Anthony Chefles
Research Fellow
Email: anthony.chefles@hp.com
Phone: +44 (0)117 312 9983
FAX: +44 (0)117 312 9870
Location:
Quantum Information Processing Group
HewlettPackard Laboratories, Bristol
Before arriving at HP, Tony held postdoctoral and lecturing positions at the
Universities of Strathclyde and Hertfordshire, NUI Maynooth and University
College Dublin. His work focuses on the theory of quantum states and channels
(processes) with applications to quantum information science. His main
research interests are in relation to the informationtheoretic properties of
quantum states and the quantum channels which are used to process them. Among
the issues that arise, and which are the focus of much of his research activity,
are:
Distinguishability: Sending classical information
using quantum states requires us to distinguish among the possible states in
order to extract the message. To distinguish among quantum channels, we must
likewise distinguish among the states that the possible channels can create.
One problem that arises with quantum states, which has no classical analogue,
is that arbitrary quantum states cannot, in principle, be perfectly
distinguished. Tony has made numerous pioneering contributions to this field,
relating in particular to fundamental physical limitations upon how well quantum
state discrimination tasks can be accomplished. His current research is related
the applicability of quantum channel discrimination in quantum computation, in
particular, quantum searching.
Entanglement and classical communication capacities:
Quantum channels can create a novel quantum mechanical effect, and useful
information processing resource, known as entanglement. They can also be used
to transmit ordinary classical information. Part of his research relates to
how well these (related) tasks can be accomplished in general, and also on
obtaining more detailed information about specific channels that are of
importance in quantum communications and computation, such as channels that are
used to compute functions.
Quantum protocols and games: A topic under
intensive investigation is how quantum mechanics can be used carry out tasks
with certain informationtheoretic requirements relating to, e.g. security. It
is wellknown that quantum mechanics permits the secure distribution of
cryptographic keys. However, it has numerous other applications. One such
application relates to voting, where we require the voters’ identities to remain
anonymous while retaining transparency and fairness in the voting and counting
procedures. Protocols for achieving such tasks can be regarded as games. A
quantum gametheoretic framework can also be provided for assessing how noisy a
given quantum channel is, which is of paramount importance in quantum
communications. Tony's current research in this area related to both quantum
voting protocols and the global quantification of noise in quantum channels,
where we aim to determine when one channel is preferable to another for all
input quantum states.
List of publications
Thesis

A. Chefles, ‘Nonlocality and nonlinearity in quantum
optics’ PhD Thesis, University of Strathclyde (1997).
Published

A. Chefles and S. M. Barnett, ‘Complementarity and
Cirel’son’s inequality’ J. Phys. A 237 (1996).

A. Chefles and S. M. Barnett, ‘Quantum theory of
twomode nonlinear directional couplers’ J. Mod. Opt. 709 (1996).

A. Chefles, ‘Nearestneighbour level spacing
distribution for the nonperiodic discrete nonlinear Schrödinger equation’
J. Phys. A 4515 (1996).

A. Chefles and S. M. Barnett, ‘Diagonalisation of the
BellCHSH operator’ Phys. Lett. A 4 (1997).

A. Chefles and S. M. Barnett, ‘Collective observables
and enhanced violation of Bell’s inequality’ Phys. Rev. A 1721
(1997).

A. Chefles and S. M. Barnett, ‘Entanglement and
unambiguous discrimination between nonorthogonal states’ Phys. Lett. A
177 (1997).

A. Chefles, ‘Unambiguous discrimination between
linearlyindependent quantum states’, Phys. Lett. A 339 (1998).

A. Chefles and S. M. Barnett, ‘Optimum unambiguous
discrimination between linearlyindependent symmetric states’, Phys. Lett.
A 223 (1998).

A. Chefles and S. M. Barnett, ‘Strategies for
discriminating between nonorthogonal quantum states’ J. Mod. Opt.
1295 (1998)

A. Chefles and S. M. Barnett, ‘Quantum state
separation, unambiguous discrimination and exact cloning’, J. Phys. A
10097 (1998).

S. M. Barnett, A. Chefles, D. T. Pegg and L. S.
Phillips, ‘Generalised measurements, retrodiction and state manipulation’ In
Proceedings of the 4th International Conference of Quantum Communication,
Measurement and Computing, Evanston, Illinois, 1998 (Plenum).

