Joan Vaccaro, BSc ( Hon ), PhD (Griffith), FInstP


Contact details


Joan was educated at Griffith University in the 1980's.  Her PhD degree in Theoretical Quantum Optics was supervised by Prof. David Pegg FAA and was awarded in 1990.  Her research has since broadened to coherent phenomena in laser cooled gases, robust states of open quantum systems, ultra cold quantum gases (Bose-Einstein condensation), superselection rules and entanglement, quantum data security, quantum information processing and more recently, the physics of time.   She worked in the UK and Europe for about 12 years at the

  • University of Strathclyde, Glasgow, UK,
  • Max Planck Society Workgroup, Humboldt University, Berlin, Germany,
  • The Open University, Milton Keynes, UK, and
  • University of Hertfordshire, Hatfield, UK

before returning to Griffith University in 2005.


Academic Positions

  • 1989-1994 Lecturer, Griffith University
  • 1994-1995 Postdoctoral Research Fellow, Max Planck Society Workgroup on Nonclassical Light, Humboldt University, Berlin, Germany
  • 1995-1997 Postdoctoral Research Assistant, The Open University, Milton Keynes, UK
  • 1997-2000 Senior Lecturer, University of Hertfordshire, Hatfield, UK
  • 2000-2005 Reader, University of Hertfordshire, Hatfield, UK
  • 2004-2005 Leverhulme Trust Research Fellowship
  • 2005-2010 Senior Lecturer, Griffith University
  • 2011-....... Associate Professor, Griffith University

Media Impact

Wikipedia article references


  • "Optical apparatus for implementing Schumacher's quantum data compression",
    GB 2400252 A, 6 April 2005.
  • "Quantum information source coding device and quantum information communication system",
    Japan 3858067, 29 September 2006.
  • "Quantum source coding apparatus and quantum information communication system",
    US 07403713 B2, 22 July 2008 (2008).


  • S.M. Barnett and J.A. Vaccaro, "The Quantum Phase Operator: A Review" (Taylor and Francis, London, 2007)

Selected Talks

Symposium organisation


  • Leverhulme Trust Research Fellowship, 1 September 2004 - 31 October 2005.
  • British Council Travel Grant, 14-18 February 2005.
  • Royal Society Travel Grant, 2-6 May 2005.
  • Griffith University, Research Grant, 2009.
  • Australian Research Council, Linkage Grant 2014-2017.

Lists of Publications

A complete list of my publications can be found at the following websites:


  • Publications (refereed):  74
  • Citations (Web of Science): 1623
  • h-index (Web of Science): 23

Publications by Research Topic

Quantum states of light - squeezing

  • Amplifying squeezing light
    • J.A. Vaccaro and D.T. Pegg, "Squeezing of light by coherent attenuation", Optica Acta, 33, 1141-1147 (1986);
    • D.T. Pegg and J.A. Vaccaro,"Squeezing in the output of a high-gain atomic light amplifier", Optics Commun., 61, 317-320, (1987);
    • J.A. Vaccaro and D.T. Pegg, "Squeezed atomic light amplifiers", J. Mod. Optics, 34, 855-872 (1987).
  • Phase properties
    • J.A. Vaccaro and D.T. Pegg, "Phase properties of squeezed states of light", Optics Commun. 70, 529-534 (1989);
    • J.A. Vaccaro and D.T. Pegg, "Phase properties of optical linear-amplifiers", Phys. Rev. A, 49, 4985-4995 (1994);
    • J.A. Vaccaro and D.T. Pegg, "Nondiffusive phase dynamics from linear-amplifiers and attenuators in the weak-field regime", J. Mod. Optics 41, 1079-1086 (1994);
    • J.A. Vaccaro, S.M. Barnett and D.T. Pegg, "Phase fluctuations and squeezing", J. Mod. Optics 39, 603-614 (1992).

