low temperatures. In this paper, we experimentally analyse a Michelson–Sagnac interferometer including a translucent silicon nitride (SiN) membrane with subwavelength thickness. We found that such an interferometer provides an operational point that is optimally suited for quantum opto-mechanical experiments with translucent oscillators. In the case of a balanced beam splitter of the interferometer, the membrane can be placed at a node of the electro-magnetic field, which simultaneously provides lowest absorption and optimum laser noise rejection at the signal port. We compare the optical and mechanical models of our interferometer with experimental data and confirm that the SiN membrane can be coupled to a laser power of the order of 1 W at 1064 nm without significantly degrading the membrane's quality factor of the order of 106, at room temperature.
Highlights
Quantum fluctuations of a light field couple to the motion of macroscopic test mass mirrors via momentum transfer of reflected photons, leading to back action noise for a position measurement [1, 2, 3, 4]
Forthcoming 2nd generation interferometric gravitational wave detectors such as Advanced LIGO [5], Advanced Virgo [6], GEOHF [7] and LCGT [8] will be limited by quantum noise in most of their detection band
The observation of quantum radiation pressure will enable to test the principle of back-action noise in a continuous position measurement
Summary
Quantum fluctuations of a light field couple to the motion of macroscopic test mass mirrors via momentum transfer of reflected photons, leading to back action noise for a position measurement [1, 2, 3, 4]. One major adversary for high precision experiments targeting the quantum regime is thermal noise caused by mechanical dissipation related to optical multilayer coatings [11, 12] Avoiding such coatings comes at the expense of low reflectivity, which raises the need of novel interferometer topologies. If a semi-transparent component is used (e.g. SiN membranes with a reflectivity ≤ 40 % at a laser wavelength of 1064 nm) as common end mirror for the two arms of a Michelson interferometer the transmitted light forms a Sagnac interferometer This Michelson-Sagnac interferometer is compatible with advanced interferometer techniques such as power-recycling and signal-recycling [17, 18], which potentially increase optomechanical coupling as investigated in Ref. At its dark fringe, which will enable the implementation of advanced interferometer techniques
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