arXiv subjects

Chunnong Zhao

Publications and source records attributed to Chunnong Zhao.

At least 19 recordsLinked to original sources

arXiv2026

First Demonstration of Optical Feedback Control to Parametric Instability at Advanced LIGO

Increasing the circulating power in gravitational-wave detectors to the megawatt level is essential for future sensitivity improvement, but this is critically limited by optomechanical parametric instabilities. Current mitigation strategies are projected to be inadequate against instabilities when circulating power reaches a megawatt. Optical feedback offers a novel independent paradigm to mitigate parametric instability. In this Letter, we report the first demonstration of optical feedback control in a full-scale gravitational wave detector. We successfully suppressed an unstable mode at 10.428 kHz, reducing the parametric gain from R = 2 to R < 0.02. This work validates optical feedback control as an effective mitigation scheme for kilometre-scale interferometric gravitational-wave detectors, providing an effective strategy to allow detectors to reach the megawatt level.

gr-qc↗

arXiv2026

A Novel Arm-Length Stabilization Scheme for Gravitational-Wave Detectors with AlGaAs/GaAs Coated Mirrors

The arm length stabilisation system is employed in gravitational-wave detectors to reduce the velocity of the mirrors such that the arm cavities can be brought onto resonance in a controlled manner required to attain the detector operating point. For future upgrades of current gravitational wave detectors such as A#, which will incorporate AlGaAs/GaAs coatings, the current frequency-doubled arm length stabilisation system is unsuitable due to excessive absorption of the frequency-doubled 532nm beam by the AlGaAs/GaAs coating. We propose a novel multi-wavelength arm length stabilisation scheme that uses both frequency-doubled and frequency-tripled beams. The 1596nm auxiliary locking beam is outside the absorption bands of AlGaAs/GaAs coating. It is frequencytripled to 532nm and phase-locked with the 1064nm science laser through its second harmonic at 532 nm. In a tabletop setup, we experimentally demonstrated the stable cavity detuning and robust cavity locking transition by controlling the 1596nm laser and 1064nm laser phase locked loop. This demonstration confirmed that the proposed novel arm length stabilisation scheme is compatible with future upgrades or third-generation gravitational wave detectors that use AlGaAs/GaAs-coated test masses.

physics.optics↗

arXiv2025

Seismic Isolation of Optical Tables Using Piezo Actuators

Seismic isolation is crucial for gravitational wave detectors as it minimizes ground vibrations, enabling the detection of faint gravitational wave signals. An active seismic isolation platform for precision measurement experiments is described. The table features piezo actuation along five degrees of freedom: three translational actuations and two tip-tilt degrees of freedom along the horizontal axes. It is stiff in rotation about the vertical axes. A seismometer is used to sense table motion. Piezo actuators are used to suppress seismic noise with feedback control bandwidth of 0.3 to 3 Hz. Suppression levels ranging from 21 to 36 dB of seismic noise within the frequency range of 0.5 to 1.3 Hz are demonstrated, as measured by a witness seismometer on the table, with the suppression direction along the axis of the longitudinal translation of the suspended mirror on the table. The suppression results in 1 $\mathrm{\mathrm{nm/\sqrt{Hz}}}$ residual horizontal motion at 1 Hz. Limitations such as tilt-to-translation coupling that prevent actuation over the desired range of 0.03 to 3 Hz are discussed.

astro-ph.IM↗

arXiv2024

Birefringence in a Silicon Beamsplitter at 2um for Future Gravitational Wave Detectors

The next generation of gravitational wave detectors will move to cryogenic operation in order to reduce thermal noise and thermal distortion. This necessitates a change in mirror substrate with silicon being a good candidate. Birefringence is an effect that will degrade the sensitivity of a detector and is of greater concern in silicon due to its crystalline nature. We measure the birefringence in a <100> float zone silicon beamsplitter since we expect there to be a large inherent birefringence due to the spatial dispersion effect. We observe that the birefringence varied between $3.44 \pm 0.12 \times 10^{-7}$ and $1.63 \pm 0.05 \times 10^{-7}$ and estimate the birefringence along the <110> axis to be $1.64 \pm 0.5 \times 10^{-6}$ at 2um. We demonstrate this effect and argue that it strengthens the case for 2um and <100> silicon.

physics.optics↗

arXiv2024

Demonstration of optical spring in an un-detuned cavity containing an optical parametric amplifier

