Generation and application of strongly squeezed vacuum states of light
Final Report Abstract
The potential of using squeezed states of light to enhance measurement processes beyond their classical limit has been demonstrated, for example, in spectroscopy experiments, laser-based particle tracking of living cells, to generate entangled quantum states for quantum-dense metrology or to establish universally secure quantum key distribution. The most prominent application of squeezed states of light so far is to increase the sensitivity of gravitational wave (GW) detectors as demonstrated in GEO600 and LIGO. Squeezing enhancement has also become an integral part of the conceptual layout of planned third-generation GW-detectors. For these future generation instruments the aim is to apply squeezed states of light and achieve a level of 10 dB non-classical quantum noise reduction. A prerequisite for such a sensitivity enhancement is a squeezed light source that provides strongly enough squeezed vacuum states of light at the expected GW-frequencies. Todays most efficient squeezed light sources typically employ cavity-enhanced parametric down-conversion, also called optical parametric amplification (OPA), where the interaction between the fundamental and second harmonic fields via a χ(2) -process inside a non-linear crystal produces non-classical photon-pair correlations that yield a reduced noise variance in a certain field quadrature. The objective of this research project was to improve the generated and measured squeezing level beyond current limitations, both at audio-band and MHz Fourier frequencies. In the first experiment a highly efficient squeezed light experiment based on a doubly resonant, nonmonolithic, linear OPA cavity, was realized. With only 7 mW pump power 10 dB squeezing with 11 dB anti-squeezing were measured which are the purest strongly squeezed states observed to date. With an increased pump power up to 15 dB squeezing was measurable for the first time. These states were used for an absolute calibration of the photo-electric external quantum efficiency of a custom-made InGaAs photo diode to 99.5 % with 0.5 % (k = 2) uncertainty at a wavelength of 1064 nm. Since this novel method does not require any reference detector nor the photon flux needs to be known, it is rather a direct measurement of the external quantum efficiency. The experimental setup was extended by the implementation of a coherent control scheme to get access and control to the generated squeezed vacuum states at Fourier frequencies between 10 Hz and 100 kHz. Here, up to 12 dB squeezing was directly measured for the first time and a maximum available squeezing level of 14 dB for downstream application was derived. The experimental setup is fully compatible to current and future GW-detectors. Finally, the first non-classical light enhanced laser power stabilization was demonstrated by substituting the vacuum fluctuations sensed in a classical laser power stabilization scheme by squeezed vacuum states. An improvement of 9.4 dB beyond the classical shot noise limit at Fourier frequencies between 5 and 80 kHz was demonstrated. The observed noise reduction is in good agreement with the theoretical prediction and corresponds to an almost tenfold increase in detected optical power required in a purely classical scheme.
Publications
- Detection of 15 dB Squeezed States of Light and their Application for the Absolute Calibration of Photoelectric Quantum Efficiency. PRL 117, 110801 (2016)
Henning Vahlbruch, Moritz Mehmet, Karsten Danzmann, and Roman Schnabel
(See online at https://doi.org/10.1103/PhysRevLett.117.110801) - Laser Power Stabilization beyond the Shot Noise Limit Using Squeezed Light. PRL 121, 173601 (2018)
Henning Vahlbruch, Dennis Wilken, Moritz Mehmet, and Benno Willke
(See online at https://doi.org/10.1103/PhysRevLett.121.173601) - High-efficiency squeezed light generation for gravitational wave detectors. Class. Quantum Grav. 36, 015014 (8pp) (2019)
Moritz Mehmet and Henning Vahlbruch
(See online at https://doi.org/10.1088/1361-6382/aaf448)
