It is usually believed that coarse-graining of quantum correlations leads to classical correlations in the macroscopic limit. Such a principle, known as macroscopic locality, has been proved for correlations arising from independent and identically distributed (IID) entangled pairs. In this work we consider the generic (non-IID) scenario. We find that the Hilbert space structure of quantum theory can be preserved in the macroscopic limit. This leads directly to a Bell violation for coarse-grained collective measurements, thus breaking the principle of macroscopic locality.
The Mpemba effect is the phenomenon for which a hotter liquid can cool at a faster rate than a colder one. This effect is nowadays receiving much attention; it has been predicted for different classical systems and it has even been observed experimentally for a trapped colloid particle. In this talk, I will propose an analogue of the Mpemba effect for Markovian open quantum systems. I will show that the relaxation dynamics of these systems can be exponentially accelerated by devising an optimal unitary transformation, that is applied to the quantum state immediately before the actual dynamics. This preliminary “rotation” is engineered in such a way that the state of the quantum system becomes orthogonal to the slowest decaying dynamical mode. I will illustrate potential applications of this effect by showing how it can be used to achieve an exponential speed-up in the convergence to stationarity in Dicke models as well as to avoid metastable regimes in an all-to-all interacting spin system.
Ponente: Dr. Federico Carollo. University of Tübingen.
Fecha y hora: viernes, 23 de abril de 2021 a las 12:00.
Firstly, I will introduce digital-analog and purely digital methods for quantum simulations of fermionic models. The digital-analog approach provides a higher degree of scalability than purely digital or analog techniques, and it is suitable for implementing quantum simulations of interacting fermions and bosons in condensed matter, and quantum field theories . Purely digital quantum simulations [2,3,4] are grouped under standard discrete-variable quantum computation, while analog quantum simulators with bosonic fields can be described with the language of continuous-variable (CV) quantum computation.
The second part of the talk is devoted to analyzing the factors that may yield quantum advantage. In particular, Wigner negativity is known to be a necessary resource for computational advantage in several quantum-computing architectures, including those based on continuous variables [5,6]. However, it is not a sufficient resource, and it is an open question under which conditions CV circuits displaying Wigner negativity offer the potential for quantum advantage. I will present large families of circuits that display large Wigner negativity and yet are classically efficiently simulatable , although they were not recognized as such by previously available theorems.
Ponente: Laura García-Álvarez. Chalmers University of Technology.
Fecha y hora: viernes, 16 de abril de 2021 a las 10:30.
Local perturbations can bring an integrable quantum many-body system to the chaotic regime. This fact has been known for the XXZ model since 2004, and such results have been recently extended to two other models: the transverse-field Ising chain and the Lai-Sutherland spin 1 chain. The nature of different quantum chaos indicators, static and dynamic, will be reviewed, to discuss how a single local effect can bring three different integrable systems to the chaotic regime. Among the possible indicators, the distribution of off-diagonal matrix elements of local operators and the correlation hole will be presented with more detail.
Ponente: Francisco Perez-Bernal. Universidad de Huelva.
Fecha y hora: viernes, 26 de marzo de 2021 a las 12:30.
Microbial communities are highly dimensional, with many species and many variable environmental factors. Macroecology, which studies communities as statistical ensembles, is a promising way to connect these complex data to mechanistic models. In this talk, I will discuss a minimal set of macroecological patterns that characterize the statistical properties of species abundance fluctuations across communities and over time. A mathematical model based on environmental stochasticity quantitatively predicts these three macroecological laws, as well as non-stationary properties of community dynamics. Building on these results, it is possible to disentangle the (statistical) properties that determine ecosystems’ stability over time and reproducibility across communities.
Ponente: Jacopo Grilli. International Centre for Theoretical Physics (ICTP, Trieste, Italy).
Fecha y hora: viernes, 19 de marzo de 2021 a las 12:00.
