## International Summer Research Program in Gravitational-Wave Physics:

Research Experiences for Undergraduates around the world

**University of Birmingham**

- Optimal inertial isolation (the '6D' project):

The LIGO Gravitational-wave detectors use 40 kilogram mirrors as 'test-masses' for measuring changes in spacetime. To act as true probes of spacetime, the mirrors must be in pure free-fall, which means free from the effects of external forces including 'seismic noise'. Despite using active control systems with the best seismometers in the world, the residual motion is still too large and must be controlled. We propose to re-invent seismic isolation by using a completely new kind of isolation system that uses interferometers to dramatically improve sensitivity. This IREU will focus on developing our new, compact laser-interferometers for the 6D system. The same kind of interferometer will be included in the newest Advanced LIGO upgrade, called A+.

**Mentor:**Conor Mow-Lowry

- Frequency stabilisation in coupled optical cavities: numerical modelling, theory and experiment:

The development of new instruments and experimental techniques for precision and quantum measurements is one of the key research activities in the Institute for Gravitational Wave Astronomy. In this project you will learn frequency stabilisation techniques that are used in state-of-the-art laser systems, such as interferometric gravitational-wave detectors and atomic clocks, and use this knowledge to contribute to the ongoing development of novel coupled optical cavity systems that can improve the sensitivity of gravitational wave interferometers and an entirely new class of optomechanical resonators with strong quantum interaction between the optical field and mechanical states. The project provides two distinct options:

- In the theoretical/numerical part of the project you will work with interferometer simulation tools that are used for design of gravitational wave detectors such as LIGO and include advance features that are crucial for modelling interferometric systems for precise quantum measurements.

- On the experimental side you will get a hands-on experience of experimental work in a research optical laboratory with modern state-of-the-art tools such as ultra-stable lasers, low-noise detectors and digital real-time control hardware.

**Mentors:**Andreas Freise and Dr Artemiy Dmitriev

- Massive black hole binaries and Pulsar Timing Array observations:

Pulsar Timing Arrays (PTA) are galactic scale gravitational wave detectors that use radio pulsars as ultra-stable clocks to detect gravitational waves. Massive black hole binary systems are the primary sources of gravitational waves observable by PTAs. The goal of this project is to use the results from Monte Carlo simulations of the formation and evolution of these binaries to explore the sensitivity of current and future PTAs to this class of sources.

**Mentor:**Alberto Vecchio

- Quantum physics in gravitational-wave detectors:

The current approach for detecting gravitational wave on earth is to use kilometer-scale laser interferometric detectors with tens of kilogram size suspended mirrors forming two arms of the interferometer. To detect tiny gravitational wave signals from the distant universe, these detectors need to be extremely sensitive. For instance, Advanced LIGO detectors are expected to measure a displacement as small as 10^{-19} meter, which becomes even comparable to the de-Broglie wavelength - the characteristic quantum length - of their 40 kilogram mirrors. This means that macroscopic though these detectors are, we have to account for quantum effects. Indeed, one of the major factors that limits the detector sensitivity has to do with the Heisenberg Uncertainty Principle in quantum mechanics. In this project, we will look into the quantum physics of these detectors and study approaches to pushing the quantum limit by applying both analytical analysis and numerical modeling.

**Mentors:**Haixing Miao and Andreas Freise

**Related Project 2018:**"Using MAGIC to Validate and Optimize Interferometers"

- Numerical Fundamental quantum limit of gravitational wave detection:

Use our new understanding of the fundamental quantum limit of laser interferometers, to test, analytically and with numerical models, new configurations and devices that can significantly lower the quantum noise in future detectors.

**Mentor:**Andreas Freise

**Related Project 2018:**"Maximizing GW-Detector Sensitivity through Brute Force Differential Evolution Optimization"

- Staying in shape:

Use numerical models and table-top experiments to investigate the effects of laser beam shape distortions on precision metrology, from optical reference cavities to LIGO-like interferometers.

**Mentor:**Andreas Freise

- Tests of the inverse square law of gravitation at short ranges:

Interactions that violate Newton's law are predicted by theories that aim to unify gravitation with the quantum gauge forces. Our experimental setup enables the Newtonian attraction between sub-mm sized masses to be measured against the background of electromagnetic forces. It includes cryogenic suspension, precise mass characterization and optimized minimization of electromagnetic effects. The student's project would involve investigating potential violations of the inverse square law of gravitation at sub-mm ranges.

**Mentor:**Clive Speake - Preferred frame laboratory:

We are interested in searching for a sidereal anisotropy of the space-time through the detection of "preferential frame" effects. So far, we have built a low frequency torsion balance facility to search for variations in the gravitational strength between laboratory masses as a function of their orientation with respect to the fixed stars. With it we have set new upper limits on the Lorentz Symmetry violations posited by some theories. The student's project would focus on searches for new forces coupling mass and spin at short and long ranges. Scope exists for designing and conducting new experiments and well as developing robust analysis methods.

**Mentor:**Clive Speake - Development and applications of compact interferometers:

For our Preferred Frame and Inverse Square Law experiments, we have developed a novel interferometric sensor which is capable of high sensitivity to displacement, is compact and is tolerant to a high degree to the tilt of the target mirror. Prototypes are now being tested for use in Advanced LIGO as geophone readout devices in the vibration isolation system and we are now collaborating on a space qualified system that could potentially be used in a number of space missions. A summer student's project would entail investigating compact interferometers in the laboratory and/or modeling new configurations numerically.

**Mentor:**Clive Speake

**Related Project 2011:**"Design Considerations of a Fiber Feed for a Cryogenic Polarizing Interferometer"

**Past Projects: University of Birmingham**

- What can we learn about Black Holes with Gravitational Waves?

One of the main goals of gravitational-wave searches lies in the possibility of inferring the parameters of the sources from their gravitational-wave signature. For coalescing compact binaries, the parameter space can be quite large, e.g. 15 parameters for black-hole binaries with arbitrary spins. The presence of strong correlations and degeneracies in this large parameter space brings up a variety of challenges in searching for the true source parameters. We typically use stochastic techniques, such as Markov Chain Monte Carlo, to sample this parameter space. These techniques rely on accurate models of gravitational waveforms. We will explore the accuracy requirements for waveforms models, account for uncertainty in the waveforms, and develop techniques for computationally efficient parameter estimation on very long-duration waveforms.

**Mentor:**Ilya Mandel

**Related Project 2012:**"Improving Parameter Estimation on Gravitational-Wave Signals"

**Related Project 2013:**"Parameter Estimation Accuracy in Hybrid Gravitational Waveform Modeling"

- Improving Parameter Estimation on Gravitational-Wave Signals:

One of the main goals of gravitational-wave searches lies in the possibility of inferring the parameters of the sources from their gravitational-wave signature. For coalescing compact binaries, the parameter space can be quite large, e.g. 15 parameters for black-hole binaries with arbitrary spins. The presence of strong correlations and degeneracies in this large parameter space brings up a variety of challenges in searching for the true source parameters. We typically use stochastic techniques, such as Markov Chain Monte Carlo, to sample this parameter space. These techniques can be made more efficient by gaining a better understanding of the expected correlations. The goal of this project will be to search for such correlations and use the gained knowledge to improve jump proposal distributions.

**Mentor:**Ilya Mandel

**Related Project 2012:**"Improving Parameter Estimation on Gravitational-Wave Signals"

**Related Project 2013:**"Parameter Estimation Accuracy in Hybrid Gravitational Waveform Modeling"

- The dance of death of black hole binary systems:

The last few minutes of the dance macabre of a black hole binary can be studied in exquisite detail by gravitational-wave laser interferometers. These instruments record the signature of the structure of space-time in these extreme conditions by detecting the gravitational radiation that is emitted in the final stages of coalescence of binary black holes . Depending on the masses, spins and eccentricity of the binary, the orbit and space-time structure can be fantastically complex. The goal of the project is to develop a video and audio illustration of the structure of the space-time based on codes that we have developed within our group to model the evolution of these astrophysical systems. Such tools are extremely useful to develop a better intuition of the complex physics at work.

**Mentor:**Alberto Vecchio

**Related Project 2012:**"The dance of Death of Binary Black Hole Systems"

**Related Project 2013:**"The Impact of Gravitational Waves: Detectability and Signatures"

- Shaping a laser beam using a spatial light modulator:

Current gravitational wave detectors use the fundamental Gaussian beam mode of ultra-stable lasers for measuring a gravitational-wave induced differential position change of the end mirror test masses in a long baseline interferometer. Unfortunately, Brownian motion of the mirror surface couples into the phase of the reflected laser light. It is well known that employing lasers with a different, more uniform, mode shape can reduce this thermal noise. Commercially available 'spatial light modulators' can turn a Gaussian beam shape into an arbitrary user defined pattern. The goal of the project is to learn how the spatial light modulator can be used to produce so-called higher-order Laguerre-Gaussian modes (which feature concentric rings) and to optimize the optical setup such that a pure mode shape is generated.

**Mentor:**Andreas Freise

**Related Project 2011:**"Experimental Inquiry into the Feasibility of Generating Laguerre-Gauss Modes at Laser Powers of Order 100W"

- The Optical Resonator Calculator:

Optical resonators are a standard tool in precision optics and interferometry. They come in a variety of different shapes (linear, triangular, etc) and sizes (between microns and kilometers). Optical resonators are used in current gravitational wave detectors for various purposes, such as filtering or enhancing of individual light fields. The aim of this project is to develop an easy to use 'Optical Resonator Calculator' which would enable quick visualization of the characteristics of an optical resonator. The proposed application should have cross-platform operability, either through a web interface or by being based on JAVA. It should not only be fun to play with but also a useful illustrative tool for educational and outreach purposes.

**Mentor:**Andreas Freise

**Related Project 2009:**"Optical Resonator Calculator: Gravitational Wave Detector Cavity Simulations with Processing"

**Past IREU Projects**

**Other Prior Projects**