Here we demonstrate the capacity to manipulate the optical spring (OS) effect by employing an optical parametric amplifier (OPA) within an optical cavity. We observed more than a factor of 2 increase in the OS frequency shift with the OPA. We also showed for the first time that the OS can be tuned by solely adjusting the OPA phase and showing an un-detuned cavity exhibiting an optical spring. The method can be applied to gravitational wave detectors in the signal recycling configuration to realize narrow bandwidth high sensitivity. The OS can be tuned to align the detector peak sensitivity frequency to known frequency continuous gravitational wave signals, dynamically tuned to track the gravitational wave signal from merging compact binaries or tuned to search for the post-merger signal of known binary coalescence.

physics.optics↗

arXiv2023

Single and coupled cavity mode sensing schemes using a diagnostic field

Precise optical mode matching is of critical importance in experiments using squeezed-vacuum states. Automatic spatial-mode matching schemes have the potential to reduce losses and improve loss stability. However, in quantum-enhanced coupled-cavity experiments, such as gravitational-wave detectors, one must also ensure that the sub-cavities are also mode matched. We propose a new mode sensing scheme, which works for simple and coupled cavities. The scheme requires no moving parts, nor tuning of Gouy phases. Instead a diagnostic field tuned to the HG20/LG10 mode frequency is used. The error signals are derived to be proportional to the difference in waist position, and difference in Rayleigh ranges, between the sub-cavity eigenmodes. The two error signals are separable by 90 degrees of demodulation phase. We demonstrate reasonable error signals for a simplified Einstein Telescope optical design. This work will facilitate routine use of extremely high levels of squeezing in current and future gravitational-wave detectors.

physics.optics↗

arXiv2023

Seismic noise characterization at a potential gravitational wave detector site in Australia

A critical consideration in the design of next generation gravitational wave detectors is the understanding of the seismic environment that can introduce coherent and incoherent noise of seismic origin at different frequencies. We present detailed low-frequency ambient seismic noise characterization (0.1--10~Hz) at the Gingin site in Western Australia. Unlike the microseism band (0.06--1~Hz) for which the power shows strong correlations with nearby buoy measurements in the Indian Ocean, the seismic spectrum above 1~Hz is a complex superposition of wind induced seismic noise and anthropogenic seismic noise which can be characterized using beamforming to distinguish between the effects of coherent and incoherent wind induced seismic noise combined with temporal variations in the spatio-spectral properties of seismic noise. This also helps characterizing the anthropogenic seismic noise. We show that wind induced seismic noise can either increase or decrease the coherency of background seismic noise for wind speeds above 6~m/s due to the interaction of wind with various surface objects. In comparison to the seismic noise at the Virgo site, the secondary microseism (0.2~Hz) noise level is higher in Gingin, but the seismic noise level between 1 and 10~Hz is lower due to the sparse population and absence of nearby road traffic.

astro-ph.IM↗

arXiv2022

Design of a tabletop interferometer with quantum amplification

The sensitivity of laser interferometers is fundamentally limited by the quantum nature of light. Recent theoretical studies have opened a new avenue to enhance their quantum-limited sensitivity by using active parity-time-symmetric and phase-insensitive quantum amplification. These systems can enhance the signal response without introducing excess noise in the ideal case. However, such active systems must be causal, stable, and carefully tuned to be practical and applicable to precision measurements. In this paper, we show that phase-insensitive amplification in laser interferometers can be implemented in a tabletop experiment. The layout consists of two coupled cavities and an active medium comprised of a silicon nitride membrane and an auxiliary pump field. Our design relies on existing membrane and cryogenic technology and can demonstrate three distinct features: (i) the self-stabilized dynamics of the optical system, (ii) quantum enhancement of its sensitivity in the presence of the amplifier, and (iii) optical control of the amplifier gain. These features are needed to enhance the sensitivity of future interferometric gravitational-wave and axion detectors.

quant-ph↗

arXiv2022

Boosting the sensitivity of high frequency gravitational wave detectors by PT-symmetry

