%0 Journal Article
%J Physics Letters A
%D 2020
%T Reinforcement learning for optimal error correction of toric codes
%A Domingo Colomer, Laia
%A Skotiniotis, Michalis
%A Muñoz-Tapia, Ramon
%B Physics Letters A
%V 384
%P 126353
%8 Jan-06-2020
%U https://linkinghub.elsevier.com/retrieve/pii/S0375960120301638
%! Physics Letters A
%R 10.1016/j.physleta.2020.126353
%0 Journal Article
%J Physica Scripta
%D 2010
%T Recycling of qubits
%A P Rapcan
%A John Calsamiglia
%A Muñoz-Tapia, Ramon
%A Bagan, Emilio
%A V Buzek
%X We consider a finite number, N, of qubits that encode a pure single qubit state SU(2) covariantly. Given the N-qubit state has already been measured optimally to estimate the single-qubit state, we analyse the maximum information obtainable by a second, and subsequent observers ignorant of important details of the previous measurements. We quantify the information acquired by each observer as a function of N and of the number of independent observers that in succession have independently measured the same ensemble of qubits before him.
%B Physica Scripta
%V T140
%P 014059
%U http://iopscience.iop.org/1402-4896/2010/T140/014059?fromSearchPage=true
%R 10.1088/0031-8949/2010/T140/014059
%0 Journal Article
%J arXiv
%D 2007
%T Recycling of quantum information: Multiple observations of quantum systems
%A Rapcan, Peter
%A John Calsamiglia
%A Muñoz-Tapia, Ramon
%A Bagan, Emili
%A Bużek, Vladimir
%X Given a finite number of copies of an unknown qubit state that have already been measured optimally, can one still extract any information about the original unknown state? We give a positive answer to this question and quantify the information obtainable by a given observer as a function of the number of copies in the ensemble, and of the number of independent observers that, one after the other, have independently measured the same ensemble of qubits before him. The optimality of the protocol is proven and extensions to other states and encodings are also studied. According to the general lore, the state after a measurement has no information about the state before the measurement. Our results manifestly show that this statement has to be taken with a grain of salt, specially in situations where the quantum states encode confidential information.
%B arXiv
%8 08/2007
%G eng
%U http://arxiv.org/abs/0708.1086
%0 Journal Article
%J Physical Review A (Atomic, Molecular, and Optical Physics)
%D 2006
%T Relative states, quantum axes, and quantum references
%A Bagan, Emili
%A Iblisdir, Sofyan
%A Muñoz-Tapia, Ramon
%K quantum theory
%B Physical Review A (Atomic, Molecular, and Optical Physics)
%V 73
%P 022341–6
%8 02/2006
%G eng
%U http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PLRAAN000073000002022341000001&idtype=cvips&gifs=yes
%R 10.1103/PhysRevA.73.022341