Berta, M, Scholz, VB & Tomamichel, M 2018, 'Rényi Divergences as Weighted Non-commutative Vector-Valued Lp-Spaces', Annales Henri Poincaré, vol. 19, no. 6, pp. 1843-1867.
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© 2018, Springer International Publishing AG, part of Springer Nature. We show that Araki and Masuda’s weighted non-commutative vector-valued Lp-spaces (Araki and Masuda in Publ Res Inst Math Sci Kyoto Univ 18:339–411, 1982) correspond to an algebraic generalization of the sandwiched Rényi divergences with parameter α=p2. Using complex interpolation theory, we prove various fundamental properties of these divergences in the setup of von Neumann algebras, including a data-processing inequality and monotonicity in α. We thereby also give new proofs for the corresponding finite-dimensional properties. We discuss the limiting cases α→{12,1,∞} leading to minus the logarithm of Uhlmann’s fidelity, Umegaki’s relative entropy, and the max-relative entropy, respectively. As a contribution that might be of independent interest, we derive a Riesz–Thorin theorem for Araki–Masuda Lp-spaces and an Araki–Lieb–Thirring inequality for states on von Neumann algebras.
Boixo, S, Isakov, SV, Smelyanskiy, VN, Babbush, R, Ding, N, Jiang, Z, Bremner, MJ, Martinis, JM & Neven, H 2018, 'Characterizing Quantum Supremacy in Near-Term Devices'.
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A critical question for the field of quantum computing in the near future is
whether quantum devices without error correction can perform a well-defined
computational task beyond the capabilities of state-of-the-art classical
computers, achieving so-called quantum supremacy. We study the task of sampling
from the output distributions of (pseudo-)random quantum circuits, a natural
task for benchmarking quantum computers. Crucially, sampling this distribution
classically requires a direct numerical simulation of the circuit, with
computational cost exponential in the number of qubits. This requirement is
typical of chaotic systems. We extend previous results in computational
complexity to argue more formally that this sampling task must take exponential
time in a classical computer. We study the convergence to the chaotic regime
using extensive supercomputer simulations, modeling circuits with up to 42
qubits - the largest quantum circuits simulated to date for a computational
task that approaches quantum supremacy. We argue that while chaotic states are
extremely sensitive to errors, quantum supremacy can be achieved in the
near-term with approximately fifty superconducting qubits. We introduce cross
entropy as a useful benchmark of quantum circuits which approximates the
circuit fidelity. We show that the cross entropy can be efficiently measured
when circuit simulations are available. Beyond the classically tractable
regime, the cross entropy can be extrapolated and compared with theoretical
estimates of circuit fidelity to define a practical quantum supremacy test.
Chapman, RJ, Karim, A, Huang, Z, Flammia, ST, Tomamichel, M & Peruzzo, A 2018, 'Beating the classical limits of information transmission using a quantum decoder', Physical Review A, vol. 97, no. 1.
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© 2018 American Physical Society. Encoding schemes and error-correcting codes are widely used in information technology to improve the reliability of data transmission over real-world communication channels. Quantum information protocols can further enhance the performance in data transmission by encoding a message in quantum states; however, most proposals to date have focused on the regime of a large number of uses of the noisy channel, which is unfeasible with current quantum technology. We experimentally demonstrate quantum enhanced communication over an amplitude damping noisy channel with only two uses of the channel per bit and a single entangling gate at the decoder. By simulating the channel using a photonic interferometric setup, we experimentally increase the reliability of transmitting a data bit by greater than 20% for a certain damping range over classically sending the message twice. We show how our methodology can be extended to larger systems by simulating the transmission of a single bit with up to eight uses of the channel and a two-bit message with three uses of the channel, predicting a quantum enhancement in all cases.
Cheng, HC & Hsieh, MH 2018, 'Moderate deviation analysis for classical-quantum channels and quantum hypothesis testing', IEEE Transactions on Information Theory, vol. 64, no. 2, pp. 1385-1403.
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© 1963-2012 IEEE. In this paper, we study the tradeoffs between the error probabilities of classical-quantum channels and the blocklength n when the transmission rates approach the channel capacity at a rate lower than 1 {n} , a research topic known as moderate deviation analysis. We show that the optimal error probability vanishes under this rate convergence. Our main technical contributions are a tight quantum sphere-packing bound, obtained via Chaganty and Sethuraman's concentration inequality in strong large deviation theory, and asymptotic expansions of error-exponent functions. Moderate deviation analysis for quantum hypothesis testing is also established. The converse directly follows from our channel coding result, while the achievability relies on a martingale inequality.
Chitambar, E, Fortescue, B & Hsieh, MH 2018, 'The Conditional Common Information in Classical and Quantum Secret Key Distillation', IEEE Transactions on Information Theory, vol. 64, no. 11, pp. 7381-7394.
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© 2018 IEEE. In this paper, we consider two extensions of the Gács-Körner common information to three variables, the conditional common information (cCI) and the coarse-grained conditional common information (ccCI). Both quantities are shown to be useful technical tools in the study of classical and quantum resource transformations. In particular, the ccCI is shown to have an operational interpretation as the optimal rate of secret key extraction from an eavesdropped classical source pXYZ when Alice (X) and Bob (Y) are unable to communicate but share common randomness with the eavesdropper Eve (Z). Moving to the quantum setting, we consider two different ways of generating a tripartite quantum state from classical correlations pXYZ : 1) coherent encodings ∑xyz√pxyz|xyz〉 and 2) incoherent encodings ∑xyzpxyz|xyz〉〈xyz|. We study how well can Alice and Bob extract secret key from these quantum sources using quantum operations compared with the extraction of key from the underlying classical sources pXYZ using classical operations. While the power of quantum mechanics increases Alice and Bob's ability to generate shared randomness, it also equips Eve with a greater arsenal of eavesdropping attacks. Therefore, it is not obvious who gains the greatest advantage for distilling secret key when replacing a classical source with a quantum one. We first demonstrate that the classical key rate of pXYZ is equivalent to the quantum key rate for an incoherent quantum encoding of the distribution. For coherent encodings, we next show that the classical and quantum rates are generally incomparable, and in fact, their difference can be arbitrarily large in either direction. Finally, we introduce a "zoo" of entangled tripartite states all characterized by the conditional common information of their encoded probability distributions. Remarkably, for these states almost all entanglement measures, such as Alice and Bob's entanglement cost, squashed entanglement, and relative entropy of...
Chou, KP, Prasad, M, Wu, D, Sharma, N, Li, DL, Lin, YF, Blumenstein, M, Lin, WC & Lin, CT 2018, 'Robust Feature-Based Automated Multi-View Human Action Recognition System', IEEE Access, vol. 6, pp. 15283-15296.
