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Research philosophy:
I maintain an active interest in both theoretical and experimental research in a
broad range of
topics, including Condensed Matter, Quantum Field Theory, Quantum Information Theory,
Quantum Optics and Quantum Foundations. I continually seek to draw together results from
disparate fields.
The theme of retaining a comprehensive `big picture' view of the work I do
is extremely important to me. I am far more interested in initiating and provoking
new avenues of inquiry, and then encouraging others into them with me, than in following
established lines of research that I consider obvious.
I continually
evaluate my work under the criterion that it should still be relevant to fundamental
physics if and when the fields I am working in become primarily engineering.
I avoid mathematical machinations for their own
sake; seeking a deeper understanding of the connections between different areas of
physics is my primary passion.
I continually examine my work to see
if there is some feasible experiment to be gleaned from it.
Experiments motivated directly by my theoretical work have been
performed, and others are underway, at several different research institutions.
Notable research impact:
Quantum Information is Physical
In 1998 I wrote a pair of articles
which presented arguments against the trend in Quantum Information toward
mathematical abstraction, which had resulted in all physical incarnations of qubits being
treated equivalently with respect to their information processing capabilities. Asher
Peres told me, many years later, that my line of thinking formed part of the motivation
for his well known program of study into `unspeakable information'. Charles Bennett has
told me that he has presented my arguments in several talks. By contrast, Gilles Brassard
once stated that I am trying to `drag us back into the dark ages' of information theory!
Reference Frames and Superselection Rules in Quantum Information Theory
Expanding on the aforementioned ideas has led naturally to me being an initiator of
investigation into the role of reference frames and superselection rules in quantum
information theory. Particularly infamous is my work in 2001 with Barry Sanders on
optical coherence in quantum teleportation, and my more recent work
with Robert Spekkens and Stephen Bartlett on quantum communication without reference
frames. The former work has affected the
design of several quantum information experiments, the latter work has recently been
experimentally demonstrated by two different research groups. Some of my work on reference frames was
Quantum Cryptography
In this field I am best known for my work performed in
2001/2 with Rob Spekkens on two-party cryptographic protocols, in particular for
discovering the (then) best known protocols} for weak coin flipping and bit commitment
and co-discovering the best known protocol for strong coin flipping. We also
presented the first provably cheat sensitive protocol - this has opened up an
exciting vista of tasks that become possible under the assumption the communicating
parties value an ongoing relationship (i.e. that there is a strong disincentive for being
caught cheating); these form the focus of much current research. This research was
My work on two-party cryptography has been well cited, some experiments based on this work have recently been completed and further
experiments are currently underway.
Quantum Computation
Over the course of my research career I have done
various pieces of work aimed at finding practical quantum computation architectures. Very
recently, I, along with Dan Browne, proposed a new scheme for linear optics quantum
computation that has generated a large amount of interest. In addition to being many
orders of magnitude more resource efficient than all other proposals, it is also the
first scheme that does not require phase sensitive interference - it thus avoids the
immense problems other proposals encounter because they require keeping a very large
interferometer stable to within an optical photon's wavelength. This work has already
been incorporated as a key part of two separate funding proposals by prominent
experimental groups.
Current projects
To give some flavour of the research I am currently pursuing, the following are just a
few specific projects I am presently immersed in; most are near completion:
Reference Frames as a resource
In the
context of quantum information/communication it turns out that reference frames should be
considered a consumable resource in a variety of practical situations. Together with several collaborators I have studied numerically how
reference frame states degrade with the number of non-orthogonal quantum states measured
against them; we are in the process of seeking an analytical description of this effect.
Quantizing and Dequantizing Reference Frames
Much confusion over the use
of classical objects and fields in quantum mechanics has resulted from incorrect
assumptions about how to quantize a reference frame. Together with Rob Spekkens and
Stephen Bartlett I have constructed a general group-theoretic description of the correct
procedure for doing so.
Relative parameter localization
Certain
measurements can localize relative parameters of various systems - the phases of
independent BEC's or the relative position of particles being simple examples. The
majority of work on this problem has been performed numerically. Together with Hugo Cable
and Peter Knight I have devised a simple analytical framework for explaining this process
in a wide variety of different physical systems. Our work provides insight into how this
process is related to various decoherence models.
Measurement as a quantum computational primitive
One paradigm for quantum computation involves using measurement, instead of coherent
unitary evolution, as a mechanism for enabling the nontrivial interactions necessary for
building a quantum computer. Together with Shashank Virmani I have shown how certain
physically interesting measurements are universal - such as parity and total spin
measurements. At present we are optimising these schemes.
New `nonlocality' proof
I recently discovered an
interesting new way of deriving and elucidating Bell's theorem (that local hidden
variables do not suffice for explaining quantum effects). The proof is closely related
to some recent work I have done on `preparation noncontextuality', in much the same way
that Bell's inequalities are related to the Kochen-Specker theorem on measurement
noncontextuality.
Future research themes
I am interested in developing a deep understanding of
the restrictions on information processing that result from both abstract physical laws,
and the limited set of physical interactions which are experimentally feasible. As such,
a large part of my current, and future, research falls under the banner of examining what
is necessary, as opposed to what is merely sufficient, to obtain the power of quantum
information. In particular, because of my close association with a number of experimental
quantum optics groups, I focus on optical and hybrid optical/solid state realizations of
quantum information processing.
My work on reference frames has opened up a series of
interesting questions. In particular I would like this area of my work to lead toward an
understanding of how to formulate a quantum mechanical theory without background
classical objects, and in a completely relational manner.
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