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Is there a problem with our Hamiltonians for quantum nonlinear optical processes?Jun 14 2018The models we use, habitually, to describe quantum nonlinear optical processes have been remarkably successful yet, with few exceptions, they each contain a mathematical flaw. We present this flaw, show how it can be fixed and, in the process, suggest ... More

Schrodinger picture analysis of the beam splitter: an application of the Janszky representationJun 14 2018The Janszky representation constructs quantum states of a field mode as a superposition of coherent states on a line in the complex plane. We show that this provides a natural Schr\"{o}dinger picture description of the interference between a pair of modes ... More

Gravitational Field TensorDec 05 2014We present a tensorial relative of the familiar affine connection and argue that it should be regarded as the gravitational field tensor. Remarkably, the Lagrangian density expressed in terms of this tensor has a simple form, which depends only on the ... More

On the conditions for discrimination between quantum states with minimum errorOct 10 2008We provide a simple proof for the necessity of conditions for discriminating with minimum error between a known set of quantum states.

The Roentgen interaction and forces on dipoles in time-modulated optical fieldsApr 06 2017Sep 01 2017The Roentgen term is an often neglected contribution to the interaction between an atom and an electromagnetic field in the electric dipole approximation. In this work we discuss how this interaction term leads to a difference between the kinetic and ... More

Quantum state discriminationOct 10 2008It is a fundamental consequence of the superposition principle for quantum states that there must exist non-orthogonal states, that is states that, although different, have a non-zero overlap. This finite overlap means that there is no way of determining ... More

Security against eavesdropping in quantum cryptographyNov 18 1997In this article we deal with the security of the BB84 quantum cryptography protocol over noisy channels using generalized privacy amplification. For this we estimate the fraction of bits needed to be discarded during the privacy amplification step. This ... More

Difficulty of distinguishing product states locallyJan 10 2017Non-locality without entanglement is a rather counter-intuitive phenomenon in which information may be encoded entirely in product (unentangled) states of composite quantum systems in such a way that local measurement of the subsystems is not enough for ... More

Vacuum FrictionSep 14 2017Nov 06 2017We know that in empty space there is no preferred state of rest. This is true both in special relativity but also in Newtonian mechanics with its associated Galilean relativity. It comes as something of a surprise, therefore, to discover the existence ... More

Mutually unbiased measurements for high-dimensional time-bin based photonic statesNov 12 2013The task of measuring in two mutually unbiased bases is central to many quantum information protocols, as well as being of fundamental interest. Increasingly, there is an experimental focus on generating and controlling high-dimensional photonic states. ... More

Creation of coherence in Bose-Einstein condensates by atom detectionMar 05 1999We investigate the creation of a relative phase between two Bose-Einstein condensates, initially in number states, by detection of atoms and show how the system approaches a coherent state. Two very distinct time scales are found: one for the creation ... More

Analytic stochastic treatment of a nonlinear quantum model with negative diffusionSep 21 2001Apr 29 2002We apply a proposal of Yuen and Tombesi, for treating stochastic problems with negative diffusion, to the analytically soluble problem of the single-mode anharmonic oscillator. We find that the associated stochastic realizations include divergent trajectories. ... More

Theory of the radiation pressure on magneto-dielectric materialsFeb 18 2015We present a classical linear response theory for a magneto-dielectric material and determine the polariton dispersion relations. The electromagnetic field fluctuation spectra are obtained and polariton sum rules for their optical parameters are presented. ... More

Resolution in rotation measurementsMar 30 2005The limiting resolution in optical interferometry is set by the number of photons used, with the functional dependence determined by the state of light that is prepared. We consider the problem of measuring the rotation of a beam of light about an optical ... More

Information communicated by entangled photon pairsMar 07 2012A key goal of quantum communication is to determine the maximum number of bits shared between two quantum systems. An important example of this is in entanglement based quantum key distribution (QKD) schemes. A realistic treatment of this general communication ... More

Strategies and Networks for State-Dependent Quantum CloningDec 15 1998State-dependent cloning machines that have so far been considered either deterministically copy a set of states approximately, or probablistically copy them exactly. In considering the case of two equiprobable pure states, we derive the maximum global ... More

Quantum State Separation, Unambiguous Discrimination and Exact CloningAug 11 1998Unambiguous discrimination and exact cloning reduce the square-overlap between quantum states, exemplifying the more general type of procedure we term state separation. We obtain the maximum probability with which two equiprobable quantum states can be ... More

Mass-energy and anomalous friction in quantum opticsJun 01 2018Oct 04 2018The usual multipolar Hamiltonian for atom-light interaction features a non-relativistic moving atom interacting with electromagnetic fields which inherently follow Lorentzian symmetry. This combination can lead to situations where atoms appear to experience ... More

Nonlocality Without Inequalities for all Pure Entangled StatesJul 31 1998Aug 09 1999This paper has been withdrawn by the authors.

