Imperial College London News Release

For immediate release
Wednesday 1 September 2010

Researchers describe how to carry out the first experimental test of string theory in a paper published tomorrow in Physical Review Letters.

String theory was originally developed to describe the fundamental particles and forces that make up our universe. The new research, led by a team from Imperial College London, describes the unexpected discovery that string theory also seems to predict the behaviour of entangled quantum particles. As this prediction can be tested in the laboratory, researchers can now test string theory.

Professor Michael Duff FRS, lead author of the new study

Over the last 25 years, string theory has become physicists’ favourite contender for the ‘theory of everything’, reconciling what we know about the incredibly small from particle physics with our understanding of the very large from our studies of cosmology. Using the theory to predict how entangled quantum particles behave provides the first opportunity to test string theory by experiment.

“If experiments prove that our predictions about quantum entanglement are correct, this will demonstrate that string theory ‘works’ to predict the behaviour of entangled quantum systems,” said Professor Mike Duff FRS, lead author of the study from the Department of Theoretical Physics at Imperial College London.

“This will not be proof that string theory is the right ‘theory of everything’ that is being sought by cosmologists and particle physicists. However, it will be very important to theoreticians because it will demonstrate whether or not string theory works, even if its application is in an unexpected and unrelated area of physics,” added Professor Duff.

Professor Duff recalled sitting in a conference in Tasmania where a colleague was presenting the mathematical formulae that describe quantum entanglement: “I suddenly recognised his formulae as similar to some I had developed a few years earlier while using string theory to describe black holes. When I returned to the UK I checked my notebooks and confirmed that the maths from these very different areas was indeed identical.”

The discovery that string theory seems to make predictions about quantum entanglement is completely unexpected, but because quantum entanglement can be measured in the lab, it does mean that at last researchers can test predictions based on string theory. There is no obvious connection to explain why a theory that is being developed to describe the fundamental workings of our universe is useful for predicting the behaviour of entangled quantum systems. “This may be telling us something very deep about the world we live in, or it may be no more than a quirky coincidence”, concluded Professor Duff. “Either way, it’s useful."

The study was carried out by researchers from Imperial College London and Stanford University. It was partly funded by the UK Science and Technology Facilities Council (STFC).

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Laura Gallagher
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Imperial College London
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Notes to editors:

1. Image of Professor Duff available on request

2. “Four-qubit entanglement from string theory.” Physical Review Letters 2010

Corresponding authors: Professor M. J. Duff FRS, Imperial College London.
Co-authors: L. Borsten, D. Dahanayke , W. Rubens (Imperial College London), A. Marrani (Stanford University)

3. String theory

String theory, and its extension M-theory, are mathematical descriptions of the universe. They have been developed, over the last 25 years, by theoreticians seeking to reconcile the theories of general relativity and quantum mechanics. (The former describes the universe at the level of cosmology – the very large, while the latter describes the universe at the level of particle physics – the incredibly small). One of the major bugbears, especially of M-theory, is that it describes billions of different universes and ‘anything’ can be accommodated in one or other of the M-theory universes. Researchers have no way of testing which of the answers that string/M-theory gives us is ‘right’. Indeed, they all may be right and we live in one universe among an infinite number of universes. So far no one has been able to make a prediction, using string theory, that can be tested to see if it is correct or not.

4. Qubit (quantum bit) entanglement

Under very precisely controlled conditions it is possible to entangle the properties of two quantum particles (two quantum bits, or qubits), for example two photons. If you then measure the state of one of these entangled particles, you immediately affect the state of its partner. And this is true if the particles are close to one another or separated by enormous distance. Hence Einstein’s apposite description of quantum entanglement as ‘spooky action at a distance’. It is possible to entangle more than two qubits, but calculating how the particles are entangled with one another becomes increasingly complex as more particles are included.

Professor Duff and his colleagues realised that the mathematical description of the pattern of entanglement between three qubits resembles the mathematical description, in string theory, of a particular class of black holes. Thus, by combining their knowledge of two of the strangest phenomena in the universe, black holes and quantum entanglement, they realised they could use string theory to produce a prediction that could be tested. Using the string theory mathematics that describes black holes, they predicted the pattern of entanglement that will occur when four qubits are entangled with one another. (The answer to this problem has not been calculated before.) Although it is technically difficult to do, the pattern of entanglement between four entangled qubits could be measured in the laboratory and the accuracy of this prediction tested.

5. Science and Technology Facilities Council

The Science and Technology Facilities Council ensures the UK retains its leading place on the world stage by delivering world-class science; accessing and hosting international facilities; developing innova tive technologies; and increasing the socio-economic impact of its research through eff ective kn owledge exchange partnerships.

The Council has a broad science portfolio including Astronomy, Particle Physics, Particle Astrophysics, Nuclear Physics, Space Science, Synchrotron Radiation, Neutron Sources and High Power Lasers. In addition the Council manages and operates three internationally renowned laboratories:

• The Rutherford Appleton Laboratory, Oxfordshire
• The Daresbury Laboratory, Cheshire
• The UK Astronomy Technology Centre, Edinburgh

The Council gives researchers access to world-class facilities and funds the UK membership of international bodies such as the European Laboratory for Particle Physics (CERN), the Institute Laue Langevin (ILL), European Synchrotron Radiation Facility (ESRF), the European organisation for Astronomical Research in the Southern Hemisphere (ESO) and the European Space Agency (ESA). It also contributes money for the UK telescopes overseas on La Palma, Hawaii and in Chile, and the MERLIN/VLBI National Facility, which includes the Lovell Telescope at Jodrell Bank Observatory.

The Council distributes public money from the Government to support scientific research. 

6. About Imperial College London

Consistently rated amongst the world's best universities, Imperial College London is a science-based institution with a reputation for excellence in teaching and research that attracts 14,000 students and 6,000 staff of the highest international quality. Innovative research at the College explores the interface between science, medicine, engineering and business, delivering practical solutions that improve quality of life and the environment - underpinned by a dynamic enterprise culture.

Since its foundation in 1907, Imperial's contributions to society have included the discovery of penicillin, the development of holography and the foundations of fibre optics. This commitment to the application of research for the benefit of all continues today, with current focuses including interdisciplinary collaborations to improve global health, tackle climate change, develop sustainable sources of energy and address security challenges.

In 2007, Imperial College London and Imperial College Healthcare NHS Trust formed the UK's first Academic Health Science Centre. This unique partnership aims to improve the quality of life of patients and populations by taking new discoveries and translating them into new therapies as quickly as possible.

Website: www.imperial.ac.uk