Pegg-Barnett Quantum Phase Operator

  • Minimum uncertainty states
    • J.A. Vaccaro and D.T. Pegg, "Physical number phase intelligent and minimum-uncertainty states of light", J. Mod. Optics 37, 17-29 (1990).
  • Generalized canonical observables
    • D.T. Pegg, J.A. Vaccaro and S.M. Barnett, "Quantum-optical phase and canonical conjugation", J. Mod. Optics 37, 1703 (1990).
  • Mathematical formalism
    • U. Leonhardt, J.A. Vaccaro, B. Bohmer and H. Paul, "Canonical and measured phase distributions", Phys. Rev. A 51, 84-95 (1995);
    • J.A. Vaccaro, "Phase operators on Hilbert-space", Phys. Rev. A 51, 3309-3317 (1995);
    • J.A. Vaccaro and R.F. Bonner, "Pegg-Barnett phase operators of infinite rank", Phys. Lett. A, 198, 167-174 (1995);
    • J.A. Vaccaro and Y. Benaryeh, "Antinormally ordering of phase operators and the algebra of weak limits", Optics Commun., 113, 427-432 (1995).
  • Wigner function for photon number and phase
    • J.A. Vaccaro and D.T. Pegg, "Wigner function for number and phase", Phys. Rev. A 41, 5156-5163 (1990);
    • J. Vaccaro, "Number-phase Wigner function on Fock space", Phys. Rev. A 52, 3474-3488 (1995);
    • J.A. Vaccaro, "New Wigner function for number and phase", Optics Commun. 113, 421-426 (1995).
  • General aspects of phase
    • J.A. Vaccaro and D.T. Pegg, "On measuring extremely small phase fluctuations", Optics Commun. 105, 335-340 (1994);
    • J.A. Vaccaro and D.T. Pegg, "Consistency of quantum descriptions of phase", Physica Scripta T48, 22-28 (1993);
    • J.A. Vaccaro and A. Orlowski, "Phase properties of Kerr media via variance and entropy as measures of uncertainty", Phys. Rev. A 51, 4172-4180 (1995);
    • A.R. Gonzalez, J.A. Vaccaro and S.M. Barnett, "Entropic uncertainty relations for canonically conjugate operators", Phys. Lett. A 205, 247-254 (1995).

Quantum nonlocality

  • Bell correlations and the Wigner function
    • U. Leonhardt and J.A. Vaccaro, "Bell correlations in phase-space - application to quantum optics", J. Mod. Optics, 42, 939-943 (1995).

Quantum state determination

  • Reconstructing the wave function
    • J.A. Vaccaro and S.M. Barnett, "Reconstructing the wave-function in quantum optics", J. Mod. Optics, 42, 2165-2171 (1995);
    • O. Steuernagel and J.A. Vaccaro, "Reconstructing the density operator via simple projectors", Phys. Rev. Lett. 75, 3201-3205 (1995) [arXiv:quant-ph/9510014].

Stochastic Schrödinger equations

  • From quantum jumps to quantum state diffusion
    • J.A. Vaccaro and D. Richards, "Stochastic Schrodinger equations for optical fields based on atom detection", Phys. Rev. A., 58 2690-2698 (1998).

Electromagnetically-induced transparency (EIT)

  • Transient EIT
    • H.X. Chen, A.V. Durrant,  J.P. Marangos, and J.A. Vaccaro, "Observation of transient electromagnetically induced transparency in a rubidium Lambda system", Phys. Rev. A 58 1545-1548 (1998);
    • S.R. de Echaniz, A.D. Greentree, A.V. Durrant, D.M. Segal, J.P. Marangos and J.A. Vaccaro, "Observation of transient gain without population inversion in a laser-cooled rubidium Lambda system", Phys. Rev. A 64 055801 (2001);
    • A.D. Greentree, T.B. Smith, S.R. de Echaniz, A.V. Durrant, J.P. Marangos, D.M. Segal and J.A. Vaccaro, "Resonant and off-resonant transients in electromagnetically induced transparency: Turn-on and turn-off dynamics", Phys. Rev. A 65, 053802 (2002) [arXiv:quant-ph/0109090].
  • Hyperfine sublevels in laser cooled samples
    • A.V. Durrant, H.X. Chen, S.A. Hopkins, and J.A. Vaccaro, "Zeeman-coherence-induced transparency and gain without inversion in laser-cooled rubidium", Optics Commun., 151, 135-146 (1998).
  • 4 and 5 level systems
    • A.D. Greentree, J.A. Vaccaro, S.R. de Echaniz, A.V. Durrant and J.P. Marangos, "Prospects for photon blockade in four-level systems in the N configuration with more than one atom",Journal of Optics B 2, 252-259 (2000) [ arXiv:quant-ph/0002091] ;
    • S.R. de Echaniz, A.D. Greentree, A.V. Durrant, D.M. Segal, J.P. Marangos and J.A. Vaccaro, "Observations of a doubly driven V system probed to a fourth level in laser-cooled rubidium", Phys Rev. A 64, 013812 (2001) [arXiv:quant-ph/0102098];
    • A.D. Greentree, D. Richards, J.A. Vaccaro, A.V. Durrant, S.R. de Echaniz, D.M. Segal and J.P. Marangos, "Intensity-dependent dispersion under conditions of electromagnetically induced transparency in coherently prepared multistate atoms", Phys Rev. A 67, 023818 (2002)  [ arXiv:quant-ph/0209067 ].
  • Vector model of EIT
    • J.A. Vaccaro, A.V. Durrant, D. Richards, S.A. Hopkins, H.X. Chen and K.E. Hill, "Stochastic wavefunction diagrams for electromagnetically induced transparency, inversionless gain and shelving", J. Mod. Optics 45, 315-333 (1998).

