Dr Adrian Kent

My office in the Cambridge Centre for Quantum Information and Foundations is on the ground floor of Pavilion F of the Centre for Mathematical Sciences.

Academic Affiliations

Reader in Quantum Physics, DAMTP, University of Cambridge
Distinguished Visiting Research Chair at Perimeter Institute for Theoretical Physics in Waterloo, Ontario
Fellow of Wolfson College, Cambridge
Director of Studies in Mathematics at Darwin College, Cambridge
Affiliate at the Institute for Quantum Computing, University of Waterloo, Ontario
Visiting Scholar at Wolfson College, Oxford
Visiting Scholar at Massey College, Toronto

Research: Quantum foundations, quantum information theory and quantum cryptography

These are my main current research interests. Most of my papers on these subjects are on the physics arxiv. Some of the research topics I've worked on, and relevant papers and talks, are described below. (These descriptions and lists are incomplete: work in progress. Note that some papers belong in more than one list.)

Relativistic Quantum Cryptography

Talks

My talk on relativistic quantum cryptography at QCRYPT 2012 is here.

Papers

Security Details for Bit Commitment by Transmitting Measurement Outcomes
Secure and Robust Transmission and Verification of Unknown Quantum States in Minkowski Space
Fundamental quantum optics experiments conceivable with satellites -- reaching relativistic distances and velocities
Quantum Tasks in Minkowski Space
Unconditionally Secure Bit Commitment by Transmitting Measurement Outcomes
Location-Oblivious Data Transfer with Flying Entangled Qudits
Unconditionally Secure Bit Commitment with Flying Qudits
A No-summoning theorem in Relativistic Quantum Theory
Quantum Tagging for Tags Containing Secret Classical Data
Quantum Tagging: Authenticating Location via Quantum Information and Relativistic Signalling Constraints
Variable Bias Coin Tossing
Why Classical Certification is Impossible in a Quantum World
Unconditionally Secure Commitment of a Certified Classical Bit is Impossible
Secure Classical Bit Commitment using Fixed Capacity Communication Channels
Unconditionally Secure Bit Commitment
Coin Tossing is Strictly Weaker Than Bit Commitment

Quantum Key Distribution with security based (only) on No-Signalling

Papers

Unconditionally secure device-independent quantum key distribution with only two devices
Maximally Non-Local and Monogamous Quantum Correlations
No Signalling and Quantum Key Distribution

Talks

Our results on unconditionally secure device-independent quantum key distribution with only two devices were presented at QIP 2013. Here are the slides of Roger Colbeck's talk.

Device-Independent Quantum Cryptography

Papers

Unconditionally secure device-independent quantum key distribution with only two devices
Prisoners of their own device: Trojan attacks on device-independent quantum cryptography
Maximally Non-Local and Monogamous Quantum Correlations
No Signalling and Quantum Key Distribution

Talks

Roger Colbeck's talk at QCRYPT 2012 on our joint work with Jonathan Barrett on memory attacks on device-independent quantum cryptography is here.

Commentaries

Quantum Randomness Expansion

Quantum Tagging (Quantum Position Authentication)

Papers

Quantum Tagging for Tags Containing Secret Classical Data
Quantum Tagging: Authenticating Location via Quantum Information and Relativistic Signalling Constraints

Commentaries

A piece by Gilles Brassard in Nature on this topic is here. (Link requires subscription.)

Quantum Cryptography (without using the no-signalling principle)

Quantum Channels and Quantum Communication

Quantum Computing and Quantum Gates

Many Worlds Quantum Theory and its problems

Our book

More information can be found on the book's amazon page.

Unlike the other editors, I'm sceptical about whether many-worlds quantum theory can actually be made into a well-defined and scientifically useful theory, and one of my contributions to the book is the question mark in the title.

Another is my chapter One World Versus Many, which includes an extended critique of recent attempts to make sense of Everett's many-worlds ideas.

Synopsis

What would it mean to apply quantum theory, without restriction and without involving any notion of measurement and state reduction, to the whole universe? What would realism about the quantum state then imply?

This book brings together an illustrious team of philosophers and physicists to debate these questions. The contributors broadly agree on the need, or aspiration, for a realist theory that unites micro- and macro-worlds. But they disagree on what this implies. Some argue that if unitary quantum evolution has unrestricted application, and if the quantum state is taken to be something physically real, then this universe emerges from the quantum state as one of countless others, constantly branching in time, all of which are real. The result, they argue, is many worlds quantum theory, also known as the Everett interpretation of quantum mechanics. No other realist interpretation of unitary quantum theory has ever been found.

Others argue in reply that this picture of many worlds is in no sense inherent to quantum theory, or fails to make physical sense, or is scientifically inadequate. The stuff of these worlds, what they are made of, is never adequately explained, nor are the worlds precisely defined; ordinary ideas about time and identity over time are compromised; no satisfactory role or substitute for probability can be found in many worlds theories; they can't explain experimental data; anyway, there are attractive realist alternatives to many worlds.

