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Search Results: 1 - 10 of 85301 matches for " W. Winter "
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How many copies are needed for state discrimination?
Aram W. Harrow,Andreas Winter
Physics , 2006, DOI: 10.1109/TIT.2011.2169544
Abstract: Given a collection of states (rho_1, ..., rho_N) with pairwise fidelities F(rho_i, rho_j) <= F < 1, we show the existence of a POVM that, given rho_i^{otimes n}, will identify i with probability >= 1-epsilon, as long as n>=2(log N/eps)/log (1/F). This improves on previous results which were either dimension-dependent or required that i be drawn from a known distribution.
Commutative C*-subalgebras of simple stably finite C*-algebras with real rank zero
P. W. Ng,Wilhelm Winter
Mathematics , 2006,
Abstract: Let X be a path connected, compact metric space and let A be a unital separable simple nuclear Z-stable real rank zero C*-algebra. We classify all the unital *-embeddings (up to approximate unitary equivalence) of C(X) into A. Specifically, we provide an existence and a uniqueness theorem for unital *-embeddings from C(X) into A.
Uncertainties of soil parameterisation in process-based simulation of distributed flood control measures
W. Rieger, F. Winter,M. Disse
Advances in Geosciences (ADGEO) , 2010,
Abstract: Distributed flood control measures such as land-use changes or differing soil tillage practices which affect the runoff generation process, are hard to simulate physically based due to a high degree of uncertainty with regard to soil parameterisation. In this study the physically based rainfall runoff model WaSiM-ETH (Version 8.4.2) was used with a multi-layered vegetation and soil parameterisation. The modelling area was the meso-scaled and rurally characterised Windach catchment. In addition, soil measurement datasets were compared to demonstrate the uncertainties in soil parameterisation of physically based models. The datasets were gained from the hillslope scale at the Scheyern research farm with similar soil conditions to the Windach catchment. While parameterising and calibrating the model, seven different pedotransfer functions were used with strong influence on the simulated hydrographs. The differing bulk densities of soils depending on land-use and soil tillage must be taken into consideration due to their high impact on modelling results, and they also offer a comprehensive way to model distributed flood control measures. These measures have noticeable effects on flood events under HQ10, especially if the land-use type which is affected by the distributed flood control measure is the dominating land-use form in the catchment area. To account for the variability of soils in the investigation area of Scheyern, different approaches were applied to estimate soil hydraulic properties and saturated hydraulic conductivity, and were compared to field measurements.
A family of quantum protocols
I. Devetak,A. W. Harrow,A. Winter
Physics , 2003, DOI: 10.1103/PhysRevLett.93.230504
Abstract: We introduce two dual, purely quantum protocols: for entanglement distillation assisted by quantum communication (``mother'' protocol) and for entanglement assisted quantum communication (``father'' protocol). We show how a large class of ``children'' protocols (including many previously known ones) can be derived from the two by direct application of teleportation or super-dense coding. Furthermore, the parent may be recovered from most of the children protocols by making them ``coherent''. We also summarize the various resource trade-offs these protocols give rise to.
A Resource Framework for Quantum Shannon Theory
I. Devetak,A. W. Harrow,A. Winter
Physics , 2005, DOI: 10.1109/TIT.2008.928980
Abstract: Quantum Shannon theory is loosely defined as a collection of coding theorems, such as classical and quantum source compression, noisy channel coding theorems, entanglement distillation, etc., which characterize asymptotic properties of quantum and classical channels and states. In this paper we advocate a unified approach to an important class of problems in quantum Shannon theory, consisting of those that are bipartite, unidirectional and memoryless. We formalize two principles that have long been tacitly understood. First, we describe how the Church of the larger Hilbert space allows us to move flexibly between states, channels, ensembles and their purifications. Second, we introduce finite and asymptotic (quantum) information processing resources as the basic objects of quantum Shannon theory and recast the protocols used in direct coding theorems as inequalities between resources. We develop the rules of a resource calculus which allows us to manipulate and combine resource inequalities. This framework simplifies many coding theorem proofs and provides structural insights into the logical dependencies among coding theorems. We review the above-mentioned basic coding results and show how a subset of them can be unified into a family of related resource inequalities. Finally, we use this family to find optimal trade-off curves for all protocols involving one noisy quantum resource and two noiseless ones.
