Speedmeter: Quantum back-action noise-free interferometry for improving the science capabilities of future gravitational wave observatories

The discoveries enabled by observations of gravitational waves (GW) from merging black holes and neutron stars provided us with a stunning glimpse of the immense potential of GW multi-messenger astronomy and cosmology.

In order to discover new phenomena and better understand the constituents of the Universe and the forces driving it, it is vital to improve the sensitivity of future GW observatories.

Indeed, to maximise the observation capacity of future GW observatories such as the Einstein Telescope (ET) it is imperative to go beyond the current quantum noise limit imposed by the uncertainty relation originating from a continuous position measurement of the interferometer mirrors, i.e. [x(t),x(t')]≠0.

Quantum mechanics provides speedmeter interferometers (SMI) as a more elegant approach: measuring momentum (speed) of the test masses evades the uncertainty limit, i.e. [p(t),p(t')]=0.

However, though SMI have been shown theoretically to offer superior sensitivity compared to currently used Michelson interferometers with squeezed light injection, the SMI concept lags behind in technical readiness and hence is currently not yet considered mature enough to build the baseline for ET.This grant will enable me to change this.

In particular I will focus on two novel SMI concepts, we invented and which (in contrast to earlier SMI concepts) are easily implementable into current long-baseline interferometers.

The main objectives of this proposal are: 1) development of the required new optical components and quantum noise analysis tools; 2) experimental demonstration, initially in proof-of-concept table-top experiments, followed by implementation in ETpathfinder, a unique cryogenic interferometer test facility; 3) verification of the SMI concept with complementary quantum technologies such as squeezed light; 4) development of a detailed SMI practical design for ET including a science case detailing possible improvements in astrophysics, cosmology and fundamental physics.