Squeezing the quantum noise of laser light

Light is quantized, and the statistics of the photons results in unpredictable uncertainties of the amplitude and the phase of the light field. This inherent uncertainty results in quantum (shot) noise and limits the phase sensitivity of laser interferometers. However, Heisenberg's famous Uncertainty Relation allows the reduction of phase uncertainty at the expense of increased amplitude noise. In that case the quantum noise of light becomes "squeezed". The figure shows measurement results performed on squeezed states of light [1]. The statistics of measurement results is not symmetrically distributed among amplitude and phase but is squeezed, i.e. represented by an ellipse. This is in contrast to coherent laser light that always provides symmetric, circular quantum noise distributions.
In recent experiments the AEI has achieved a breakthrough regarding squeezed states for quantum noise reduction in future gravitational wave detectors. A 1-meter prototype of the GEO600 configuration with squeezed quantum noise has been demonstrated [2], as well as squeezed states for all the detection frequencies of ground based gravitational wave detectors [3].

[1] S. Chelkowski, H. Vahlbruch, B. Hage, A. Franzen, N. Lastzka, K. Danzmann, and R. Schnabel: Experimental characterization of frequency-dependent squeezed light, Phys. Rev. A 71, 013806 (2005),

[2] H. Vahlbruch, S. Chelkowski, B. Hage, A. Franzen, K. Danzmann, and R. Schnabel: Demonstration of a squeezed light enhanced power- and signal-recycled Michelson interferometer, Phys. Rev. Lett. 95, 211102 (2005),

[3] H. Vahlbruch, S. Chelkowski, B. Hage, A. Franzen, K. Danzmann, and R. Schnabel: Coherent control of vacuum squeezing in the gravitational-wave detection band, Phys. Rev. Lett. 97, 011101 (2006).