Browsing Quantum Systems, Information and Control by Issue Date

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Browsing Quantum Systems, Information and Control by Issue Date

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  • Quantum defragmentation algorithm 
    Giovannetti, Vittorio; Burgarth, Daniel (2010-08-19)
    In this addendum to our paper [ D. Burgarth and V. Giovannetti Phys. Rev. Lett. 99 100501 (2007)] we prove that during the transformation that allows one to enforce control by relaxation on a quantum system, the ancillary ...
  • Quantum Filtering in Coherent States 
    Koestler, Claus; Gough, John E. (2010-12-01)
    We derive the form of the Belavkin-Kushner-Stratonovich equa- tion describing the ltering of a continuous observed quantum system via non-demolition measurements when the statistics of the input eld used for the indirect ...
  • Symmetry and Independence in Quantum Probability 
    Koestler, Claus (2010-12-08)
  • Quantum filtering for systems driven by Fermion field 
    Gough, John E.; Guta, Madalin I.; James, Matthew R.; Nurdin, Hendra I. (2011)
    Recent developments in quantum technology mean that is it now possible to manipulate systems and measure fermion fields (e.g. reservoirs of electrons) at the quantum level. This progress has motivated some recent work on ...
  • Indirect quantum tomography of quadratic Hamiltonians 
    Burgarth, Daniel; Maruyama, Koji; Nori, Franco (2011-01-14)
    A number of many-body problems can be formulated using Hamiltonians that are quadratic in the creation and annihilation operators. Here, we show how such quadratic Hamiltonians can be efficiently estimated indirectly, ...
  • On Lehner's `free' noncommutative analogue of the de Finetti theorem 
    Köstler, Claus (2011-01-31)
    Inspired by Lehner's results on exchangeability systems in [Leh06] we define `weak conditional freeness' and `conditional freeness' for stationary processes in an operator algebraic framework of noncommutative probability. ...
  • Controlling qubit arrays with anisotropic XXZ Heisenberg interaction by acting on a single qubit 
    Heule, Rahel; Bruder, Christoph; Stojanović, Vladimir M.; Burgarth, Daniel (2011-08-31)
    We investigate anisotropic XXZ Heisenberg spin-1/2 chains with control fields acting on one of the end spins, with the aim of exploring local quantum control in arrays of interacting qubits. In this work, which uses a recent ...
  • Dynamics of nonequilibrium thermal entanglement 
    Burgarth, Daniel; Sinaysky, Ilya; Petruccione, Francesco (2011-09-26)
    The dynamics of a simple spin chain (two spins) coupled to bosonic baths at different temperatures is studied. The analytical solution for the reduced density matrix of the system is found. The dynamics and temperature ...
  • Coupling strength estimation for spin chains despite restricted access 
    Nori, Franco; Maruyama, Koji; Burgarth, Daniel (2011-09-26)
    Quantum control requires full knowledge of the system many-body Hamiltonian. In many cases this information is not directly available due to restricted access to the system. Here we show how to indirectly estimate all the ...
  • Scalable quantum computation via local control of only two qubits 
    Montangero, Simone; Murphy, Michael; Burgarth, Daniel; Maryuama, Koji; Nori, Franco; Plenio, Martin B.; Calarco, Tommaso (2011-09-26)
    We apply quantum control techniques to a long spin chain by acting only on two qubits at one of its ends, thereby implementing universal quantum computation by a combination of quantum gates on these qubits and indirect ...
  • Efficient generation of a maximally entangled state by repeated on- and off-resonant scattering of ancilla qubits 
    Burgarth, Daniel; Yuasa, Kazuya; Nakazato, Hiromichi; Giovannetti, Vittorio (2011-09-26)
    A scheme for preparing two fixed noninteracting qubits in a maximally entangled state is presented. By repeating on- and off-resonant scattering of ancilla qubits, the target qubits are driven from an arbitrary initial ...
  • A Protocol For Cooling and Controlling Composite Systems by Local Interactions 
    Burgarth, Daniel; Giovannetti, Vittorio (2011-09-27)
    We discuss an explicit protocol which allows one to externally cool and control a composite system by operating on a small subset of it. The scheme permits to transfer arbitrary and unknown quantum states from a memory on ...
  • When is the Cuntz-Krieger algebra of a higher-rank graph approximately finite-dimensional? 
    Sims, Aidan; Evans, D. Gwion (2012-01-18)
    We investigate the question: when is a higher-rank graph C*-algebra approximately finite dimensional? We prove that the absence of an appropriate higher-rank analogue of a cycle is necessary. We show that it is not in ...
  • Estimation of coupling constants of a three-spin chain: a case study of Hamiltonian tomography with nuclear magnetic resonance 
    Lapasar, Elham Hosseini; Maruyama, Koji; Burgarth, Daniel; Takui, Takeji; Nakahara, Mikio; Kondo, Yasushi (2012-01-23)
    It has been shown that inter-spin interaction strengths in a spin-1/2 chain can be evaluated by accessing one of the edge spins only. We demonstrate this experimentally for the simplest case, a three-spin chain, with the ...
  • Quantum System Identification 
    Yuasa, Kazuya; Burgarth, Daniel K. (2012-03-13)
    The aim of quantum system identification is to estimate the ingredients inside a black box, in which some quantum-mechanical unitary process takes place, by just looking at its input-output behavior. Here we establish a ...
  • Dynamical Recurrence and the Quantum Control of Coupled Oscillators 
    Genoni, Marco; Serafini, Alessio; Kim, Myungshik; Burgarth, Daniel (2012-04-09)
    Controllability - the possibility of performing any target dynamics by applying a set of available operations - is a fundamental requirement for the practical use of any physical system. For finite-dimensional systems, ...
  • Quantum filtering for systems driven by fermion fields 
    Guta, Madalin; Gough, John; James, Matthew; Nurdin, Hendra (2012-05-14)
    Recent developments in quantum technology mean that is it now possible to manipulate systems and measure fermion elds (e.g. reservoirs of electrons) at the quantum level. This progress has motivated some recent work on ...
  • Quantum Filtering for Systems Driven by Fields in Single Photon States and Superposition of Coherent States 
    Gough, John Edward; James, Matthew R.; Nurdin, H. I.; Combes, Joshua (2012-10-15)
    We derive the stochastic master equations, that is to say, quantum filters, and master equations for an arbitrary quantum system probed by a continuous-mode bosonic input field in two types of nonclassical states. Specifically, ...
  • Application of indirect Hamiltonian tomography to complex systems with short decoherence times 
    Burgarth, Daniel; Takui, Takeji; Whaley, K. Birgitta; Maruyama, Koji; Ishizaki, Akihito (2012-10-15)
    The identification of parameters in the Hamiltonian that describes complex many-body quantum systems is generally a very hard task. Recent attention has focused on such problems of Hamiltonian tomography for networks ...
  • Non-abelian Weyl Commutation Relations and the Series Product of Quantum Stochastic Evolutions 
    Evans, D. Gwion; Gough, John; James, Matthew (2012-11-07)
    We show that the series product, which serves as an algebraic rule for connecting state-based input/output systems, is intimately related to the Heisenberg group and the canonical commutation relations. The series product ...

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