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© 2013 IEEE. Automated human action recognition has the potential to play an important role in public security, for example, in relation to the multiview surveillance videos taken in public places, such as train stations or airports. This paper compares three practical, reliable, and generic systems for multiview video-based human action recognition, namely, the nearest neighbor classifier, Gaussian mixture model classifier, and the nearest mean classifier. To describe the different actions performed in different views, view-invariant features are proposed to address multiview action recognition. These features are obtained by extracting the holistic features from different temporal scales which are modeled as points of interest which represent the global spatial-temporal distribution. Experiments and cross-data testing are conducted on the KTH, WEIZMANN, and MuHAVi datasets. The system does not need to be retrained when scenarios are changed which means the trained database can be applied in a wide variety of environments, such as view angle or background changes. The experiment results show that the proposed approach outperforms the existing methods on the KTH and WEIZMANN datasets.
Dickel, C, Wesdorp, JJ, Langford, NK, Peiter, S, Sagastizabal, R, Bruno, A, Criger, B, Motzoi, F & DiCarlo, L 2018, 'Chip-to-chip entanglement of transmon qubits using engineered measurement fields', Physical Review B, vol. 97, no. 6.
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© 2018 American Physical Society. While the on-chip processing power in circuit QED devices is growing rapidly, an open challenge is to establish high-fidelity quantum links between qubits on different chips. Here, we show entanglement between transmon qubits on different cQED chips with 49% concurrence and 73% Bell-state fidelity. We engineer a half-parity measurement by successively reflecting a coherent microwave field off two nearly identical transmon-resonator systems. By ensuring the measured output field does not distinguish |01) from |10), unentangled superposition states are probabilistically projected onto entangled states in the odd-parity subspace. We use in situ tunability and an additional weakly coupled driving field on the second resonator to overcome imperfect matching due to fabrication variations. To demonstrate the flexibility of this approach, we also produce an even-parity entangled state of similar quality, by engineering the matching of outputs for the |00) and |11) states. The protocol is characterized over a range of measurement strengths using quantum state tomography showing good agreement with a comprehensive theoretical model.
Fan, J, Hsieh, MH, Chen, H, Chen, H & Li, Y 2018, 'Construction and Performance of Quantum Burst Error Correction Codes for Correlated Errors', IEEE International Symposium on Information Theory - Proceedings, vol. 2018-June, pp. 2336-2340.
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© 2018 IEEE. In practical communication and computation systems, errors occur predominantly in adjacent positions rather than in a random manner. In this paper, we develop a stabilizer formalism for quantum burst error correction codes (QBECC) to combat such error patterns in the quantum regime. Our contributions are as follows. Firstly, we derive an upper bound for the correctable burst errors of QBECCs, the quantum Reiger bound (QRB). Secondly, we propose two constructions of QBECCs: one by heuristic computer search and the other by concatenating two quantum tensor product codes (QTPCs). We obtain several new QBECCs with better parameters than existing codes with the same coding length. Moreover, some of the constructed codes can saturate the quantum Reiger bounds. Finally, we perform numerical experiments for our constructed codes over Markovian correlated depolarizing quantum memory channels, and show that QBECCs indeed outperform standard QECCs in this scenario.
Guan, J, Feng, Y & Ying, M 2018, 'Decomposition of quantum Markov chains and its applications', Journal of Computer and System Sciences, vol. 95, pp. 55-68.
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© 2018 Elsevier Inc. Markov chains have been widely employed as a fundamental model in the studies of probabilistic and stochastic communicating and concurrent systems. It is well-understood that decomposition techniques play a key role in reachability analysis and model-checking of Markov chains. (Discrete-time) quantum Markov chains have been introduced as a model of quantum communicating systems [1] and also a semantic model of quantum programs [2]. The BSCC (Bottom Strongly Connected Component) and stationary coherence decompositions of quantum Markov chains were introduced in [3–5]. This paper presents a new decomposition technique, namely periodic decomposition, for quantum Markov chains. We further establish a limit theorem for them. As an application, an algorithm to find a maximum dimensional noiseless subsystem of a quantum communicating system is given using decomposition techniques of quantum Markov chains.
Herr, D, Paler, A, Devitt, SJ & Nori, F 2018, 'A local and scalable lattice renormalization method for ballistic quantum computation', npj Quantum Information, vol. 4, no. 1.
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Herr, D, Paler, A, Devitt, SJ & Nori, F 2018, 'Lattice surgery on the Raussendorf lattice', Quantum Science and Technology, vol. 3, no. 3.
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© 2018 IOP Publishing Ltd. Lattice surgery is a method to perform quantum computation fault-tolerantly by using operations on boundary qubits between different patches of the planar code. This technique allows for universal planar code computation without eliminating the intrinsic two-dimensional nearest-neighbor properties of the surface code that eases physical hardware implementations. Lattice surgery approaches to algorithmic compilation and optimization have been demonstrated to be more resource efficient for resource-intensive components of a fault-tolerant algorithm, and consequently may be preferable over braid-based logic. Lattice surgery can be extended to the Raussendorf lattice, providing a measurement-based approach to the surface code. In this paper we describe how lattice surgery can be performed on the Raussendorf lattice and therefore give a viable alternative to computation using braiding in measurement-based implementations of topological codes.
Huang, HL, Wang, XL, Rohde, PP, Luo, YH, Zhao, YW, Liu, C, Li, L, Liu, NL, Lu, CY & Pan, JW 2018, 'Demonstration of topological data analysis on a quantum processor', Optica, vol. 5, no. 2, pp. 193-198.
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© 2018 Optical Society of America. Topological data analysis offers a robust way to extract useful information from noisy, unstructured data by identifying its underlying structure. Recently, an efficient quantum algorithm was proposed [Nat. Commun. 7, 10138 (2016)] for calculating Betti numbers of data points—topological features that count the number of topological holes of various dimensions in a scatterplot. Here, we implement a proof-of-principle demonstration of this quantum algorithm by employing a six-photon quantum processor to successfully analyze the topological features of Betti numbers of a network including three data points, providing new insights into data analysis in the era of quantum computing.
Kaljahi, MA, Palaiahnakote, S, Anisi, MH, Idris, MYI, Blumenstein, M & Khan, MK 2018, 'A scene image classification technique for a ubiquitous visual surveillance system', Multimedia Tools and Applications, pp. 1-28.
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© 2018 Springer Science+Business Media, LLC, part of Springer Nature The concept of smart cities has quickly evolved to improve the quality of life and provide public safety. Smart cities mitigate harmful environmental impacts and offences and bring energy-efficiency, cost saving and mechanisms for better use of resources based on ubiquitous monitoring systems. However, existing visual ubiquitous monitoring systems have only been developed for a specific purpose. As a result, they cannot be used for different scenarios. To overcome this challenge, this paper presents a new ubiquitous visual surveillance mechanism based on classification of scene images. The proposed mechanism supports different applications including Soil, Flood, Air, Plant growth and Garbage monitoring. To classify the scene images of the monitoring systems, we introduce a new technique, which combines edge strength and sharpness to detect focused edge components for Canny and Sobel edges of the input images. For each focused edge component, a patch that merges nearest neighbor components in Canny and Sobel edge images is defined. For each patch, the contribution of the pixels in a cluster given by k-means clustering on edge strength and sharpness is estimated in terms of the percentage of pixels. The same percentage values are considered as a feature vector for classification with the help of a Support Vector Machine (SVM) classifier. Experimental results show that the proposed technique outperforms the state-of-the-art scene categorization methods. Our experimental results demonstrate that the SVM classifier performs better than rule and template-based methods.
