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arXiv:2306.06827 · Classical and Quantum Gravity

A potential third-generation gravitational-wave detector based on autocorrelative weak-value amplification

Jing-Hui Huang, Feifan He, Xue-Ying Duan, Guangjun Wang, Xiangyun Hu

Published Jul 27, 2023• 2 citations
arXivHTMLPDF

Abstract

Abstract Reducing noises and enhancing signal-to-noise ratios (SNRs) have become critical for designing third-generation gravitational-wave (GW) detectors with a GW strain of less than 10 − 23 H z − 1 . In this paper, we propose a potential third-generation GW detector based on autocorrelative weak-value amplification (AWVA) for GW detection with a strain of h g = 4 × 10 − 25 H z − 1 . In our scheme, a GW event induces a phase difference Δ ϕ by passing through a 11-bounce delay line, 10-km arm-length, zero-area Sagnac interferometer illuminated with a 1064-nm laser. Subsequently, Δ ϕ is amplified as the parameter of post-selection by choosing the appropriate pre-selected state and coupling strength in AWVA. In particular, we theoretically investigate the AWVA measurements for GW detection within the frequency band of 200 Hz ⩽ f g ⩽ 800 Hz, considering Gaussian noises with negative-decibel SNRs. The peak response of the AWVA sensitivity κ ( f g ) occurs at frequency f g , m a x = 500 Hz, which falls within the frequency band of interest of the current third-generation GW detectors. Our simulation results indicate that AWVA can demonstrate a measurable sensitivity of the autocorrelation coefficient Θ ( f g ) within the frequency band of interest. Moreover, the robustness of WVA shows promising potential in mitigating the effects of Gaussian noises.

