DFG-NSF: Demonstration of position and speed measurements in the quantum non-demolition regime towards a new gravitational-wave detector topology
Final Report Abstract
Gravitational-wave (GW) observatories are laser interferometers that measure the alternating stretching and shrinking of space-time volume caused be remote astrophysical events such as black-hole and neutron-star mergers. The sensitivity of GW observatories is limited to a large extent by the quantum uncertainty of the laser light, which produces photon counting noise at the detection photo diode and photon radiation pressure noise on the mirrors that reflect the light. In principle, the signal-to-quantum-noise ratio can be arbitrarily improved by increasing the power of the laser light and simultaneously increasing the mass of the pendulum suspended mirrors. In addition, the kilometer-size dimension of these observatories might be further increased. All these approaches are extremely cost-intensive, and other options need to be researched and developed. This project researched the idea to monitor not the distance between mirrors but the speed at which the distance changes. Such an interferometer is called a ‘speedmeter’. Its fundamental advantage is that the light’s photon radiation pressure noise on the mirrors cancel to a large extent. In the language of quantum physics, one says that ‘speed’ is a quantum nondemolition observable. On top, this project developed new alternative ideas how to reduce the quantum noise in GW observatories. For the investigation of the speedmeter concept, this project developed, built and characterized the optomechanical ring-cavity setup. The special feature of this new interferometer type is the existence of two output ports: one provides the characteristic of a conventional interferometer, the other that of a speedmeter. This feature in principle allows for direct comparison of the two types, which this project indeed proved. It turned out, however, that the optomechanical ring-cavity shows optical-mode splitting, which made it impossible reaching the photon radiation pressure noise regime in this project. This result had impact on the project goals. New and different approaches were theoretically as well as experimentally researched. The project proposed in collaboration with the California Institute of Technology that Einstein-Podolsky-Rosen entangled light can also reduce photon radiation pressure noise. The proof-of-concept experiment was successfully performed in this project in Hamburg. On top, another experiment in this project combined for the first time cryo-cooling of mirrors with the application of quantum-squeezed states of light. While the project’s speedmeter results may influence the design of second-next generation GW observatories, the results on entangled and quantum-squeezed interferometers will have impact already on the designs of next-generation GW observatories, such as the European ‘Einstein Telescope’.
Publications
- Beating the Standard Sensitivity-Bandwidth Limit of Cavity-Enhanced Interferometers with Internal Squeezed- Light Generation, Phys. Rev. Lett. 118, 143601 (2017)
M. Korobko, L. Kleybolte, S. Ast, H. Miao, Y. Chen, and R. Schnabel
(See online at https://doi.org/10.1103/PhysRevLett.118.143601) - Proposal for gravitational-wave detection beyond the standard quantum limit through EPR entanglement, Nature Phys. (2017)
Y. Ma, H. Miao, B.H. Pang, M. Evans, C. Zhao, J. Harms, R. Schnabel and Y. Chen
(See online at https://doi.org/10.1038/nphys4118) - Squeezed states of light and their applications in laser interferometers, Physics Reports 684, 1–51 (2017)
R. Schnabel
(See online at https://doi.org/10.1016/j.physrep.2017.04.001) - Coherent coupling completing an unambiguous optomechanical classification framework, Phys. Rev. A 100 (5), 053855 (2019)
X. Li, M. Korobko, Y. Ma, R. Schnabel, and Y. Chen
(See online at https://doi.org/10.1103/PhysRevA.100.053855) - Quantum expander for gravitationalwave observatories. Light Sci. Appl. 8, 118 (2019)
M. Korobko, Y. Ma, Y. Chen, and R. Schnabel
(See online at https://doi.org/10.1038/s41377-019-0230-2) - Demonstration of interferometer enhancement through EPR entanglement, Nat. Photonics 14, 240 (2020)
J. Südbeck, S. Steinlechner, M. Korobko, and R. Schnabel
(See online at https://doi.org/10.1038/s41566-019-0583-3)
