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Browsing Quantum Systems, Information and Control by Title

Now showing items 2-21 of 43

Communication through a quantum link

Giovannetti, Vittorio; Mancini, Stefano; Burgarth, Daniel (2009-01-13)

A chain of interacting spin behaves like a quantum mediator (quantum link), which allows two distant parties that control the ends of the chain to exchange quantum messages. We show that over repeated uses without resetting ...
Commutativity of the adiabatic elimination limit of fast oscillatory components and the instantaneous feedback limit in quantum feedback networks

Wildfeuer, Sebastian; Nurdin, Hendra; Gough, John E. (2010-01-01)

We show that, for arbitrary quantum feedback networks consisting of several quantum mechanical components connected by quantum fields, the limit of adiabatic elimination of fast oscillator modes in the components and the ...
Continuous measurement of canonical observables and limit stochastic Schrödinger equations

Sobolev, Andrei; Gough, John E. (2004-03-17)

We derive the stochastic Schrödinger equation for the limit of continuous weak measurement where the observables monitored are canonical position and momentum. To this end we extend an argument due to Smolianov and Truman ...
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 ...
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 ...
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, ...
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 ...
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 ...
Enhancement of Field Squeezing Using Coherent Feedback

Wildfeuer, Sebastian; Gough, John E. (2009-10-14)

The theory of quantum feedback networks has recently been developed with the aim of showing how quantum input-output components may be connected together so as to control, stabilize, or enhance the performance of one of ...
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 ...
Holevo-Ordering and the Continuous-Time Limit for Open Floquet Dynamics

Gough, John E. (2004-03)

We consider an atomic beam reservoir as a source of quantum noise. The atoms are modelled as two-state systems and interact one-at-a-time with the system. The Floquet operators are described in terms of the Fermionic ...
Indirect Hamiltonian Identification through a small gateway

Burgarth, Daniel; Maruyama, Koji (2009-10-07)

Identifying the many-body Hamiltonian of a large quantum system is essential in understanding many physical phenomena, yet extremely difficult in general. We show that coupling strengths in networks of spin-1/2 particles ...
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, ...
Local controllability of quantum networks

Burgarth, Daniel; Bose, Sougato; Bruder, Christoph; Giovannetti, Vittorio (2009)

We give a sufficient criterion that guarantees that a many-body quantum system can be controlled by properly manipulating the (local) Hamiltonian of one of its subsystems. The method can be applied to a wide range of ...
Local quantum control of Heisenberg spin chains

Heule, Rahel; Bruder, Christoph; Burgarth, Daniel; Stojanović, Vladimir M. (2010)

Motivated by some recent results of quantum control theory, we discuss the feasibility of local operator control in arrays of interacting qubits modeled as isotropic Heisenberg spin chains. Acting on one of the end spins, ...
Memory Effects in spin-chain channels for information transmission

Bayat, Abolfazl; Burgarth, Daniel; Mancini, Stefano; Bose, Sougato (2008)

We investigate the multiple use of a ferromagnetic spin chain for quantum and classical communications without resetting. We find that the memory of the state transmitted during the first use makes the spin chain a ...
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 ...
A Noncommutative de Finetti Theorem: Invariance under Quantum Permutations is Equivalent to Freeness with Amalgamation

Köstler, Claus; Speicher, Roland (2009-12-31)

We showthat the classical de Finetti theorem has a canonical noncommutative counterpart if we strengthen 'exchangeability' (i.e., invariance of the joint distribution of the random variables under the action of the permutation ...
A noncommutative extended de Finetti theorem

Köstler, Claus (2010-02-15)

The extended de Finetti theorem characterizes exchangeable infinite sequences of random variables as conditionally i.i.d. and shows that the apparently weaker distributional symmetry of spreadability is equivalent to ...
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. ...

Now showing items 2-21 of 43

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