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- Adrian Kent

Reader in Quantum Physics

University of Cambridge - Department of Applied Mathematics and Theoretical Physics (DAMTP)

Areas of Research:

My research currently covers quantum foundations and quantum information science, the

intriguing interplay between them, and experimental tests of foundational ideas and cryptographic proposals. I have for some time been investigating the combined power of the relativistic no-signaling principle and quantum information for quantum cryptographic tasks. This has lately led to the invention of several new protocols, including some for completely new and intrinsically relativistic tasks. It has also led to a previously unappreciated feature of relativistic quantum theory, the so-called no-summoning theorem, which has powerful applications in quantum cryptography, including unconditionally secure and practical protocols for the key cryptographic primitive of bit commitment.

Other recent results include (1) (with Munro, Spiller) the invention of the task of quantum tagging (i.e. authenticating the position of a remote object using quantum information and the no-signaling principle), showing that some protocols for this task proposed by others are insecure, and (2) showing that the task can be securely implemented by a tag that contains secret classical data; (3) (with Colbeck) the invention of quantum randomness expansion schemes, which allow a user who has a finite supply of secret random numbers to generate more using a quantum device, even though that device is purchased from an adversary who is not trusted; also the observation of a subtle flaw in another published scheme for this task; (4) the invention of an intrinsically relativistic task, location-oblivious data transfer -- which allows the transfer of data at a variable location in space-time, which is concealed from the transferrer --and of secure protocols for this task.

In quantum foundations, I am currently working on a Lorentz invariant solution to the "quantum reality problem". The aim here is to find a precise mathematical characterisation of a sample space of histories for a closed quantum system (in principle, the universe) to which quantum probabilities apply, that is defined in a Lorentz invariant way, that is unique (i.e. it defines a one world theory rather than a many worlds theory), and that (as far as we can test) describes the sort of quasiclassical reality we actually observe and do experiments on. In other words, to give a new way of thinking about quantum theory, that applies to cosmology, and is purely algorithmic -- so that in principle we could program a computer to start from the theory and make precise (probabilistic) predictions of everything that will happen throughout space and time. I have a new proposal on this in press, which I'm very excited about, and am currently refining it further. This work has also led to a detailed analysis of attempts to make precise sense of the structure of worlds and a meaning for probabilities in many-worlds quantum theory (which, if it works, would itself be a naturally Lorentz invariant solution to the reality problem - hence the interest), and to the foundations of probability itself.

I have also been working on new tests of quantum theory and the nonlocality of the gravitational field (one of which was recently carried out by the Geneva group), and on natural -- i.e. well motivated and precisely defined -- alternatives to quantum theory which motivate such tests.

On another experimental frontier, I'm one of a group of people at IQC, PI and elsewhere, led by Thomas Jennewein at IQC, who have been collaborating to put together experimental ideas for a proposal to the Canadian Space Agency for new satellite-based quantum experiments and quantum crytographic implementations.

- 2006-present Reader in Quantum Physics, DAMTP, University of Cambridge

- Leverhulme Research Fellowship 2011-12, awarded by the Leverhulme Trust

- Unconditionally Secure Bit Commitment with Flying Qudits, Adrian Kent (Centre for Quantum Information and Foundations, DAMTP, University of Cambridge and Perimeter Institute). To appear in New Journal of Physics. (2011) arxiv:quant-ph/1101.4620.
- Real World Interpretations of Quantum Theory, Adrian Kent, To appear in Foundations of Physics. arXiv: 0708.3710
- Adrian Kent, Why Classical Certification is Impossible in a Quantum World, Quantum Information Processing, DOI: 10.1007/s11128-011-0262-x (2011)
- Adrian Kent, Location-Oblivious Data Transfer with Flying Entangled Qudits Phys. Rev. A 84, 012328 (2011). arXiv: 1102.2816
- Adrian Kent, Quantum Tagging for Tags Containing Secret Classical Data Phys. Rev. A 84, 022335 (2011). arXiv: 1008.5380
- Adrian Kent, William J. Munro, Timothy P. Spiller, Quantum Tagging: Authenticating Location via Quantum Information and Relativistic Signalling Constraints, Phys. Rev. A 84, 012326 (2011). arXiv: 1008.2147
- Roger Colbeck, Adrian Kent, Private Randomness Expansion With Untrusted Devices, Journal of Physics A: Mathematical and Theoretical 44(9), 095305 (2011). arXiv: 1011.4474
- Jonathan Barrett, Adrian Kent, Stefano Pironio, Maximally Non-Local and Monogamous Quantum Correlations, Phys. Rev. Lett. 97, 170409 (2006)., arxiv:quant-ph/605182
- Jonathan Barrett (Universite Libre de Bruxelles), Lucien Hardy (Perimeter Institute), Adrian Kent (Centre for Quantum Computation, DAMTP, University of Cambridge), No Signalling and Quantum Key Distribution, Phys. Rev. Lett. 95, 010503 (2005), arxiv:quant-ph/405101
- Jonathan Barrett, Daniel Collins, Lucien Hardy, Adrian Kent, Sandu Popescu, Quantum nonlocality, Bell inequalities and the memory loophole, Phys. Rev. A 66, 042111 (2002), arxiv:quant-ph/205016
- Unconditionally Secure Bit Commitment by Transmitting Measurement Outcomes, Adrian Kent (Centre for Quantum Information and Foundations, DAMTP, University of Cambridge and Perimeter Institute for Theoretical Physics), arXiv: 1108.2879
- Too Damned Quiet?, Adrian Kent, arXiv: 1104.0624
- A No-summoning theorem in Relativistic Quantum Theory, Adrian Kent (Centre for Quantum Information and Foundations, DAMTP, University of Cambridge and Perimeter Institute), arXiv: 1101.4612
- "The Many Worlds of Hugh Everett III", Adrian Kent, Am.J.Phys.79: 790 (2011). arXiv: 1103.4163
- "One world versus many: the inadequacy of Everettian accounts of evolution, probability, and scientific confirmation", Adrian Kent. Chapter 10 in "Many Worlds? Everett, Quantum Theory and Reality", Simon Saunders, Jonathan Barrett, Adrian Kent and David Wallace (eds), Oxford University Press (Oxford). (2010) arXiv: 0905.0624
- "Many Worlds? Everett, Quantum Theory and Reality", Simon Saunders, Jonathan Barrett, Adrian Kent and David Wallace (eds), Oxford University Press (Oxford, 2010).
- Quantum imaging: Scattered observations on "Copenhagen" Alternatives Theatrales, 102-3, pp 81-2 (2009). arXiv: 1001.1996

- Quantum Theory, Relativity, Information and Cryptography, invited talk at the International Workshop on Relativistic Quantum Information, Madrid
- Quantum Theory, Relativity and Information, invited webinar given at Cambridge, Imperial College London, University College London, ETH Zurich, Edinburgh, Aberystwyth.
- Relativity, Quantum Theory, Information, invited talk at "Quantum Physics and the Nature of Reality" workshop, Internationale Akademie Traunkirchen, Austria
- Relativistic Quantum (Im)Possibilities, invited colloquium at Oxford University
- A No-Summoning Theorem for Relativistic Quantum Theory, invited talk given at "New Frontiers in Quantum Foundations", Clemson University
- Testing the (Non)locality of the Gravitational Field, talk at Experimental Search for Quantum Gravity workshop, NORDITA
- Quantum Tagging, seminar at Centre for Quantum Information and Foundations, DAMTP, University of Cambridge
- One World versus Many, invited colloquium at Centre for Quantum Technologies, National University of Singapore
- One World versus Many, invited talk at QNET workshop, Oxford University

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