Quantum noise reduction for new-generation gravitational-wave detectors


Second generation gravitational wave (GW) detectors opened era of gravitational wave astronomy with the first GW detection in 2015 and are now approaching their design sensitivity. During the 3 past observations runs, they detected 90 GW signals produced by the merging of binary compact objects, providing a wealth of scientific results ranging from the general relativity, to astrophysics and cosmology.
New generation of gravitational wave (GW) detectors, including the European Einstein Telescope (ET), are currently under study, with the goal of a tenfold improvement of the sensitivity with respect to LIGO and Virgo. This will allow investigating fundamental open questions as the nature of gravitation and dark energy, the properties of nuclear matter and the formation of neutron star and black-hole through the cosmic history.
A key-technology to reduce the quantum noise, one of the main limitations of detector sensitivity, is the so-called “squeezing”. Since quantum noise is imposed by vacuum fluctuations entering the detector from its output port (also called “antisymmetric”), it can be mitigated by replacing the vacuum with a “squeezed” vacuum, whose fluctuations are redistributed among the phase and the amplitude of the field. Squeezed states, produced by quantum correlations obtained using non-linear crystals, have already been used in Virgo and LIGO, providing a remarkable sensitivity increase in the high-frequency part of the detector bandwidth. In the next future, a more sophisticated "frequency-dependent squeezing”, will be used to mitigate quantum noise in the whole detection bandwidth, by reflecting the squeezed states off a 300-m optical cavity. This technique will need to be further adapted to Einstein Telescope and will need more than a simple filter cavity.
The PhD project aims to demonstrate the optimization of this squeezing technique of Einstein Telescope.
The candidate will study, at first in simulation, two alternative filter cavity configurations and then will experimentally demonstrate the most promising one with a table-top experiment. The overall goal of the project will be the design of a FDS source optimized for ET, and the demonstration of a squeezing source adapted to 3rdgeneration detectors.


Matteo Barsuglia, Eleonora Capocasa






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