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Evan D. Hall

Publications and source records attributed to Evan D. Hall.

At least 19 recordsLinked to original sources
arXiv2026

Loss-tolerant hybrid metasurface mirror for reducing coating Brownian noise in precision optical cavities

We propose a hybrid mirror design that places an embedded metasurface beneath a Bragg reflector, combining the low coating Brownian noise of metasurface mirrors with the low optical loss of conventional multilayer coatings. Unlike previous hybrid designs, which place the metasurface at the input surface, our design positions it below the Bragg stack, reducing the optical field incident on the loss-prone resonant layer. For a design operating at 1064 nm, we show that this reduces absorption from 24 ppm for a bare metasurface to 7 ppm for the hybrid. We introduce a general method for calculating the coating Brownian noise of hybrid metasurface-multilayer mirrors at arbitrary coupling strength, extending prior methods to coherently combine a beam-scale mean-field contribution with the periodic, sub-wavelength-scale response of the metasurface. Applying this to our design, we find a reduction in Brownian noise amplitude spectral density relative to an equivalent-reflectance Bragg mirror by a factor of 1.6. Finally, we show that this design has higher angular tolerance than a bare metasurface mirror, maintaining higher reflectance over an angular range of 1 degree. This work provides a practical path towards incorporating low-noise metasurface mirrors into precision optical cavities, while minimizing optical loss and angular sensitivity.

physics.optics↗
arXiv2026

Coating-free monolithic fused silica resonator via total internal reflection for precision laser stabilization

Brownian noise in the thin-film mirror coatings of optical reference cavities is a fundamental limitation in precision metrology, including gravitational-wave detectors and optical atomic clocks. We demonstrate a monolithic fused silica resonator that eliminates the use of thin-film coatings by operating via total internal reflection (TIR), achieving a finesse of 1225 and an optical mode volume of \qty{50}{mm^3}. To our knowledge, this is the largest mode volume reported for any coating-free monolithic resonator, comparable to state-of-the-art reference cavities. We use the cavity to frequency-stabilize an Nd:YAG laser, and demonstrate its application to precision metrology by operating it in a passive ring gyroscope configuration. This platform circumvents the dominant noise source of conventional reference cavities and provides a pathway toward cryogenic silicon TIR resonators that could surpass current frequency stabilization limits.

physics.optics↗
arXiv2026

Precision dynamics of resonantly enhanced optical parametric amplifiers

Optical parametric amplification is a crucial technology for the production of continuous-wave squeezed vacuum, which is now applied to gravitational-wave interferometry and other highly sensitive measurements of optical phase. The amplifiers employed in gravitational-wave detection are resonantly enhanced with optical cavities, which introduces nontrivial dynamics to their operation and requires a frequency-domain model of the relations between optical fields. In this work, input-output relations between optical fields entering, circulating in, and exiting a model amplifier are solved directly to produce frequency-domain relations that fully incorporate the cavity dynamics. We also provide low-order zero-pole-gain expansions for these relations to facilitate their analysis from a feedback control perspective. In the limit of small cavity decay rates, our relations are shown to reduce to relations previously derived under a Hamiltonian formalism. Expressions for amplifier figures of merit and for squeezed quadrature variances are also analyzed. Along the way, we examine how information about the amplifier performance can be extracted from the frequency dependence of the input-output relations, providing characterization methods that are complementary to methods that examine the static amplifier behavior.

quant-ph↗
arXiv2025

Wave-particle duality in the measurement of gravitational radiation

In a consistent description of the quantum measurement process, whether the wave or particle-like aspect of a system is revealed depends on the details of the measurement chain, and cannot be interpreted as an objective fact about the system independent of the measurement. We show precisely how this comes to be in the measurement of gravitational radiation. Whether a wave or particle-like aspect is revealed is a property of the detector employed at the end of the quantum measurement chain, rather than of the meter, such as a gravitational-wave (GW) antenna or resonant bar, used to couple the radiation to the detector. A linear detector yields no signal for radiation in a Fock state and a signal proportional to the amplitude in a coherent state -- supporting a wave-like interpretation. By contrast, the signal from a detector coupled to the meter's energy is non-zero only when the incident radiation contains at least a single graviton. Thus, conceptually simple modifications of contemporary GW antennae can reveal wave-particle duality in the measurement of gravitational radiation.

quant-ph↗
arXiv2024

True and apparent motion of optomechanical resonators, with applications to feedback cooling of gravitational wave detector test masses

