%0 Journal Article
%J PHYSICAL REVIEW A
%D 2017
%T Enhancement of low-temperature thermometry by strong coupling
%A Correa, Luis A.
%A Perarnau-Llobet, Marti
%A Hovhannisyan, Karen V.
%A Hernandez-Santana, Senaida
%A Mehboudi, Mohammad
%A Sanpera, Anna
%X We consider the problem of estimating the temperature T of a very cold equilibrium sample. The temperature estimates are drawn from measurements performed on a quantum Brownian probe strongly coupled to it. We model this scenario by resorting to the canonical Caldeira-Leggett Hamiltonian and find analytically the exact stationary state of the probe for arbitrary coupling strength. In general, the probe does not reach thermal equilibrium with the sample, due to their nonperturbative interaction. We argue that this is advantageous for low-temperature thermometry, as we show in our model that (i) the thermometric precision at low T can be significantly enhanced by strengthening the probe-sampling coupling, (ii) the variance of a suitable quadrature of our Brownian thermometer can yield temperature estimates with nearly minimal statistical uncertainty, and (iii) the spectral density of the probe-sample coupling may be engineered to further improve thermometric performance. These observations may find applications in practical nanoscale thermometry at low temperatures-a regime which is particularly relevant to quantum technologies.
%B PHYSICAL REVIEW A
%V 96
%R 10.1103/PhysRevA.96.062103
%0 Journal Article
%J Physical Review A
%D 2017
%T Entanglement and nonlocality in diagonal symmetric states of
%A Quesada, Ruben
%A Rana, Swapan
%A Sanpera, Anna
%B Physical Review A
%V 95
%8 Jan-04-2017
%U http://link.aps.org/doi/10.1103/PhysRevA.95.042128http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevA.95.042128/fulltexthttp://link.aps.org/article/10.1103/PhysRevA.95.042128
%! Phys. Rev. A
%R 10.1103/PhysRevA.95.042128
%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 Letters
%D 2004
%T Experimental Detection of Multipartite Entanglement using Witness Operators
%A Bourennane, Mohamed
%A Eibl, Manfred
%A Kurtsiefer, Christian
%A Gaertner, Sascha
%A Weinfurter, Harald
%A Gühne, Otfried
%A Hyllus, Philipp
%A Bruß, Dagmar
%A Lewenstein, Maciej
%A Sanpera, Anna
%B Physical Review Letters
%V 92
%G eng
%U http://prl.aps.org/abstract/PRL/v92/i8/e087902
%R 10.1103/PhysRevLett.92.087902
%0 Book Section
%B Quantum Information Processing
%D 2003
%T Entanglement properties of composite quantum systems
%A Eckert, Kai
%A Guhne, O.
%A Hulpke, Florian
%A Hyllus, Philipp
%A Korbicz, J.
%A Mompart, Jordi
%A Bruss, Dagmar
%A Lewenstein, Maciej
%A Sanpera, Anna
%E Leuchs, G.
%E Beth, T.
%B Quantum Information Processing
%I Wilew-VCH
%C Berlin
%P 87–95
%@ 352740371X
%G eng
%0 Journal Article
%J Journal of Modern Optics
%D 2003
%T Experimental detection of entanglement via witness operators and local measurements
%A Gühne, Otfried
%A Hyllus, Philipp
%A Bruss, Dagmar
%A Ekert, Artur K.
%A Lewenstein, Maciej
%A Macchiavello, Chiara
%A Sanpera, Anna
%B Journal of Modern Optics
%V 50
%P 1079–1102
%G eng
%U http://www.informaworld.com/smpp/36433790-99697256/content\~{}db=all\~{}content=a713826204
%R 10.1080/09500340308234554