Employing the principle of quantum teleportation in gravitational-wave detectors provides a method to address technical challenges associated with implementing quantum filters for squeezed-light injection. A recent proposal [Phys. Rev. A 110, 022601] has shown that an arbitrary number of effective squeezing-angle rotations can be achieved by cascading quantum teleportation, yielding sensitivity equivalent to frequency-dependent prefiltering. A natural question is whether the teleportation-based protocol can also realize frequency-dependent postfiltering. In this work, we examine this possibility and show that, with perfect teleportation fidelity, postfiltering can be fully implemented. In practice, however, various imperfections make the sensitivity nearly equivalent to that of teleportation-based prefiltering. We apply this scheme to the low-frequency detector in the Einstein Telescope xylophone configuration and find that teleportation-based postfiltering could also be a candidate for the detector's design.
Employing the principle of quantum teleportation in gravitational-wave detectors provides a method to address technical challenges associated with implementing quantum filters for squeezed-light injection. A recent proposal [Phys. Rev. A 110, 022601] has shown that an arbitrary number of effective squeezing-angle rotations can be achieved by cascading quantum teleportation, yielding sensitivity equivalent to frequency-dependent prefiltering. A natural question is whether the teleportation-based protocol can also realize frequency-dependent postfiltering. In this work, we examine this possibility and show that, with perfect teleportation fidelity, postfiltering can be fully implemented. In practice, however, various imperfections make the sensitivity nearly equivalent to that of teleportation-based prefiltering. We apply this scheme to the low-frequency detector in the Einstein Telescope xylophone configuration and find that teleportation-based postfiltering could also be a candidate for the detector's design.
Abstract Ground-based interferometric gravitational wave detectors are highly precise sensors for weak forces, limited in sensitivity across their detection band by quantum fluctuations of light. Current and future instruments address this limitation by injecting frequency-dependent squeezed vacuum into the detection port, utilizing narrow-band, low-loss optical cavities for optimal rotation of the squeezing ellipse at each signal frequency. This study introduces a novel scheme employing the principles of quantum teleportation and entangled states of light. It allows achieving broadband suppression of quantum noise in detuned signal recycled-Fabry-Perot--Michelson interferometers, which is the baseline design of the low-frequency detector within the Einstein Telescope xylophone detector, without requiring additional filter cavities or modifications to the core optics of the main interferometer.
Abstract We propose several quantum noise reduction schemes for gravitational-wave detectors based on quantum teleportation. Gravitational-wave detectors, as highly precise displacement-measurement devices, are ultimately limited by quantum shot noise and radiation pressure noise. The trade-off between these two noise sources imposes the so-called standard quantum limit (SQL), as a natural consequence of Heisenberg’s uncertainty principle. Numerous schemes to enhance the quantum noise- limited sensitivity beyond the SQL have been proposed, some of which require nontrivial modifications to the basic Michelson configuration of the detectors. Recently, it has been found that the principles of quantum teleportation can solve this issue; the detector’s sensitivity can be enhanced beyond the SQL at minimal cost via parallel processing, which is a key concept in quantum information processing. We theoretically demonstrate ways to implement quantum teleportation in (1) frequency-dependent squeezing [1] and (2) quantum speed measurement [2], without requiring additional infrastructure or the manufacture of optics. We conclude that these ideas can be viable candidates for future detectors.
Gravitational-wave detectors use state-of-the-art quantum technologies to reduce the noise induced by vacuum fluctuations, via injection of squeezed states of light. Future detectors, such as Einstein Telescope, may require the use of two filter cavities or a three-mirror coupled filter cavity to achieve a complex rotation of the squeezing ellipse, in order to reduce the quantum noise over the whole detector bandwidth. In this work, we compare the theoretical feasibility and performances of these two optical layouts and their resilience with respect to different degradation sources (optical losses, mismatching, locking precision), analytically and numerically. We extend previous analysis on squeezing degradation and find that the coupled cavity scheme provides similar or better performances than the two-cavity option, in terms of resilience with respect to imperfections and optical losses. We further highlight the role of mode-mismatch phases in limiting squeezing. Finally, we propose a possible two-step implementation scheme for Einstein Telescope using a single filter cavity that can be possibly upgraded into a coupled filter cavity.