Modern optomechanical systems employ increasingly sophisticated quantum-mechanical states of light to probe and manipulate mechanical motion. Squeezed states are now used routinely to enhance the sensitivity of gravitational-wave interferometers to small external forces, and they are also used in feedback-based trapping and damping experiments on the same interferometers to enhance the achievable cooling of fluctuations in the differential test mass mode (arXiv:2102.12665). In this latter context, an accurate accounting of the true test mass motion, incorporating all sources of loss, the effect of feedback control, and the influence of classical force and sensing noises, is paramount. We work within the two-photon formalism to provide such an accounting, which extends a previously described decomposition of the quantum-mechanical noise of the light field (arxiv:2105.12052). This decomposition provides insight, rooted in physically motivated parameters, into the optimal squeezed state and feedback control configuration that should be employed to achieve the lowest fluctuations. We apply this formalism to feedback damping experiments in current and possible future gravitational-wave interferometers -- LIGO A+, LIGO Voyager, Cosmic Explorer (CE), and CE Voyager -- and discuss how these multi-degree-of-freedom systems might be compared to a single degree-of-freedom oscillator. We find that, for the oscillator definition used most commonly in the literature so far, occupation numbers below 1 are possible in these interferometers over a frequency range comparable to the bandwidth of the trapped and cooled oscillator. We also discuss several technical issues in cooling experiments with gravitational-wave detectors

quant-ph↗
arXiv2024

First results from the Axion Dark-Matter Birefringent Cavity (ADBC) experiment

Axions and axion-like particles are strongly motivated dark matter candidates that are the subject of many current ground based dark matter searches. We present first results from the Axion Dark-Matter Birefringent Cavity (ADBC) experiment, which is an optical bow-tie cavity probing the axion-induced birefringence of electromagnetic waves. Our experiment is the first optical axion detector that is tunable and quantum noise limited, making it sensitive to a wide range of axion masses. We have iteratively probed the axion mass range 40.9-43.3$\text{ neV/c}^2$, 49.3-50.6$\text{ neV/c}^2$, and 54.4-56.7$\text{ neV/c}^2$, and found no dark matter signal. On average, we constrain the ALP-photon coupling at the level $g_{a\gamma\gamma} \leq 1.9\times 10^{-8} \text{ GeV}^{-1}$. We also present prospects for future axion dark matter detection experiments using optical cavities.

hep-ex↗
arXiv2024

Characterizing Gravitational Wave Detector Networks: From A$^\sharp$ to Cosmic Explorer

Gravitational-wave observations by the Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo have provided us a new tool to explore the Universe on all scales from nuclear physics to the cosmos and have the massive potential to further impact fundamental physics, astrophysics, and cosmology for decades to come. In this paper we have studied the science capabilities of a network of LIGO detectors when they reach their best possible sensitivity, called A#, given the infrastructure in which they exist and a new generation of observatories that are factor of 10 to 100 times more sensitive (depending on the frequency), in particular a pair of L-shaped Cosmic Explorer observatories (one 40 km and one 20 km arm length) in the US and the triangular Einstein Telescope with 10 km arms in Europe. The presence of one or two A# observatories in a network containing two or one next generation observatories, respectively, will provide good localization capabilities for facilitating multimessenger astronomy and precision measurement of the Hubble parameter. Two Cosmic Explorer observatories are indispensable for achieving precise localization of binary neutron star events, facilitating detection of electromagnetic counterparts and transforming multimessenger astronomy. Their combined operation is even more important in the detection and localization of high-redshift sources, such as binary neutron stars, beyond the star-formation peak, and primordial black hole mergers, which may occur roughly 100 million years after the Big Bang. The addition of the Einstein Telescope to a network of two Cosmic Explorer observatories is critical for accomplishing all the identified science metrics. For most metrics the triple network of next generation terrestrial observatories are a factor 100 better than what can be accomplished by a network of three A# observatories.