DOI
10.1088/1361-6382/aceb47

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Abstract Reducing noises and enhancing signal-to-noise ratios (SNRs) have become critical for designing third-generation gravitational-wave (GW) detectors with a GW strain of less than 10 − 23 H z − 1 . In this paper, we propose a potential third-generation GW detector based on autocorrelative weak-value amplification (AWVA) for GW detection with a strain of h g = 4 × 10 − 25 H z − 1 . In our scheme, a GW event induces a phase difference Δ ϕ by passing through a 11-bounce delay line, 10-km arm-length, zero-area Sagnac interferometer illuminated with a 1064-nm laser. Subsequently, Δ ϕ is amplified as the parameter of post-selection by choosing the appropriate pre-selected state and coupling strength in AWVA. In particular, we theoretically investigate the AWVA measurements for GW detection within the frequency band of 200 Hz ⩽ f g ⩽ 800 Hz, considering Gaussian noises with negative-decibel SNRs. The peak response of the AWVA sensitivity κ ( f g ) occurs at frequency f g , m a x = 500 Hz, which falls within the frequency band of interest of the current third-generation GW detectors. Our simulation results indicate that AWVA can demonstrate a measurable sensitivity of the autocorrelation coefficient Θ ( f g ) within the frequency band of interest. Moreover, the robustness of WVA shows promising potential in mitigating the effects of Gaussian noises.
Weak-value amplification (WVA), a postselection-based technique that amplifies weak physical signals by preparing nearly orthogonal pre- and postselected quantum states, is intrinsically limited by various kinds of technical noise, which distorts amplified weak values, especially when discarding photons in postselection. While prior work established the efficacy of autocorrelative weak-value amplification (AWVA) under Gaussian noise, practical implementations face challenges from band-limited laser-source noise and detection noise (including shot noise and electrical noise). Here, we demonstrate that the AWVA protocol robustly suppresses both laser-power fluctuations and detection noise. Numerical experiments in Simulink further reveal AWVA's dual advantage: under high-power conditions, the noise-reduction superiority of AWVA over WVA becomes in- creasingly pronounced as input laser power increases, whereas in detection-limited regimes AWVA achieves an order-of-magnitude lower uncertainty, closely approaching the Cram\'er-Rao bound. Crucially, this work demonstrates that AWVA improves precision in both high-power (laser-noise-dominated) and photon-starved (detector-noise-dominated) regimes, thereby bridging these operating extremes and advancing precision in applications from gravitational-wave detection to hybrid quantum systems.
By choosing more orthogonality between preselection and postselection states, one can significantly improve the sensitivity in general optical quantum metrology based on the weak-value amplification (WVA) approach. However, increasing the orthogonality decreases the probability of detecting photons and makes the weak measurement difficult, especially when the weak measurement is disturbed by strong noise and the pointer is drowned in noise with a negative-decibel signal-to-noise ratio (SNR). In this article we introduce and numerically evaluate a modified weak-measurement protocol with a temporal pointer, namely, the autocorrelative weak-value amplification (AWVA) approach. Specifically, a small longitudinal time delay (tiny phase shift) $\ensuremath{\tau}$ of a Gaussian pulse is measured by implementing two simultaneous autocorrelative weak measurements under Gaussian white noise with different SNRs. The small quantities $\ensuremath{\tau}$ are obtained by measuring the autocorrelation coefficient of the pulses instead of fitting the shift of the mean value of the probe in the standard WVA technique. Simulation results show that the AWVA approach outperforms the standard WVA technique in the time domain with smaller statistical errors, remarkably increasing the precision of weak measurement under a strong noise background.
The ability to directly detect gravitational waves will open a completely new branch of astronomy to view the Universe, one that is inaccessible to electromagnetic-based astronomy. First generation ground-based interferometric gravitational-wave detectors have achieved strain sensitivities of order one part in ten to the twenty-one, at 100 Hz detection frequency. A new generation of detectors are under construction, designed to improve on the sensitivity of the first-generation detectors by a factor of 10. The quantum nature of light will broadly limit the sensitivity of these new instruments. This quantum noise will originate from the quantum vacuum fluctuations that enter the unused port of the interferometer. One of the most promising options for reducing the quantum noise impact and further increasing the sensitivity is applying quantum squeezed vacuum states. These squeezed states have lower noise in one quadrature than the vacuum state. By replacing the quantum vacuum fluctuations entering the interferometer with squeezed vacuum states, the quantum noise impact is reduced. This thesis firstly details the development of a squeezed light source that produces squeezed states applicable for enhancing interferometric gravitational-wave detectors. A doubly-resonant, travelling-wave bow-tie cavity squeezed light source is presented. For the first time, greater than 10 dB of quantum noise suppression across the gravitational-wave detection band is directly observed, and 11.6 dB of quantum noise suppression is observed above 200 Hz. This squeezing cavity design also has benefits with intrinsic isolation to backscattered light. Experiments that quantify this isolation are reported. The properties affecting squeezing magnitude and low-frequency squeezing measurement are discussed. In addition, a modified squeezing-ellipse-phase control technique for squeezed vacuum states is presented. This thesis secondly presents results from the LIGO Squeezed Light Injection Experiment, undertaken to test squeezed light injection into a 4 km interferometric gravitational-wave