ICFO – The Institute of Photonic Sciences

About: ICFO – The Institute of Photonic Sciences is a facility organization based out in Barcelona, Spain. It is known for research contribution in the topics: Quantum & Quantum entanglement. The organization has 872 authors who have published 1965 publications receiving 56273 citations.

Speed-ups to isothermality: Enhanced quantum thermal machines through control of the system-bath coupling

Abstract: Isothermal transformations are minimally dissipative but slow processes, as the system needs to remain close to thermal equilibrium along the protocol. Here, we show that smoothly modifying the system-bath interaction can significantly speed up such transformations. In particular, we construct protocols where the overall dissipation $W_{\rm diss}$ decays with the total time $\tau_{\rm tot}$ of the protocol as $W_{\rm diss} \propto \tau_{\rm tot}^{-2\alpha-1}$, where each value $\alpha > 0$ can be obtained by a suitable modification of the interaction, whereas $\alpha=0$ corresponds to a standard isothermal process where the system-bath interaction remains constant. Considering heat engines based on such speed-ups, we show that the corresponding efficiency at maximum power interpolates between the Curzon-Ahlborn efficiency for $\alpha =0$ and the Carnot efficiency for $\alpha \to \infty$. Analogous enhancements are obtained for the coefficient of performance of refrigerators. We confirm our analytical results with two numerical examples where $\alpha = 1/2$, namely the time-dependent Caldeira-Leggett and resonant-level models, with strong system-environment correlations taken fully into account. We highlight the possibility of implementing our proposed speed-ups with ultracold atomic impurities and mesoscopic electronic devices.

Proximity effects in cold atom artificial graphene

Abstract: Cold atoms in an optical lattice with brick-wall geometry have been used to mimic graphene, a two-dimensional material with characteristic Dirac excitations. Here we propose to bring such artificial graphene into the proximity of a second atomic layer with a square lattice geometry. For non-interacting fermions, we find that such bilayer system undergoes a phase transition from a graphene-like semi-metal phase, characterized by a band structure with Dirac points, to a gapped band insulator phase. In the presence of attractive interactions between fermions with pseudospin-1/2 degree of freedom, a competition between semi-metal and superfluid behavior is found at the mean-field level. Using the quantum Monte Carlo method, we also investigate the case of strong repulsive interactions. In the Mott phase, each layer exhibits a different amount of long-range magnetic order. Upon coupling both layers, a valence-bond crystal is formed at a critical coupling strength. Finally, we discuss how these bilayer systems could be realized in existing cold atom experiments.

Antireflective Multilayer Surface with Self-Cleaning Subwavelength Structures

Abstract: The suppression of optical reflection from a surface is essential in many applications, ranging from displays with reduced disturbance from ambient light to high-efficiency photovoltaic cells and s...

Understanding the electromagnetic response of graphene/metallic nanostructures hybrids of different dimensionality

Abstract: N.M.R. P. and F. H.L.K. acknowledge support from the European Commission through the Project "Graphene-Driven Revolutions in ICT and Beyond" (Ref. No. 881603, CORE 3). N. M.R. P. and T.G.R. acknowledge COMPETE 2020, PORTUGAL 2020, FEDER and the Portuguese Foundation for Science and Technology (FCT) through Project POCI-01-0145-FEDER-028114. F.H.L.K. acknowledges financial support from the Government of Catalonia through the SGR Grant, and from the Spanish Ministry of Economy and Competitiveness through the "Severo Ochoa" Programme for Centres of Excellence in RD (SEV-2015-0522); support by Fundacio Cellex Barcelona, Generalitat de Catalunya through the CERCA Program, and the Mineco Grants Ramo ' n y Cajal (RYC-2012-12281, Plan Nacional (FIS2013-47161-P and FIS2014-59639-JIN) and the Agency for Management of University and Research Grants (AGAUR) 2017 SGR 1656. This work was supported by the ERC TOPONANOP under Grant Agreement No. 726001 and the MINECO Plan Nacional Grant 2D-NANOTOP under Reference No. FIS2016-81044-P.