Synergies between the first-generation JHF-SK and NuMI superbeam experiments
P. Huber,M. Lindner,W. Winter
Physics , 2002, DOI: 10.1016/S0550-3213(03)00063-4
Abstract: We discuss synergies in the combination of the first-generation JHF to Super-Kamiokande and NuMI off-axis superbeam experiments. With synergies we mean effects which go beyond simply adding the statistics of the two experiments. As a first important result, we do not observe interesting synergy effects in the combination of the two experiments as they are planned right now. However, we find that with minor modifications, such as a different NuMI baseline or a partial antineutrino running, one could do much richer physics with both experiments combined. Specifically, we demonstrate that one could, depending on the value of the solar mass squared difference, either measure the sign of the atmospheric mass squared difference or CP violation already with the initial stage experiments. Our main results are presented in a way that can be easily interpreted in terms of the forthcoming KamLAND result.
Simulation of long-baseline neutrino oscillation experiments with GLoBES
P. Huber,M. Lindner,W. Winter
Physics , 2004, DOI: 10.1016/j.cpc.2005.01.003
Abstract: We present the GLoBES (``General Long Baseline Experiment Simulator'') software package, which allows the simulation of long-baseline and reactor neutrino oscillation experiments. One part of the software is the abstract experiment definition language to define experiments with beam and full detector descriptions as accurate as possible. Many systematics options are provided, such as normalization and energy calibration errors, or the choice between spectral or total rate information. For the definition of experiments, a new transparent building block concept is introduced. In addition, an additional program provides the possibility to develop and test new experiment definitions quickly. Another part of GLoBES is the user's interface, which provides probability, rate, and $\Delta \chi^2$ information for a given experiment or any combination of up to 32 experiments in C. Especially, the $\Delta \chi^2$ functions allow a simulation with statistics only, systematics, correlations, and degeneracies. In particular, GLoBES can handle the full multi-parameter correlation among the oscillation parameters, external input, and matter density uncertainties.
A classical analogue of negative information
Jonathan Oppenheim,Robert W. Spekkens,Andreas Winter
Physics , 2005,
Abstract: Recently, it was discovered that the `quantum partial information' needed to merge one party's state with another party's state is given by the conditional entropy, which can be negative [Horodecki, Oppenheim, and Winter, Nature 436, 673 (2005)]. Here we find a classical analogue of this, based on a long known relationship between entanglement and shared private correlations: namely, we consider a private distribution held between two parties, and correlated to a reference system, and ask how much secret communication is needed for one party to send her distribution to the other. We give optimal protocols for this task, and find that private information can be negative - the sender's distribution can be transferred and the potential to send future distributions in secret is gained through the distillation of a secret key. An analogue of `quantum state exchange' is also discussed and one finds cases where exchanging a distribution costs less than for one party to send it. The results give new classical protocols, and also clarify the various relationships between entanglement and privacy.
Aspects of generic entanglement
Patrick Hayden,Debbie W. Leung,Andreas Winter
Mathematics , 2004, DOI: 10.1007/s00220-006-1535-6
Abstract: We study entanglement and other correlation properties of random states in high-dimensional bipartite systems. These correlations are quantified by parameters that are subject to the "concentration of measure" phenomenon, meaning that on a large-probability set these parameters are close to their expectation. For the entropy of entanglement, this has the counterintuitive consequence that there exist large subspaces in which all pure states are close to maximally entangled. This, in turn, implies the existence of mixed states with entanglement of formation near that of a maximally entangled state, but with negligible quantum mutual information and, therefore, negligible distillable entanglement, secret key, and common randomness. It also implies a very strong locking effect for the entanglement of formation: its value can jump from maximal to near zero by tracing over a number of qubits negligible compared to the size of total system. Furthermore, such properties are generic. Similar phenomena are observed for random multiparty states, leading us to speculate on the possibility that the theory of entanglement is much simplified when restricted to asymptotically generic states. Further consequences of our results include a complete derandomization of the protocol for universal superdense coding of quantum states.
Random quantum codes from Gaussian ensembles and an uncertainty relation
Patrick Hayden,Peter W. Shor,Andreas Winter
Mathematics , 2007, DOI: 10.1142/S1230161208000079
Abstract: Using random Gaussian vectors and an information-uncertainty relation, we give a proof that the coherent information is an achievable rate for entanglement transmission through a noisy quantum channel. The codes are random subspaces selected according to the Haar measure, but distorted as a function of the sender's input density operator. Using large deviations techniques, we show that classical data transmitted in either of two Fourier-conjugate bases for the coding subspace can be decoded with low probability of error. A recently discovered information-uncertainty relation then implies that the quantum mutual information for entanglement encoded into the subspace and transmitted through the channel will be high. The monogamy of quantum correlations finally implies that the environment of the channel cannot be significantly coupled to the entanglement, and concluding, which ensures the existence of a decoding by the receiver.
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