A5083721767- Quantum Information and Cryptography
- Quantum Computing Algorithms and Architecture
- Quantum Mechanics and Applications
- Quantum and electron transport phenomena
- Quantum optics and atomic interactions
- Quantum-Dot Cellular Automata
- Cold Atom Physics and Bose-Einstein Condensates
- Quantum many-body systems
- Particle physics theoretical and experimental studies
- Spectroscopy and Quantum Chemical Studies
- Physical Unclonable Functions (PUFs) and Hardware Security
- Neutrino Physics Research
- Quantum chaos and dynamical systems
- Neural Networks and Reservoir Computing
- Computability, Logic, AI Algorithms
- Atomic and Subatomic Physics Research
- Advanced Thermodynamics and Statistical Mechanics
- Wireless Communication Security Techniques
- Chaos-based Image/Signal Encryption
- Quantum Mechanics and Non-Hermitian Physics
- Error Correcting Code Techniques
- History and advancements in chemistry
- Optical Network Technologies
- Scientific Measurement and Uncertainty Evaluation
- Atomic and Molecular Physics
Heinrich Heine University Düsseldorf
2015-2024
Institut de recherche mathématique de Rennes
2010
Leibniz University Hannover
1999-2006
University of Vienna
2004
Research Institute for Philosophy Hannover
2000
Institute for Scientific Interchange
1998-2000
University of Oxford
1997-1998
Heidelberg University
1995-1998
Clarendon College
1998
Heidelberg Institute for Theoretical Studies
1995
A generalization of the quantum cryptographic protocol by Bennett and Brassard is discussed, using three conjugate bases, i.e., six states. By calculating optimal mutual information between sender eavesdropper it shown that this scheme safer against eavesdropping on single qubits than one based two bases. We also address question for a connection maximal classical correlation in generalized Bell inequality intersection informations sender/receiver sender/eavesdropper.
We introduce a classification of mixed three-qubit states, in which we define the classes separable, biseparable, W- and GHZ-states. These are successively embedded into each other. show that contrary to pure W-type W-class is not measure zero. construct witness operators detect class state. discuss conjecture all entangled states with positive partial transpose (PPTES) belong W-class. Finally, present new family PPTES "edge" maximal ranks.
We establish the best possible approximation to a perfect quantum cloning machine that produces two clones out of single input. analyze both universal and state-dependent cloners. The maximal fidelity is shown be 5/6 for It can achieved either by special unitary evolution or teleportation scheme. construct optimal cloners operating on any prescribed nonorthogonal states discuss their fidelities use auxiliary physical resources in process cloning. permit us derive an upper bound capacity...
We present the experimental detection of genuine multipartite entanglement using witness operators. To this aim, we introduce a canonical way constructing and decomposing operators so that they can be directly implemented with technology. apply method to three- four-qubit entangled states polarized photons, giving evidence considered contain true entanglement.
Quantum entanglement is at the heart of many tasks in quantum information. Apart from simple cases (low dimensions, few particles, pure states), however, mathematical structure not yet fully understood. This tutorial an introduction to our present knowledge about how decide whether a given state separable or entangled, characterize via witness operators, classify entangled states according their usefulness (i.e., distillability), and quantify with appropriate measures.
We study optimal eavesdropping in quantum cryptography with three-dimensional systems, and show that this scheme is more secure against symmetric attacks than protocols using two-dimensional states. generalize the according transformation to arbitrary dimensions, discuss connection cloning.
We consider an $\stackrel{\ensuremath{\rightarrow}}{N}M$ quantum cloning transformation acting on pure two-level states lying the equator of Bloch sphere. An upper bound for its fidelity is presented, by establishing a connection between optimal phase-covariant and phase estimation. give explicit form that achieves case $N=1,$ $M=2,$ find link this eavesdropping in cryptographic scheme BB84.
We derive a tight upper bound for the fidelity of universal N to M qubit cloner, valid any \geq N, where output cloner is required be supported on symmetric subspace. Our proof based concatenation two cloners and connection between quantum cloning state estimation. generalise operation mixed and/or entangled input qubits described by density matrix subspace constituent qubits. also extend validity optimal estimation methods inputs this kind.
We introduce a general method for the experimental detection of entanglement by performing only few local measurements, assuming some prior knowledge density matrix. The idea is based on minimal decomposition witness operators into pseudomixture operators. discuss an experimentally relevant case two qubits, and show example how bound can be detected with measurements.