The kilo-Hertz gravitational waves radiated by the neutron star merger remnants carry rich information about the physics of high-density nuclear matter states, and many important astrophysical phenomena such as gamma-ray bursts and black hole formation. Current laser interferometer gravitational wave detectors, such as LIGO, VIRGO, and KAGRA have limited signal response at the kilo-Hertz band, thereby unable to capture these important physical phenomena. This work proposes an alternative protocol for boosting the sensitivity of the gravitational wave detectors at high frequency by implementing an optomechanical quantum amplifier. With the auxiliary quantum amplifier, this design has the feature of Parity-Time (PT) symmetry so that the detection band will be significantly broadened within the kilo-Hertz range. In this work, we carefully analyze the quantum-noise-limited sensitivity and the dynamical stability of this design. Based on our protocol, our result shows that the quantum-noise-limited sensitivity will be improved by one order of magnitude around 3kHz, which indicates the potential of our design for a future search of neutron star merger signals.

gr-qc↗

arXiv2022

Low coherency of wind induced seismic noise: Implications for gravitational wave detection

Seismic noise poses challenges for gravitational wave detection. Effective vibration isolation and methods to subtract unsheildable Newtonian Noise are examples. Seismic arrays offer one way to deal with these issues assuming seismic coherency. In this paper we find that wind induced seismic noise is incoherent and will dramatically reduce the projected low frequency sensitivity of future gravitational wave detectors. To quantify this, we measure the coherence length of wind induced seismic noise from 0.06--20~Hz in three distinct locations: close to a building, among tall trees and in shrubs. We show that wind induced seismic noise is ubiquitous and reduces the coherence lengths form several hundred meters to 2--40~m for 0.06--0.1~Hz, from $>$60~m to 3--16~m for 1.5--2.5~Hz and from $>$35~m to 1--16~m around 16.6 Hz frequency bands in the study area. This leads to significant loss of velocity and angular resolution of the array for primary microseism, 5 times worse Newtonian Noise cancellation by wiener filtering at 2~Hz, while it does not pose additional challenge for Newtonian Noise cancellation between 10--20~Hz.

physics.geo-ph↗

arXiv2022

Demonstration of Parametric Instability suppression through optical feedback

We demonstrate the suppression of parametric instability using through optical actuation in an electro-optical feedback loop, stabilising the high order optical mode content in an 80 metre long Fabry-Perot cavity. The loop suppression of the high order mode is achieved by injecting a high order mode with the same frequency and opposite phase. Frequency matching is achieved by measuring the beat note signal between the fundamental and high order mode in transmission of the cavity and applying that signal to an electro-optical modulator to create the required frequency sideband. Spatial mode matching of the sideband to the high order mode is accomplished through the inherent mode overlap between the input injected beam and the high order mode of the cavity. The paper presents the theoretical analysis and experimental demonstration of parametric instability suppression, for an instability which would normally ring up with a parametric gain of approximately 2.5.

physics.optics↗

arXiv2022

Observing the optical modes of parametric instability

Parametric Instability (PI) is a phenomenon that results from resonant interactions between optical and acoustic modes of a laser cavity. This is problematic in gravitational wave interferometers where the high intra-cavity power and low mechanical loss mirror suspension systems create an environment where three mode PI will occur without intervention. We demonstrate a technique for real time imaging of the amplitude and phase of the optical modes of PI yielding the first ever images of this phenomenon which could form part of active control strategies for future detectors.

physics.optics↗

arXiv2020

Broadband sensitivity improvement via coherent quantum feedback with PT symmetry

A conventional resonant detector is often subject to a trade-off between bandwidth and peak sensitivity that can be traced back to quantum Cramer-Rao Bound. Anomalous dispersion has been shown to improve it by signal amplification and is thus more robust against decoherence, while it leads to instabilities. We propose a stable quantum amplifier applicable to linear systems operating at the fundamental detection limits, enabled by two-mode non-degenerate parametric amplification. At threshold, one mode of the amplifier forms a PT-symmetric system of original detector mode. Sensitivity improvements are shown for laser-interferometric gravitational-wave detectors and microwave cavity axion detectors.

