Session Z01: Next-generation Gravitational Wave Detectors, Methods, and Forecasts

Passive Laser Power Stabilization via an Optical Spring

Metrology experiments can be limited by the noise produced by the laser involved via small fluctuations in the laser’s power or frequency. Typically, active power stabilization schemes consisting of an in-loop sensor and a feedback control loop are employed. Those schemes are fundamentally limited by shot noise coupling at the in-loop sensor. In this letter we propose a passive power stabilization scheme via the optical spring effect. In a proof of principle experiment, we show that the free running relative power noise of the laser is stabilized from approximately 2 × 10⁻⁵ Hz^−1/2 to a minimum value of 1.6 × 10⁻⁷ Hz^−1/2 , corresponding to the power noise reduction by a factor of 125. The bandwidth at which stabilization occurs ranges from 400 Hz to 100 kHz. The work reported in this letter further paves the way for high power laser stability techniques which could be implemented in optomechanical experiments and in gravitational wave detectors.   

Surpassing the Standard Quantum Limit using an Optical Spring

Quantum mechanics places noise limits and sensitivity restrictions on physical measurements. The balance between unwanted backaction and precision of optical measurements impose a standard quantum limit (SQL) on interferometric devices. In order to surpass this limit, this back action effect must be evaded or one must devise a way to cancel unwanted noise. Many proof of principle experiments have been tested, but only until recently has a sub-SQL technique been successfully demonstrated. We show that by exploiting quantum correlations created by an optical spring, we measure a total sensitivity below the SQL by 2.8 dB, corresponding to a reduction in the noise power by 72 % below the limit. This result further pushes the noise limit below the SQL, and at frequencies ranges more applicable to LIGO. Additionally, this technique is directly applicable to Advanced LIGO, which could observe similar effects with a detuned signal recycling cavity.   

Characterizing dimensional stability of the LISA telescope at the University of Florida

LISA, the future space-based gravitational wave observatory, will form a constellation made of three spacecraft, separated by 2.5 Gm in a triangular formation in a heliocentric orbit. Laser links between the three spacecraft sense the position of free-falling test masses housed inside them to detect a passing gravitational wave. Along each laser link, afocal telescopes send and receive light between the two spacecraft after magnifying it 134 times. In the current performance models, the telescopes are allotted a length noise budget of 1 pm/√Hz.u_OMS in the 0.1 mHz to 0.1 Hz band, where u_OMS provides the frequency dependence, and μm-level overall length change over the mission duration. The telescopes are a NASA deliverable and the current design uses a combination of four mirrors with a 300 mm primary mirror and an overall length of 1 m. Dimensional stability measurements of the LISA telescope Engineering Development Units will be conducted at the University of Florida starting late 2022 as a part of the effort to demonstrate technology readiness level 6. This presentation will give an overview of the technology development being undertaken by our group and the progress made so far towards measuring the dimensional stability of the LISA telescope.   

Detecting Neutron Star-Black Hole Mergers with Next Generation Ground-Based Gravitational-Wave Detectors

Gravitational-wave detections by the Laser Interferometer Gravitational-Wave Observatory have been pivotal in expanding our understanding of the universe. Though the detector has observed tens of exciting compact binary mergers since its inception, neutron star-black hole (NSBH) mergers have been elusive, with the first confident detection made as late as last year. This statistic is expected to improve with the proposed construction of new detectors and advancements in the current detectors. In this work, we explore the potential of the current networks and assess the science case of the next generation detectors for NSBH detections using the following metrics: network detection efficiency and detection rate as a function of redshift, signal-to-noise ratios (SNRs) and the errors in measurement of intrinsic and extrinsic parameters, accuracy of sky-area measurement in relation to SNR and redshift, and enabling multimessenger astronomy with early-warning alerts.   

Precision cosmology with gravitational waves using next-generation ground-based gravitational-wave detectors

Gravitational-wave detectors have started a new era in precision cosmology. The detection of the binary neutron star (BNS) merger GW170817 alongwith its kilonova emission allowed for the first measurement of the Hubble constant through the luminosity distance-redshift relation. Future detectors will observe BNS mergers from far greater distances and, therefore, we can measure other cosmological parameters as well. We determine the capabilities of current networks, planned upgrades, and future observatories in doing precision cosmology with gravitational waves from BNS mergers using an inspiral-merger-ringdown waveform, including tidal terms, to model the BNS signal. We measure the redshift directly from the gravitational-wave signal with the mass-redshift degeneracy of a binary black-hole waveform broken by the additional tidal terms.   

