Quantum information science: tools and applications for fundamental physics (Ext.)

This is an extension of the Fellowship 'Quantum information science: tools and applications for fundamental physics'. The fellowship initially focused on applying tools from computer science to study thermodynamics and statistical mechanics, and the extension will focus on applying them to better understand quantum gravity.

Computer science has led to a new paradigm in physics, where one understands the laws of nature in terms of the manipulation of information. Computer science also has tools which can be used to analyse how efficient these manipulations are. In the last two decades, this has led to fundamental breakthroughs in our understanding of quantum mechanics, and we now know that quantum computers can be much faster than classical computers, and that quantum particles can be used to transmit information privately, in a way that is impossible in the classical world. The proposed research will develop and apply tools from computer science and quantum information theory to other areas of physics, in a way which aims to deepen our understanding of fundamental laws.

Our current theory of gravity -- Einstein's general relativity -- is the theory of space-time and it is incompatible with quantum mechanics. Finding a consistent theory of gravity and quantum mechanics is one of the holy grails of modern physics. One of the few clues we have to reconciling the two theories is the black hole. These are objects which are so heavy, not even light can escape from them. Tantalizing hints from their study, such as the discovery that their entropy is proportional to their area, and that this area obeys thermodynamical laws suggest that information plays a fundamental role in quantum gravity. We know from previous work that thermodynamics is a field which can also be understood, in terms of information theory. Likewise, the black hole information problem, posed by Hawking, appears to suggest that black holes destroy information. If they do, then this requires radical changes to fundamental physics, and if instead they do preserve information, then we need to understand how this can be the case. The black hole information problem is precisely about the way information behaves and is stored in space-time. All these clues strongly suggests that in order to understand quantum gravity, we need to use tools from quantum information theory.

It is thus no surprise, that increasingly, quantum gravity researchers are turning to quantum information theory to provide clues as to what a consistent theory of gravity will look like. This has led to a flurry of new ideas in the field. For example, there are some indications that entanglement (an important property of some quantum states) plays an important role in determining the geometry of space time. Likewise there are some indications that nature is holographic, in that information about a region can be described on its boundary (indeed this is the case for black holes). Understanding holography, and whether it holds, is another example where information theory is important, since holography is a statement about how and where information is stored.

This project aims to apply and strengthen existing tools from quantum information theory -- many of them developed by the PI -- so that we may better understand what a consistent theory of quantum field theory and space-time will look like.

Research into the fundamentals of theoretical physics through new paradigms such as quantum information theory has the potential to radically reshape our world, both through challenging the basis of theoretical physics and commonly held assumptions, and through increasing our understanding of quantum systems which can lead to technological change. While much of the research based on quantum information theory is driven by the view that it will revolutionize technology and the way information is processed, applying it to fundamental physics adds to its disruptive potential.

One only needs to look at Claude Shannon and Alan Turing's seminal work on classical information theory and computing, and the effect it has had in so many different disciplines and fields, to see the far reaching impact that quantum information theory is likely to have on other areas of science and our lives. Much of their initial work in classical information theory and computation was abstract and theoretical when first formulated, but now underpins research in so many different fields, from biology, to economics and mathematics, and all aspects of physics. In the future, we expect quantum information and computing to have a similar disruptive influence across all disciplines.

In the more short term, it is already having an impact on a number of fields, including quantum gravity (both the string theory, loop quantum gravity, and independent community), high energy physics, and condensed matter physics. This is a remarkable example of what might be called the unreasonable connectivity of physics. This circumstance has led to a highly productive multi-directional flow of ideas among research areas.

There are also experimental groups testing aspects of quantum gravity through macroscopic superpositions of massive objects, and quantum information theory has provided new insights into possible experiments. An example of this is that one day it may be possible to test the quantum nature of the graviton by using the fact that entanglement cannot be created under local operations and classical communication.

The current research also aims to improve our understanding of quantum mechanics and gravity at the fundamental level. The potential impact on science and society with respect to this is clearly long term, and difficult to predict, as is often the case for more high risk theoretical work. At the same time, the potential for exciting breakthroughs (and hence, significant impact) is perhaps greatest.

Finally, the development of mathematical tools and building blocks of information theory, is likely to find application in a wide variety of applied mathematical research areas. The impact on industry or technology is likely to be long term and difficult to predict, but such mathematical tools tend to have very broad utility.