gr-qc↗
arXiv2023

Cosmic Explorer: A Submission to the NSF MPSAC ngGW Subcommittee

Gravitational-wave astronomy has revolutionized humanity's view of the universe, a revolution driven by observations that no other field can make. This white paper describes an observatory that builds on decades of investment by the National Science Foundation and that will drive discovery for decades to come: Cosmic Explorer. Major discoveries in astronomy are driven by three related improvements: better sensitivity, higher precision, and opening new observational windows. Cosmic Explorer promises all three and will deliver an order-of-magnitude greater sensitivity than LIGO. Cosmic Explorer will push the gravitational-wave frontier to almost the edge of the observable universe using technologies that have been proven by LIGO during its development. With the unprecedented sensitivity that only a new facility can deliver, Cosmic Explorer will make discoveries that cannot yet be anticipated, especially since gravitational waves are both synergistic with electromagnetic observations and can reach into regions of the universe that electromagnetic observations cannot explore. With Cosmic Explorer, scientists can use the universe as a laboratory to test the laws of physics and study the nature of matter. Cosmic Explorer allows the United States to continue its leading role in gravitational-wave science and the international network of next-generation observatories. With its extraordinary discovery potential, Cosmic Explorer will deliver revolutionary observations across astronomy, physics, and cosmology including: Black Holes and Neutron Stars Throughout Cosmic Time, Multi-Messenger Astrophysics and Dynamics of Dense Matter, New Probes of Extreme Astrophysics, Fundamental Physics and Precision Cosmology, Dark Matter and the Early Universe.

astro-ph.IM↗
arXiv2022

Thermorefringent noise in crystalline optical materials

Any material in thermal equilibrium exhibits fundamental thermodynamic fluctuations of its mechanical and optical properties. Such thermodynamic fluctuations of length, elastic constants, and refractive index of amorphous materials -- like dielectric mirror coatings and substrates -- limit the performance of today's most precise optical instruments. Crystalline materials are increasingly employed in optical systems because of their reduced mechanical dissipation, which implies a reduction of thermo-mechanical fluctuations. However, the anisotropy of the crystalline state implies a fundamental source of thermal noise: depolarization induced by thermal fluctuations of its birefringence. We establish the theory of this effect, elucidate its consequences, discuss its relevance for precision optical experiments with crystalline materials, and hint at the conditions under which it can be evaded.

physics.optics↗
arXiv2022

Optimizing the third generation of gravitational-wave observatories for Galactic astrophysics

Gravitational-wave (GW) astrophysics is a rapidly expanding field, with plans to enhance the global ground-based observatory network through the addition of larger, more sensitive observatories: Einstein Telescope and Cosmic Explorer. These observatories will allow us to peer deeper into the sky, collecting GW events from farther away and earlier in the Universe. Within our own Galaxy, there is a plethora of interesting GW sources, including core-collapse supernovae, phenomena in isolated neutron stars and pulsars, and potentially novel sources. As GW observatories are directionally sensitive, their placement on the globe will affect the observation of Galactic sources. We analyze the performance of one-, two-, and three-observatory networks, both for sources at the Galactic center, as well as a source population distributed over the Galactic disk. We find that, for a single Cosmic Explorer or Einstein Telescope observatory, placement at near-equatorial latitudes provides the most reliable observation of the Galactic center. When a source population distributed over the Galactic disk is considered, the observatory location is less impactful, although equatorial observatories still confer an advantage over observatories at more extreme latitudes. For two- and three-node networks, the longitudes of the observatories additionally become important for consistent observation of the Galaxy.

astro-ph.IM↗
arXiv2021

A Horizon Study for Cosmic Explorer: Science, Observatories, and Community

This Horizon Study describes a next-generation ground-based gravitational-wave observatory: Cosmic Explorer. With ten times the sensitivity of Advanced LIGO, Cosmic Explorer will push gravitational-wave astronomy towards the edge of the observable universe ($z \sim 100$). The goals of this Horizon Study are to describe and evaluate design concepts for Cosmic Explorer; to plan for the United States' leadership in gravitational-wave astronomy; and to envisage the role of Cosmic Explorer in the international effort to build a "Third-Generation" (3G) observatory network that will make discoveries transformative across astronomy, physics, and cosmology.

astro-ph.IM↗
arXiv2021

Approaching the motional ground state of a 10 kg object

The motion of a mechanical object -- even a human-sized object -- should be governed by the rules of quantum mechanics. Coaxing them into a quantum state is, however, difficult: the thermal environment masks any quantum signature of the object's motion. Indeed, the thermal environment also masks effects of proposed modifications of quantum mechanics at large mass scales. We prepare the center-of-mass motion of a 10 kg mechanical oscillator in a state with an average phonon occupation of 10.8. The reduction in temperature, from room temperature to 77 nK, is commensurate with an 11 orders-of-magnitude suppression of quantum back-action by feedback -- and a 13 orders-of-magnitude increase in the mass of an object prepared close to its motional ground state. This begets the possibility of probing gravity on massive quantum systems.

quant-ph↗
arXiv2021

Gravitational-wave physics with Cosmic Explorer: limits to low-frequency sensitivity