Twenty original essays, accompanied by commentaries and discussions, examine these claims and counterclaims in depth. They consider questions of ontology - the existence of worlds; probability - whether and how probability can be related to the branching structure of the quantum state; alternatives to many worlds - whether there are one-world realist interpretations of quantum theory that leave quantum dynamics unchanged; and open questions even given many worlds, including the multiverse concept as it has arisen elsewhere in modern cosmology. A comprehensive introduction lays out the main arguments of the book, which provides a state-of-the-art guide to many worlds quantum theory and its problems.

Reviews

Popular Account

Other articles on many worlds quantum theory

Conferences

The conference details are here.

The talks are archived here.

Generalizations of Quantum Theory and Experimental Tests

Papers

Fundamental quantum optics experiments conceivable with satellites -- reaching relativistic distances and velocities
Beable-Guided Quantum Theories: Generalising Quantum Probability Laws
Beyond Boundary Conditions: General Cosmological Theories
A Proposed Test of the Local Causality of Spacetime
Nonlinearity without Superluminality
Causal Quantum Theory and the Collapse Locality Loophole

Conferences

With Joseph Emerson, Wayne Myrvold and Rafael Sorkin, I'm organizing a meeting, The Quantum Landscape: Generalizations of Quantum Theory and Experimental Tests, at Perimeter Institute in May 2013. Registration is now open.

Quantum Non-Locality and Experimental Tests

Quantum Non-Contextuality and the Finite Precision Loophole

The Consistent or Decoherent Histories Approach to Quantum Theory and Its Problems

Work on the Quantum Reality Problem

Other topics

Risk Analysis for hypothetical extinction catastrophes

I am a member of the advisory panel for the Cambridge Project for Existential Risk.

Papers

A critical look at risk assessments for global catastrophes

Commentaries

The paper is discussed by Martin Rees in his book Our Final Century and by Richard Posner in his book Catastrophe, Risk and Response.
An article by Dennis Overbye in the New York Times is here.
American Mensa has a collection of references on global risk reduction and comments here.

Speculative Exobiology and the Fermi Problem

Papers

Too Damned Quiet?

Commentaries

The MIT Technology Review blog's report.

Earlier research: Conformal field theory, representation theory and integrable models

My earlier papers on these subjects include a classification of the unitary highest weight representations of the Virasoro, Ramond and Neveu-Schwarz algebras, which uses the so-called GKO construction (also known as the coset construction), which relates highest weight representations of these algebras to those of affine Kac-Moody algebras.

These results are central to understanding two-dimensional conformal field theories, which describe the scaling behaviour of a large class of two-dimensional systems at criticality. At the critical point, lattice models, and the physical systems they represent, have a fractal-like structure and become scale invariant. Here is an example of an Ising model critical state at various scales:



Because the physics is local, the models actually display local scale invariance or conformal invariance, which in two dimensions is a very rich symmetry, represented in field theory by the action of an infinite dimensional Lie algebra, the Virasoro algebra. The unitary classification of Virasoro algebra highest weight representations explains the previously puzzling appearance of particular simple rational numbers as critical exponents for the Ising model, tricritical Ising model, 3-state Potts model, tricritical 3-state Potts model, and an infinite series of two dimensional lattice models, several of which describe the critical behaviour of naturally occurring two dimensional systems. The unitary classification of Ramond and Neveu-Schwarz algebra highest weight representations highlights the naturally occurring supersymmetry occurring in two dimensional systems described by the tricritical Ising model and a further infinite series of models.

Some results on the representation theory of N=2 superconformal algebras, which also describe naturally occurring two dimensional systems (and have applications in string theory) are here.

An early paper on the ADHM construction in 4k dimensions is here.

My other work on the representation theory of the Virasoro algebra includes descriptions of its singular vectors (see also here) and a recursion formula for the signature characters of its highest weight representations. The technique for calculating signature characters gives an alternative way of characterising unitary highest weight representations of Lie algebras: some calculations for simple Lie algebras are here.

Research Students

Former PhD students:

Current PhD students:

Patents

Tagging Systems,
A. Kent, R. Beausoleil, W. Munro and T. Spiller,
US patent 7075438 (2006).

Quantum Information Processing using Electromagnetically Induced Transparency,
R. Beausoleil, A. Kent, P. Kuekes, W. Munro, T. Spiller and R. Williams,
US patent 7560726 (2009).

Security systems and monitoring methods using quantum states,
A Kent, WJ Munro, TP Spiller, RG Beausoleil,
US Patent 7483142 (2009).

Quantum cryptography,
A. Kent, R. Beausoleil, W. Munro and T. Spiller,
US Patent 7983422 (2011).

Science and Literature

I belong to the splendid Cambridge Science and Literature Reading Group and the Wolfson Contemporary Reading Group.

A review of Michael Frayn's play "Copenhagen", published in Alternatives Theatrales, is here.

Email:
A.P.A.Kent at damtp.cam.ac.uk

Mail: