Instrumentation for interferometric gravitational-wave detectors

Gravitational waves are 'ripples' in space-time caused by some of the most violent and energetic processes in the Universe. In outer space that means objects like neutron stars or black holes orbiting around each other at ever increasing rates, or stars that blow themselves up. Explore the links below to learn more about these ephemeral phenomena.

Quantum enhanced kHz gravitational wave detector with internal squeezed-light generation

We propose adding a nonlinear element to a long signal recycling cavity to enhance the high-frequency sensitivity of the interferometric gravitational wave detectors. At the CGA laboratory, we setup a table-top prototype to verify a broadband sensitivity improvement via internally generated squeezing.

Please find the related theoretical proposal at Class. Quantum Grav. 37, 07LT02 (2020).

Quantum optical methods for entangled devices

This project aims to develop experimental quantum optics methods and techniques for enhancing the performance of sensitive devices. Entangled photons will be used to probe separate devices, yielding an improved detection of correlated signals. This new technique will benefit laboratory searches for new fundamental physics effects such as space-time fluctuations due to quantum gravity and exotic dark matter candidates. The project is expected to train scientists and students in advanced quantum methods, promoting and securing Australia's position as a leader in the development of quantum technologies.

Photothermal effects as new interaction dynamics to optomechanics

What is new

Photothermal effects arise from the absorption of light by an object, followed by thermal expansion or a thermo-optic refractive index change that contributes into system dynamics. Those effects are sometimes overlooked, considered as parasitic effects to be gotten rid of. Our studies shine more light into how they can be harnessed to one's advantage for novel scientific discoveries. 

Cancellation of photothermally induced instability in an optical resonator

High intensity optical resonators are often subjected to photo-thermal effects that give rise to instability. This instability introduces new nonlinear interactions and parasitic parametric dynamics. The authors report a method of controlling photo-thermal effect by inverting the sign of the interaction. This is achieved by inserting suitable optical substrates inside the optical resonator. The modified photo-thermal effect can deliver a cooperative interaction with the intra-cavity radiation pressure. The paper reports control of system dynamics to a stable equilibrium regime through the inverted photo-thermal coefficient. This control provides stable optical feedback control useful for precise metrology, opto-mechanics, and high-power laser applications.

See the journal article publication at Optica 9, 924-932 (2022) and media release article "Noise cancelling glasses for quantum sensors".

Photothermally induced transparency

Induced transparency is a common but remarkable effect in optics. It occurs when a strong driving field is used to render an otherwise opaque material transparent. The effect is known as electromagnetically induced transparency in atomic media and optomechanically induced transparency in systems that consist of coupled optical and mechanical resonators. In this work, we introduce the concept of photothermally induced transparency (PTIT). It happens when an optical resonator exhibits nonlinear behavior due to optical heating of the resonator or its mirrors. Similar to the established mechanisms for induced transparency, PTIT can suppress the coupling between an optical resonator and a traveling optical field. We further show that the dispersion of the resonator can be modified to exhibit slow or fast light. Because of the relatively slow thermal response, we observe the bandwidth of the PTIT to be 2π × 15.9 Hz, which theoretically suggests a group velocity of as low as 5 m/s.

See the journal article publication at Science Advances 6, eaax8256 (2020).

Laser Levitation of a Macroscopic Mirror

Scientific interest

Optomechanics is a growing branch of physics research that involves the interaction of photon radiation pressure and small mechanical objects. Due to its simple and yet ubiquitous principles, this modern research field is relevant to many physical systems. From nano-resonators to kilometre-long interferometres such as the LIGO gravitational-wave detectors, optomechanics finds applications ranging from precise metrology to the investigation of macroscopic quantum effects. Many advanced optomechanical sensors are currently limited in sensitivity by the properties of the mechanical components. In most cases, the supporting structure to a device acts like a bridge to the outside environment, thus inevitably coupling external noise and thermal fluctuations to the sensor. Levitation of the mechanical elements has been suggested as a valid alternative to decouple the noise and increase the sensitivity.

Project framework

Our program at the Australian National University adopts a radically new approach in the design of optomechanical systems, where the mechanical device is floated by radiation pressure without any mechanical support. Laser levitation can greatly increase the quality factor of the device, and moreover it can be realised in a coherent manner, where the optical fields are not scattered away but reflected and recycled.
The aim of this project is towards the realisation of the world's first laser levitation of a macroscopic mirror. The nature of the project requires an inventive, flexible approach across a diversity of topics. We equip students to function in a complex research landscape where quantum physics meets devices, materials, software and hardware engineering.

You can read our original proposal in Phys. Rev. Lett. 111, 183001 (2013) and a more general article in The Conversation: "Levitation is just part of the power of pushy light". More publications can be found at:

•  "Dynamics and stability of an optically levitated mirror", Phys. Rev. A 101, 053857 (2020).
• "Observation of nonlinear dynamics in an optical levitation system", Communications Physics 3, 197 (2020).