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Search Results: 1 - 10 of 3614 matches for " Jens Siewert "
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Lava channel formation during the 2001 eruption on Mount Etna: evidence for mechanical erosion
Carmelo Ferlito,Jens Siewert
Physics , 2005, DOI: 10.1103/PhysRevLett.96.028501
Abstract: We report the direct observation of a peculiar lava channel that was formed near the base of a parasitic cone during the 2001 eruption on Mount Etna. Erosive processes by flowing lava are commonly attributed to thermal erosion. However, field evidence strongly suggests that models of thermal erosion cannot explain the formation of this channel. Here, we put forward the idea that the essential erosion mechanism was abrasive wear. By applying a simple model from tribology we demonstrate that the available data agree favorably with our hypothesis. Consequently, we propose that erosional processes resembling the wear phenomena in glacial erosion are possible in a volcanic environment.
Invariant-based entanglement monotones as expectation values and their experimental detection
Andreas Osterloh,Jens Siewert
Physics , 2010,
Abstract: Characterization and quantification of multipartite entanglement is one of the challenges in state-of-the-art experiments in quantum information processing. According to theory, this is achieved via entanglement monotones, that is, functions that do not increase under stochastic local operations and classical communication (SLOCC). Typically such monotones include the wave function and its time-reversal (antilinear-operator formalism) or they are based on not completely positive maps (e.g., partial transpose). Therefore, they are not directly accessible to experimental observations. We show how entanglement monotones derived from polynomial local SL$(2,\CC)$ invariants can be re-written in terms of expectation values of observables. Consequently, the amount of entanglement---of specific SLOCC classes---in a given state can be extracted from the measurement of correlation functions of local operators.
Even-odd effect in the thermopower and strongly enhanced thermoelectric efficiency for superconducting single-electron transistors
Christopher Eltschka,Jens Siewert
Physics , 2011,
Abstract: It is well known that the transport properties of single-electron transistors with a superconducting island and normal-conducting leads (NSN SET) may depend on whether or not there is a single quasiparticle on the island. This parity effect has pronounced consequences for the linear transport properties. Here we analyze the thermopower of NSN SET with and without parity effect, for entirely realistic values of device parameters. Besides a marked dependence of the thermopower on the superconducting gap $\Delta$ we observe an enhancement in the parity regime which is accompanied by a dramatic increase of the thermoelectric figure of merit ZT. The latter can be explained within a simple re-interpretation of ZT in terms of averages and variances of transport energies.
Quantum algorithms for Josephson networks
Jens Siewert,Rosario Fazio
Physics , 2001, DOI: 10.1103/PhysRevLett.87.257905
Abstract: We analyze possible implementations of quantum algorithms in a system of (macroscopic) Josephson charge qubits. System layout and parameters to realize the Deutsch algorithm with up to three qubits are provided. Special attention is paid to the necessity of entangled states in the various implementations. Further, we demonstrate explicitely that the gates to implement the Bernstein-Vazirani algorithm can be realized by using a system of uncoupled qubits.
Natural two-qubit gate for quantum computation using the XY interaction
Norbert Schuch,Jens Siewert
Physics , 2002, DOI: 10.1103/PhysRevA.67.032301
Abstract: The two-qubit interaction Hamiltonian of a given physical implementation determines whether or not a two-qubit gate such as the CNOT gate can be realized easily. It can be shown that, e.g., with the XY interaction more than one two-qubit operation is required in order to realize CNOT. Here we propose a two-qubit gate for the XY interaction which combines CNOT with the SWAP operation. By using this gate quantum circuits can be implemented efficiently, even if only nearest-neighbor coupling between the qubits is available.
Programmable networks for quantum algorithms
Norbert Schuch,Jens Siewert
Physics , 2003, DOI: 10.1103/PhysRevLett.91.027902
Abstract: The implementation of a quantum computer requires the realization of a large number of N-qubit unitary operations which represent the possible oracles or which are part of the quantum algorithm. Until now there are no standard ways to uniformly generate whole classes of N-qubit gates. We have developed a method to generate arbitrary controlled phase shift operations with a single network of one-qubit and two-qubit operations. This kind of network can be adapted to various physical implementations of quantum computing and is suitable to realize the Deutsch-Jozsa algorithm as well as Grover's search algorithm.
Implementation of the Deutsch-Jozsa algorithm with Josephson charge qubits
Jens Siewert,Rosario Fazio
Physics , 2001, DOI: 10.1080/09500340110114902
Abstract: We investigate the realization of a simple solid-state quantum computer by implementing the Deutsch-Jozsa algorithm in a system of Josephson charge qubits. Starting from a procedure to carry out the one-qubit Deutsch-Jozsa algorithm we show how the N-qubit version of the Bernstein-Vazirani algorithm can be realized. For the implementation of the three-qubit Deutsch-Jozsa algorithm we study in detail a setup which allows to produce entangled states.
Entanglement monotones and maximally entangled states in multipartite qubit systems
Andreas Osterloh,Jens Siewert
Physics , 2005, DOI: 10.1142/S0219749906001980
Abstract: We present a method to construct entanglement measures for pure states of multipartite qubit systems. The key element of our approach is an antilinear operator that we call {\em comb} in reference to the {\em hairy-ball theorem}. For qubits (or spin 1/2) the combs are automatically invariant under $SL(2,\CC)$. This implies that the {\em filters} obtained from the combs are entanglement monotones by construction. We give alternative formulae for the concurrence and the 3-tangle as expectation values of certain antilinear operators. As an application we discuss inequivalent types of genuine four-, five- and six-qubit entanglement.
Applications of adiabatic passage in solid-state devices
Jens Siewert,Tobias Brandes
Physics , 2005,
Abstract: Coherent population transfer by adiabatic passage is a well-known method in quantum optics. This remarkable technique which is based on simple ideas has remained largely unknown to solid-state physicists. Here we provide an introduction to the basic principles of this method and discuss also some applications in solid-state systems.
Constructing N-qubit entanglement monotones from anti-linear operators
Andreas Osterloh,Jens Siewert
Mathematics , 2004, DOI: 10.1103/PhysRevA.72.012337
Abstract: We present a method to construct entanglement measures for pure states of multipartite qubit systems. The key element of our approach is an antilinear operator that we call {\em comb} in reference to the {\em hairy-ball theorem}. For qubits (or spin 1/2) the combs are automatically invariant under $SL(2,\CC)$. This implies that the {\em filters} obtained from the combs are entanglement monotones by construction. We give alternative formulae for the concurrence and the 3-tangle as expectation values of certain antilinear operators. As an application we discuss inequivalent types of genuine four-qubit entanglement.
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