Quantum Information Processing

Robust states of open quantum systems

  • Quantum state of Bose-Einstein condensates and atom lasers
    • S.M. Barnett, K. Burnett and J.A. Vaccaro, "Why a condensate can be thought of as having a definite phase", Journal of Research of the National Institute of Standards and Technology 101, 593 (1996);
    • H.M. Wiseman and J.A. Vaccaro, "Atom lasers, coherent states, and coherence. I. Physically realizable ensembles of pure states", Phys. Rev. A 65, 043605 (2002) [arXiv:quant-ph/9906125];
    • H.M. Wiseman and J.A. Vaccaro, "Atom lasers, coherent states, and coherence II. Maximally robust ensembles of pure states", Phys. Rev. A 65, 043606 (2002) [arXiv:quant-ph/0112145].
  • Robust states as the preferred ensemble
    • H.M. Wiseman and J.A. Vaccaro, "Maximally Robust Unravelings of Quantum Master Equations", Phys. Lett. A 250, 241-248 (1998) [arXiv:quant-ph/9709014];
    • H.M. Wiseman and J.A. Vaccaro, "Inequivalence of pure state ensembles for open quantum systems: The preferred ensembles are those that are physically realizable", Phys. Rev. Lett. 87, 240402 (2001) [arXiv:quant-ph/0112115].

Superselection Rules, Reference Systems and Entanglement

Particle-wave Duality and Complementarity

Foundations of Thermodynamics

Physical Nature of Time


Quantum thermodynamics

Landauer argued that information is physical because the process of erasing the information stored in a memory device incurs an energy cost in the form of a minimum amount of mechanical work. We have recently found, however, that this energy cost can be reduced to zero by paying a cost in angular momentum or another conserved quantity. Erasing the memory of Maxwell's demon in this way implies that work can be extracted from a single thermal reservoir at a cost of angular momentum and an increase in total entropy. The new erasure mechanism calls for a fundamental restatement of the Second Law of thermodynamics [Proc. R. Soc. A 467, 1770-1778 (2011), eprint arXiv:1004.5330 , Entropy 15, 4956-4968 (2013) ].  It also imposes new restrictions for perpetual machines of the second kind.  We have examined the nature of the discrete fluctuations in the cost of erasing information using spin angular momentum [Phys. Rev. Lett. 118, 060602 (2017)]. We are currently exploring experimental implementations of the erasure protocol.
Further information:  see the Centre for Quantum Dynamics entry on Quantum Thermodynamics.