A. Chefles and S. M. Barnett, ‘Strategies and networks
for statedependent quantum cloning’, Phys. Rev. A 136 (1999).

A. Chefles, ‘Quantum state discrimination’,
Contemporary Physics 401 (2000).

S. J. D. Phoenix, S. M. Barnett and A. Chefles,
‘Threestate quantum cryptography’, J. Mod. Opt 507 (2000).

A. Chefles, ‘Deterministic quantum state
transformations’, Phys. Lett. A 14 (2000).

A. Chefles, C. R. Gilson and S. M. Barnett,
‘Entanglement and collective quantum operations’, Phys. Lett. A 10
(2000).

S. F. Huelga, J. A. Vaccaro, A. Chefles and M. B.
Plenio, ‘Quantum remote control: teleportation of unitary operations’,
Phys. Rev. A , 042303 (2001)

A. Chefles, C. R. Gilson and S. M. Barnett,
‘Entanglement, information and multiparticle quantum operations’, Phys.
Rev. A , 032314 (2001).

S. M. Barnett, R. B. M. Clarke, V. M. Kendon, E. Riis,
A. Chefles and M. Sasaki, ‘Experimental Quantum State Discrimination’ In
Proceedings of the 3rd International Conference of Quantum Communication,
Measurement and Computing, Capri, Italy, 2000 (Plenum).

R. B. M. Clarke, A. Chefles, S. M. Barnett and E. Riis,
‘Experimental demonstration of optimal unambiguous state discrimination’,
Phys. Rev. A , 042305 (2001).

R. B. M. Clarke, V. M. Kendon, A. Chefles, S. M.
Barnett, E. Riis and M. Sasaki, ‘Experimental realisation of optimal
detection strategies for overcomplete states’, Phys. Rev. A , 012303
(2001).

M. Sasaki, A. Carlini and A. Chefles, ‘Optimal phase
estimation and squareroot measurement’, J. Phys. A 7017 (2001).

A. Chefles, ‘Unambiguous discrimination between
linearly dependent states with multiple copies’, Phys. Rev. A ,
063025 (2001).

A. Chefles, ‘Quantum operations, state transformations
and probabilities’, Phys. Rev. A 052314 (2002).

A. Chefles, ‘Distinguishability measures and ensemble
orderings’, Phys. Rev. A 042325 (2002).

A. Chefles and M. Sasaki, ‘Retrodiction of generalised
measurement outcomes’, Phys. Rev. A. 032112 (2003).

S. M. Barnett, A. Chefles and I. Jex, ‘Comparison of
two unknown quantum states’, Phys. Lett. A 189 (2003).

I. Jex, E. Andersson and A. Chefles, ‘Comparing the
states of many quantum systems’, J. Mod. Opt. 505 (2004).

A. Chefles, R. Jozsa and A. Winter, ‘On the existence
of physical transformations between sets of quantum states’, Int. J.
Quant. Info. 11 (2004).

A. Chefles, ‘Condition for unambiguous state
discrimination with local operations and classical communication’, Phys.
Rev. A 050307(R) (2004).

*A. Chefles, E. Andersson and I. Jex, ‘Unambiguous
comparison of the states of multiple quantum systems’, J. Phys. A: Math.
Gen 7315 (2004).

*A. Chefles, ‘Quantum states: discrimination and
classical information transmission. A review of experimental progress’.
Invited contributed chapter to monograph on ‘Quantum State Estimation’ (ed.
M. Paris and J. Rehacek) (Springer, 2004).

F. Anselmi, A. Chefles and M. B. Plenio, ‘Local copying
of orthogonal entangled quantum states’, New. J. Phys. 164 (2004).

A. Chefles, ‘Entangling capacity and distinguishability
of twoqubit unitary operators’. Phys. Rev. A 042332 (2005).

A. Kitagawa, M. Takeoka, M. Sasaki and A. Chefles,
‘Entanglement evaluation of nonGaussian states generated by photon
subtraction from squeezed states’. Phys. Rev. A 042310 (2006).
Submitted

*J. A. Vaccaro, J. Spring and A. Chefles, ‘Quantum
protocols for anonymous voting and surveying’. ArXiv quantph/0504161. To
appear in Physical Review A.
In preparation

A. Chefles, ‘Theory of maximally nonlocal bipartite
unitary operations (working title)’.

A. Chefles, ‘On the quantum generalisation of
Blackwell’s theorem’.

A. Chefles, A. Kitagawa, M. Takeoka, M. Sasaki and J.
Twamley, ’Unambiguous discrimination among oracle operators’.