Kong, S, Lee, JH & Li, S 2018, 'A new distributed algorithm for efficient generalized arc-consistency propagation', Autonomous Agents and Multi-Agent Systems, vol. 32, no. 5, pp. 569-601.
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© 2018, The Author(s). Generalized arc-consistency propagation is predominantly used in constraint solvers to efficiently prune the search space when solving constraint satisfaction problems. Although many practical applications can be modelled as distributed constraint satisfaction problems, no distributed arc-consistency algorithms so far have considered the privacy of individual agents. In this paper, we propose a new distributed arc-consistency algorithm, called DisAC3.1, which leaks less private information of agents than existing distributed arc-consistency algorithms. In particular, DisAC3.1 uses a novel termination determination mechanism, which allows the agents to share domains, constraints and communication addresses only with relevant agents. We further extend DisAC3.1 to DisGAC3.1, which is the first distributed algorithm that enforces generalized arc-consistency on k-ary (k≥ 2) constraint satisfaction problems. Theoretical analyses show that our algorithms are efficient in both time and space. Experiments also demonstrate that DisAC3.1 outperforms the state-of-the-art distributed arc-consistency algorithm and that DisGAC3.1 ’s performance scales linearly in the number of agents.
Kong, S, Li, S & Sioutis, M 2018, 'Exploring Directional Path-Consistency for Solving Constraint Networks', The Computer Journal, vol. 61, no. 9.
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Lanese, I & Devitt, S 2018, 'Preface for the special issue of the 8th Conference on Reversible Computation (RC 2016)', Science of Computer Programming, vol. 151, p. 1.
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Li, Y, Qiao, Y, Wang, X & Duan, R 2018, 'Tripartite-to-Bipartite Entanglement Transformation by Stochastic Local Operations and Classical Communication and the Structure of Matrix Spaces', Communications in Mathematical Physics, vol. 358, no. 2, pp. 791-814.
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© 2018, Springer-Verlag GmbH Germany, part of Springer Nature. We study the problem of transforming a tripartite pure state to a bipartite one using stochastic local operations and classical communication (SLOCC). It is known that the tripartite-to-bipartite SLOCC convertibility is characterized by the maximal Schmidt rank of the given tripartite state, i.e. the largest Schmidt rank over those bipartite states lying in the support of the reduced density operator. In this paper, we further study this problem and exhibit novel results in both multi-copy and asymptotic settings, utilizing powerful results from the structure of matrix spaces. In the multi-copy regime, we observe that the maximal Schmidt rank is strictly super-multiplicative, i.e. the maximal Schmidt rank of the tensor product of two tripartite pure states can be strictly larger than the product of their maximal Schmidt ranks. We then provide a full characterization of those tripartite states whose maximal Schmidt rank is strictly super-multiplicative when taking tensor product with itself. Notice that such tripartite states admit strict advantages in tripartite-to-bipartite SLOCC transformation when multiple copies are provided. In the asymptotic setting, we focus on determining the tripartite-to-bipartite SLOCC entanglement transformation rate. Computing this rate turns out to be equivalent to computing the asymptotic maximal Schmidt rank of the tripartite state, defined as the regularization of its maximal Schmidt rank. Despite the difficulty caused by the super-multiplicative property, we provide explicit formulas for evaluating the asymptotic maximal Schmidt ranks of two important families of tripartite pure states by resorting to certain results of the structure of matrix spaces, including the study of matrix semi-invariants. These formulas turn out to be powerful enough to give a sufficient and necessary condition to determine whether a given tripartite pure state can be transformed to the bipa...
Liu, Y, Lan, C, Blumenstein, M & Li, J 2018, 'Bi-level error correction for PacBio long reads', IEEE/ACM Transactions on Computational Biology and Bioinformatics.
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IEEE The latest sequencing technologies such as the Pacific Biosciences (PacBio) and Oxford Nanopore machines can generate long reads at the length of thousands of nucleic bases which is much longer than the reads at the length of hundreds generated by Illumina machines. However, these long reads are prone to much higher error rates, for example 15%, making downstream analysis and applications very difficult. Error correction is a process to improve the quality of sequencing data. Hybrid correction strategies have been recently proposed to combine Illumina reads of low error rates to fix sequencing errors in the noisy long reads with good performance. In this paper, we propose a new method named Bicolor, a bi-level framework of hybrid error correction for further improving the quality of PacBio long reads. At the first level, our method uses a de Bruijn graph-based error correction idea to search paths in pairs of solid < formula > < tex > $k$ < /tex > < /formula > -mers iteratively with an increasing length of < formula > < tex > $k$ < /tex > < /formula > -mer. At the second level, we combine the processed results under different parameters from the first level. In particular, a multiple sequence alignment algorithm is used to align those similar long reads, followed by a voting algorithm which determines the final base at each position of the reads. We compare the superior performance of Bicolor with three state-of-the-art methods on three real data sets. Results demonstrate that Bicolor always achieves the highest identity ratio. Bicolor also achieves a higher alignment ratio ( < formula > < tex > $ & #x003E; 1.3\%$ < /tex > < /formula > ) and a higher number of aligned reads than the current methods on two data sets. On the third data set, our method is closely competitive to the current methods in terms of number of aligned reads and genome coverage. The C++ source codes of our algorithm are freely available at https://github.com/yuansliu/Bicolor.
Lu, S, Huang, S, Li, K, Li, J, Chen, J, Lu, D, Ji, Z, Shen, Y, Zhou, D & Zeng, B 2018, 'Separability-entanglement classifier via machine learning', Physical Review A, vol. 98, no. 1.
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© 2018 American Physical Society. The problem of determining whether a given quantum state is entangled lies at the heart of quantum information processing. Despite the many methods - such as the positive partial transpose criterion and the k-symmetric extendibility criterion - to tackle this problem, none of them enables a general, practical solution due to the problem's NP-hard complexity. Explicitly, separable states form a high-dimensional convex set of vastly complicated structures. In this work, we build a different separability-entanglement classifier underpinned by machine learning techniques. We use standard tools from machine learning to learn the entanglement feature of arbitrary given quantum states. We perform substantial numerical tests on two-qubit and two-qutrit systems, and the results indicate that our method can outperform the existing methods in generic cases in terms of both speed and accuracy. This opens up avenues to explore quantum entanglement via the machine learning approach.
Luthi, F, Stavenga, T, Enzing, OW, Bruno, A, Dickel, C, Langford, NK, Rol, MA, Jespersen, TS, Nygård, J, Krogstrup, P & DiCarlo, L 2018, 'Evolution of Nanowire Transmon Qubits and Their Coherence in a Magnetic Field.', Physical review letters, vol. 120, no. 10, p. 100502.
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We present an experimental study of flux- and gate-tunable nanowire transmons with state-of-the-art relaxation time allowing quantitative extraction of flux and charge noise coupling to the Josephson energy. We evidence coherence sweet spots for charge, tuned by voltage on a proximal side gate, where first order sensitivity to switching two-level systems and background 1/f noise is minimized. Next, we investigate the evolution of a nanowire transmon in a parallel magnetic field up to 70 mT, the upper bound set by the closing of the induced gap. Several features observed in the field dependence of qubit energy relaxation and dephasing times are not fully understood. Using nanowires with a thinner, partially covering Al shell will enable operation of these circuits up to 0.5 T, a regime relevant for topological quantum computation and other applications.
Mandal, R, Roy, PP, Pal, U & Blumenstein, M 2018, 'Bag-of-visual-words for signature-based multi-script document retrieval', Neural Computing and Applications, pp. 1-25.
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© 2018 The Natural Computing Applications Forum An end-to-end architecture for multi-script document retrieval using handwritten signatures is proposed in this paper. The user supplies a query signature sample, and the system exclusively returns a set of documents that contain the query signature. In the first stage, a component-wise classification technique separates the potential signature components from all other components. A bag-of-visual-words powered by SIFT descriptors in a patch-based framework is proposed to compute the features and a support vector machine (SVM)-based classifier was used to separate signatures from the documents. In the second stage, features from the foreground (i.e., signature strokes) and the background spatial information (i.e., background loops, reservoirs etc.) were combined to characterize the signature object to match with the query signature. Finally, three distance measures were used to match a query signature with the signature present in target documents for retrieval. The ‘Tobacco’ (The Legacy Tobacco Document Library (LTDL). University of California, San Francisco, 2007. http://legacy.library.ucsf.edu/) document database and an Indian script database containing 560 documents of Devanagari (Hindi) and Bangla scripts were used for the performance evaluation. The proposed system was also tested on noisy documents, and the promising results were obtained. A comparative study shows that the proposed method outperforms the state-of-the-art approaches.
Marshman, RJ, Lund, AP, Rohde, PP & Ralph, TC 2018, 'Passive quantum error correction of linear optics networks through error averaging', Physical Review A, vol. 97, no. 2.
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© 2018 American Physical Society. We propose and investigate a method of error detection and noise correction for bosonic linear networks using a method of unitary averaging. The proposed error averaging does not rely on ancillary photons or control and feedforward correction circuits, remaining entirely passive in its operation. We construct a general mathematical framework for this technique and then give a series of proof of principle examples including numerical analysis. Two methods for the construction of averaging are then compared to determine the most effective manner of implementation and probe the related error thresholds. Finally we discuss some of the potential uses of this scheme.
Paler, A & Devitt, SJ 2018, 'Specification format and a verification method of fault-tolerant quantum circuits', Physical Review A, vol. 98, no. 2.
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© 2018 American Physical Society. Quantum computations are expressed in general as quantum circuits, which are specified by ordered lists of quantum gates. The resulting specifications are used during the optimization and execution of the expressed computations. However, the specification format makes it difficult to verify that optimized or executed computations still conform to the initial gate list specifications: showing the computational equivalence between two quantum circuits expressed by different lists of quantum gates is exponentially complex in the worst case. In order to solve this issue, this work presents a derivation of the specification format tailored specifically for fault-tolerant quantum circuits. The circuits are considered a form consisting entirely of single qubit initializations, cnot gates, and single qubit measurements (ICM form). This format allows, under certain assumptions, to efficiently verify optimized (or implemented) computations. Two verification methods based on checking stabilizer circuit structures are presented.
Pfister, C, Rol, MA, Mantri, A, Tomamichel, M & Wehner, S 2018, 'Capacity estimation and verification of quantum channels with arbitrarily correlated errors.', Nature communications, vol. 9, no. 1, pp. 27-27.
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The central figure of merit for quantum memories and quantum communication devices is their capacity to store and transmit quantum information. Here, we present a protocol that estimates a lower bound on a channel's quantum capacity, even when there are arbitrarily correlated errors. One application of these protocols is to test the performance of quantum repeaters for transmitting quantum information. Our protocol is easy to implement and comes in two versions. The first estimates the one-shot quantum capacity by preparing and measuring in two different bases, where all involved qubits are used as test qubits. The second verifies on-the-fly that a channel's one-shot quantum capacity exceeds a minimal tolerated value while storing or communicating data. We discuss the performance using simple examples, such as the dephasing channel for which our method is asymptotically optimal. Finally, we apply our method to a superconducting qubit in experiment.
Sioutis, M, Long, Z & Li, S 2018, 'Leveraging Variable Elimination for Efficiently Reasoning about Qualitative Constraints', International Journal on Artificial Intelligence Tools, vol. 27, no. 4.
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© 2018 World Scientific Publishing Company. We introduce, study, and evaluate a novel algorithm in the context of qualitative constraint-based spatial and temporal reasoning that is based on the idea of variable elimination, a simple and general exact inference approach in probabilistic graphical models. Given a qualitative constraint network N, our algorithm utilizes a particular directional local consistency, which we denote by G-consistency, in order to efficiently decide the satisfiability of N. Our discussion is restricted to distributive subclasses of relations, i.e., sets of relations closed under converse, intersection, and weak composition and for which weak composition distributes over non-empty intersections for all of their relations. We demonstrate that enforcing G-consistency in a given qualitative constraint network defined over a distributive subclass of relations allows us to decide its satisfiability, and obtain similar useful results for the problems of minimal labelling and redundancy. Further, we present a generic method that allows extracting a scenario from a satisfiable network, i.e., an atomic satisfiable subnetwork of that network, in a very simple and effective manner. The experimentation that we have conducted with random and real-world qualitative constraint networks defined over a distributive subclass of relations of the Region Connection Calculus and the Interval Algebra, shows that our approach exhibits unparalleled performance against state-of-the-art approaches for checking the satisfiability of such constraint networks.
Stapelberg, NJC, Pratt, R, Neumann, DL, Shum, DHK, Brandis, S, Muthukkumarasamy, V, Stantic, B, Blumenstein, M & Headrick, JP 2018, 'From feedback loop transitions to biomarkers in the psycho-immune-neuroendocrine network: Detecting the critical transition from health to major depression', Neuroscience and Biobehavioral Reviews, vol. 90, pp. 1-15.
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© 2018 Elsevier Ltd Background: Biological pathways underlying major depressive disorder (MDD) can be viewed as systems biology networks. The psycho-immune-neuroendocrine (PINE) network comprises central nervous, immune, endocrine and autonomic systems, integrating biological mechanisms of MDD. Such networks exhibit recurrent motifs with specific functions, including positive and negative feedback loops, and are subject to critical transitions, influenced by feedback loop transitions (FLTs). Aims: We aim to identify critical feedback loops and their FLTs, as well sentinel network nodes (SNNs), key network nodes that drive FLTs, within the PINE network. Examples of biomarkers are provided which may reflect early warning signs of impending critical transition to MDD. Results: Disruption of homeostatic feedback loops reflects the physiological transition to MDD. Putative FLTs are identified within hypothalamic-pituitary-adrenal (HPA) and sympathetic-parasympathetic axes, the kynurenine pathway, gut function and dysbiosis. Conclusions: Progression from health to disease is driven by FLTs in the PINE network, which is likely to undergo changes characteristic of system instability. Biomarkers of system instability may effectively predict the critical transition to MDD.
Stewart, RA, Nguyen, K, Beal, C, Zhang, H, Sahin, O, Bertone, E, Vieira, AS, Castelletti, A, Cominola, A, Giuliani, M, Giurco, D, Blumenstein, M, Turner, A, Liu, A, Kenway, S, Savić, DA, Makropoulos, C & Kossieris, P 2018, 'Integrated intelligent water-energy metering systems and informatics: Visioning a digital multi-utility service provider', Environmental Modelling and Software, vol. 105, pp. 94-117.
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© 2018 Elsevier Ltd Advanced metering technologies coupled with informatics creates an opportunity to form digital multi-utility service providers. These providers will be able to concurrently collect a customers’ medium-high resolution water, electricity and gas demand data and provide user-friendly platforms to feed this information back to customers and supply/distribution utility organisations. Providers that can install low-cost integrative systems will reap the benefits of derived operational synergies and access to mass markets not bounded by historical city, state or country limits. This paper provides a vision of the required transformative process and features of an integrated multi-utility service provider covering the system architecture, opportunities and benefits, impediments and strategies, and business opportunities. The heart of the paper is focused on demonstrating data modelling processes and informatics opportunities for contemporaneously collected demand data, through illustrative examples and four informative water-energy nexus case studies. Finally, the paper provides an overview of the transformative R&D priorities to realise the vision.
Tan, SH, Ouyang, Y & Rohde, PP 2018, 'Practical somewhat-secure quantum somewhat-homomorphic encryption with coherent states', Physical Review A, vol. 97, no. 4.
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© 2018 American Physical Society. We present a scheme for implementing homomorphic encryption on coherent states encoded using phase-shift keys. The encryption operations require only rotations in phase space, which commute with computations in the code space performed via passive linear optics, and with generalized nonlinear phase operations that are polynomials of the photon-number operator in the code space. This encoding scheme can thus be applied to any computation with coherent-state inputs, and the computation proceeds via a combination of passive linear optics and generalized nonlinear phase operations. An example of such a computation is matrix multiplication, whereby a vector representing coherent-state amplitudes is multiplied by a matrix representing a linear optics network, yielding a new vector of coherent-state amplitudes. By finding an orthogonal partitioning of the support of our encoded states, we quantify the security of our scheme via the indistinguishability of the encrypted code words. While we focus on coherent-state encodings, we expect that this phase-key encoding technique could apply to any continuous-variable computation scheme where the phase-shift operator commutes with the computation.
Tomamichel, M & Hayashi, M 2018, 'Operational interpretation of Rényi information measures via composite hypothesis testing against product and markov distributions', IEEE Transactions on Information Theory, vol. 64, no. 2, pp. 1064-1082.
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© 1963-2012 IEEE. We revisit the problem of asymmetric binary hypothesis testing against a composite alternative hypothesis. We introduce a general framework to treat such problems when the alternative hypothesis adheres to certain axioms. In this case, we find the threshold rate, the optimal error and strong converse exponents (at large deviations from the threshold), and the second order asymptotics (at small deviations from the threshold). We apply our results to find the operational interpretations of various Rényi information measures. In case the alternative hypothesis is comprised of bipartite product distributions, we find that the optimal error and strong converse exponents are determined by the variations of Rényi mutual information. In case the alternative hypothesis consists of tripartite distributions satisfying the Markov property, we find that the optimal exponents are determined by the variations of Rényi conditional mutual information. In either case, the relevant notion of Rényi mutual information depends on the precise choice of the alternative hypothesis. As such, this paper also strengthens the view that different definitions of Rényi mutual information, conditional entropy, and conditional mutual information are adequate depending on the context in which the measures are used.
Vijayan, MK, Chitambar, E & Hsieh, M-H 2018, 'One-shot assisted concentration of coherence', JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICAL, vol. 51, no. 42.
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Wang, X & Duan, R 2018, 'Separation between quantum Lovász number and entanglement-assisted zero-error classical capacity', IEEE Transactions on Information Theory, vol. 64, no. 3, pp. 1454-1460.
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© 1963-2012 IEEE. Quantum Lovász number is a quantum generalization of the Lovász number in graph theory. It is the best known efficiently computable upper bound of the entanglement-assisted zero-error classical capacity of a quantum channel. However, it remains an intriguing open problem whether quantum entanglement can always enhance the zero-error capacity to achieve the quantum Lovász number. In this paper, by constructing a particular class of qutrit-to-qutrit channels, we show that there exists a strict gap between the entanglement-assisted zero-error capacity and the quantum Lovász number. Interestingly, for this class of quantum channels, the quantum generalization of fractional packing number is strictly larger than the zero-error capacity assisted with feedback or no-signaling correlations, which differs from the case of classical channels.
Wang, X, Xie, W & Duan, R 2018, 'Semidefinite programming strong converse bounds for classical capacity', IEEE Transactions on Information Theory, vol. 64, no. 1, pp. 640-653.
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IEEE We investigate the classical communication over quantum channels when assisted by no-signalling (NS) and PPT-preserving (PPT) codes, for which both the optimal success probability of a given transmission rate and the oneshot & #x03F5;-error capacity are formalized as semidefinite programs (SDPs). Based on this, we obtain improved SDP finite blocklength converse bounds of general quantum channels for entanglement-assisted codes and unassisted codes. Furthermore, we derive two SDP strong converse bounds for the classical capacity of general quantum channels: for any code with a rate exceeding either of the two bounds of the channel, the success probability vanishes exponentially fast as the number of channel uses increases. In particular, applying our efficiently computable bounds, we derive an improved upper bound on the classical capacity of the amplitude damping channel. We also establish the strong converse property for the classical and private capacities of a new class of quantum channels. We finally study the zero-error setting and provide efficiently computable upper bounds on the one-shot zero-error capacity of a general quantum channel
Zhang, J, Devitt, SJ, You, JQ & Nori, F 2018, 'Holonomic surface codes for fault-tolerant quantum computation', Physical Review A, vol. 97, no. 2.
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© 2018 American Physical Society. Surface codes can protect quantum information stored in qubits from local errors as long as the per-operation error rate is below a certain threshold. Here we propose holonomic surface codes by harnessing the quantum holonomy of the system. In our scheme, the holonomic gates are built via auxiliary qubits rather than the auxiliary levels in multilevel systems used in conventional holonomic quantum computation. The key advantage of our approach is that the auxiliary qubits are in their ground state before and after each gate operation, so they are not involved in the operation cycles of surface codes. This provides an advantageous way to implement surface codes for fault-tolerant quantum computation.
Adak, C, Chaudhuri, BB & Blumenstein, M 2017, 'Legibility and Aesthetic Analysis of Handwriting', Proceedings of the International Conference on Document Analysis and Recognition, ICDAR, IAPR International Conference on Document Analysis and Recognition, IEEE, Kyoto, Japan, pp. 175-182.
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© 2017 IEEE. This paper deals with computer-based cognitive analysis towards legibility and aesthetics of a handwritten document. The legible text creates a human perception that the writing can be read effortlessly because of its orthographic clarity. The aesthetic property relates to the beautiful appearance of a handwritten document. In this study, we deal with these properties on offline Bengali handwriting. We formulate both legibility and aesthetic analysis tasks as machine learning problems supervised by the human cognitive system. We employ automatically derived feature-based recurrent neural networks to investigate writing legibility. For aesthetics evaluation, we employ hand-crafted feature-based support vector machines (SVMs). We have collected contemporary Bengali handwritings, on which the subjective legibility and aesthetic scores are provided by human readers. On this corpus containing legibility and aesthetic ground-Truth information, we executed our experiments. The experimental results obtained on various handwritings are encouraging.
Adak, C, Marinai, S, Chaudhuri, BB & Blumenstein, M 2018, 'Offline Bengali writer verification by PDF-CNN and siamese net', Proceedings - 13th IAPR International Workshop on Document Analysis Systems, DAS 2018, pp. 381-386.
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© 2018 IEEE. Automated handwriting analysis is a popular area of research owing to the variation of writing patterns. In this research area, writer verification is one of the most challenging branches, having direct impact on biometrics and forensics. In this paper, we deal with offline writer verification on complex handwriting patterns. Therefore, we choose a relatively complex script, i.e., Indic Abugida script Bengali (or, Bangla) containing more than 250 compound characters. From a handwritten sample, the probability distribution functions (PDFs) of some handcrafted features are obtained and input to a convolutional neural network (CNN). For such a CNN architecture, we coin the term 'PDFCNN', where handcrafted feature PDFs are hybridized with auto-derived CNN features. Such hybrid features are then fed into a Siamese neural network for writer verification. The experiments are performed on a Bengali offline handwritten dataset of 100 writers. Our system achieves encouraging results, which sometimes exceed the results of state-of-The-Art techniques on writer verification.
Alaei, F, Alaei, A, Pal, U & Blumenstein, M 2018, 'Evaluation of GIST operator for document image retrieval', Proceedings - 13th IAPR International Workshop on Document Analysis Systems, DAS 2018, pp. 369-374.
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© 2018 IEEE. As digitised documents normally contain a large variety of structures, a page segmentation-and layout-free method for document image retrieval is preferable. In this research work, therefore, wavelet transform as a transform-based approach is initially used to provide different under-sampled images from the original image. Then, GIST operator, as a feature extraction technique, is employed to extract a set of global features from the original image as well as the sub-images obtained from the wavelet transform. Moreover, the column-wise variances of the values in each sub-image are computed and they are then concatenated to obtain another set of features. Considering each feature set, locality-sensitive hashing is employed to compute similarity distances between a query and the document images in the database. Finally, a classifier fusion technique using the mean function is taken into account to provide a document image retrieval result. The combination of these features and a clustering score fusion strategy provides higher document image retrieval accuracy. Two different databases of the document image are considered for experimentation. The results obtained from the experimental study are detailed and the results are encouraging.
Cheng, HC, Hanson, EP, Datta, N & Hsieh, MH 2018, 'Error Exponents and Strong Converse Exponents for Classical Data Compression with Quantum Side Information', IEEE International Symposium on Information Theory - Proceedings, pp. 2162-2166.
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© 2018 IEEE. In this paper, we analyze classical data compression with quantum side information (also known as the classical-quantum Slepian- Wolf protocol) in the so-called large and moderate deviation regimes. In the non-asymptotic setting, the protocol involves compressing classical sequences of finite length n and decoding them with the assistance of quantum side information. In the large deviation regime, the compression rate is fixed, and we obtain bounds on the error exponent function, which characterizes the minimal probability of error as a function of the rate. Devetak and Winter showed that the asymptotic data compression limit for this protocol is given by a conditional entropy. For any protocol with a rate below this quantity, the probability of error converges to one asymptotically and its speed of convergence is given by the strong converse exponent function. We obtain finite blocklength bounds on this function, and determine exactly its asymptotic value, thus improving on previous results by Tomamichel. In the moderate deviation regime for the compression rate, the latter is no longer considered to be fixed. It is allowed to depend on the blocklength n, but assumed to decay slowly to the asymptotic data compression limit. Starting from a rate above this limit, we determine the speed of convergence of the error probability to zero and show that it is given in terms of the conditional information variance. Our results complement earlier results obtained by Tomamichel and Hayashi, in which they analyzed the so-called small deviation regime of this protocol.
Das, A, Pal, U, Ferrer, MA, Blumenstein, M, Stepec, D, Rot, P, Emersic, Z, Peer, P & Struc, V 2018, 'SSBC 2018: Sclera segmentation benchmarking competition', Proceedings - 2018 International Conference on Biometrics, ICB 2018, pp. 303-308.
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© 2018 IEEE. This paper summarises the results of the Sclera Segmentation Benchmarking Competition (SSBC 2018). It was organised in the context of the 11th IAPR International Conference on Biometrics (ICB 2018). The aim of this competition was to record the developments on sclera segmentation in the cross-sensor environment (sclera trait captured using multiple acquiring sensors). Additionally, the competition also aimed to gain the attention of researchers on this subject of research. For the purpose of benchmarking, we have developed two datasets of sclera images captured using different sensors. The first dataset was collected using a DSLR camera and the second one was collected using a mobile phone camera. The first dataset is the Multi-Angle Sclera Dataset (MASD version 1), which was used in the context of the previous versions of sclera segmentation competitions. The images in the second dataset were captured using.a mobile phone rear camera of 8-megapixel. As baseline manual segmentation mask of the sclera images from both the datasets were developed. Precision and recall-based statistical measures were employed to evaluate the effectiveness of the submitted segmentation technique and to rank them. Six algorithms were submitted towards the segmentation task. This paper analyses the results produced by these algorithms/system and defines a way forward for this subject of research. Both the datasets along with some of the accompanying ground truth/baseline mask will be freely available for research purposes upon request to authors by email.
Fu, C, Turrini, A, Huang, X, Song, L, Feng, Y & Zhang, L 2018, 'Model checking probabilistic epistemic logic for probabilistic multiagent systems', IJCAI International Joint Conference on Artificial Intelligence, pp. 4757-4763.
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© 2018 International Joint Conferences on Artificial Intelligence.All right reserved. In this work we study the model checking problem for probabilistic multiagent systems with respect to the probabilistic epistemic logic PETL, which can specify both temporal and epistemic properties. We show that under the realistic assumption of uniform schedulers, i.e., the choice of every agent depends only on its observation history, PETL model checking is undecidable. By restricting the class of schedulers to be memoryless schedulers, we show that the problem becomes decidable. More importantly, we design a novel algorithm which reduces the model checking problem into a mixed integer non-linear programming problem, which can then be solved by using an SMT solver. The algorithm has been implemented in an existing model checker and experiments are conducted on examples from the IPPC competitions.
Ji, Z, Liu, YK & Song, F 2018, 'Pseudorandom quantum states', Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics), pp. 126-152.
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© International Association for Cryptologic Research 2018. We propose the concept of pseudorandom quantum states, which appear random to any quantum polynomial-time adversary. It offers a computational approximation to perfectly random quantum states analogous in spirit to cryptographic pseudorandom generators, as opposed to statistical notions of quantum pseudorandomness that have been studied previously, such as quantum t-designs analogous to t-wise independent distributions. Under the assumption that quantum-secure one-way functions exist, we present efficient constructions of pseudorandom states, showing that our definition is achievable. We then prove several basic properties of pseudorandom states, which show the utility of our definition. First, we show a cryptographic no-cloning theorem: no efficient quantum algorithm can create additional copies of a pseudorandom state, when given polynomially-many copies as input. Second, as expected for random quantum states, we show that pseudorandom quantum states are highly entangled on average. Finally, as a main application, we prove that any family of pseudorandom states naturally gives rise to a private-key quantum money scheme.
Leung, D, Touchette, D, Nayak, A, Yao, P, Shayeghi, A & Yu, N 2018, 'Capacity approaching coding for low noise interactive quantum communication', Proceedings of the Annual ACM Symposium on Theory of Computing, pp. 926-939.
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© 2018 Copyright held by the owner/author(s). We consider the problem of implementing two-party interactive quantum communication over noisy channels, a necessary endeavor if we wish to fully reap quantum advantages for communication. For an arbitrary protocol with n messages, designed for noiseless qudit channels (where d is arbitrary), our main result is a simulation method that fails with probability less than 2−Θ(nϵ) and uses a qudit channel n 1 + Θ times, of which an fraction can be corrupted adversarially. The simulation is thus capacity achieving to leading order, and we conjecture that it is optimal up to a constant factor in the term. Furthermore, the simulation is in a model that does not require pre-shared resources such as randomness or entanglement between the communicating parties. Perhaps surprisingly, this outperforms the best known overhead of 1 + O log logϵ1in the corresponding classical model, which is also conjectured to be optimal [Haeupler, FOCS’14]. Our work also improves over the best previously known quantum result where the overhead is a non-explicit large constant [Brassard et al., FOCS’14] for low .
Salek, F, Anshu, A, Hsieh, MH, Jain, R & Fonollosa, JR 2018, 'One-shot Capacity Bounds on the Simultaneous Transmission of Public and Private Information over Quantum Channels', IEEE International Symposium on Information Theory - Proceedings, pp. 296-300.
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© 2018 IEEE. We aim to study the optimal rates of transmission of public and private classical information over a quantum channel in the most general channel model. To this end, we discuss a scenario in which a quantum channel is being used only once, i.e., one-shot regime is considered. A quantum channel can be used to send classical information (bits) either publicly or privately and for either case, one-shot bounds have been reported in the literature. This paper investigates the one-shot capacity capabilities of a quantum channel for simultaneous transmission of public and private information. We derive an achievable rate region in the form of a tradeoff between public and private rates. We also provide converse bounds assessing the " of our achievable rates. Our main tools used in the achievability proofs are position-based decoding and convex-split lemma.
Saqib, M, Daud Khan, S, Sharma, N & Blumenstein, M 2018, 'Extracting descriptive motion information from crowd scenes', International Conference Image and Vision Computing New Zealand, pp. 1-6.
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© 2017 IEEE. An important contribution that automated analysis tools can generate for management of pedestrians and crowd safety is the detection of conflicting large pedestrian flows: this kind of movement pattern, in fact, may lead to dangerous situations and potential threats to pedestrian's safety. For this reason, detecting dominant motion patterns and summarizing motion information from the scene are inevitable for crowd management. In this paper, we develop a framework that extracts motion information from the scene by generating point trajectories using particle advection approach. The trajectories obtained are then clustered by using unsupervised hierarchical clustering algorithm, where the similarity is measured by the Longest Common Sub-sequence (LCS) metric. The achieved motions patterns in the scene are summarized and represented by using color-coded arrows, where speeds of the different flows are encoded with colors, the width of an arrow represents the density (number of people belonging to a particular motion pattern) while the arrowhead represents the direction. This novel representation of crowded scene provides a clutter free visualization which helps the crowd managers in understanding the scene. Experimental results show that our method outperforms state-of-the-art methods.
Sharma, N, Sengupta, A, Sharma, R, Pal, U & Blumenstein, M 2018, 'Pincode detection using deep CNN for postal automation', International Conference Image and Vision Computing New Zealand, pp. 1-6.
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© 2017 IEEE. Postal automation has been a topic of research over a decade. The challenges and complexity involved in developing a postal automation system for a multi-lingual and multi-script country like India are many-fold. The characteristics of Indian postal documents include: multi-lingual behaviour, unconstrained handwritten addresses, structured/unstructured envelopes and postcards, being among the most challenging aspects. This paper examines the state-of-the-art Deep CNN architectures for detecting pin-code in both structured and unstructured postal envelopes and documents. Region-based Convolutional Neural Networks (RCNN) are used for detecting the various significant regions, namely Pin-code blocks/regions, destination address block, seal and stamp in a postal document. Three network architectures, namely Zeiler and Fergus (ZF), Visual Geometry Group (VGG16), and VGG M were considered for analysis and identifying their potential. A dataset consisting of 2300 multilingual Indian postal documents of three different categories was developed and used for experiments. The VGG-M architecture with Faster-RCNN performed better than others and promising results were obtained.
Wang, Z, Shivakumara, P, Lu, T, Basavanna, M, Pal, U & Blumenstein, M 2018, 'Fourier-Residual for Printer Identification', Proceedings of the International Conference on Document Analysis and Recognition, ICDAR, pp. 1114-1119.
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© 2017 IEEE. Printer identification is challenging due to advanced software technologies in the field of forgery detection. This paper presents a new idea of using the Fourier transform residual for the identification of documents printed by different printers. The proposed approach first convolves a Laplacian mask with a Fourier transform in the frequency domain to smoothen the edges. Next, we apply an inverse Fourier transform to reconstruct images from smoothed information (RFL). Similarly, the proposed approach reconstructs images using gray information of the input image (RFG). Then the residual is calculated by subtracting RFG from RFL. The set of statistical features, texture and spatial features are extracted from residual images for printer identification. Experimental results with the existing method on our dataset and a standard dataset show that the proposed approach outperforms the existing approach on both the datasets in terms of classification rate, recall, precision and F-measure.
Anshu, A, Berta, M, Jain, R & Tomamichel, M 2018, 'Partially smoothed information measures'.
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Smooth entropies are a tool for quantifying resource trade-offs in (quantum)
information theory and cryptography. In typical bi- and multi-partite problems,
however, some of the sub-systems are often left unchanged and this is not
reflected by the standard smoothing of information measures over a ball of
close states. We propose to smooth instead only over a ball of close states
which also have some of the reduced states on the relevant sub-systems fixed.
This partial smoothing of information measures naturally allows to give more
refined characterizations of various information-theoretic problems in the
one-shot setting. In particular, we immediately get asymptotic second-order
characterizations for tasks such as privacy amplification against classical
side information or classical state splitting. For quantum problems like state
merging the general resource trade-off is tightly characterized by partially
smoothed information measures as well. However, for quantum systems we can so
far only give the asymptotic first-order expansion of these quantities.
Anshu, A, Hsieh, M-H & Jain, R 2018, 'Noisy quantum state redistribution with promise and the Alpha-bit'.
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We consider a variation of the well-studied quantum state redistribution
task, in which the starting state is known only to the receiver Bob and not to
the sender Alice. We refer to this as quantum state redistribution with a
one-sided promise. In addition, we consider communication from Alice to Bob
over a noisy channel $\mathcal{N}$, instead of the noiseless channel, as is
usually considered in state redistribution. We take a natural approach towards
solution of this problem where we "embed" the promise as part of the state and
then invoke known protocols for quantum state redistribution composed with
known protocols for transfer of quantum information over noisy channels. We
interpret the communication primitive Alpha-bit, recently introduced in Ref.
[arXiv:1706.09434], as an instance of state transfer (a sub-task of state
redistribution) with a one-sided promise over noisy channels. Using our
approach, we are able to reproduce the Alpha-bit capacities with or without
entanglement assistance in Ref. [arXiv:1706.09434], using known protocols for
quantum state redistribution and quantum communication over noisy channels.
Furthermore, we generalize the entanglement assisted classical capacity of the
Alpha-bit, showing that any quantum state redistribution protocol can be used
as a black box to simulate classical communication.
Cheng, H-C, Hanson, EP, Datta, N & Hsieh, M-H 2018, 'Non-Asymptotic Classical Data Compression with Quantum Side Information'.
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In this paper, we analyze classical data compression with quantum side
information (also known as the classical-quantum Slepian-Wolf protocol) in the
so-called large and moderate deviation regimes. In the non-asymptotic setting,
the protocol involves compressing classical sequences of finite length $n$ and
decoding them with the assistance of quantum side information. In the large
deviation regime, the compression rate is fixed, and we obtain bounds on the
error exponent function, which characterizes the minimal probability of error
as a function of the rate. Devetak and Winter showed that the asymptotic data
compression limit for this protocol is given by a conditional entropy. For any
protocol with a rate below this quantity, the probability of error converges to
one asymptotically and its speed of convergence is given by the strong converse
exponent function. We obtain finite blocklength bounds on this function, and
determine exactly its asymptotic value. In the moderate deviation regime for
the compression rate, the latter is no longer considered to be fixed. It is
allowed to depend on the blocklength $n$, but assumed to decay slowly to the
asymptotic data compression limit. Starting from a rate above this limit, we
determine the speed of convergence of the error probability to zero and show
that it is given in terms of the conditional information variance. Our results
complement earlier results obtained by Tomamichel and Hayashi, in which they
analyzed the so-called small deviation regime of this protocol.
Fang, K, Wang, X, Tomamichel, M & Berta, M 2018, 'Quantum Channel Simulation and the Channel's Smooth Max-Information'.
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We study the general framework of quantum channel simulation, that is, the
ability of a quantum channel to simulate another one using different classes of
codes. First, we show that the minimum error of simulation and the one-shot
quantum simulation cost under no-signalling assisted codes are given by
semidefinite programs. Second, we introduce the channel's smooth
max-information, which can be seen as a one-shot generalization of the mutual
information of a quantum channel. We provide an exact operational
interpretation of the channel's smooth max-information as the one-shot quantum
simulation cost under no-signalling assisted codes. Third, we derive the
asymptotic equipartition property of the channel's smooth max-information,
i.e., it converges to the quantum mutual information of the channel in the
independent and identically distributed asymptotic limit. This implies the
quantum reverse Shannon theorem in the presence of no-signalling correlations.
Finally, we explore the simulation cost of various quantum channels.
Huber, S, Koenig, R & Tomamichel, M 2018, 'Jointly constrained semidefinite bilinear programming with an application to Dobrushin curves'.
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We propose a branch-and-bound algorithm for minimizing a bilinear functional
of the form \[ f(X,Y) = \mathrm{tr}((X\otimes
Y)Q)+\mathrm{tr}(AX)+\mathrm{tr}(BY) , \] of pairs of Hermitian matrices
$(X,Y)$ restricted by joint semidefinite programming constraints. The
functional is parametrized by self-adjoint matrices $Q$, $A$ and $B$. This
problem generalizes that of a bilinear program, where $X$ and $Y$ belong to
polyhedra. The algorithm converges to a global optimum and yields upper and
lower bounds on its value in every step. Various problems in quantum
information theory can be expressed in this form. As an example application, we
compute Dobrushin curves of quantum channels, giving upper bounds on classical
coding with energy constraints.
Luo, Y, Li, Y & Hsieh, M-H 2018, 'Inequivalent Multipartite Coherence Classes and New Coherence Monotones'.
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Quantum coherence has received significant attention in recent years, but its
study is mostly conducted in single party settings. In this paper, we
generalize important results in multipartite entanglement theory to their
counterparts in quantum coherence theory. First, we give a necessary and
sufficient condition for when two pure multipartite states are equivalent under
local quantum incoherent operations and classical communication (LICC), i.e.,
two states can be deterministically transformed to each other under LICC
operations. Next, we investigate and give the conditions in which such a
transformation succeeds only stochastically. Lastly, we introduce two coherence
monotones: accessible coherence and source coherence, following the logistics
given in [\emph{Phys. Rev. Lett. 115, 150502 (2015)}]. These coherence
monotones have a straightforward operational interpretation, namely, the
accessible coherence characterizes the proficiency of a state to generate other
states via quantum incoherent operations, while the source coherence
characterizes the set of states that can be reached via quantum incoherent
operations acting on the given state of interest.
Taranto, P, Pollock, FA, Milz, S, Tomamichel, M & Modi, K 2018, 'Quantum Markov Order'.
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We formally extend the notion of Markov order to open quantum processes by
accounting for the instruments used to probe the system of interest at
different times. Our description recovers the classical Markov order property
in the appropriate limit: when the stochastic process is classical and the
instruments are non-invasive, i.e., restricted to orthogonal projective
measurements. We then prove that there do not exist non-Markovian quantum
processes that have finite Markov order with respect to all possible
instruments; the same process exhibits distinct memory effects with respect to
different probing instruments. This naturally leads to a relaxed definition of
quantum Markov order with respect to specified sequences of instruments. The
memory effects captured by different choices of instruments vary dramatically,
providing a rich landscape for future exploration.
Youssry, A, Ferrie, C & Tomamichel, M 2018, 'Efficient online quantum state estimation using a matrix-exponentiated gradient method'.
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In this paper, we explore an efficient online algorithm for quantum state
estimation based on a matrix-exponentiated gradient method previously used in
the context of machine learning. The state update is governed by a learning
rate that determines how much weight is given to the new measurement results
obtained in each step. We show convergence of the running state estimate in
probability to the true state for both noiseless and noisy measurements. We
find that in the latter case the learning rate has to be chosen adaptively and
decreasing to guarantee convergence beyond the noise threshold. As a practical
alternative we then propose to use running averages of the measurement
statistics and a constant learning rate to overcome the noise problem. The
proposed algorithm is numerically compared with batch maximum-likelihood and
least-squares estimators. The results show a superior performance of the new
algorithm in terms of accuracy and runtime complexity.