quant-ph↗

arXiv2020

Gravitational wave detectors with broadband high frequency sensitivity

The binary neutron star coalescence GW170817 was observed by gravitational wave detectors during the inspiral phase but sensitivity in the 1-5 kHz band was insufficient to observe the expected nuclear matter signature of the merger itself, and the process of black hole formation. This provides strong motivation for improving 1--5 kHz sensitivity which is currently limited by photon shot noise. Resonant enhancement by signal recycling normally improves the signal to noise ratio at the expense of bandwidth. The concept of optomechanical white light signal recycling (WLSR) has been proposed, but all schemes to date have been reliant on the development of suitable ultra-low mechanical loss components. Here for the first time we show demonstrated optomechanical resonator structures that meet the loss requirements for a WLSR interferometer with strain sensitivity below 10$^{-24}$ Hz$^{-1/2}$ at a few kHz. Experimental data for two resonators are combined with analytic models of 4km interferometers similar to LIGO, to demonstrate sensitivity enhancement across a much broader band of neutron star coalescence frequencies than dual-recycled Fabry-Perot Michelson detectors of the same length. One candidate resonator is a silicon nitride membrane acoustically isolated from the environment by a phononic crystal. The other is a single-crystal quartz lens that supports bulk acoustic longitudinal waves. Optical power requirements could prefer the membrane resonator, although the bulk acoustic wave resonator gives somewhat better thermal noise performance. Both could be implemented as add-on components to existing detectors.

physics.optics↗

arXiv2020

A Cryogenic Silicon Interferometer for Gravitational-wave Detection

The detection of gravitational waves from compact binary mergers by LIGO has opened the era of gravitational wave astronomy, revealing a previously hidden side of the cosmos. To maximize the reach of the existing LIGO observatory facilities, we have designed a new instrument that will have 5 times the range of Advanced LIGO, or greater than 100 times the event rate. Observations with this new instrument will make possible dramatic steps toward understanding the physics of the nearby universe, as well as observing the universe out to cosmological distances by the detection of binary black hole coalescences. This article presents the instrument design and a quantitative analysis of the anticipated noise floor.

astro-ph.IM↗

arXiv2020

Ground Based Gravitational Wave Astronomy in the Asian Region

The current gravitational wave detectors have identified a surprising population of heavy stellar mass black holes, and an even larger population of coalescing neutron stars. The first observations have led to many dramatic discoveries and the confirmation of general relativity in very strong gravitational fields. The future of gravitational wave astronomy looks bright, especially if additional detectors with greater sensitivity, broader bandwidth, and better global coverage can be implemented. The first discoveries add impetus to gravitational wave detectors designed to detect in the nHz, mHz and kHz frequency bands. This paper reviews the century-long struggle that led to the recent discoveries, and reports on designs and possibilities for future detectors. The benefits of future detectors in the Asian region are discussed, including analysis of the benefits of a detector located in Australia.

gr-qc↗

arXiv2019

Ground-Based Gravitational-Wave Astronomy in Australia: 2019 White Paper

The past four years have seen a scientific revolution through the birth of a new field: gravitational-wave astronomy. The first detection of gravitational waves---recognised by the 2017 Nobel Prize in Physics---provided unprecedented tests of general relativity while unveiling a previously unknown class of massive black holes, thirty times more massive than the Sun. The subsequent detection of gravitational waves from a merging binary neutron star confirmed the hypothesised connection between binary neutron stars and short gamma-ray bursts while providing an independent measurement of the expansion of the Universe. The discovery enabled precision measurement of the speed of gravity while shedding light on the origin of heavy elements. At the time of writing, the Laser Interferometer Gravitational-wave Observatory (LIGO) and its European partner, Virgo, have published the detection of eleven gravitational-wave events. New, not-yet-published detections are announced on a nearly weekly basis. This fast-growing catalogue of gravitational-wave transients is expected to yield insights into a number of topics, from the equation of state of matter at supra-nuclear densities to the fate of massive stars. The science potential of 3G observatories is enormous, enabling measurements of gravitational waves from the edge of the Universe and precise determination of the neutron star equation of state. Australia is well-positioned to help develop the required technology. The Mid-term Review for the Decadal plan for Australian astronomy 2016-2025 should consider investment in a scoping study for an Australian Gravitational-Wave Pathfinder that develops and validates core technologies required for the global 3G detector network.

astro-ph.IM↗

arXiv2019

Application of optomechanical frequency conversion on gravitational wave detection

Optomechanical interaction can be a platform for converting quantum optical sates at different frequencies. In this work, we propose to combine the idea of optomechanical frequency conversion and the dual-use of laser interferometer, for the purpose of improving the broadband sensitivity of laser interferometer gravitational wave detectors by filtering the light field. We found that compare to the previous schemes of implementing the optomechanical devices in gravitational wave detectors, this frequency converter scheme will have less stringent requirement on the thermal noise dilution.

quant-ph↗