%0 Journal Article
%J Physical Review A (Atomic, Molecular, and Optical Physics)
%D 2009
%T Preparation of decoherence-free cluster states with optical superlattices
%A Jiang, Liang
%A Rey, Ana Maria
%A Romero-Isart, Oriol
%A Garcia-Ripoll, Juan Jose
%A Sanpera, Anna
%A Lukin, Mikhail D.
%K atom-photon collisions
%K ground states
%K optical multilayers
%K quantum optics
%K superlattices
%B Physical Review A (Atomic, Molecular, and Optical Physics)
%V 79
%P 022309–16
%8 02/2009
%G eng
%U http://link.aps.org/abstract/PRA/v79/e022309 http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PLRAAN000079000002022309000001&idtype=cvips&gifs=yes http://scitation.aip.org/getpdf/servlet/GetPDFServlet?filetype=pdf&id=PLRAAN000079000002
%R 10.1103/PhysRevA.79.022309
%0 Journal Article
%J arXiv
%D 2008
%T Quantum information processing in spin chains via quantum Zeno dynamics
%A Monras, Alex
%A Romero-Isart, Oriol
%K spin chain
%X We show how the quantum Zeno effect can be exploited to control quantum information in a spin chain in a flexible way. In particular, we consider a one dimensional array of three level systems interacting via a swap operator, an interaction found in a generalized Heisenberg Hamiltonian. By encoding the qubit into two levels and using simple projective frequent measurements, the dynamics of the chain is guided to achieve basic quantum information manipulation tools, $\backslash$emph\{i.e.\}, quantum registers, single qubit operations and quantum state transfer on demand, while local addressability is not required. State transfer is perfect, robust against errors and delivers qubits at a constant rate, unconditional of the length of the transfer. Moreover, two dimensional lattices with tunable global interactions in different directions offer the possibility of performing two-qubit gates.
%B arXiv
%8 01/2008
%G eng
%U http://arxiv.org/abs/0801.1959
%0 Journal Article
%J Nature Physics
%D 2008
%T Quantum non-demolition detection of strongly correlated systems
%A Eckert, Kai
%A Romero-Isart, Oriol
%A Rodriguez, Mirta
%A Lewenstein, Maciej
%A Polzik, Eugene S.
%A Sanpera, Anna
%B Nature Physics
%V 4
%P 50–54
%8 01/2008
%G eng
%U http://www.nature.com/nphys/journal/v4/n1/full/nphys776.html
%R 10.1038/nphys776
%0 Journal Article
%J Open Systems & Information Dynamics
%D 2007
%T Efficiency in Quantum Key Distribution Protocols with Entangled Gaussian States
%A Rodó, Carles
%A Romero-Isart, Oriol
%A Eckert, Kai
%A Sanpera, Anna
%K gaussian states
%K quantum cryptography
%K quantum key distribution
%X Abstract Quantum key distribution (QKD) refers to specific quantum strategies which permit the secure distribution of a secret key between two parties that wish to communicate secretly. Quantum cryptography has proven unconditionally secure in ideal scenarios and has been successfully implemented using quantum states with finite (discrete) as well as infinite (continuous) degrees of freedom. Here, we analyze the efficiency of QKD protocols that use as a resource entangled gaussian states and gaussian operations only. In this framework, it has already been shown that QKD is possible [1] but the issue of its efficiency has not been considered. We propose a figure of merit (the efficiency E) to quantify the number of classical correlated bits that can be used to distill a key from a sample of N entangled states. We relate the efficiency of the protocol to the entanglement and purity of the states shared between the parties.
%B Open Systems & Information Dynamics
%V 14
%P 69–80
%8 03/2007
%G eng
%U http://dx.doi.org/10.1007/s11080-007-9030-x
%R 10.1007/s11080-007-9030-x
%0 Journal Article
%J New Journal of Physics
%D 2007
%T Efficient quantum-state transfer in spin chains via adiabatic passage
%A Eckert, Kai
%A Romero-Isart, Oriol
%A Sanpera, Anna
%K spin chain
%K state transfer
%B New Journal of Physics
%V 9
%P 155
%G eng
%U http://iopscience.iop.org/1367-2630/9/5/155/pdf/1367-2630\_9\_5\_155.pdf
%0 Journal Article
%J Physical Review A (Atomic, Molecular, and Optical Physics)
%D 2007
%T Quantum ratchets for quantum communication with optical superlattices
%A Romero-Isart, Oriol
%A Garcia-Ripoll, Juan Jose
%K atom-photon collisions
%K optical modulation
%K quantum entanglement
%K quantum optics
%K superlattices
%B Physical Review A (Atomic, Molecular, and Optical Physics)
%V 76
%P 052304–8
%8 11/2007
%G eng
%U http://scitation.aip.org/getpdf/servlet/GetPDFServlet?filetype=pdf&id=PLRAAN000076000005052304000001&idtype=cvips&prog=normal
%R 10.1103/PhysRevA.76.052304
%0 Journal Article
%J Physical Review A (Atomic, Molecular, and Optical Physics)
%D 2007
%T Quantum state transfer in spin-1 chains
%A Romero-Isart, Oriol
%A Eckert, Kai
%A Sanpera, Anna
%K ferromagnetic materials
%K ground states
%K Heisenberg model
%K magnetic transitions
%K quantum entanglement
%K spin chain
%K spin systems
%K state transfer
%B Physical Review A (Atomic, Molecular, and Optical Physics)
%V 75
%P 050303–4
%8 05/2007
%G eng
%U http://link.aps.org/abstract/PRA/v75/e050303
%R 10.1103/PhysRevA.75.050303
%0 Journal Article
%J Journal of Physics A: Mathematical and General
%D 2007
%T Transport and entanglement generation in the Bose-Hubbard model
%A Romero-Isart, Oriol
%A Eckert, Kai
%A Rodó, Carles
%A Sanpera, Anna
%B Journal of Physics A: Mathematical and General
%V 40
%P 8019–8032
%G eng
%U http://www.iop.org/EJ/article/1751-8121/40/28/S11/a7\_28\_s11.pdf
%0 Journal Article
%J Physical Review Letters
%D 2006
%T Separable Measurement Estimation of Density Matrices and its Fidelity Gap with Collective Protocols
%A Bagan, Emili
%A Ballester, M. A.
%A Gill, R. D.
%A Muñoz-Tapia, Ramon
%A Romero-Isart, Oriol
%K mixed states
%K state estimation
%B Physical Review Letters
%V 97
%P 130501–4
%G eng
%U http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PRLTAO000097000013130501000001&idtype=cvips&gifs=yes
%R 10.1103/PhysRevLett.97.130501
%0 Journal Article
%J Physical Review Letters
%D 2005
%T Purity Estimation with Separable Measurements
%A Bagan, Emili
%A Ballester, M. A.
%A Muñoz-Tapia, Ramon
%A Romero-Isart, Oriol
%X Given a large number N of copies of a qubit state of which we wish to estimate its purity, we prove that separable-measurement protocols can be as efficient as the optimal joint-measurement one if classical communication is used. This shows that the optimal estimation of the entanglement of a two-qubit state can also be achieved asymptotically with fully separable measurements. Thus, quantum memories provide no advantage in this situation. The relationship between our global Bayesian approach and the quantum Cramér-Rao bound is discussed.
%B Physical Review Letters
%I American Physical Society
%V 95
%P 110504
%8 09/2005
%G eng
%U http://link.aps.org/doi/10.1103/PhysRevLett.95.110504
%R 10.1103/PhysRevLett.95.110504