The first detection of gravitational waves by the Laser Interferometer Gravitational-Wave Observatory (LIGO) in 2015 launched the era of gravitational-wave astronomy. The quest for gravitational-wave signals from objects that are fainter or farther away impels technological advances to realize ever more sensitive detectors. Since 2019, one advanced technique, the injection of squeezed states of light, is being used to improve the shot-noise limit to the sensitivity of the Advanced LIGO detectors, at frequencies above ∼50 Hz. Below this frequency, quantum backaction, in the form of radiation pressure induced motion of the mirrors, degrades the sensitivity. To simultaneously reduce shot noise at high frequencies and quantum radiation pressure noise at low frequencies requires a quantum noise filter cavity with low optical losses to rotate the squeezed quadrature as a function of frequency. We report on the observation of frequency-dependent squeezed quadrature rotation with rotation frequency of 30 Hz, using a 16-m-long filter cavity. A novel control scheme is developed for this frequency-dependent squeezed vacuum source, and the results presented here demonstrate that a low-loss filter cavity can achieve the squeezed quadrature rotation necessary for the next planned upgrade to Advanced LIGO, known as "A+."
Quantum noise is one of the limiting factors in laser-interferometric gravitational-wave (GW) detectors. The application of squeezed states in these interferometers allows the reduction of quantum noise in one quadrature. Due to opto-mechanical coupling in a GW detector the squeezed quadrature needs to be rotated within the spectrum to achieve a broadband noise reduction. So far, the implementation of additional filter cavities is considered that allow for the optimal, frequency-dependent rotation of the squeezed quadrature. However, these cavities need to have low loss, a length in the order of \unit[100]{m} and must be situated in the vacuum system, making them cost-intensive. In 2017, Ma and coworkers proposed a scheme for the broadband quantum-noise reduction without the need of additional filter cavities. It was shown by Brown et al. that a similar scheme can be used to broadband-enhance interferometers with a detuned signal-recycling cavity. Here, we performed a proof-of-principle experiment of the proposal on a table-top-scale. Squeezed states were produced detuned to the carrier field of a \unit[2.5]{m}-linear cavity and read out in a bichromatic homodyne detection. The frequencies of the lower and upper local oscillator were at entangled sidebands of the squeezed field. Depending on the relations between the involved frequencies, we can address both variants of the proposal. We show, that the frequency-dependences of the resulting noise spectra fit to a theoretical model we derived from the theory used by Ma et al. With this work we set the path towards an implementation of these schemes in a GW-detector prototype, where the compatibility of the approach with a low-frequency suspended interferometer can be tested. Moreover, we used the same setup to show nonclassical interferometer enhancement at low frequencies by high-frequency squeezed states. Here, a heterodyne readout scheme was implemented to avoid limiting noises at low frequencies. The application of squeezed states centered around the local oscillator frequency yielded an improvement in signal-to-noise ratio of $\unit[3.4]{dB}\pm\unit[0.3]{dB}$. Additionally, I designed, built and characterized a compact source of squeezed vacuum-states at \unit[1064]{nm} with a footprint of just $\unit[0.8]{m^2}$. I show measurements of squeezed states from this source with a reduction of quantum noise of $\unit[10.7]{dB}\pm\unit[0.2]{dB}$ below the vacuum noise and present a noise reduction in the frequency range from \unit[70]{kHz} to \unit[65]{MHz}.
Sensitivity of gravitational-wave detectors (GWDs) is constrained at low frequencies by quantum radiation-pressure noise, a manifestation of the measurement's back action. One strategy to mitigate this back action involves employing variational readout, which entails cross-correlating the measurement shot noise with radiation-pressure noise. Prior research has demonstrated that variational readout in GWDs can be accomplished through the use of a filter cavity. However, current gravitational-wave detectors necessitate filter cavity lengths on the order of ∼100 meters, with future detectors anticipated to reach lengths of a few kilometers. This paper introduces a novel approach to variational readout utilizing principle of quantum teleportation, which eliminates the need for a filter cavity. *This document will not be published any journals, since it turned out to be not very useful for the real detectors. The main reason is that one does not need the EPR entanglement to obtain the same result, which does not even shows true variational readout. In other words, both schemes do not exceed the EPR squeezing. Nevertheless this document will be uploaded to stimulate discussions how to realize "true" back action evasion, such as variational readout or speed meter, via quantum entanglement.