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Trapped-ion quantum platforms are subject to "anomalous" heating due to interactions with electric-field noise sources of nature not yet completely known. There is ample experimental evidence that this noise originates at the surfaces of the trap electrodes, and models assuming fluctuating pointlike dipoles are consistent with observations, but the exact microscopic mechanisms behind anomalous heating remain undetermined. Here we show how a two-ion probe displays a transition in its dissipation properties, enabling experimental access to the mean orientation of the dipoles and the spatial extent of dipole-dipole correlations. This information can be used to test the validity of candidate microscopic models, which predict correlation lengths spanning several orders of magnitude. Furthermore, we propose an experiment to measure these effects with currently available traps and techniques. ; This work has been supported by the European Union through the H2020 Project QuProCS (Grant No. 641277), by MINECO/AEI/FEDER through NoMaQ Project No. FIS2014-60343-P, QuStruct Project No. FIS2015-66860-P, and EPheQuCS Project No. FIS2016-78010-P. The research is partly based upon work supported by the Office of the Director of National Intelligence (ODNI), Intelligence Advanced Research Projects Activity (IARPA), via the U.S. Army Research Office Grant No. W911NF-16-1-0070. necessarily reflect the view of the U.S. Army Research Office. ; Peer reviewed

We analyze the symmetries in an open quantum system composed by three coupled and detuned harmonic oscillators in the presence of a common heat bath. It is shown analytically how to engineer the couplings and frequencies of the system so as to have several degrees of freedom unaffected by decoherence, irrespective of the specific spectral density or initial state of the bath. This partial thermalization allows observing asymptotic entanglement at moderate temperatures, even in the nonresonant case. This latter feature cannot be seen in the simpler situation of only two oscillators, highlighting the richer structural variety of the three-body case. When departing from the strict conditions for partial thermalization, a hierarchical structure of dissipation rates for the normal modes is observed, leading to a long transient where quantum correlations such as the quantum discord are largely preserved, as well as to synchronous dynamics of the oscillators quadratures. © 2013 American Physical Society. ; This work was funded by the CSIC postdoctoral JAE program, the Balearic Government, the MICINN project FIS2007-60327, and the MINECO project FIS2011-23526 and FPI fellowship (BES-2012-054025). ; Peer Reviewed

We introduce the use of entanglement entropy as a tool for studying the amount of information shared between the nodes of quantum complex networks. By considering the ground state of a network of coupled quantum harmonic oscillators, we compute the information that each node has on the rest of the system. We show that the nodes storing the largest amount of information are not the ones with the highest connectivity, but those with intermediate connectivity, thus breaking down the usual hierarchical picture of classical networks. We show both numerically and analytically that the mutual information characterizes the network topology. As a by-product, our results point out that the amount of information available for an external node connecting to a quantum network allows one to determine the network topology. © 2013 American Physical Society. ; We acknowledge Diego Blas for discussions and support from the Spanish DGICYT under Projects No. FIS2011-14539-E (EXPLORA program), No. FIS2011-23526, and No. FIS2011-25167, and by the Aragón (Grupo FENOL) and Balearic Governments. F.G. acknowledges the CSIC postdoctoral JAE program and the TIQS (FIS2011-23526) project. J.G.G. is supported by MINECO through the Ramón y Cajal program. ; Peer Reviewed

[EN] We present a magnet and high power electronics for Prepolarized Magnetic Resonance Imaging (PMRI) in a home-made, special-purpose preclinical system designed for simultaneous visualization of hard and soft biological tissues. The sensitivity of MRI systems grows with field strength, but so do their costs. PMRI can boost the signal-to-noise ratio (SNR) in affordable low-field scanners by means of a long and strong magnetic pulse. However, this must be rapidly switched off prior to the imaging pulse sequence, in timescales shorter than the spin relaxation (or T1) time of the sample. We have operated our prepolarizer at up to 0.5 T and demonstrated enhanced magnetization, image SNR and tissue contrast with PMRI of tap water, an ex vivo mouse brain and food samples. These have T1 times ranging from hundreds of milli-seconds to single seconds, while the preliminary high-power electronics setup employed in this work can switch off the prepolarization field in tens of milli-seconds. In order to make this system suitable for solid-state matter and hard tissues, which feature T1 times as short as 10 ms, we are developing new electronics which can cut switching times to ~ 300 ¿s. This does not require changes in the prepolarizer module, opening the door to the first experimental demonstration of PMRI on hard biological tissues. ; This work was supported in part by the European Commission under Grant 737180 (FET-Open: HistoMRI), in part by the Ministerio de Ciencia e Innovación of Spain for Research under Grant PID2019-111436RB-C21, and in part by the European Union through the Programa Operativo del Fondo Europeo de Desarrollo Regional (FEDER) of the Comunitat Valenciana 2014¿2020 under Grant IDIFEDER/2018/022. The work of José M. González was supported by the Innodocto Program of the Agencia Valenciana de la Innovación under Grant INNTA3/2020/22. The work of Juan V. Sanchez-Andres was supported by the Universitat Jaume I - Fundación para el Fomento de la Investigación Sanitaria y Biomédica de la Comunitat Valenciana ...

[EN] Magnetic Resonance Imaging (MRI) of hard biological tissues is challenging due to the fleeting lifetime and low strength of their response to resonant stimuli, especially at low magnetic fields. Consequently, the impact of MRI on some medical applications, such as dentistry, continues to be limited. Here, we present three-dimensional reconstructions of ex-vivo human teeth, as well as a rabbit head and part of a cow femur, all obtained at a field strength of 260 mT. These images are the first featuring soft and hard tissues simultaneously at sub-Tesla fields, and they have been acquired in a home-made, special-purpose, pre-medical MRI scanner designed with the goal of demonstrating dental imaging at low field settings. We encode spatial information with two pulse sequences: Pointwise-Encoding Time reduction with Radial Acquisition and a new sequence we have called Double Radial Non-Stop Spin Echo, which we find to perform better than the former. For image reconstruction we employ Algebraic Reconstruction Techniques (ART) as well as standard Fourier methods. An analysis of the resulting images shows that ART reconstructions exhibit a higher signal-to-noise ratio with a more homogeneous noise distribution. ; We thank anonymous donors for their tooth samples, Andrew Webb and Thomas O'Reilly (LUMC) for discussions on hardware and pulse sequences, and Antonio Tristan (UVa) for information on reconstruction techniques. This work was supported by the European Commission under Grants 737180 (FET-OPEN: HISTO-MRI) and 481 (ATTRACT: DentMRI). Action co-financed by the European Union through the Programa Operativo del Fondo Europeo de Desarrollo Regional (FEDER) of the Comunitat Valenciana 2014-2020 (IDIFEDER/2018/022). Santiago Aja-Fernandez acknowledges Ministerio de Ciencia e Innovacion of Spain for research grant RTI2018-094569-B-I00. ; Algarín-Guisado, JM.; Díaz-Caballero, E.; Borreguero-Morata, J.; Galve, F.; Grau-Ruiz, D.; Rigla, JP.; Bosch-Esteve, R. (2020). Simultaneous imaging of hard and soft biological ...