We study the distillability of a certain class bipartite density operators which can be obtained via depolarization starting from an arbitrary one. Our results suggest that non-positivity partial transpose operator is not sufficient condition for distillability, when dimension both subsystems higher than two.
The Schmidt number of a mixed state characterizes the minimum rank pure states needed to construct it. We investigate an arbitrary by studying Schmidt-number witnesses that detect present canonical form such and provide constructive methods for their optimization. Finally, we strong evidence all bound entangled with positive partial transpose in ${\mathcal{C}}^{3}\ensuremath{\bigotimes}{\mathcal{C}}^{3}$ have 2.
We present an abstract formulation of the so-called Innsbruck-Hannover programme that investigates quantum correlations and entanglement in terms convex sets. a unified description optimal decompositions states optimization witness operators detect whether given state belongs to set. illustrate with several examples, discuss relations between witnesses n-copy non-distillable non-positive partial transpose.
We characterize the behavior of quantum correlations under influence local noisy channels. Intuition suggests that such noise should be detrimental for quantumness. When considering qubit systems, we show which channels this is indeed case: The amount can only decrease action unital However, nonunital (e.g., as dissipation) create some initially classical states. Furthermore, higher-dimensional systems even may increase correlations. Thus, counterintuitively, decoherence generate
Establishing quantum entanglement between two distant parties is an essential step of many protocols in information processing. One possibility for providing long-distance to create entangled composite state within a lab and then physically send one subsystem lab. However, this the "cheapest" way? Here, we investigate minimal "cost" that necessary establishing certain amount parties. We prove cost intrinsically quantum, specified by correlations. Our results provide optimal protocol...
We introduce a class of multiqubit quantum states which generalizes graph states. These correspond to an underlying mathematical hypergraph, i.e. where edges connecting more than two vertices are considered. derive generalized stabilizer formalism describe this the notion k-uniformity and show that gives rise classes inequivalent under action local Pauli group. Finally we disclose one-to-one correspondence with employed in algorithms, such as Deutsch–Jozsa's Grover's.
The laws of quantum mechanics allow for the distribution a secret random key between two parties. Here we analyse security protocol establishing common N parties (i.e. conference key), using resource states with genuine N-partite entanglement. We compare this to via bipartite entanglement, regarding required resources, achievable rates and threshold qubit error rates. Furthermore discuss networks bottlenecks which our multipartite entanglement-based can benefit from network coding, while...
The resource theory of quantum coherence studies the off-diagonal elements a density matrix in distinguished basis, whereas purity all deviations from maximally mixed state. We establish direct connection between two theories, by identifying as maximal which is achievable unitary operations. states that saturate this maximum identify universal family coherent states. These are optimal resources under incoherent operations, and thus independent way quantified. For distance-based quantifiers...
The establishment of a world-wide quantum communication network relies on the synergistic integration satellite-based links and fiber-based networks. first are helpful for long-distance communication, as photon losses introduced by optical fibers too detrimental lengths greater than about 200 km. This work aims at giving, one hand, comprehensive fundamental model suffered signals during propagation along an atmospheric free-space link. On other performance analysis different Quantum Key...
Quantum coherence is a fundamental feature of quantum mechanics and an underlying requirement for most information tasks. In the resource theory coherence, incoherent states are diagonal with respect to fixed orthonormal basis, i.e., they can be seen as arising from von Neumann measurement. Here, we introduce study generalization defined general measurement, arbitrary positive-operator-valued measure (POVM). We establish POVM-based measures POVM-incoherent operations which coincide case...
Long-distance entanglement is a very precious resource, but its distribution difficult due to the exponential losses of light in optical fibres. A possible solution consists use quantum repeaters, based on swapping or error correction. Alternatively, satellite-based free-space links can be exploited, achieving better loss-distance scaling. We propose combine these two ingredients, repeaters and links, into scheme that allows achieve over global distances with small number intermediate...
We present a network consisting of quantum gates which produces two imperfect copies an arbitrary qubit. The quality the does not depend on input also show that for restricted class inputs it is possible to use very similar produce three instead two. For qubits in this class, copy again independent and same as produced by two-copy network.
We introduce the notion of distributed quantum dense coding, i.e., generalization coding to more than one sender and receiver. show that global operations (as compared local operations) senders do not increase information transfer capacity, in case a single For two receivers, using classical communication, nontrivial upper bound for capacity is derived. propose general classification scheme states according their usefulness coding. In bipartite (for any dimensions), entanglement useful this task.