Optimum Unambiguous Discrimination Between Linearly Independent Symmetric StatesJul 08 1998The quantum formalism permits one to discriminate sometimes between any set of linearly-independent pure states with certainty. We obtain the maximum probability with which a set of equally-likely, symmetric, linearly-independent states can be discriminated. ... More

Momentum exchange between light and a single atom: Abraham or Minkowski?Nov 17 2008We consider the forces exerted by a pulse of plane-wave light on a single atom. The leading edge of the pulse exerts a dispersive force on the atom, and this modifies the atomic momentum while the atom is enveloped in the light. The standard view of the ... More

Interference of composite bosonsMar 25 2010We investigate multi-boson interference. A Hamiltonian is presented that treats pairs of bosons as a single composite boson. This Hamiltonian allows two pairs of bosons to interact as if they were two single composite bosons. We show that this leads to ... More

Cloning and Joint Measurements of Incompatible Components of SpinJan 16 2006A joint measurement of two observables is a {\it simultaneous} measurement of both quantities upon the {\it same} quantum system. When two quantum-mechanical observables do not commute, then a joint measurement of these observables cannot be accomplished ... More

Relay QKD Networks & Bit TransportFeb 23 2015We show how it is possible to operate end-to-end relays on a QKD network by treating each relay as a trusted eavesdropper operating an intercept/resend strategy. It is shown that, by introducing the concept of bit transport, the key rate compared to that ... More

No-Signalling Bound on Quantum State DiscriminationAug 29 2007Quantum correlations do not allow signalling, and any operation which may be performed on one system of an entangled pair cannot be detected by measurement of the other system alone. This no-signalling condition limits allowed operations and, in the context ... More

Frictional quantum decoherenceJul 19 2007The dynamics associated with a measurement-based master equation for quantum Brownian motion are investigated. A scheme for obtaining time evolution from general initial conditions is derived. This is applied to analyze dissipation and decoherence in ... More

Joint measurements of spin, operational locality and uncertaintySep 21 2005Joint, or simultaneous, measurements of non-commuting observables are possible within quantum mechanics, if one accepts an increase in the variances of the jointly measured observables. In this paper, we discuss joint measurements of a spin 1/2 particle ... More

Comparison of unitary transformsAug 26 2002We analyze the problem of comparing unitary transformations. The task is to decide, with minimal resources and maximal reliability, whether two given unitary transformations are identical or different. It is possible to make such comparisons without obtaining ... More

Will a decaying atom feel a friction force?Oct 07 2016Jan 04 2017We show how a simple calculation leads to the surprising result that an excited two-level atom moving through vacuum sees a tiny friction force of first order in v/c. At first sight this seems to be in obvious contradiction to other calculations showing ... More

Securing a Quantum Key Distribution Network Using Secret SharingMar 03 2012We present a simple new technique to secure quantum key distribution relay networks using secret sharing. Previous techniques have relied on creating distinct physical paths in order to create the shares. We show, however, how this can be achieved on ... More

Information erasure without an energy costApr 29 2010Jun 01 2011Landauer argued that 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 find, however, that this energy cost can be reduced to zero by paying a cost in angular ... More

Conditional beam splitting attack on quantum key distributionJul 30 2001We present a novel attack on quantum key distribution based on the idea of adaptive absorption [calsam01]. The conditional beam splitting attack is shown to be much more efficient than the conventional beam spitting attack, achieving a performance similar ... More

Sequential measurements: Busch-Gleason theorem and its applicationsApr 24 2017Probabilities enter quantum mechanics via Born's rule, the uniqueness of which was proven by Gleason. Busch subsequently relaxed the assumptions of this proof, expanding its domain of applicability in the process. Extending this work to sequential measurement ... More

Proposed optical realisation of a two photon, four-qubit entangled $χ$ stateMar 06 2017The four-qubit states $\lvert\chi^{ij}\rangle$, exhibiting genuinely multi-partite entanglement have been shown to have many interesting properties and have been suggested for novel applications in quantum information processing. In this work we propose ... More

Beyond Landauer erasureOct 29 2013In thermodynamics one considers thermal systems and the maximization of entropy subject to the conservation of energy. A consequence is Landauer's erasure principle, which states that the erasure of 1 bit of information requires a minimum energy cost ... More

Extending the Reach of QKD Using RelaysMar 03 2012One of the obstacles to deployment of QKD solutions has been the distance limitation. Solutions using relays have been proposed but these rely on link-by-link key establishment. We present a new technique to extend the distance of a quantum key distribution ... More

Optimal parameter estimation of depolarizing channelMar 22 2002We investigate strategies for estimating a depolarizing channel for a finite dimensional system. Our analysis addresses the double optimization problem of selecting the best input probe state and the measurement strategy that minimizes the Bayes cost ... More

Interference in dielectrics and pseudo-measurementsDec 11 1996Inserting a lossy dielectric into one arm of an interference experiment acts in many ways like a measurement. If two entangled photons are passed through the interferometer, a certain amount of information is gained about which path they took, and the ... More

Will a decaying atom feel a friction force?Oct 07 2016We show how a simple calculation leads to the surprising result that an excited two-level atom moving through vacuum sees a tiny friction force of first order in v/c. At first sight this seems to be in obvious contradiction to other calculations showing ... More

Detecting an Eavesdropper in QKD Without Public Bit ComparisonMar 03 2012We present a method for determining the presence of an eavesdropper in QKD systems without using any public bit comparison. Alice and Bob use a duplex QKD channel and the bit transport technique for relays. The only information made public is the respective ... More

Quantum Optical State Comparison AmplifierNov 22 2013It is a fundamental principle of quantum theory that an unknown state cannot be copied or, as a consequence, an unknown optical signal cannot be amplified deterministically and perfectly. Here we describe a protocol that provides nondeterministic quantum ... More

Entropic uncertainties for joint quantum measurementsDec 08 2008Sep 11 2009We investigate the uncertainty associated with a joint quantum measurement of two components of spin of a spin-1/2 particle and quantify this in terms of entropy. We consider two entropic quantities: the joint entropy and the sum of the marginal entropies, ... More

Comparison of two unknown pure quantum statesFeb 15 2002Nov 01 2002We investigate the extent to which we can establish whether or not two quantum systems have been prepared in the same state. We investigate the possibility of universal unambiguous state comparison. We show that it is impossible to conclusively identify ... More

Coherent dynamics of Bose-Einstein condensates in high-finesse optical cavitiesJun 24 1999Jul 07 1999We study the mutual interaction of a Bose-Einstein condensed gas with a single mode of a high-finesse optical cavity. We show how the cavity transmission reflects condensate properties and calculate the self-consistent intra-cavity light field and condensate ... More

Optimal sequential measurements for bi-partite state discriminationApr 05 2017State discrimination is a useful test problem with which to clarify the power and limitations of different classes of measurement. We consider the problem of discriminating between given states of a bi-partite quantum system via sequential measurement ... More

Optimal discrimination of single-qubit mixed statesApr 04 2017Sep 22 2017We consider the problem of minimum-error quantum state discrimination for single-qubit mixed states. We present a method which uses the Helstrom conditions constructively and analytically; this algebraic approach is complementary to existing geometric ... More

Vorticity and the birth of optical vorticesJun 12 2019We exploit the vorticity, familiar from fluid mechanics and the theory of superfluids, as a tool to track the birth and subsequent development of optical vortices at a spiral phase plate.

Full characterisation of the quantum spiral bandwidth of entangled biphotonsNov 27 2010Feb 03 2011Spontaneous parametric down conversion has been shown to be a reliable source of entangled photons. Amongst the wide range of properties that have been shown to be entangled, it is the orbital angular momentum that is the focus of our study. We investigate, ... More

Chiral Rotational SpectroscopyNov 14 2015Apr 08 2016We introduce chiral rotational spectroscopy: a new technique that enables the determination of the orientated optical activity pseudotensor components $B_{XX}$, $B_{YY}$ and $B_{ZZ}$ of chiral molecules, in a manner that reveals the enantiomeric constitution ... More

General U(4) gate for photon polarization and orbital angular momentumDec 13 2010We examine the implementation of an arbitrary U(4) gate consisting of CNOT gates and single qubit unitary gates for the Hilbert space of photon spin polarization and two states of photon orbital angular momentum. Our scheme improves over a recently proposed ... More

On the mechanical properties of matter wavesJul 05 2004Electromagnetic waves and fluids have locally conserved mechanical properties associated with them and we may expect these to exist for matter waves. We present a semiclassical description of the continuity equations relating to these conserved properties ... More

Macroscopic quantum fluctuations in noise-sustained optical patternsAug 07 2001Apr 29 2002We investigate quantum effects in pattern-formation for a degenerate optical parametric oscillator with walk-off. This device has a convective regime in which macroscopic patterns are both initiated and sustained by quantum noise. Familiar methods based ... More

Quantum retrodiction in open systemsAug 13 2002Quantum retrodiction involves finding the probabilities for various preparation events given a measurement event. This theory has been studied for some time but mainly as an interesting concept associated with time asymmetry in quantum mechanics. Recent ... More

Holographic quantum imaging: reconstructing spatial properties via two-particle interferenceDec 16 2016Two particle interference phenomena, such as the Hong-Ou-Mandel effect, are a direct manifestation of the nature of the symmetry properties of indistinguishable particles as described by quantum mechanics. The Hong-Ou-Mandel effect has recently been applied ... More

Optical helicity of interfering wavesAug 06 2013Helicity is a property of light which is familiar from particle physics but less well-known in optics. In this paper we recall the explicit form taken by the helicity of light within classical electromagnetic theory and reflect upon some of its remarkable ... More

Response to recent works on the discriminatory optical force for chiral moleculesJun 24 2015We respond to recent works by Bradshaw and Andrews on the discriminatory optical force for chiral molecules, in particular to the erroneous claims made by them concerning our earlier work.

Non-classical behavior in multimode and disordered transverse structures in OPO. Use of the Q representationNov 23 2002We employ the Q representation to study the non-classical correlations that are present from below to above-threshold in the degenerate optical parametric oscillator. Our study shows that such correlations are present just above threshold, in the regime ... More

Grassmann Phase Space Methods for Fermions. II. Field TheoryApr 12 2016Apr 19 2016In both quantum optics and cold atom physics, the behaviour of bosonic photons and atoms is often treated using phase space methods, where mode annihilation and creation operators are represented by c-number phase space variables, with the density operator ... More

Semiclassical theory of matter-wave detectionJun 11 2003We derive a semiclassical theory for the detection of matter-waves. This theory draws on the theories of semiclassical optical detection and fluid mechanics. We observe that the intrinsically dispersive nature of matter-waves is important in deriving ... More

Removal of a single photon by adaptive absorptionJun 15 2001We present a method to remove, using only linear optics, exactly one photon from a field-mode. This is achieved by putting the system in contact with an absorbing environment which is under continuous monitoring. A feedback mechanism then decouples the ... More

Bayes' theorem and quantum retrodictionJun 25 2001We derive on the basis of Bayes' theorem a simple but general expression for the retrodicted premeasurement state associated with the result of any measurement. The retrodictive density operator is the normalised probability operator measure element associated ... More

Optimal measurement strategies for the trine states with arbitrary prior probabilitiesMar 09 2018We investigate the optimal measurement strategy for state discrimination of the trine ensemble of qubit states prepared with arbitrary prior probabilities. Our approach generates the minimum achievable probability of error and also the maximum confidence ... More

Theory of the strongly-damped quantum harmonic oscillatorAug 10 2015We analyse the properties of a strongly-damped quantum harmonic oscillator by means of an exact diagonalisation of the full Hamiltonian, including both the oscillator and the reservoir degrees of freedom to which it is coupled. Many of the properties ... More

Elementary Excitations of a Bose-Einstein Condensate in an Effective Magnetic FieldJun 14 2007We calculate the low energy elementary excitations of a Bose-Einstein Condensate in an effective magnetic field. The field is created by the interplay between light beams carrying orbital angular momentum and the trapped atoms. We examine the role of ... More

Retrodiction as a tool for micromaser field measurementsJul 16 2002We use retrodictive quantum theory to describe cavity field measurements by successive atomic detections in the micromaser. We calculate the state of the micromaser cavity field prior to detection of sequences of atoms in either the excited or ground ... More

Entanglement, Information and Multiparticle Quantum OperationsJun 23 2000Jun 28 2000Collective operations on a network of spatially-separated quantum systems can be carried out using local quantum (LQ) operations, classical communication (CC) and shared entanglement (SE). Such operations can also be used to communicate classical information ... More

Is coherence catalytic?Apr 14 2018Quantum coherence, the ability to control the phases in superposition states is a resource, and it is of crucial importance, therefore, to understand how it is consumed in use. It has been suggested that catalytic coherence is possible, that is repeated ... More

Were there two forms of Stegosaurus?Aug 15 2015We recognise that Stegosaurus exhibited exterior chirality and could, therefore, have assumed either of two distinct, mirror-image forms. Our preliminary investigations suggest that both existed. Stegosaurus's exterior chirality raises new questions such ... More

Quantum Walk with a four-dimensional coinMar 01 2011We examine the physical implementation of a discrete time quantum walk with a four-dimensional coin. Our quantum walker is a photon moving repeatedly through a time delay loop, with time being our position space. The quantum coin is implemented using ... More

Maximum Fidelity Retransmission of Mirror Symmetric Qubit StatesSep 25 2002In this paper we address the problem of optimal reconstruction of a quantum state from the result of a single measurement when the original quantum state is known to be a member of some specified set. A suitable figure of merit for this process is the ... More

Vortex nucleation in Bose-Einstein Condensates subject to light induced effective magnetic fieldsSep 06 2007We numerically simulate vortex nucleation in a Bose-Einstein Condensate (BEC) subject to an effective magnetic field. The effective magnetic field is generated from the interplay between light with a non-trivial phase structure and the BEC, and can be ... More

Fidelity and the communication of quantum informationJul 05 2001We compare and contrast the error probability and fidelity as measures of the quality of the receiver's measurement strategy for a quantum communications system. The error probability is a measure of the ability to retrieve {\it classical} information ... More

Retrodiction with two-level atoms: atomic previvalsJul 30 2002In the Jaynes-Cummings model a two-level atom interacts with a single-mode electromagnetic field. Quantum mechanics predicts collapses and revivals in the probability that a measurement will show the atom to be excited at various times after the initial ... More

Quantum theory of preparation and measurementJul 30 2002The conventional postulate for the probabilistic interpretation of quantum mechanics is asymmetric in preparation and measurement, making retrodiction reliant on inference by use of Bayes' theorem. Here, a more fundamental symmetric postulate is presented, ... More

Master Equation for Retrodiction of Quantum Communication SignalsJul 27 2001We derive the master equation that governs the evolution of the measured state backwards in time in an open system. This allows us to determine probabilities for a given set of preparation events from the results of subsequent measurements, which has ... More

Chiral Rotational SpectroscopyNov 14 2015Jan 13 2018We introduce chiral rotational spectroscopy: a new technique that enables the determination of the orientated optical activity pseudotensor components $B_{XX}$, $B_{YY}$ and $B_{ZZ}$ of chiral molecules, in a manner that reveals the enantiomeric constitution ... More

Decision problems with quantum black boxesSep 22 2011We examine how to distinguish between unitary operators, when the exact form of the possible operators is not known. Instead we are supplied with "programs" in the form of unitary transforms, which can be used as references for identifying the unknown ... More

Angular EPR paradoxJun 28 2005The violation of local uncertainty relations is a valuable tool for detecting entanglement, especially in multi-dimensional systems. The orbital angular momentum of light provides such a multi-dimensional system. We study quantum correlations for the ... More

Atomic RetrodictionJul 04 2001Measurement of a quantum system provides information concerning the state in which it was prepared. In this paper we show how the retrodictive formalism can be used to evaluate the probability associated with any one of a given set of preparation events. ... More

Minimum-error discrimination between three mirror-symmetric statesJan 17 2002We present the optimal measurement strategy for distinguishing between three quantum states exhibiting a mirror symmetry. The three states live in a two-dimensional Hilbert space, and are thus overcomplete. By mirror symmetry we understand that the transformation ... More

Entanglement and Collective Quantum OperationsMar 16 2000Jun 16 2000We show how shared entanglement, together with classical communication and local quantum operations, can be used to perform an arbitrary collective quantum operation upon N spatially-separated qubits. A simple teleportation-based protocol for achieving ... More

Experimental realization of optimal detection strategies for overcomplete statesAug 04 2000Mar 05 2001We present the results of generalized measurements of optical polarization designed to provide one of three or four distinct outcomes. This has allowed us to discriminate between nonorthogonal polarization states with an error probability that is close ... More

Schmidt modes generated in parametric downconversionJan 14 2012Aug 01 2012This paper presents the general Schmidt decomposition of two-photon fields generated in spontaneous parametric down-conversion (SPDC). It discusses in particular the separation of the radial and azimuthal degrees of freedom, the role of projection in ... More

Experimental Demonstration of Optimal Unambiguous State DiscriminationJul 19 2000We present the first full demonstration of unambiguous state discrimination between non-orthogonal quantum states. Using a novel free space interferometer we have realised the optimum quantum measurement scheme for two non-orthogonal states of light, ... More

The information of high-dimensional time-bin encoded photonsJun 14 2015Aug 08 2016We determine the shared information that can be extracted from time-bin entangled photons using frame encoding. We consider photons generated by a general down-conversion source and also model losses, dark counts and the effects of multiple photons within ... More

Measurement master equationFeb 17 2006We derive a master equation describing the evolution of a quantum system subjected to a sequence of observations. These measurements occur randomly at a given rate and can be of a very general form. As an example, we analyse the effects of these measurements ... More

Maximum Confidence Quantum MeasurementsApr 05 2006We consider the problem of discriminating between states of a specified set with maximum confidence. For a set of linearly independent states unambiguous discrimination is possible if we allow for the possibility of an inconclusive result. For linearly ... More

Accessible information and optimal strategies for real symmetrical quantum sourcesDec 22 1998Jan 18 1999We study the problem of optimizing the Shannon mutual information for sources of real quantum states i.e. sources for which there is a basis in which all the states have only real components. We consider in detail the sources ${\cal E}_M$ of $M$ equiprobable ... More

Grassmann Variables and the Jaynes-Cummings ModelMar 22 2012This paper shows that phase space methods using a positive P type distribution function involving both c-number variables (for the cavity mode) and Grassmann variables (for the two level atom) can be used to treat the Jaynes-Cummings model. Although it ... More

Angular minimum uncertainty states with large uncertaintiesDec 09 2005Apr 27 2006The uncertainty relation for angle and angular momentum has a lower bound which depends on the form of the state. Surprisingly, this lower bound can be very large. We derive the states which have the lowest possible uncertainty product for a given uncertainty ... More

Statistics of photon-subtracted and photon-added statesJun 25 2018The subtraction or addition of a prescribed number of photons to a field mode does not, in general, simply shift the probability distribution by the number of subtracted or added photons. Subtraction of a photon from an initial coherent state, for example, ... More

Quantum Formulation of Fractional Orbital Angular MomentumNov 15 2006The quantum theory of rotation angles (S. M. Barnett and D. T. Pegg, Phys. Rev. A, 41, 3427-3425 (1990)) is generalised to non-integer values of the orbital angular momentum. This requires the introduction of an additional parameter, the orientation of ... More

Experimental Realization of Maximum Confidence State Discrimination for the Extraction of Quantum InformationOct 27 2006We present the first experimental demonstration of the maximum confidence measurement strategy for quantum state discrimination. Applying this strategy to an arbitrary set of states assigns to each input state a measurement outcome which, when realized, ... More

Quantum, Nonlocal Aberration CancellationJun 11 2019Phase distortions, or aberrations, can negatively influence the performance of an optical imaging system. Through the use of position-momentum entangled photons, we nonlocally correct for aberrations in one photon's optical path by intentionally introducing ... More

Spatially dependent electromagnetically induced transparencyDec 03 2014Recent years have seen vast progress in the generation and detection of structured light, with potential applications in high capacity optical data storage and continuous variable quantum technologies. Here we measure the transmission of structured light ... More

Experimental Implementation of a Quantum Optical State Comparison AmplifierApr 16 2014Quantum optical amplification that beats the noise addition limit for deterministic amplifiers has been realized experimentally using several different nondeterministic protocols. These schemes either require single-photon sources, or operate by noise ... More

Retrodictive states and two-photon quantum imagingMar 17 2003We use retrodictive quantum theory to analyse two-photon quantum imaging systems. The formalism is particularly suitable for calculating conditional probability distributions.

Security of high-dimensional quantum key distribution protocols using Franson interferometersMay 20 2013Franson interferometers are increasingly being proposed as a means of securing high-dimensional energy-time entanglement-based quantum key distribution (QKD) systems. Heuristic arguments have been proposed that purport to demonstrate the security of these ... More

Skymionic beamsJun 12 2019Vector vortex beams possess a topological property that derives both from the spatially varying amplitude of the field and also from its varying polarization. This property arises as a consequence of the natural Skyrmionic nature of such beams and is ... More

Quantum probability rule: a generalisation of the theorems of Gleason and BuschAug 05 2013Apr 16 2014Busch's theorem deriving the standard quantum probability rule can be regarded as a more general form of Gleason's theorem. Here we show that a further generalisation is possible by reducing the number of quantum postulates used by Busch. We do not assume ... More