The Nano & Quantum World

Measurement and observation at the quantum limit

The International Max Planck Partnership (IMPP) brings physicists from five Scottish Universities and five German Max Planck Institutes together to establish collaborations around the theme of 'measurement and observation at the quantum limit'.

By working together and sharing their expertise, the partners are establishing new ideas in a wide range of experimental and theoretical research, and delivering new technologies.

Developing the next generation of gravitational wave detectors

One example of the topics covered by IMPP is the instrumentation for laser-interferometric gravitational wave detectors. Professor Stefan Hild has spent his research career trying to improve the sensitivity of gravitational wave detectors. This is quite a challenge when you consider the Advanced LIGO detectors can already sense length changes of its four-kilometre-long arms equivalent to 1000th of the diameter of a proton.

It was at this sensitivity that the historic first detections of gravitational waves occurred. 

As you attempt to increase this level of sensitivity, you deal with measurement and observation at the quantum limit. For example, individual photons bouncing off the 40kg mirror within the detector could introduce enough push of the mirror to mask potential signals. 

For Professor Hild, this means developing ever more sophisticated methods for making measurements at a scale where the weird effects of quantum physics are becoming the dominant driver.

His European Research Council funded work at the Institute of Gravitational Research centres on developing a proof-of-concept for a different type of interferometer than that which is currently installed in gravitational wave observatories like Advanced LIGO. This speed-meter configuration employs a specific quantum measurement, a so-called ‘quantum non-demolition’ technique. This has the potential to reduce the amount of noise interfering with a gravitational wave signal.

This concept will improve the sensitivity of a gravitational wave detector, especially towards lower frequencies where many gravitational wave sources stay for longer periods. This will extend the time you can observe phenomena like the 'cosmic dance' of coalescing black holes. Longer observation time in turn allows for more accurate observation of these systems. 

Image: 270 degrees panorama of the Glasgow 10m prototype lab and the ERC Speed-Meter experiment (vacuum tanks on the left).

Combining research strengths

Earlier in his career, Prof Hild worked at another one of Europe’s premier research environments for Gravitation Waves, the Albert Einstein Institute in Hannover. 

Having worked at both a Scottish and a German member of the IMPP, he is well placed to appreciate the benefits of collaboration and understanding between them. It makes him an ideal advocate for the opportunities that the International Max Planck Partnership offers for researchers in both countries.

“The Max Planck Partnership originated from the fact that although we share strengths on photonics and quantum measurement, we have different sets of expertise across the member institutions in the UK and Germany.

What this partnership does is to combine excellence from different institutions and provide us with the means to create logical and complementary collaborations.

In my area of gravitational waves, and our efforts to get measurement apparatus closer to the quantum limit, there is a split of expertise. The mechanic thermal noise systems, low-noise mirrors suspensions, coatings and fibres as well as interferometry are areas of Glasgow expertise. While Hannover has a focus on the lasers themselves, seismic isolation and non-classical, so-called squeezed light.

To build the full instrument you need all of these areas of expertise working together.

We’ve had a spirit of collaboration over the last twenty-five years working on the GEO 600 Gravitational Wave detector. The International Max Planck Partnership offers opportunities to enhance our existing collaborations and foster exciting new ones too."

Professor Stefan Hild

Facilitating new and novel research collaborations

What Prof Hild appreciates more about the IMPP is the collaborations it has fostered among scientists who hadn't previously worked together. Prior to the establishment of the IMPP, all of the Max Planck Institutes had some connection to Scotland. But it was usually with just a single institution. The cross-institutional workshops that IMPP delivers, as well as other initiatives like combined lecture weeks for PhD students have expanded these networks.

These new connections between Scottish Universities and Max Planck Institutes have spawned many new interesting projects and papers that were not in the original proposal. It has also led to many PhD graduates taking on postdoctorate positions with other groups within the IMPP.

Although his own move to Scotland predates the establishment of the IMPP, Prof Hild appreciates the opportunities it offers to experience a new research environment.

“I was drawn to the way that scholarship is acknowledged within the Scottish system. Initiatives like the Scottish Young Academy and Scottish Crucible not only pulled me in but kept me here.

I had the great opportunity not only to work on my core research but meeting with politicians and policy makers and actually work on how our research outcomes can help our society and to engage with broader global challenges. Scotland is the ideal place to be doing my research.” 

Professor Stefan Hild

High capacity communications using light's twist

The IMPP assisted Glasgow scientist, Dr Martin Lavery, to team up with a research group at the Max Planck Institute for the Science of Light, Erlangen, led by Professor Gerd Leuchs.

Having completed a PhD in the Optics group, Martin is now a Royal Academy of Engineering Research Fellow, he leads the Structured Photonics research group in the School of Engineering. His research is focused on the potential applications of the orbital angular momentum (OAM) of light, or light with a twist. Scientists can prepare light in a number of these twisted states, or modes. Utilising this technique offers the potential for very high capacity communication links through free space.

For his EPSRC First Time grant, Dr Lavery was investigating the how atmospheric turbulence can affect these OAM modes – or spatially shaped quantum states – as they travel from point to point.

“The temperature and pressure variation in the atmosphere results in a change to the optical density of the air, which in turn distorts the light as it travels from point a to point b. This same effect occurs when one sees stars twinkling at night, or distortions that occur on a hot day.”

Dr Martin Lavery

This interference can degrade the signal sent. In order to transform these OAM techniques into a viable technology, it is important to understand and minimise the effects of this interference.

The collaboration with Max Planck Erlangen meant Dr Lavery could use their 1-mile free-space link to conduct these tests. This simulated conditions in which the technology could be used in a real world setting.

“The focus of this research was on building-to-building optical links for high capacity communication links, similar to optical fibre communications. Such links can allow buildings to be connected without the requirement for expensive and time-consuming installation of optical fibre. Optical fibre costs around $100k per mile to install, free-space optical solutions could be considerably more cost effective.”

Dr Martin Lavery

The first study of its kind. It has produced a data set that will have substantial impact on the field of free-space quantum and classical optical communications. The work will be published soon. 

“The International Max Planck Partnership was central to the formation of this collaboration, where an initial visit to the UofG by Prof Leuchs served as the first technical meeting on the project. The IMPP supported my travel to Erlangen to complete the research, and supported the work being presented at two international conferences.”

Dr Martin Lavery

What is the International Max Planck Partnership?

The multi-million pound partnership, with five prestigious Max-Planck Institutes (MPI) in Germany, is a major boost to the future development of new quantum technologies and fundamental science in Scotland.

It incorporates leading physics research groups from the universities of Glasgow, Strathclyde, St Andrews, Heriot-Watt and Edinburgh with The Max Planck Institute for Gravitational Physics (Albert Einstein Institute) Hannover; the MPI for the Science of Light, Erlangen; the MPI for Quantum Optics, Garching; the MPI for Chemical Physics, Dresden; and the MPI for Solid State Physics, Stuttgart.

The IMPP is supported by funding from the Scottish Funding Council, and a joint grant from the Engineering and Physical Sciences Research Council and the Science & Technology Facilities Council.

The Max Planck Society is Germany's most successful research organisation. Since its establishment in 1948, no fewer than 17 Nobel laureates have emerged from the ranks of its scientists, putting it on a par with the best and most prestigious research institutions worldwide.

The more than 15,000 publications each year in internationally renowned scientific journals are proof of the outstanding research work conducted at Max Planck Institutes – and many of those articles are among the most-cited publications in the relevant field.