Constraining Screened Massive Gravitons with Cosmic Explorer

Third generation gravitational wave (GW) detectors will soon initiate precision tests of GR at cosmological scales.  Currently LIGO's recent GW observations have put new constraints on the graviton mass.  Yet, in various viable massive graviton theories the massive carriers for gravitational interactions can be screened within galaxy distributions.  This is accomplished through the Vainshtein mechanism and could explain null results in local regions.  Screening can also hold for gravitational radiation, where beyond-GR effects are suppressed within matter distributions but accumulate in the phase outside such distributions.  Here detectors like Cosmic Explorer will allow accurate observations at vast scales to probe this screening effect.  This talk will discuss a framework for next generation detectors, i.e., Cosmic Explorer, to probe fundamental physics in GW propagation screened by multiple galaxy distributions.  Using realistic galaxy population models the constraint on the graviton mass and screening radius will also be discussed.   

Identification of primordial black hole mergers at cosmological distances

The abundance of primordial black holes (PBHs), which may form from the collapse of primordial overdensities right after the Big Bang, is still uncertain. One of the smoking gun evidence can be the gravitational wave (GWs) emitted from binary black hole (BBH) mergers of PBHs at redshifts $z\gtrsim 30$, where the formation of astrophysical black holes is unlikely. Future ground-based GW detectors, Cosmic Explorer ICE) and Einstein Telescope (ET), will be able to observe equal-mass BBH mergers with total mass of $\mathcal{O}(10-100)~\msun$ at such distances. We simulate BBHs of different masses, mass ratios and orbital orientations to investigate whether the redshift measurement of a single BBH source can be precise enough to establish its primordial origin. With a network of one ET in Europe, one 40-km CE in the US and one 20-km CE in Australia, we show that one can constrain $z>30$ at up to 97\% credibility for BBHs with total masses between $20~\msun$ and $40~\msun$ merging at $z \geq 40$ one.

We then assess the dependence of this result on the Bayesian redshift priors used for the analysis, specifically on the relative abundance of the BBH mergers originated from the first stars, and the primordial BBH mergers.   

Imaging through Gravitational Waves

Gravitational-Wave observatories are one of the newest additions to the suite of instruments used by astronomers to study the universe. From the first detection announced just six years ago to the 90+ detections announced to date, this new messenger has provided a wealth of results across a variety of astrophysical disciplines. However, despite the oft-used analogy of gravitational waves opening a "new window" on the universe, we have yet to produce an actual image of an astronomical object using gravitational waves. This is in part due to the (nearly) all-sky sensitivity of GW interferometers, as well as the isolated point-source nature of the GW-emitting systems observed thus far. In addition to these point sources, the universe contains extended GW sources of astrophysical or perhaps cosmological origin that may be detectable with future GW observatories in various wavebands. In this talk, we use the concept of "Gravitational Wave Imaging" as a theme for considering the future of Gravitational Wave astronomy beyond the currently planned instruments on ground and in space. We ask the questions: What constitutes a GW Image? What science opportunities are enabled by making such images? What observing and measurement concepts are required to produce them?     

The last three years: multiband gravitational wave observations of stellar mass binary black holes

Over the final years of their life, stellar-mass binary black holes radiate gravitational waves that will be observable by both space-based (such as LISA) and ground-based instruments (such as LIGO, Virgo and the next generation observatories Cosmic Explorer and the Einstein Telescope). We present results from a full Bayesian parameter estimation on both the space and ground-based observations for some typical sources using state-of-the-art waveforms that include eccentricity and spin induced precession. We show multi-band observations of these sources allow for measurement of their 17 parameter with exquisite precision. Furthermore, we quantify advance time and accuracy of fore-warnings together with realistic three-dimensional source localizations. These multi-band sources will be a gold-mine for astrophysics studies.