The quantum nature of time

Time reversal invariance (T) refers to the symmetry between the past and future.  All physical processes obey this invariance.  The one exception is the weak force in the decay of K and B mesons.  The violation of T symmetry in these systems signifies a fundamental asymmetry between the past and future. I have recently shown that processes which violate T symmetry induce destructive interference between different paths that the universe can take through time. This work resolves the long-standing problem of modeling the dynamics of T violation processes. It shows that T violation has previously unknown, large-scale physical effects and that these effects underlie the origin of the unidirectionality of time [Found. Phys. 41 1569-1596 (2011) DOI, eprint arxiv:0911.4528, Found. Phys. 45 , 691-706 (2015) DOI, eprint arXiv:1503.06523].
Current work is exploring the implications for the difference between space and time [Proc. R. Soc. Lond. A 472, 20150670 (2016) DOI ,  Book chapter DOI].

New Scientist included my quantum theory of time in the article "One time or another: Our best 5 theories of the fourth dimension" by Anil Ananthaswamy, 1 February 2017.

Particle-wave duality

The nature of physical objects to have both particle and wave properties is one of the foundational elements of quantum theory. Essentially a particle-like state is represented by a narrow wave function which is displaced by spatial translations. In contrast a wave-like state is represented by a spread out wave function which is invariant to spatial translations. The wave-particle dichotomy can therefore be seen as a competition between displacement and invariance of the state with respect to spatial translations. We have generalised this dichotomy to arbitrary quantum systems with finite dimensional Hilbert spaces as follows. We use arbitrary finite symmetry groups to represent transformations of the quantum system. The symmetry (i.e. invariance) or asymmetry (i.e. displacement) of a given state with respect to transformations of the group are identified with the generalised wave and particle nature, respectively. We adopt a measure of wave and particle properties based on the amount of information that can be encoded in the symmetric and asymmetric parts of the state [Proc. R. Soc. A 468, 1065-1084 (2012) DOI, eprint arXiv:1105.0083].

Quantum reference frames and entanglement

Our description of physical objects is always relative to reference frames of some sort. For example, the position of a car on campus might be "in the third car park from the main entrance of East Car Park". For this description to make sense we need to know where East Car Park is. Presumably its position is known with respect to the campus site etc. Likewise a description of a quantum system, in the form of a quantum state, is relative to a number of implicit references which are represented by other physical systems. Often the reference systems are large and can be treated as classical. For example, if a spin-1/2 particle is described as being in the "spin-up" state it is presumed that the direction of the positive z-axis ("up") is known, perhaps relative to the orientation of a string bob. However when we include the reference systems in the full quantum description we find that matters change. In particular, the clarity of the description of quantum systems depends on the 'size' of the accompanying quantum references. This has an impact when high-fidelity quantum states are needed in areas such as quantum computing. We are exploring the optimum states for quantum references and the effects on quantum entanglement. [See e.g. Phys. Rev. A 77, 032114 (2008), eprint arxiv:quant-ph/0501121; Phys. Rev. A  79, 032109 (2008), eprint arxiv:0807.0064].

Quantum data security

Data security is a major issue in everyday life, from electronic fund transfers to voting in an election. A revolution has occurred relatively recently in this field with advent of quantum information science. This new branch of research uses the quantum nature of physical systems as a basis for security. A range of applications have been developed such as quantum secret sharing, quantum data hiding, quantum anonymous transfer, quantum oblivious transfer, quantum broadcast communication, quantum identity authentication, quantum finger printing, quantum seals, quantum signatures and quantum exams. We recently introduced a secure protocol for voting (quantum voting) in elections where the privacy of the vote and the anonymity of the voter is protected by quantum physics [Phys. Rev. A 75, 012333 (2007), eprint arxiv:quant-ph/0504161]. A vote is made by performing an operation at one site, a voting booth if you will, but the information of the vote cannot be accessed from that site alone. This effect is spontaneous and due to the entangled nature of the quantum states used. Areas of interest include exploring how quantum physics beats classical systems in data security, examining the robustness of particular applications and examining security-anonymity trade offs.

Teaching Areas

  • Optics
  • Thermodynamics
  • Relativity
  • Electromagnetism
  • Group Theory
  • Tensor Calculus
  • Particle Physics
  • Classical Physics: Lagrange and Hamilton formalisms
  • Quantum Physics: mathematical formalism, quantum information basics
  • Physics of Time

Other webpages

Griffith Experts gives further information regarding Joan's profile as generated from internal records at Griffith University:

More information, including personal opinions, appreciation of surreal art, description of a quantum computer and so on, can be found on Joan's personal homepage: