Publications

Meng, H & Li, S 2014, 'A Topological Characterisation of Belief Revision over Infinite Propositional Languages' in Lecture Notes in Computer Science, Springer International Publishing, pp. 77-90.
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Chen, J, Ji, Z, Li, C-K, Poon, Y-T, Shen, Y, Yu, N, Zeng, B & Zhou, D 2014, 'Discontinuity of Maximum Entropy Inference and Quantum Phase Transitions', New J. Phys., vol. 17, no. 8, pp. 083019-19.
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In this paper, we discuss the connection between two genuinely quantumphenomena --- the discontinuity of quantum maximum entropy inference andquantum phase transitions at zero temperature. It is shown that thediscontinuity of the maximum entropy inference of local observable measurementssignals the non-local type of transitions, where local density matrices of theground state change smoothly at the transition point. We then propose to usethe quantum conditional mutual information of the ground state as an indicatorto detect the discontinuity and the non-local type of quantum phase transitionsin the thermodynamic limit.

Chen, W, Cao, Y, Wang, H & Feng, Y 2014, 'Minimum guesswork discrimination between quantum states', Computation, vol. 15, no. 9-10, pp. 9-758.
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Error probability is a popular and well-studied optimization criterion indiscriminating non-orthogonal quantum states. It captures the threat from anadversary who can only query the actual state once. However, when the adversaryis able to use a brute-force strategy to query the state, discriminationmeasurement with minimum error probability does not necessarily minimize thenumber of queries to get the actual state. In light of this, we take Massey'sguesswork as the underlying optimization criterion and study the problem ofminimum guesswork discrimination. We show that this problem can be reduced to asemidefinite programming problem. Necessary and sufficient conditions when ameasurement achieves minimum guesswork are presented. We also reveal therelation between minimum guesswork and minimum error probability. We show thatthe two criteria generally disagree with each other, except for the specialcase with two states. Both upper and lower information-theoretic bounds onminimum guesswork are given. For geometrically uniform quantum states, weprovide sufficient conditions when a measurement achieves minimum guesswork.Moreover, we give the necessary and sufficient condition under which making nomeasurement at all would be the optimal strategy.

Cohn, AG, Li, S, Liu, W & Renz, J 2014, 'Reasoning about Topological and Cardinal Direction Relations Between 2-Dimensional Spatial Objects', Journal of Artificial Intelligence Research, vol. 51, pp. 493-532.
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Increasing the expressiveness of qualitative spatial calculi is an essential step towards meeting the requirements of applications. This can be achieved by combining existing calculi in a way that we can express spatial information using relations from multiple calculi. The great challenge is to develop reasoning algorithms that are correct and complete when reasoning over the combined information. Previous work has mainly studied cases where the interaction between the combined calculi was small, or where one of the two calculi was very simple. In this paper we tackle the important combination of topological and directional information for extended spatial objects. We combine some of the best known calculi in qualitative spatial reasoning, the RCC8 algebra for representing topological information, and the Rectangle Algebra (RA) and the Cardinal Direction Calculus (CDC) for directional information. We consider two different interpretations of the RCC8 algebra, one uses a weak connectedness relation, the other uses a strong connectedness relation. In both interpretations, we show that reasoning with topological and directional information is decidable and remains in NP. Our computational complexity results unveil the significant differences between RA and CDC, and that between weak and strong RCC8 models. Take the combination of basic RCC8 and basic CDC constraints as an example: we show that the consistency problem is in P only when we use the strong RCC8 algebra and explicitly know the corresponding basic RA constraints.

Combes, J, Ferrie, C, Jiang, Z & Caves, CM 2014, 'Quantum limits on postselected, probabilistic quantum metrology', Physical Review A, vol. 89, no. 5.
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Probabilistic metrology attempts to improve parameter estimation by occasionally reporting an excellent estimate and the rest of the time either guessing or doing nothing at all. Here we show that probabilistic metrology can never improve quantum limits on estimation of a single parameter, both on average and asymptotically in number of trials, if performance is judged relative to mean-square estimation error. We extend the result by showing that for a finite number of trials, the probability of obtaining better estimates using probabilistic metrology, as measured by mean-square error, decreases exponentially with the number of trials. To be tight, the performance bounds we derive require that likelihood functions be approximately normal, which in turn depends on how rapidly specific distributions converge to a normal distribution with number of trials. © 2014 American Physical Society.

Datta, N, Tomamichel, M & Wilde, MM 2014, 'On the Second-Order Asymptotics for Entanglement-Assisted Communication', Quantum Information Processing, vol. 15, no. 6, pp. 6-2591.
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The entanglement-assisted classical capacity of a quantum channel is known toprovide the formal quantum generalization of Shannon's classical channelcapacity theorem, in the sense that it admits a single-letter characterizationin terms of the quantum mutual information and does not increase in thepresence of a noiseless quantum feedback channel from receiver to sender. Inthis work, we investigate second-order asymptotics of the entanglement-assistedclassical communication task. That is, we consider how quickly the rates ofentanglement-assisted codes converge to the entanglement-assisted classicalcapacity of a channel as a function of the number of channel uses and the errortolerance. We define a quantum generalization of the mutual informationvariance of a channel in the entanglement-assisted setting. For covariantchannels, we show that this quantity is equal to the channel dispersion, andthus completely characterize the convergence towards the entanglement-assistedclassical capacity when the number of channel uses increases. Our results alsoapply to entanglement-assisted quantum communication, due to the equivalencebetween entanglement-assisted classical and quantum communication establishedby the teleportation and super-dense coding protocols.

Devitt, SJ, Greentree, AD, Stephens, AM & Meter, RV 2014, 'High-speed quantum networking by ship', Sci. Rep, vol. 6, no. 1, p. 36163.
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Networked entanglement is an essential component for a plethora of quantumcomputation and communication protocols. Direct transmission of quantum signalsover long distances is prevented by fibre attenuation and the no-cloningtheorem, motivating the development of quantum repeaters, designed to purifyentanglement, extending its range. Quantum repeaters have been demonstratedover short distances, but error-corrected, global repeater networks with highbandwidth require new technology. Here we show that error corrected quantummemories installed in cargo containers and carried by ship can provide aflexible connection between local networks, enabling low-latency, high-fidelityquantum communication across global distances at higher bandwidths thanpreviously proposed. With demonstrations of technology with sufficient fidelityto enable topological error-correction, implementation of the quantum memoriesis within reach, and bandwidth increases with improvements in fabrication. Ourapproach to quantum networking avoids technological restrictions of repeaterdeployment, providing an alternate path to a worldwide Quantum Internet.

Everitt, MS, Devitt, S, Munro, WJ & Nemoto, K 2014, 'High-fidelity gate operations with the coupled nuclear and electron spins of a nitrogen-vacancy center in diamond', Physical Review A, vol. 89, no. 5.
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Feng, Y, Deng, Y & Ying, M 2014, 'Symbolic Bisimulation for Quantum Processes', ACM TRANSACTIONS ON COMPUTATIONAL LOGIC, vol. 15, no. 2, pp. 1-35.
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With the previous notions of bisimulation presented in the literature, to check if two quantum processes are bisimilar, we have to instantiate their free quantum variables with arbitrary quantum states, and verify the bisimilarity of the resulting configurations. This makes checking bisimilarity infeasible from an algorithmic point of view, because quantum states constitute a continuum. In this article, we introduce a symbolic operational semantics for quantum processes directly at the quantum operation level, which allows us to describe the bisimulation between quantum processes without resorting to quantum states. We show that the symbolic bisimulation defined here is equivalent to the open bisimulation for quantum processes in previous work, when strong bisimulations are considered. An algorithm for checking symbolic ground bisimilarity is presented. We also give a modal characterisation for quantum bisimilarity based on an extension of Hennessy-Milner logic to quantum processes. © 2014 ACM.

Ferrie, C 2014, 'Quantum Model Averaging', New J. Phys., vol. 16, p. 093035.
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Standard tomographic analyses ignore model uncertainty. It is assumed that agiven model generated the data and the task is to estimate the quantum state,or a subset of parameters within that model. Here we apply a model averagingtechnique to mitigate the risk of overconfident estimates of model parametersin two examples: (1) selecting the rank of the state in tomography and (2)selecting the model for the fidelity decay curve in randomized benchmarking.

Ferrie, C 2014, 'Self-guided quantum tomography', Phys. Rev. Lett., vol. 113, no. 19, p. 190404.
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We introduce a self-learning tomographic technique in which the experimentguides itself to an estimate of its own state. Self-guided quantum tomography(SGQT) uses measurements to directly test hypotheses in an iterative algorithmwhich converges to the true state. We demonstrate through simulation on manyqubits that SGQT is a more efficient and robust alternative to the usualparadigm of taking a large amount of informationally complete data and solvingthe inverse problem of post-processed state estimation.

Ferrie, C 2014, 'The best Fisher is upstream: data processing inequalities for quantum metrology', Phys. Rev. A, vol. 90, no. 1, p. 014101.
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We apply the classical data processing inequality to quantum metrology toshow that manipulating the classical information from a quantum measurementcannot aid in the estimation of parameters encoded in quantum states. Wefurther derive a quantum data processing inequality to show that coherentmanipulation of quantum data also cannot improve the precision in estimation.In addition, we comment on the assumptions necessary to arrive at theseinequalities and how they might be avoided providing insights into enhancementprocedures which are not provably wrong.

Ferrie, C & Combes, J 2014, 'How the result of a single coin toss can turn out to be 100 heads', Phys. Rev. Lett., vol. 113, no. 12, p. 120404.
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We show that the phenomenon of anomalous weak values is not limited toquantum theory. In particular, we show that the same features occur in a simplemodel of a coin subject to a form of classical backaction with pre- andpost-selection. This provides evidence that weak values are not inherentlyquantum, but rather a purely statistical feature of pre- and post-selectionwith disturbance.

Ferrie, C & Moussa, O 2014, 'Robust and efficient in situ quantum control', Phys. Rev. A, vol. 91, no. 5, p. 052306.
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Precision control of quantum systems is the driving force for both quantumtechnology and the probing of physics at the quantum and nano-scale. We proposean implementation independent method for in situ quantum control that leveragesrecent advances in the direct estimation of quantum gate fidelity. Ouralgorithm takes account of the stochasticity of the problem and is suitable forclosed-loop control and requires only a constant number of fidelity estimatingexperiments per iteration independent of the dimension of the control space. Itis efficient and robust to both statistical and technical noise.

Furrer, F, Franz, T, Berta, M, Leverrier, A, Scholz, VB, Tomamichel, M & Werner, RF 2014, 'Erratum: Continuous Variable Quantum Key Distribution: Finite-Key Analysis of Composable Security Against Coherent Attacks [Phys. Rev. Lett. 109, 100502 (2012)]', Physical Review Letters, vol. 112, no. 1.
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Gupta, A, Kayal, N & Qiao, Y 2014, 'Random arithmetic formulas can be reconstructed efficiently', computational complexity, vol. 23, no. 2, pp. 207-303.
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Informally stated, we present here a randomized algorithm that given black-box access to the polynomial f computed by an unknown/hidden arithmetic formula φ reconstructs, on the average, an equivalent or smaller formula φ̌ in time polynomial in the size of its output φ̌. Specifically, we consider arithmetic formulas wherein the underlying tree is a complete binary tree, the leaf nodes are labeled by affine forms (i.e., degree one polynomials) over the input variables and where the internal nodes consist of alternating layers of addition and multiplication gates. We call these alternating normal form (ANF) formulas. If a polynomial f can be computed by an arithmetic formula μ of size s, it can also be computed by an ANF formula φ, possibly of slightly larger size s O(1). Our algorithm gets as input black-box access to the output polynomial f (i.e., for any point x in the domain, it can query the black box and obtain f(x) in one step) of a random ANF formula φ of size s (wherein the coefficients of the affine forms in the leaf nodes of φ are chosen independently and uniformly at random from a large enough subset of the underlying field). With high probability (over the choice of coefficients in the leaf nodes), the algorithm efficiently (i.e., in time s O(1)) computes an ANF formula φ̌ of size s computing f. This then is the strongest model of arithmetic computation for which a reconstruction algorithm is presently known, albeit efficient in a distributional sense rather than in the worst case. © 2014 Springer Basel.

Hayashi, M & Tomamichel, M 2014, 'Correlation Detection and an Operational Interpretation of the Renyi Mutual Information', Journal of Mathematical Physics, vol. 57, no. 10, p. 102201.
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A variety of new measures of quantum Renyi mutual information and quantumRenyi conditional entropy have recently been proposed, and some of theirmathematical properties explored. Here, we show that the Renyi mutualinformation attains operational meaning in the context of composite hypothesistesting, when the null hypothesis is a fixed bipartite state and the alternatehypothesis consists of all product states that share one marginal with the nullhypothesis. This hypothesis testing problem occurs naturally in channel coding,where it corresponds to testing whether a state is the output of a givenquantum channel or of a 'useless' channel whose output is decoupled from theenvironment. Similarly, we establish an operational interpretation of Renyiconditional entropy by choosing an alternative hypothesis that consists ofproduct states that are maximally mixed on one system. Specialized to classicalprobability distributions, our results also establish an operationalinterpretation of Renyi mutual information and Renyi conditional entropy.

Kaniewski, J, Tomamichel, M & Wehner, S 2014, 'Entropic uncertainty from effective anti-commutators', Phys. Rev. A, vol. 90, no. 1, p. 012332.
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We investigate entropic uncertainty relations for two or more binarymeasurements, for example spin-$\frac{1}{2}$ or polarisation measurements. Weargue that the effective anti-commutators of these measurements, i.e. theanti-commutators evaluated on the state prior to measuring, are an expedientmeasure of measurement incompatibility. Based on the knowledge of pairwiseeffective anti-commutators we derive a class of entropic uncertainty relationsin terms of conditional R\'{e}nyi entropies. Our uncertainty relations areformulated in terms of effective measures of incompatibility, which can becertified device-independently. Consequently, we discuss potential applicationsof our findings to device-independent quantum cryptography. Moreover, toinvestigate the tightness of our analysis we consider the simplest (and verywell-studied) scenario of two measurements on a qubit. We find that our resultsoutperform the celebrated bound due to Maassen and Uffink [Phys. Rev. Lett. 60,1103 (1988)] and provide a new analytical expression for the minimumuncertainty which also outperforms some recent bounds based on majorisation.

Kieferová, M & Wiebe, N 2014, 'On the power of coherently controlled quantum adiabatic evolutions', New Journal of Physics, vol. 16, no. 12, pp. 123034-123034.
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Lai, C-Y, Hsieh, M-H & Lu, H-F 2014, 'On the MacWilliams Identity for Classical and Quantum Convolutional Codes', IEEE Transactions on Communications, vol. 64, no. 8, pp. 3148-3159, Aug 2016, vol. 64, no. 8, pp. 3148-3159.
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The weight generating functions associated with convolutional codes (CCs) arebased on state space realizations or the weight adjacency matrices (WAMs). TheMacWilliams identity for CCs on the WAMs was first established by Gluesing-Luerssen and Schneider in the case of minimal encoders, and generalized byForney. We consider this problem in the viewpoint of constraint codes andobtain a simple and direct proof of this MacWilliams identity in the case ofminimal encoders. For our purpose, we choose a different representation for theexact weight generating function (EWGF) of a block code, by defining it as alinear combination of orthonormal vectors in Dirac bra-ket notation. Thisrepresentation provides great flexibility so that general split weightgenerating functions and their MacWilliams identities can be easily obtainedfrom the MacWilliams identity for EWGFs. As a result, we also obtain theMacWilliams identity for the input-parity weight adjacency matrices of asystematic convolutional code and its dual. Finally, paralleling thedevelopment of the classical case, we establish the MacWilliams identity forquantum convolutional codes.

Law, YZ, Thinh, LP, Bancal, J-D & Scarani, V 2014, 'Quantum randomness extraction for various levels of characterization of the devices', Journal of Physics A: Mathematical and Theoretical, vol. 47, no. 42, pp. 424028-424028.
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Li, S, Long, Z, Liu, W, Duckham, M & Both, A 2014, 'On Redundant Topological Constraints', Artificial Intelligence, vol. 225, pp. 51-76.
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The Region Connection Calculus (RCC) is a well-known calculus forrepresenting part-whole and topological relations. It plays an important rolein qualitative spatial reasoning, geographical information science, andontology. The computational complexity of reasoning with RCC5 and RCC8 (twofragments of RCC) as well as other qualitative spatial/temporal calculi hasbeen investigated in depth in the literature. Most of these works focus on theconsistency of qualitative constraint networks. In this paper, we consider theimportant problem of redundant qualitative constraints. For a set $\Gamma$ ofqualitative constraints, we say a constraint $(x R y)$ in $\Gamma$ is redundantif it is entailed by the rest of $\Gamma$. A prime subnetwork of $\Gamma$ is asubset of $\Gamma$ which contains no redundant constraints and has the samesolution set as $\Gamma$. It is natural to ask how to compute such a primesubnetwork, and when it is unique. In this paper, we show that this problem is in general intractable, butbecomes tractable if $\Gamma$ is over a tractable subalgebra $\mathcal{S}$ of aqualitative calculus. Furthermore, if $\mathcal{S}$ is a subalgebra of RCC5 orRCC8 in which weak composition distributes over nonempty intersections, then$\Gamma$ has a unique prime subnetwork, which can be obtained in cubic time byremoving all redundant constraints simultaneously from $\Gamma$. As abyproduct, we show that any path-consistent network over such a distributivesubalgebra is weakly globally consistent and minimal. A thorough empiricalanalysis of the prime subnetwork upon real geographical data sets demonstratesthe approach is able to identify significantly more redundant constraints thanpreviously proposed algorithms, especially in constraint networks with largerproportions of partial overlap relations.

Li, Y & Ying, M 2014, 'Debugging quantum processes using monitoring measurements', PHYSICAL REVIEW A, vol. 89, no. 4.
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Since observation on a quantum system may cause the system state collapse, it is usually hard to find a way to monitor a quantum process, which is a quantum system that continuously evolves. We propose a protocol that can debug a quantum process by monitoring, but not disturb the evolution of the system. This protocol consists of an error detector and a debugging strategy. The detector is a projection operator that is orthogonal to the anticipated system state at a sequence of time points, and the strategy is used to specify these time points. As an example, we show how to debug the computational process of quantum search using this protocol. By applying the Skolem-Mahler-Lech theorem in algebraic number theory, we find an algorithm to construct all of the debugging protocols for quantum processes of time-independent Hamiltonians.

Li, Y, Yu, N & Ying, M 2014, 'Termination of nondeterministic quantum programs', ACTA INFORMATICA, vol. 51, no. 1, pp. 1-24.
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We define a language-independent model of nondeterministic quantum programs in which a quantum program consists of a finite set of quantum processes. These processes are represented by quantum Markov chains over the common state space, which formalize the quantum mechanical behaviors of the machine. An execution of a nondeterministic quantum program is modeled by a sequence of actions of individual processes, and at each step of an execution a process is chosen nondeterministically to perform the next action. This execution model formalize the users behavior of calling the processes in the classical world. Applying the model to a quantum walk as an instance of physically realizable systems, we describe an execution step by step. A characterization of reachable space and a characterization of diverging states of a nondeterministic quantum program are presented. We establish a zero-one law for termination probability of the states in the reachable space. A combination of these results leads to a necessary and sufficient condition for termination of nondeterministic quantum programs. Based on this condition, an algorithm is found for checking termination of nondeterministic quantum programs within a fixed finite-dimensional state space.

Lin, MS & Tomamichel, M 2014, 'Investigating Properties of a Family of Quantum Renyi Divergences', Quantum Information Processing, vol. 14, no. 4, pp. 1501-1512.
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Audenaert and Datta recently introduced a two-parameter family of relativeR\'{e}nyi entropies, known as the $\alpha$-$z$-relative R\'{e}nyi entropies.The definition of the $\alpha$-$z$-relative R\'{e}nyi entropy unifies allpreviously proposed definitions of the quantum R\'{e}nyi divergence of order$\alpha$ under a common framework. Here we will prove that the$\alpha$-$z$-relative R\'{e}nyi entropies are a proper generalization of thequantum relative entropy by computing the limit of the $\alpha$-$z$ divergenceas $\alpha$ approaches one and $z$ is an arbitrary function of $\alpha$. Wealso show that certain operationally relevant families of R\'enyi divergencesare differentiable at $\alpha = 1$. Finally, our analysis reveals that thederivative at $\alpha = 1$ evaluates to half the relative entropy variance, aquantity that has attained operational significance in second-order quantumhypothesis testing.

Lunghi, T, Kaniewski, J, Bussieres, F, Houlmann, R, Tomamichel, M, Wehner, S & Zbinden, H 2014, 'Practical relativistic bit commitment', Phys. Rev. Lett., vol. 115, no. 3, p. 030502.
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Bit commitment is a fundamental cryptographic primitive in which Alice wishesto commit a secret bit to Bob. Perfectly secure bit commitment between twomistrustful parties is impossible through asynchronous exchange of quantuminformation. Perfect security is however possible when Alice and Bob each splitinto several agents exchanging classical information at times and locationssuitably chosen to satisfy specific relativistic constraints. In this Letter wefirst revisit a previously proposed scheme that realizes bit commitment usingonly classical communication. We prove that the protocol is secure againstquantum adversaries for a duration limited by the light-speed communicationtime between the locations of the agents. We then propose a novel multi-roundscheme based on finite-field arithmetic that extends the commitment time beyondthis limit, and we prove its security against classical attacks. Finally, wepresent an implementation of these protocols using dedicated hardware and weshow how it could be used to realize commitments of duration ranging up to 212milliseconds by agents occupying antipodal locations on the Earth.

Mao, Z, Le, TP, Vakhshouri, K, Fernando, R, Ruan, F, Muller, E, Gomez, ED & Sauvé, G 2014, 'Processing additive suppresses phase separation in the active layer of organic photovoltaics based on naphthalene diimide', Organic Electronics, vol. 15, no. 11, pp. 3384-3391.
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Metcalf, BJ, Spring, JB, Humphreys, PC, Thomas-Peter, N, Barbieri, M, Kolthammer, WS, Jin, X-M, Langford, NK, Kundys, D, Gates, JC, Smith, BJ, Smith, PGR & Walmsley, IA 2014, 'Quantum teleportation on a photonic chip', Nature Photonics, vol. 8, no. 10, pp. 770-774.
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Mor, GK, Jones, D, Le, TP, Shang, Z, Weathers, PJ, Woltermann, MKB, Vakhshouri, K, Williams, BP, Tohran, SA, Saito, T, Verduzco, R, Salleo, A, Hickner, MA & Gomez, ED 2014, 'Contact Doping with Sub‐Monolayers of Strong Polyelectrolytes for Organic Photovoltaics', Advanced Energy Materials, vol. 4, no. 13.
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Barriers to charge transfer at electrode‐semiconductor contacts are ubiquitous and limit the applicability of organic semiconductors in electronic devices. Molecular or ionic doping near contacts can alleviate charge injection or extraction problems by enabling charge tunneling through contact barriers, but the soft nature of organic materials allows for small molecule dopants to diffuse and migrate, degrading the performance of the device and limiting effective interfacial doping. Here, it is demonstrated that contact doping in organic electronics is possible through ionic polymer dopants, which resist diffusion or migration due to their large size. Sub‐monolayer deposition of non‐conjugated strong polyelectrolytes, e.g., sulfonated poly(sulfone)s, at the anode‐semiconductor interface of organic photovoltaics enables efficient hole extraction at the anode. The performance of contact‐doped organic photo­voltaics nearly matches the performance of devices composed of traditional hole transport layers such as poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The degree of sulfonation of the dopant polymer and the thickness of the ionic dopant layer is shown to be critical for optimizing doping and the efficiency of the device.

Mor, GK, Le, TP, Vakhshouri, K, Kozub, DR & Gomez, ED 2014, 'Elemental Mapping of Interfacial Layers at the Cathode of Organic Solar Cells', ACS Applied Materials & Interfaces, vol. 6, no. 22, pp. 19638-19643.
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Nemoto, K, Trupke, M, Devitt, SJ, Stephens, AM, Scharfenberger, B, Buczak, K, Nöbauer, T, Everitt, MS, Schmiedmayer, J & Munro, WJ 2014, 'Photonic Architecture for Scalable Quantum Information Processing in Diamond', Physical Review X, vol. 4, no. 3.
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Paler, A, Devitt, SJ, Nemoto, K & Polian, I 2014, 'Mapping of Topological Quantum Circuits to Physical Hardware', Sci. Rep., vol. 4, p. 4657.
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Topological quantum computation is a promising technique to achievelarge-scale, error-corrected computation. Quantum hardware is used to create alarge, 3-dimensional lattice of entangled qubits while performing computationrequires strategic measurement in accordance with a topological circuitspecification. The specification is a geometric structure that defines encodedinformation and fault-tolerant operations. The compilation of a topologicalcircuit is one important aspect of programming a quantum computer, another isthe mapping of the topological circuit into the operations performed by thehardware. Each qubit has to be controlled, and measurement results are neededto propagate encoded quantum information from input to output. In this work, weintroduce an algorithm for mapping an topological circuit to the operationsneeded by the physical hardware. We determine the control commands for eachqubit in the computer and the relevant measurements that are needed to trackinformation as it moves through the circuit.

Qiao, Y, Sun, X & Yu, N 2014, 'Characterization of multipartite entanglement in terms of local transformations', IEEE Journal on Selected Areas in Communications 38 (3), 568-574 2020, pp. 1-6.
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The degree of the generators of invariant polynomial rings of is a longstanding open problem since the very initial study of the invariant theory inthe 19th century. Motivated by its significant role in characterizingmultipartite entanglement, we study the invariant polynomial rings of localunitary group---the tensor product of unitary group, and local general lineargroup---the tensor product of general linear group. For these two groups, weprove polynomial upper bounds on the degree of the generators of invariantpolynomial rings. On the other hand, systematic methods are provided to toconstruct all homogenous polynomials that are invariant under these two groupsfor any fixed degree. Thus, our results can be regarded as a completecharacterization of the invariant polynomial rings. As an interestingapplication, we show that multipartite entanglement is additive in the sensethat two multipartite states are local unitary equivalent if and only if$r$-copies of them are LU equivalent for some $r$.

Tomamichel, M, Martinez-Mateo, J, Pacher, C & Elkouss, D 2014, 'Fundamental Finite Key Limits for One-Way Information Reconciliation in Quantum Key Distribution', Quantum Information Processing (2017) 16:280, vol. 16, no. 11.
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The security of quantum key distribution protocols is guaranteed by the lawsof quantum mechanics. However, a precise analysis of the security propertiesrequires tools from both classical cryptography and information theory. Here,we employ recent results in non-asymptotic classical information theory to showthat one-way information reconciliation imposes fundamental limitations on theamount of secret key that can be extracted in the finite key regime. Inparticular, we find that an often used approximation for the informationleakage during information reconciliation is not generally valid. We propose animproved approximation that takes into account finite key effects andnumerically test it against codes for two probability distributions, that wecall binary-binary and binary-Gaussian, that typically appear in quantum keydistribution protocols.

Tomamichel, M, Wilde, MM & Winter, A 2014, 'Strong converse rates for quantum communication', IEEE Transactions on Information Theory, vol. 63, no. 1, pages 715-727, January 2017, vol. 63, no. 1, pp. 715-727.
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We revisit a fundamental open problem in quantum information theory, namelywhether it is possible to transmit quantum information at a rate exceeding thechannel capacity if we allow for a non-vanishing probability of decoding error.Here we establish that the Rains information of any quantum channel is a strongconverse rate for quantum communication: For any sequence of codes with rateexceeding the Rains information of the channel, we show that the fidelityvanishes exponentially fast as the number of channel uses increases. Thisremains true even if we consider codes that perform classical post-processingon the transmitted quantum data. As an application of this result, forgeneralized dephasing channels we show that the Rains information is alsoachievable, and thereby establish the strong converse property for quantumcommunication over such channels. Thus we conclusively settle the strongconverse question for a class of quantum channels that have a non-trivialquantum capacity.

Wiebe, N, Granade, C, Ferrie, C & Cory, D 2014, 'Quantum Hamiltonian learning using imperfect quantum resources', Physical Review A, vol. 89, no. 4.
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Wiebe, N, Granade, C, Ferrie, C & Cory, DG 2014, 'Hamiltonian Learning and Certification Using Quantum Resources', Physical Review Letters, vol. 112, no. 19.
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Ying, M, Li, Y, Yu, N & Feng, Y 2014, 'Model-Checking Linear-Time Properties of Quantum Systems', ACM TRANSACTIONS ON COMPUTATIONAL LOGIC, vol. 15, no. 3.
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© 2014 ACM. We define a formal framework for reasoning about linear-time properties of quantum systems in which quantum automata are employed in the modeling of systems and certain (closed) subspaces of state Hilbert spaces are used as the atomic propositions about the behavior of systems. We provide an algorithm for verifying invariants of quantum automata. Then, an automata-based model-checking technique is generalized for the verification of safety properties recognizable by reversible automata and ω?properties recognizable by reversible Büchi automata.

Ying, S & Ying, M 2014, 'Reachability Analysis of Quantum Markov Decision Processes', Information and Computation, vol. 263, pp. 31-51.
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We introduce the notion of quantum Markov decision process (qMDP) as asemantic model of nondeterministic and concurrent quantum programs. It is shownby examples that qMDPs can be used in analysis of quantum algorithms andprotocols. We study various reachability problems of qMDPs both for thefinite-horizon and for the infinite-horizon. The (un)decidability andcomplexity of these problems are settled, or their relationships with certainlong-standing open problems are clarified. We also develop an algorithm forfinding optimal scheduler that attains the supremum reachability probability.

Yu, N, Duan, R & Ying, M 2014, 'Distinguishability of Quantum States by Positive Operator-Valued Measures With Positive Partial Transpose', IEEE TRANSACTIONS ON INFORMATION THEORY, vol. 60, no. 4, pp. 2069-2079.
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We study the distinguishability of bipartite quantum states by positive operator-valued measures with positive partial transpose (PPT POVMs). The contributions of this paper include: 1) we give a negative answer to an open problem of showing a limitation of a previous known method for detecting nondistinguishability; 2) we show that a maximally entangled state and its orthogonal complement, no matter how many copies are supplied, cannot be distinguished by the PPT POVMs, even unambiguously. This result is much stronger than the previous known ones; and 3) we study the entanglement cost of distinguishing quantum states. It is proved that √2/3|00〉 + √1/3|11〉 is sufficient and necessary for distinguishing three Bell states by the PPT POVMs. An upper bound of entanglement cost of distinguishing a d ⊗ d pure state and its orthogonal complement is obtained for separable operations. Based on this bound, we are able to construct two orthogonal quantum states, which cannot be distinguished unambiguously by separable POVMs, but finite copies would make them perfectly distinguishable by local operations and classical communication. We further observe that a two-qubit maximally entangled state is always enough for distinguishing a d ⊗ d pure state and its orthogonal complement by the PPT POVMs, no matter the value of d. In sharp contrast, an entangled state with Schmidt number at least d is always needed for distinguishing such two states by separable POVMs. As an application, we show that the entanglement cost of distinguishing a d ⊗ d maximally entangled state and its orthogonal complement must be a maximally entangled state for d = 2, which implies that teleportation is optimal, and in general, it could be chosen as O{script} (log d/d). © 1963-2012 IEEE.

Yu, N, Guo, C & Duan, R 2014, 'Obtaining a W State from a Greenberger-Horne-Zeilinger State via Stochastic Local Operations and Classical Communication with a Rate Approaching Unity', PHYSICAL REVIEW LETTERS, vol. 112, no. 16.
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We introduce a notion of the entanglement transformation rate to characterize the asymptotic comparability of two multipartite pure entangled states under stochastic local operations and classical communication (SLOCC). For two well known SLOCC inequivalent three-qubit states |GHZ=(1/2)(|000+|111) and |W=(1/3)(|100+|010+|001), we show that the entanglement transformation rate from |GHZ to |W is exactly 1. That means that we can obtain one copy of the W state from one copy of the Greenberg-Horne-Zeilinger (GHZ) state by SLOCC, asymptotically. We then apply similar techniques to obtain a lower bound on the entanglement transformation rates from an N-partite GHZ state to a class of Dicke states, and prove the tightness of this bound for some special cases which naturally generalize the |W state. A new lower bound on the tensor rank of the matrix permanent is also obtained by evaluating the tensor rank of Dicke states. © 2014 American Physical Society.

Alon, N, Lee, T & Shraibman, A 1970, 'The cover number of a matrix and its algorithmic applications', Leibniz International Proceedings in Informatics, LIPIcs, pp. 34-47.
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Given a matrix A, we study how many ε-cubes are required to cover the convex hull of the columns of A. We show bounds on this cover number in terms of VC dimension and the γ2 norm and give algorithms for enumerating elements of a cover. This leads to algorithms for computing approximate Nash equilibria that unify and extend several previous results in the literature. Moreover, our approximation algorithms can be applied quite generally to a family of quadratic optimization problems that also includes finding the densest κ-by-k combinatorial rectangle of a matrix. In particular, for this problem we give the first quasi-polynomial time additive approximation algorithm that works for any matrix A ∈ [0, 1]m×n..

Binti Adnan, NA, Yamashita, S, Devitt, SJ & Nemoto, K 1970, '2D Qubit Layout Optimization for Topological Quantum Computation', REVERSIBLE COMPUTATION, RC 2014, 6th International Conference on Reversible Computation (RC), Springer International Publishing, Kyoto, JAPAN, pp. 176-188.
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Decker, T, Ivanyos, G, Kulkarni, R, Qiao, Y & Santha, M 1970, 'An Efficient Quantum Algorithm for Finding Hidden Parabolic Subgroups in the General Linear Group', Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics), International Symposium on Mathematical Foundations of Computer Science, Springer Berlin Heidelberg, Budapest, Hungary, pp. 226-238.
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In the theory of algebraic groups, parabolic subgroups form a crucial building block in the structural studies. In the case of general linear groups over a finite field, given a sequence of positive integers n 1 , ⋯, n k , where n=n 1 +⋯+n k , a parabolic subgroup of parameter (n 1 , ⋯, n k ) in GL is a conjugate of the subgroup consisting of block lower triangular matrices where the ith block is of size n i . Our main result is a quantum algorithm of time polynomial in logq and n for solving the hidden subgroup problem in GL, when the hidden subgroup is promised to be a parabolic subgroup. Our algorithm works with no prior knowledge of the parameter of the hidden parabolic subgroup. Prior to this work, such an efficient quantum algorithm was only known for minimal parabolic subgroups (Borel subgroups), for the case when q is not much smaller than n (G. Ivanyos: Quantum Inf. Comput., Vol. 12, pp. 661-669). © 2014 Springer-Verlag Berlin Heidelberg.

Devitt, SJ 1970, 'Classical Control of Large-Scale Quantum Computers', RC2014, Springer Lecture Notes on Computer Science (LNCS) 8507, pp. 26-39. Springer International Publishing, Switzerland (2014), Y. Shigeru and M.Shin-ichi (Eds.), 6th International Conference on Reversible Computation (RC), SPRINGER INTERNATIONAL PUBLISHING AG, Kyoto, JAPAN, pp. 26-39.
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The accelerated development of quantum technology has reached a pivotalpoint. Early in 2014, several results were published demonstrating that severalexperimental technologies are now accurate enough to satisfy the requirementsof fault-tolerant, error corrected quantum computation. While there are manytechnological and experimental issues that still need to be solved, the abilityof experimental systems to now have error rates low enough to satisfy thefault-tolerant threshold for several error correction models is a tremendousmilestone. Consequently, it is now a good time for the computer science andclassical engineering community to examine the {\em classical} problemsassociated with compiling quantum algorithms and implementing them on futurequantum hardware. In this paper, we will review the basic operational rules ofa topological quantum computing architecture and outline one of the mostimportant classical problems that need to be solved; the decoding of errorcorrection data for a large-scale quantum computer. We will endeavour topresent these problems independently from the underlying physics as much ofthis work can be effectively solved by non-experts in quantum information orquantum mechanics.

Devitt, SJ 1970, 'The quantum memory stick', Conference on Lasers and Electro-Optics Europe - Technical Digest.
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We introduce a design a design for a quantum memory stick that uses active quantum error correction to coherently store a qubit of encoded information for months or years. This device is based on the model of topological error correction and can increase the storage time of a qubit of information by 10-11 orders of magnitude with a physical qubit overhead of several hundreds.

Devitt, SJ 1970, 'The Quantum Memory Stick', Optics InfoBase Conference Papers.
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We introduce a design a design for a quantum memory stick that uses active quantum error correction to coherently store a qubit of encoded information for months or years. This device is based on the model of topological error correction and can increase the storage time of a qubit of information by 10-11 orders of magnitude with a physical qubit overhead of several hundreds. © 2014 OSA.

Devitt, SJ 1970, 'The Quantum Memory Stick', CLEO: 2014, CLEO: QELS_Fundamental Science, OSA, pp. FTu3A.7-FTu3A.7.
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Duckham, M, Li, S, Liu, W & Long, Z 1970, 'On redundant topological constraints', Proceedings of the International Conference on Knowledge Representation and Reasoning, International Conference on the Principles of Knowledge Representation and Reasoning, AAAI Publications, Vienna, Austria, pp. 618-621.
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The Region Connection Calculus (RCC) is a well-known calculus for representing part-whole and topological relations. It plays an important role in qualitative spatial reasoning, geographical information science, and ontology. The computational complexity of reasoning with RCC has been investigated in depth in the literature. Most of these works focus on the consistency of RCC constraint networks. In this paper, we consider the important problem of redundant RCC constraints. For a set Γ of RCC constraints, we say a constraint (xRy) in Γ is redundant if it can be entailed by the rest of Γ. A prime subnetwork of Γ is a subset of Γ which contains no redundant constraints but has the same solution set as Γ. It is natural to ask how to compute a prime subnetwork, and when it is unique. In this paper, we show that this problem is in general intractable, but becomes tractable if S is over a tractable subclass of RCC. If S is a tractable subclass in which weak composition distributes over non-empty intersections, then we can show that Γ has a unique prime network, which is obtained by removing all redundant constraints from Γ. As a byproduct, we identify a sufficient condition for a path-consistent network being minimal.

Duckham, M, Li, S, Liu, W & Long, Z 1970, 'On Redundant Topological Constraints (Extended Abstract)', FOURTEENTH INTERNATIONAL CONFERENCE ON THE PRINCIPLES OF KNOWLEDGE REPRESENTATION AND REASONING, 14th International Conference on the Principles of Knowledge Representation and Reasoning, ASSOC ADVANCEMENT ARTIFICIAL INTELLIGENCE, AUSTRIA, Vienna Univ Technol, Vienna, pp. 618-621.

Grochow, JA & Qiao, Y 1970, 'Algorithms for Group Isomorphism via Group Extensions and Cohomology', 2014 IEEE 29th Conference on Computational Complexity (CCC), 2014 IEEE Conference on Computational Complexity (CCC), IEEE, Canada, pp. 110-119.
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The isomorphism problem for groups given by their multiplication tables (GPI) has long been known to be solvable in nO(log n) time, but only recently has there been significant progress towards polynomial time. For example, Babai et al. (ICALP 2012) gave a polynomial-time algorithm for groups with no abelian normal subgroups. Thus, at present it is crucial to understand groups with abelian normal subgroups to develop no(log n)-time algorithms. Towards this goal we advocate a strategy via the extension theory of groups, which describes how a normal subgroup N is related to G/N via G. This strategy 'splits' GPI into two sub problems: one regarding group actions on other groups, and one regarding group co homology. The solution of these problems is essentially necessary and sufficient to solve GPI. Most previous works naturally align with this strategy, and it thus helps explain in a unified way the recent polynomial-time algorithms for other group classes. In particular, most prior results in the multiplication table model focus on the group action aspect, despite the general necessity of co homology, for example for p-groups of class 2-believed to be the hardest case of GPI. To make progress on the group co homology aspect of GPI, we consider central-radical groups, proposed in Babai et al. (SODA 2011): the class of groups such that G mod its center has no abelian normal subgroups. Recall that Babai et al. (ICALP 2012) consider the class of groups G such that G itself has no abelian normal subgroups. Following the above strategy, we solve GPI in n O(log log n) time for central-radical groups, and in polynomial time for several prominent subclasses of central-radical groups. We also solve GPI in nO(log log n)-time for groups whose solvable normal subgroups are elementary abelian but not necessarily central. As far as we are aware, this is the first time that a nontrivial algorithm with worst-case guarantees has tackled both aspects of GPI-actions and coho...

Ivanyos, G, Karpinski, M, Qiao, Y & Santha, M 1970, 'Generalized Wong sequences and their applications to Edmonds' problems', Leibniz International Proceedings in Informatics, LIPIcs, pp. 397-408.
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We design two deterministic polynomial time algorithms for variants of a problem introduced by Edmonds in 1967: determine the rank of a matrix M whose entries are homogeneous linear polynomials over the integers. Given a linear subspace B of the n×n matrices over some field F, we consider the following problems: symbolic matrix rank (SMR) is the problem to determine the maximum rank among matrices in B, while symbolic determinant identity testing (SDIT) is the question to decide whether there exists a nonsingular matrix in B. The constructive versions of these problems are asking to find a matrix of maximum rank, respectively a nonsingular matrix, if there exists one. Our first algorithm solves the constructive SMR when B is spanned by unknown rank one matrices, answering an open question of Gurvits. Our second algorithm solves the constructive SDIT when B is spanned by triangularizable matrices, but the triangularization is not given explicitly. Both algorithms work over finite fields of size at least n + 1 and over the rational numbers, and the first algorithm actually solves (the non-constructive) SMR independent of the field size. Our main tool to obtain these results is to generalize Wong sequences, a classical method to deal with pairs of matrices, to the case of pairs of matrix spaces.

Ivanyos, G, Kulkarni, R, Qiao, Y, Santha, M & Sundaram, A 1970, 'On the Complexity of Trial and Error for Constraint Satisfaction Problems', Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics), International Colloquium on Automata Languages and Programming, Springer Berlin Heidelberg, Copenhagen, Denmark, pp. 663-675.
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In a recent work of Bei, Chen and Zhang (STOC 2013), a trial and error model of computing was introduced, and applied to some constraint satisfaction problems. In this model the input is hidden by an oracle which, for a candidate assignment, reveals some information about a violated constraint if the assignment is not satisfying. In this paper we initiate a systematic study of constraint satisfaction problems in the trial and error model. To achieve this, we first adopt a formal framework for CSPs, and based on this framework we define several types of revealing oracles. Our main contribution is to develop a transfer theorem for each type of the revealing oracle, under a broad class of parameters. To any hidden CSP with a specific type of revealing oracle, the transfer theorem associates another, potentially harder CSP in the normal setting, such that their complexities are polynomial time equivalent. This in principle transfers the study of a large class of hidden CSPs, possibly with a promise on the instances, to the study of CSPs in the normal setting. We then apply the transfer theorems to get polynomial-time algorithms or hardness results for hidden CSPs, including satisfaction problems, monotone graph properties, isomorphism problems, and the exact version of the Unique Games problem. © 2014 Springer-Verlag.

Lai, C-Y & Hsieh, M-H 1970, 'The MacWilliams identity for quantum convolutional codes', 2014 IEEE International Symposium on Information Theory, 2014 IEEE International Symposium on Information Theory (ISIT), IEEE, Honolulu, HI, pp. 911-915.
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In this paper, we propose a definition of the dual code of a quantum convolutional code, with or without entanglement assistance. We then derive a MacWilliams identity for quantum convolutional codes. Along the way, we obtain a direct proof of the MacWilliams identity, first found by Gluesing-Luerssen and Schneider, in the setting of classical convolutional codes. © 2014 IEEE.

Lai, C-Y, Hsieh, M-H & Lu, H-F 1970, 'A complete MacWilliams theorem for convolutional codes', 2014 IEEE Information Theory Workshop (ITW 2014), 2014 IEEE Information Theory Workshop (ITW), IEEE, Hobart, TAS, pp. 157-161.
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© 2014 IEEE. In this paper, we prove a MacWilliams identity for the weight adjacency matrices based on the constraint codes of a convolutional code (CC) and its dual. Our result improves upon a recent result by Gluesing-Luerssen and Schneider, where the requirement of a minimal encoder is assumed. We can also establish the MacWilliams identity for the input-parity weight adjacency matrices of a systematic CC and its dual. Most importantly, we show that a type of Hamming weight enumeration functions of all codewords of a CC can be derived from the weight adjacency matrix, which thus provides a connection between these two very different notions of weight enumeration functions in the convolutional code literature. Finally, the relations between various enumeration functions of a CC and its dual are summarized in a diagram. This explains why no MacWilliams identity exists for the free-distance enumerators.

Li, Y & Ying, M 1970, '(Un)decidable Problems about Reachability of Quantum Systems', Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics), International Conference on Concurrency Theory, Springer, Rome, Italy, pp. 482-496.
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We study the reachability problem of a quantum system modelled by a quantumautomaton. The reachable sets are chosen to be boolean combinations of (closed)subspaces of the state space of the quantum system. Four different reachabilityproperties are considered: eventually reachable, globally reachable, ultimatelyforever reachable, and infinitely often reachable. The main result of thispaper is that all of the four reachability properties are undecidable ingeneral; however, the last three become decidable if the reachable sets areboolean combinations without negation.

Meng, H & Li, S 1970, 'PRICAI 2014: Trends in Artificial Intelligence', PRICAI 2014: Trends in Artificial Intelligence - 13th Pacific Rim International Conference on Artificial Intelligence, Gold Coast, QLD, Australia, December 1-5, 2014. Proceedings, Pacific Rim International Conference on Artificial Intelligence, Springer International Publishing, Gold Coast, AUSTRALIA, pp. 77-90.
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Belief revision mainly concerns how an agent updates her belief with new evidence. The AGM framework of belief revision models belief revision as revising theories by propositions. To characterise AGM-style belief revision operators, Grove proposed in 1988 a representation model using systems of spheres. This ‘spheres’ model is very influential and has been extended to characterise multiple belief revision operators. Several fundamental problems remain unsettled regarding this ‘spheres’ model. In this paper we introduce a topology on the set of all worlds of an infinite propositional language and use this topology to characterise systems of spheres. For each AGM operator ∘, we show that, among all systems of spheres deriving ∘, there is a minimal one which is contained in every other system. We give a topological characterisation of these minimal systems. Furthermore, we propose a method for extending an AGM operator to a multiple revision operator and show by an example that the extension is not unique. This negatively answers an open problem raised by Peppas.

Munro, WJ, Stephens, AM, Devitt, SJ & Nemoto, K 1970, 'Quantum networks - How they will evolve from the classical ones', 2014 OptoElectronics and Communication Conference, OECC 2014 and Australian Conference on Optical Fibre Technology, ACOFT 2014, 19th OptoElectronics and Communication Conference (OECC) / 39th Australian Conference on Optical Fibre Technology (ACOFT), IEEE, Engineers Australia, Melbourne, AUSTRALIA, pp. 392-393.
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Quantum networking is a requirement for distributed quantum computation and any potential future quantum internet. Due to the no-cloning theorem, noiseless amplification is not possible and so a different technique is needed to extend the communication range. Quantum repeaters are a device that distributes entanglement over long distances. This entanglement can then be used to teleport information over the entire network with having to send the information from node to node. However the performance of currently proposed networks is quite limited. In this presentation we present a potential scheme that could be thousands of time faster and which would allow for the direct communication of quantum information. © 2014 Engineers Australia.

Munro, WJ, Stephens, AM, Devitt, SJ, Harrison, KA & Nemoto, K 1970, 'The role of memories in quantum networks', Research in Optical Sciences, Quantum Information and Measurement, OSA, pp. QTu1B.1-QTu1B.1.
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Nemoto, K, Devitt J., SJ, Trupke, M, Stephens M., AM, Everitt S., MS, Buczak, K, Noebauer, T, Schmiedmayer, J & Munro, WJ 1970, 'Memory-based quantum repeaters with NV centers', Optics InfoBase Conference Papers.
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We present a simple design of a quantum repeater design build from single NV- centers embedded in an optical cavity. We compare different quantum networks from a simple linear chain to a fully fault-tolerant quantum internet. © 2014 OSA.

Nemoto, K, Devitt, SJ, Trupke, M, Stephens, AM, Everitt, MS, Buczak, K, Noebauer, T, Schmiedmayer, J & Munro, WJ 1970, 'Memory-based Quantum Repeaters with NV Centers', CLEO: 2014, CLEO: QELS_Fundamental Science, OSA, pp. FTu1A.2-FTu1A.2.
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Nemoto, K, Devitt, SJ, Trupke, M, Stephens, AM, Everitt, MS, Buczak, K, Noebauer, T, Schmiedmayer, J & Munro, WJ 1970, 'Memory-based quantum repeaters with NV centers', Conference on Lasers and Electro-Optics Europe - Technical Digest.
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We present a simple design of a quantum repeater design build from single NV- centers embedded in an optical cavity. We compare different quantum networks from a simple linear chain to a fully fault-tolerant quantum internet.

Nemoto, K, Trupke, M, Devitt, SJ, Stephens, AM, Scharfenberger, B, Buczak, K, Nöbauer, T, Schmiedmayer, J & Munro, WJ 1970, 'Quantum repeater architecture and NV-based node technology', SPIE Proceedings, SPIE Optical Engineering + Applications, SPIE, San Diego, CA, pp. 922507-922507.
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Neville, A, Devitt J., SJ, Shadbolt J., PJ, Thackray, L, Peruzzo, A & O'Brien, JL 1970, 'Demonstration of a Characterisation Protocol for Two-qubit Hamiltonians on a Photonic Quantum Simulator', Optics InfoBase Conference Papers.
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We demonstrate an entanglement mapping based characterisation protocol for coupled-qubit Hamiltonians. This is achieved by generating and measuring time-evolved states relevant to an NV-diamond system, using a reconfigurable integrated optical device. © 2014 Optical Society of America.

Neville, A, Devitt, SJ, Shadbolt, PJ, Thackray, L, Peruzzo, A & O’Brien, JL 1970, 'Demonstration of a Characterisation Protocol for Two-qubit Hamiltonians on a Photonic Quantum Simulator', CLEO: 2014, CLEO: Applications and Technology, OSA, pp. JTu4A.43-JTu4A.43.
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We demonstrate an entanglement mapping based characterisation protocol for coupled-qubit Hamiltonians. This is achieved by generating and measuring time-evolved states relevant to an NV-diamond system, using a reconfigurable integrated optical device. © 2014 Optical Society of America.

Neville, A, Devitt, SJ, Shadbolt, PJ, Thackray, L, Peruzzo, A & O'Brien, JL 1970, 'Demonstration of a characterisation protocol for two-qubit hamiltonians on a photonic quantum simulator', Conference on Lasers and Electro-Optics Europe - Technical Digest.
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We demonstrate an entanglement mapping based characterisation protocol for coupled-qubit Hamiltonians. This is achieved by generating and measuring time-evolved states relevant to an NV-diamond system, using a reconfigurable integrated optical device.

Neville, A, Devitt, SJ, Shadbolt, PJ, Thackray, L, Peruzzo, A & O'Brien, JL 1970, 'Demonstration of a characterisation protocol for two-qubit Hamiltonians on a photonic quantum simulator', Optics InfoBase Conference Papers.
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We demonstrate an entanglement mapping based characterisation protocol for coupled-qubit Hamiltonians. This is achieved by generating and measuring time-evolved states relevant to an NV-diamond system, using a reconfigurable integrated optical device. © 2014 Optical Society of America.

Neville, A, Devitt, SJ, Shadbolt, PJ, Thackray, L, Peruzzo, A & O'Brien, JL 1970, 'Demonstration of a Characterisation Protocol for Two-qubit Hamiltonians on a Photonic Quantum Simulator', Optics InfoBase Conference Papers.
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We demonstrate an entanglement mapping based characterisation protocol for coupled-qubit Hamiltonians. This is achieved by generating and measuring time-evolved states relevant to an NV-diamond system, using a reconfigurable integrated optical device. © 2014 Optical Society of America.

Paler, A, Devitt, S, Nemoto, K & Polian, I 1970, 'Software-based Pauli tracking in fault-tolerant quantum circuits', Design, Automation & Test in Europe Conference & Exhibition (DATE), 2014, Design Automation and Test in Europe, IEEE Conference Publications, GERMANY, Dresden, pp. 1-4.
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Paler, A, Devitt, SJ, Nemoto, K & Polian, I 1970, 'Cross-level Validation of Topological Quantum Circuits', REVERSIBLE COMPUTATION, RC 2014, 6th International Conference on Reversible Computation (RC), SPRINGER INTERNATIONAL PUBLISHING AG, Kyoto, JAPAN, pp. 189-200.
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Quantum computing promises a new approach to solving difficult computationalproblems, and the quest of building a quantum computer has started. While thefirst attempts on construction were succesful, scalability has never beenachieved, due to the inherent fragile nature of the quantum bits (qubits). Fromthe multitude of approaches to achieve scalability topological quantumcomputing (TQC) is the most promising one, by being based on an flexibleapproach to error-correction and making use of the straightforwardmeasurement-based computing technique. TQC circuits are defined within a large,uniform, 3-dimensional lattice of physical qubits produced by the hardware andthe physical volume of this lattice directly relates to the resources requiredfor computation. Circuit optimization may result in non-intuitive mismatchesbetween circuit specification and implementation. In this paper we introducethe first method for cross-level validation of TQC circuits. The specificationof the circuit is expressed based on the stabilizer formalism, and thestabilizer table is checked by mapping the topology on the physical qubitlevel, followed by quantum circuit simulation. Simulation results show thatcross-level validation of error-corrected circuits is feasible.

Paler, A, Devitt, SJ, Nemoto, K & Polian, I 1970, 'Software Pauli Tracking for Quantum Computation', Design, Automation and Test in Europe Conference and Exhibition (DATE), 2014. pp. 1-4.
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The realisation of large-scale quantum computing is no longer simply ahardware question. The rapid development of quantum technology has resulted indozens of control and programming problems that should be directed towards theclassical computer science and engineering community. One such problem is knownas Pauli tracking. Methods for implementing quantum algorithms that arecompatible with crucial error correction technology utilise extensive quantumteleportation protocols. These protocols are intrinsically probabilistic andresult in correction operators that occur as byproducts of teleportation. Thesebyproduct operators do not need to be corrected in the quantum hardware itself.Instead, byproduct operators are tracked through the circuit and output resultsreinterpreted. This tracking is routinely ignored in quantum information as itis assumed that tracking algorithms will eventually be developed. In this workwe help fill this gap and present an algorithm for tracking byproduct operatorsthrough a quantum computation. We formulate this work based on quantum gatesets that are compatible with all major forms of quantum error correction anddemonstrate the completeness of the algorithm.

Spring, JB, Salter, PS, Mennea, P, Metcalf, BJ, Humphreys, PC, Moore, M, Gates, JC, Thomas-Peter, N, Barbieri, M, Jin, XM, Langford, NK, Kolthammer, WS, Smith, PGR, Booth, MJ, Smith Brian, JJ & Walmsley, IA 1970, 'Quantum interference of multiple on-chip heralded sources of pure single photons', Optics InfoBase Conference Papers.
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We demonstrate generation of heralded single photons in silica photonic chips with a preparation efficiency of 80% and single photon purity of 0:86. We show multiple indistinguishable photon sources on a single chip with HOM-dip visibilities of up to 95%. © OSA 2014.

Spring, JB, Salter, PS, Mennea, P, Metcalf, BJ, Humphreys, PC, Moore, M, Gates, JC, Thomas-Peter, N, Barbieri, M, Jin, X-M, Langford, NK, Kolthammer, WS, Smith, PGR, Booth, MJ, Smith, BJ & Walmsley, IA 1970, 'Quantum interference of multiple on-chip heralded sources of pure single photons', Research in Optical Sciences, Quantum Information and Measurement, OSA, pp. QW1B.6-QW1B.6.
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Tan, VYF & Tomamichel, M 1970, 'The third-order term in the normal approximation for the AWGN channel', 2014 IEEE International Symposium on Information Theory, 2014 IEEE International Symposium on Information Theory (ISIT), IEEE, pp. 2077-2081.
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This paper shows that, under the average error probability formalism, the third-order term in the normal approximation for the additive white Gaussian noise channel with a maximal or equal power constraint is at least 1 over 2 log n+O(1). This improves on the lower bound by Polyanskiy-Poor-Verdú (2010) and matches the upper bound proved by the same authors. © 2014 IEEE.

Tomamichel, M & Tan, VYF 1970, 'Second order refinements for the classical capacity of quantum channels with separable input states', 2014 IEEE International Symposium on Information Theory, 2014 IEEE International Symposium on Information Theory (ISIT), IEEE, Honolulu, USA, pp. 141-145.
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We study the non-asymptotic fundamental limits for transmitting classical information over memoryless quantum channels, i.e. we investigate the amount of information that can be transmitted when the channel is used a finite number of times and a finite average decoding error is permissible. We show that, if we restrict the encoder to use ensembles of separable states, the non-asymptotic fundamental limit admits a Gaussian approximation that illustrates the speed at which the rate of optimal codes converges to the Holevo capacity as the number of channel uses tends to infinity. To do so, several important properties of quantum information quantities, such as the capacity-achieving output state, the divergence radius, and the channel dispersion, are generalized from their classical counterparts. Further, we exploit a close relation between classical-quantum channel coding and quantum binary hypothesis testing and rely on recent progress in the non-asymptotic characterization of quantum hypothesis testing and its Gaussian approximation. © 2014 IEEE.

Tomamichel, M, Berta, M & Hayashi, M 1970, 'A duality relation connecting different quantum generalizations of the conditional Rényi entropy', 2014 IEEE International Symposium on Information Theory, 2014 IEEE International Symposium on Information Theory (ISIT), IEEE, Honolulu, USA, pp. 731-735.
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Recently a new quantum generalization of the Rényi divergence and the corresponding conditional Rényi entropies was proposed. Here we report on a surprising relation between conditional Rényi entropies based on this new generalization and conditional Rényi entropies based on the quantum relative Rényi entropy that was used in previous literature. This generalizes the well-known duality relation H(AB)+H(AC) = 0 for tripartite pure states to Rényi entropies of two different kinds. As a direct application, we prove a collection of inequalities that relate different conditional Rényi entropies. © 2014 IEEE.

Tomamichel, M, Martinez-Mateo, J, Pacher, C & Elkouss, D 1970, 'Fundamental finite key limits for information reconciliation in quantum key distribution', 2014 IEEE International Symposium on Information Theory, 2014 IEEE International Symposium on Information Theory (ISIT), IEEE, USA, pp. 1469-1473.
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The security of quantum key distribution protocols is guaranteed by the laws of quantum mechanics. However, a precise analysis of the security properties requires tools from both classical cryptography and information theory. Here, we employ recent results in non-asymptotic classical information theory to show that information reconciliation imposes fundamental limitations on the amount of secret key that can be extracted in the finite key regime. In particular, we find that an often used approximation for the information leakage during information reconciliation is flawed and we propose an improved estimate.

Law, YZ, Thinh, LP, Bancal, J-D & Scarani, V 2014, 'Quantum randomness extraction for various levels of characterization of the devices'.

Nemoto, K, Trupke, M, Devitt, SJ, Scharfenberger, B, Buczak, K, Schmiedmayer, J & Munro, WJ 2014, 'Photonic Quantum Networks formed from NV- Centers'.

Rol, MA & Langford, NK 2014, 'PycQED'.
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Python2 version of PycQED

Schockaert, S & Li, S 2014, 'Realizing RCC8 networks using convex regions'.

Stenberg, MPV, Sanders, YR & Wilhelm, FK 2014, 'Efficient estimation of resonant coupling between quantum systems'.

Ying, M 2014, 'Quantum Recursion and Second Quantisation'.
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This paper introduces a new notion of quantum recursion of which the controlflow of the computation is quantum rather than classical as in the notions ofrecursion considered in the previous studies of quantum programming. A typicalexample is recursive quantum walks, which are obtained by slightly modifyingthe construction of the ordinary quantum walks. The operational anddenotational semantics of quantum recursions are defined by employing thesecond quantisation method, and they are proved to be equivalent.

Ying, M, Yu, N & Feng, Y 2014, 'Alternation in Quantum Programming: From Superposition of Data to Superposition of Programs'.
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We extract a novel quantum programming paradigm - superposition of programs -from the design idea of a popular class of quantum algorithms, namely quantumwalk-based algorithms. The generality of this paradigm is guaranteed by theuniversality of quantum walks as a computational model. A new quantumprogramming language QGCL is then proposed to support the paradigm ofsuperposition of programs. This language can be seen as a quantum extension ofDijkstra's GCL (Guarded Command Language). Surprisingly, alternation in GCLsplits into two different notions in the quantum setting: classical alternation(of quantum programs) and quantum alternation, with the latter being introducedin QGCL for the first time. Quantum alternation is the key program constructfor realizing the paradigm of superposition of programs. The denotational semantics of QGCL are defined by introducing a newmathematical tool called the guarded composition of operator-valued functions.Then the weakest precondition semantics of QGCL can straightforwardly derived.Another very useful program construct in realizing the quantum programmingparadigm of superposition of programs, called quantum choice, can be easilydefined in terms of quantum alternation. The relation between quantum choicesand probabilistic choices is clarified through defining the notion of localvariables. We derive a family of algebraic laws for QGCL programs that can beused in program verification, transformations and compilation. The expressivepower of QGCL is illustrated by several examples where various variants andgeneralizations of quantum walks are conveniently expressed using quantumalternation and quantum choice. We believe that quantum programming withquantum alternation and choice will play an important role in furtherexploiting the power of quantum computing.