Dr Michael Hall is a Senior Research Fellow at the Centre for Quantum Dynamics at Griffith University in Brisbane. He works broadly in foundations of quantum mechanics with interests in quantum communication and measurement, Bell inequalities, time observables and axiomatic quantum mechanics.

We are delighted that Michael has joined the JPhysA editorial board, having been a valued member of the advisory panel for many years.

**Could you provide us with a brief summary of your career so far? **

I gained a PhD in theoretical physics from the Australian National University in 1989, with the thesis written while at home caring for my newly born son. After a couple of postdocs I became a house-spouse again, caring for my son and daughter until they reached school age, and then joined the Australian patent office in 1995. I worked as a patent examiner for 16 years*, with a year off for good behaviour in 1998 to take up a von Humboldt Fellowship at the University of Ulm in Germany. During these years I was a Visiting Fellow at ANU, pursuing my passion for physics in my spare time. I returned to full-time academia in late 2011, joining Howard Wiseman’s group in the Centre for Quantum Dynamics at Griffith University in Brisbane, where I am currently a senior research fellow.

*I like to say that I’m not as good a physicist as Einstein, but I was a better patent examiner!

**You work broadly within the field of quantum mechanics. Which areas are you interested in more specifically and what led you to this area of research?**

I have always been keen to understand how the world works at a fundamental level, and consequently have been banging my head for many years against the wall of quantum mechanics, trying to understand what it all means. For example, the famous Bell inequalities imply that we must give up at least one physical principle dear to most of us, such as locality, realism or experimental free will. I am interested in why, *and by how much,* these principles must be relaxed in a quantum world.

I am also very interested in physical limitations imposed by quantum mechanics, and the advantages and disadvantages of these limitations. For example, an advantage of the uncertainty principle implies that the properties of a quantum signal are disturbed by any measurement, and this can be usefully exploited to detect eavesdroppers. However, a disadvantage of wave-particle duality implies that the resolution of interferometric-wave sensors (used in technologies ranging from imaging to gravitational wave detection) is limited by photon number properties of the input light.

Finally, it appears that the current quantum theory must be modified in some way to incorporate gravitation. However, it is very hard to tweak quantum mechanics without breaking it – typically something like explicit faster-than-light signalling pops up. I am therefore interested in trying to extend quantum mechanics in a self-consistent manner, most recently via an approach based on modelling quantum phenomena as the consequence of interactions between many worlds.

**What kind of problems appeal to you?**

Ones which throw some light on quantum mechanics, and which have some interesting maths involved.

**What are you currently working on?**

I am currently working on various problems in quantum information and open quantum systems, and I am also co-writing a book on a new and very general formalism for modelling physical systems.

I am now spending a fair bit of time with some colleagues on developing a recent approach for explaining quantum effects as a consequence of interactions between a large but finite number of worlds. In this approach each of the worlds, including our own, would be essentially Newtonian if left to its own devices. However, by postulating a suitable interworld interaction, we have been able to simulate many quantum effects, including quantum tunnelling and double-slit interference. As well as providing a new way to think about such effects, the approach is exciting in making slightly different predictions to the standard theory (for a sufficiently small number of worlds), leading to the possibility of experimental tests. We are currently working on understanding what properties of the interworld interaction give rise to quantum entanglement.

**What do you consider to be the most significant problems to be addressed in your field?**

Solving the quantum measurement problem, and integrating quantum mechanics with gravity – both of which are likely to require a modification of current quantum theory.

**What are the challenges facing researchers in mathematical and theoretical physics?**

The biggest challenge is a stable research career. Having spent many years gaining a PhD one is only at the beginning. Postdocs are expected to travel, like mediaeval tinkers, from town to town and country to country, uprooting family or leaving them behind as they go. After some years of this, they may or may not be fortunate enough to find a tenure-track position. This challenge makes a research career unattractive to many; reducing the talent pool.

A more specific challenge for mathematical and theoretical physics researchers is selling the value of fundamental research, particularly in times when the economy is not doing well. This requires strong professional associations, such as the IOP and APS, and also individuals making the time and effort to explain their work as widely as possible.

An upside for mathematical and theoretical physics researchers is that they are relatively cheap – they don’t need experimental apparatus, just a computer and a decent library.

**Where do you think your research will take you next? Are there any other fields you are interested in exploring?**

It is impossible to predict very far ahead – something that funding organisations seem to ignore. I’m watching the emerging field of quantum thermodynamics, and I like to keep an eye on new mathematical techniques.

**Finally, do you have any advice for young researchers entering the field?**

It is important to have great passion for the field, technical ability, and deep conceptual understanding. The last can only be developed over time, generally with the help of good supervisors and by reading original papers in the field, and is essential if you are to come up with good problems of your own.

*This work is licensed under a** Creative Commons Attribution 3.0 Unported License. *Photo courtesy of Michael Hall. Image: “Quantum Phenomena Modeled by Interactions between Many Classical Worlds” by Michael J. W. Hall, Dirk-André Deckert, and Howard M. Wiseman Phys. Rev. X 4, 041013 (2014)

Categories: Journal of Physics A: Mathematical and Theoretical