The GEO600 squeezed light source

Henning Vahlbruch (1) , Alexander Khalaidovski (1) , Nico Lastzka (1) , Christian Gräf (1) , Karsten Danzmann (1) , Roman Schnabel (1)

1 AEI - Max-Planck-Institut für Gravitationsphysik ( Albert-Einstein-Institut )

The next upgrade of the GEO 600 gravitational wave detector is scheduled for 2010 and will, in particular, involve the implementation of squeezed light. The required nonclassical light source is assembled on a 1.5 m 2 breadboard and includes a full coherent control system and a diagnostic balanced homodyne detector. Here, we present the first experimental characterization of this setup as well as a detailed description of its optical layout. A squeezed quantum noise of up to 9 dB below the shot-noise level was observed in the detection band between 10 Hz and 10 kHz. We also present an analysis of the optical loss in our experiment and provide an estimation of the possible non-classical sensitivity improvement of the future squeezed light enhanced GEO 600 detector. 1. Introduction Photon shot-noise is a limiting noise source in laser interferometric gravitational wave (GW) detectors. The signal to shot-noise ratio can be improved by increasing the laser power. For this reason the planned Advanced LIGO detectors are designed to store about a megawatt of optical power inside the interferometer arms [ 1 ]. At such high laser powers thermally induced optical waveform distortion due to light absorption and the excitation of parasitic instabilities might become an issue [ 2, 3 ]. Alternatively, the signal to shot-noise ratio can also be improved by 'squeezing ' the shot-noise as proposed by Caves in 1981 [ 4 ]. In this case, the laser power inside the interferometer is not increased. In order to squeeze the shot-noise of a Michelson interferometer that is operated close to a dark fringe, squeezed (vacuum) states of light have to be injected into the signal output port. A squeezed state is a quantum state whose uncertainty in one of the field quadratures is reduced compared to the vacuum state, while the noise in the conjugate quadrature is increased. Later it was realized that squeezed states of light can also be used to reduce the overall quantum noise in interferometers including radiation pressure noise, thereby beating the standard-quantum-limit (SQL) [ 5, 6 ]. Theoretical analysis of Gea-Banacloche and Leuchs [ 7 ] and Harms et al. [ 8, 9 ] suggested that squeezing is broadly compatible with interferometer recycling techniques [ 10, 11 ] thereby further promoting the application of squeezed states in GW-detectors. The first observation of squeezed states was done by Slusher et al. [ 13 ] in 1985. Since then different techniques for the generation of squeezed light have evolved. One of the most successful approaches for squeezed light generation is optical parametric amplification (OPA), also called parametric down-conversion, based on second-order nonlinear crystals. Common materials like MgO:LiNbO 3 or periodicly poled potassium titanyl phosphate (PPKTP) can be used to produce

Mots clés: Physical Sciences

Henning Vahlbruch, Alexander Khalaidovski, Nico Lastzka, Christian Gräf, Karsten Danzmann, et al.. The GEO600 squeezed light source. Classical and Quantum Gravity, 2010, 27 (8), pp.84027. ⟨10.1088/0264-9381/27/8/084027⟩. ⟨hal-00587619⟩