detector. The results of the experiment show the first measurement of squeezing-enhancement in a 4 km gravitational-wave detector, with 2.15 dB measured above 250 Hz. This represents the best sensitivity to gravitational waves yet achieved at these frequencies by any single gravitational-wave detector to date. An unknown area was whether the addition of a squeezer would introduce noise couplings that degrade the crucial low frequency sensitivity. The results demonstrate that injected squeezed states are compatible with low frequency gravitational-wave measurement. The characterisation of squeezing-injection optical losses and fluctuations of the squeezing angle are also reported. The knowledge and processes gained, from both the squeezed light source development work and the LIGO Squeezed Light Injection Experiment, will inform the design, planning and implementation of squeezed states in future gravitational-wave detectors.
We report a quantitative evaluation of weak-value amplification (WVA) for longitudinal phase measurements using Allan variance analysis. Building on a recent double-slit interferometry experiment with real weak values [Phys. Rev. Lett. 134, 080802 (2025)], our Allan variance analysis demonstrates measurement of a few attosecond time delay approaching the shot noise limit at short averaging intervals of TTT = 0.01−0.10.01-0.10.01−0.1 s, representing two orders of magnitude variance reduction compared to the T=300T=300T=300 s operating point in prior implementations. We demonstrate that the Allan-variance noise floor scales with the inverse of the detected photon number 1/Nr1/N_r1/Nr​, confirming shot-noise-limited operation with WVA. Furthermore, this 1/Nr1/N_r1/Nr​ scaling experimentally validates that WVA can outperform conventional measurement under fixed detected photon number and detector saturation, in the presence of technical noise, as theoretically predicted [Phys. Rev. Lett. 118, 070802 (2017)]. Our results provide rigorous, quantitative evidence of the near-optimal noise performance achievable with WVA, establishing a new benchmark for precision optical metrology. This advancement is particularly relevant to applications such as gravitational-wave detection, where signals predominantly occupy the high-frequency regime (>10>10>10 Hz).
Gravitational waves manifest as a time varying straining of space: they arise from the accelerating motions of large bodies of mass and propagate across the universe at the speed of light as ripples in the fabric of space-time, a fleetingly weak effect so far eluding direct detection. The detection of gravitation waves is expected to yield a rich vein to observational astronomy, complementing existing electromagnetic surveys and revealing a hitherto unexplored range of phenomena. First generation interferometric gravitational wave detectors, notably Enhanced LIGO, achieved strain sensitivities of one part in ten to power twenty-one per square-root-Hertz at 100 Hz with an expected detection rate of 2-3 events per year. Commissioning of a new generation of Advanced LIGO interferometric detectors has concluded recently with a resultant ten-fold sensitivity improvement. Overall their potential event detection space has increased by a factor of 1000. The quantum nature of light within these detectors now limits their sensitivity over most of their frequency range. This quantum noise limit is driven by the vacuum quadrature fluctuations propagated through their open detection ports and represents a fundamental noise floor to their strain sensitivity. This thesis addresses two distinct approaches to quantum noise improvement for future upgrades to advanced detectors. The first addresses the issue of quantum noise by adopting a quantum non-demolition approach to detector readout variables, the so-called `speed-meter’ design. Such a modified instrument samples test mass momentum, a quantity for which time separated measurements commute and are therefore not bound by Heisenberg-like limits. A novel polarisation-folded sloshing cavity type speed-meter is proposed where readout fields are stored and delayed in the orthogonal polarisation of the interferometer’s arms cavities. Here frequency dependence is selected to cancel position like measurements so that only test mass momentum information remains. A quantum noise propagation model is developed and a sensitivity performance is demonstrated that beats the standard quantum limit below 100 Hz over a broad range of frequencies. A second approach to achieve quantum noise enhancement in advanced detectors involves injection of quadrature-squeezed states in the place of vacuum. This dissertation details the development of a prototype squeezed vacuum source suitable to the demanding enhancement requirements for an Advanced LIGO squeezing installation. The construction of a doubly resonant, bow-tie cavity source is presented. This employs a novel monolithic all-glass cavity construction and is vacuum compatible. This design demonstrates the viability of building a cavity using optical contacting as a construction technique for attaching mounting prisms to highly polished fused-silica breadboards. Such a design can be expected to have excellent length noise stability, provide low intrinsic phase noise and would be suitable to mount on seismic isolation stages within the LIGO vacuum envelope. Further, the travelling wave cavity design should provide excellent 50 dB intrinsic backscatter isolation. We demonstrate the first operation of such a complex non-linear device under vacuum, producing 8.6 dB of measured vacuum squeezing down to 10 Hz across the advanced LIGO ‘audio-band’ detection range.
A universal amplification scheme of ultra-small phase based on weak measurements is given and a weak measurements amplification based laser interferometer gravitational-wave observatory (WMA-LIGO) is suggested. The WMA-LIGO has potential to amplify the ultra-small phase signal to at least 10310^{3}103 order of magnitude such that the sensitivity and bandwidth of gravitational-wave detector can be further improved. Our results not only shed a new light on the quantum measurement but also open a new way to the gravitational-wave detection.