Laser Interferometry and Nonclassical Light

Michelson interferometer with signal and power recyclingLaser interferometry is a powerful tool for the precise measurement of distance changes. The currently operating gravitational wave detectors are Michelson laser interferometers and have a noise spectral density of as low as 10-19 m/sqrt(Hz). These devices are able to detect changes of the distance between two mirrors of just one billionth of the diameter of the hydrogen atom. Note that this high sensitivity is reached if the distance changes are periodic for about a second or longer and if they have periods on the millisecond timescale. Inspirals of two neutron stars or two small black holes are supposed to produce gravitational waves with such properties.
The sensitivity of laser interferometers is limited by the quantum noise of light. The quantum noise can be reduced and laser interferometers be improved by using squeezed light. Squeezed light shows reduced (squeezed) quantum noise: Its quantum noise (in one of its field quadratures) is lower than the quantum noise of the light mode’s ground state. The latter is also called the vacuum noise.


Squeezed Light SourceThe Quantum Interferometry Group develops squeezed-light sources and has designed and assembled the GEO600 squeezed-light laser.

New topologies for laser interferometers are researched experimentally. Theoretical work is done in collaboration with Y. Chen (CalTech).


The QI-Group generates and characterizes entangled laser fields for interferometric measurements and develops schemes for tomographic quantum state reconstruction.Wigner function of a squeezed vacuum state

The QI-Group demonstrated the first squeezed light enhanced Michelson interferometer with power- and signal-recycling [Vahlbruch et al. PRL (2005)] and observed for the first time a broadband squeezed field covering the complete detection band of ground-based gravitational wave detectors [Vahlbruch et al. NJP (2007)].


From 2003 to 2009 this research was partially financed by the Sonderforschungsbereich 407, projects B12, B15 and B16.

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