Cosmic Explorer (CE) is a next-generation ground-based gravitational-wave observatory concept, envisioned to begin operation in the 2030s, and expected to be capable of observing binary neutron star and black hole mergers back to the time of the first stars. Cosmic Explorer's sensitive band will extend below 10 Hz, where the design is predominantly limited by geophysical, thermal, and quantum noises. In this work, thermal, seismic, gravity-gradient, quantum, residual gas, scattered-light, and servo-control noises are analyzed in order to motivate facility and vacuum system design requirements, potential test mass suspensions, Newtonian noise reduction strategies, improved inertial sensors, and cryogenic control requirements. Our analysis shows that with improved technologies, Cosmic Explorer can deliver a strain sensitivity better than $10^{-23}/\mathrm{Hz}^{1/2}$ down to 5 Hz. Our work refines and extends previous analysis of the Cosmic Explorer concept and outlines the key research areas needed to make this observatory a reality.

gr-qc↗
arXiv2020

Tuning Advanced LIGO to kilohertz signals from neutron-star collisions

Gravitational waves produced at kilohertz frequencies in the aftermath of a neutron star collision can shed light on the behavior of matter at extreme temperatures and densities that are inaccessible to laboratory experiments. Gravitational-wave interferometers are limited by quantum noise at these frequencies but can be tuned via their optical configuration to maximize the probability of post-merger signal detection. We compare two such tuning strategies to turn Advanced LIGO into a post-merger-focused instrument: first, a wideband tuning that enhances the instrument's signal-to-noise ratio 40--80\% broadly above \SI{1}{\kHz} relative to the baseline, with a modest sensitivity penalty at lower frequencies; second, a "detuned" configuration that provides even more enhancement than the wideband tuning, but over only a narrow frequency band and at the expense of substantially worse quantum noise performance elsewhere. With an optimistic accounting for instrument loss and uncertainty in post-merger parameters, the detuned instrument has a ${\lesssim}40\%$ sensitivity improvement compared to the wideband instrument.

astro-ph.IM↗
arXiv2017

Systematic calibration error requirements for gravitational-wave detectors via the Cramér-Rao bound

Gravitational-wave (GW) laser interferometers such as Advanced LIGO transduce spacetime strain into optical power fluctuation. Converting this optical power fluctuations back into an estimated spacetime strain requires a calibration process that accounts for both the interferometer's optomechanical response and the feedback control loop used to control the interferometer test masses. Systematic errors in the calibration parameters lead to systematic errors in the GW strain estimate, and hence to systematic errors in the astrophysical parameter estimates in a particular GW signal. In this work we examine this effect for a GW signal similar to GW150914, both for a low-power detector operation similar to the first and second Advanced LIGO observing runs and for a higher-power operation with detuned signal extraction. We set requirements on the accuracy of the calibration such that the astrophysical parameter estimation is limited by errors introduced by random detector noise, rather than calibration systematics. We also examine the impact of systematic calibration errors on the possible detection of a massive graviton.

astro-ph.IM↗
arXiv2017

Calibration Uncertainty for Advanced LIGO's First and Second Observing Runs

Calibration of the Advanced LIGO detectors is the quantification of the detectors' response to gravitational waves. Gravitational waves incident on the detectors cause phase shifts in the interferometer laser light which are read out as intensity fluctuations at the detector output. Understanding this detector response to gravitational waves is crucial to producing accurate and precise gravitational wave strain data. Estimates of binary black hole and neutron star parameters and tests of general relativity require well-calibrated data, as miscalibrations will lead to biased results. We describe the method of producing calibration uncertainty estimates for both LIGO detectors in the first and second observing runs.

astro-ph.IM↗
arXiv2016

Laser Interferometers as Dark Matter Detectors

While global cosmological and local galactic abundance of dark matter is well established, its identity, physical size and composition remain a mystery. In this paper, we analyze an important question of dark matter detectability through its gravitational interaction, using current and next generation gravitational-wave observatories to look for macroscopic (kilogram-scale or larger) objects. Keeping the size of the dark matter objects to be smaller than the physical dimensions of the detectors, and keeping their mass as free parameters, we derive the expected event rates. For favorable choice of mass, we find that dark matter interactions could be detected in space-based detectors such as LISA at a rate of one per ten years. We then assume the existence of an additional Yukawa force between dark matter and regular matter. By choosing the range of the force to be comparable to the size of the detectors, we derive the levels of sensitivity to such a new force, which exceeds the sensitivity of other probes in a wide range of parameters. For sufficiently large Yukawa coupling strength, the rate of dark matter events can then exceed 10 per year for both ground- and space-based detectors. Thus, gravitational-wave observatories can make an important contribution to a global effort of searching for non-gravitational interactions of dark matter.

gr-qc↗