In this talk I will present a novel method for finding optimal paths and optimal weight distributions. It is based on the analysis of large deviations of random walks on networks, and it leads to a generalization of the standard definitions to encompass paths and weight distributions tailored to a given statistical characterization of time-extensive observables in the presence of constraints. All dynamical aspects of the problem (the random walk transition matrix, the observables and the statistical ensemble) are chosen so as to best reveal the underlying structural features of interest. After a discussion of the main aspects of the theoretical framework, some examples involving random graphs and spatial networks will be presented. Referencia: Phys. Rev. E 103, 022319 (2021).
Ponente: Ricardo Gutiérrez. Complex Systems Interdisciplinary Group, Department of Mathematics, Universidad Carlos III de Madrid.
Fecha y hora: viernes, 12 de marzo de 2021 a las 12:00.
In this talk, I will summarize some of the latest results we have published in our group on a light-matter system composed of emitters coupled to light modes which propagate in a waveguide. This setup is subject matter of many current experimental studies, as it holds promise of applications in quantum information routing and processing, e.g., as optical isolators and circulators where the light is emitted unidirectionally, or as generators of entangled atomic and photonic states. Among other results, I will show you how due to the collective light-matter interaction with the radiation field, an array of atoms can scatter light from an external laser field almost exclusively into one of the guided modes of the waveguide, allowing for almost lossless and completely unidirectional channelling of photons. Moreover, I will show you that the spectral properties of the scattered light depend strongly on the angle of incidence of the laser field on the array and the dispersive interactions between the light and the atoms, uncovering a modified Bragg condition.
Ponente: Prof. Beatriz Olmos. University of Tübingen.
Fecha y hora: viernes, 5 de marzo de 2021 a las 12:00.
Life has most likely originated as a consequence of processes taking place in non-equilibrium conditions (e.g. in the proximity of deep-sea thermal vents) selecting states of matter that would have been otherwise unfavorable at equilibrium. External sources, and the subsequent thermodynamic necessity of dissipating heat, might have driven pre-biotic molecules against their equilibrium fate. In a simple chemical network, the presence of a thermal gradient selects states participating to faster reactions and contributing the most to the dissipation rate. The furanose conundrum potentially finds a solution within this picture. Furanose is boosted beyond the limits set by equilibrium thermodynamics, exhibiting maximum selection at optimal dissipation, as gauged by the temperature gradient and energy barriers for isomerization. This predicted optimum is compatible with temperature drops found in hydrothermal vents. A byproduct of our approach is that as the complexity of the chemical network increases, the velocity of reaction paths leading to a given state determines its selection, giving rise to non-trivial localization phenomena in state space. The proposed framework singles out the role of non-equilibrium dissipation, in particular when it is declinable in terms of entropy production rate. A general non-equilibrium dissipative functional might generalize our intuition, potentially providing a better grasp on processes underpinning selection.
Ponente: Daniel Maria Busiello. EPFL, Laussane.
Fecha y hora: viernes, 26 de febrero de 2021 a las 12:00.
Quantum computing is growing in influence, thanks to interest from corporations and militaries. Many ethical decisions are thus present in this science, whether we like it or not. Thankfully, there are tools from science and technology studies that can help us make decisions with a critical eye by situating the work in a larger political and ecological context. In this talk, I will do just that for quantum work. First, I will share my own experience coming to see quantum science as ethically fraught. Then, we’ll look at the issues with the resources required to build quantum computers and with their applications in the military and corporations. Finally, I’ll connect this context to ethics and the ability to prevent a project from going forward.
Ponente: Emma McKay (they/them). York University.
Fecha y hora: jueves, 29 de octubre de 2020 a las 16:30.
Oceans host communities of plankton composed of a huge number of rare species that, as estimated in metagenomic studies, decay as a steep power law of their abundance. We propose that the way chaotic advection of oceanic currents limit protists dispersal is a key factor of such biodiversity pattern. We introduce a spatially explicit coalescence model able to reconstruct species ancestry and diversity in the presence of currents. Our model predicts a steep power law decay of the species abundance distribution and a steep increase of the number of observed species with sample size. Indeed, we find a significant correlation of the local finite-size Lyapunov exponents of our chaotic currents and the power law exponents of the species abundance distribution. Metagenomic studies of planktonic protist communities show excellent agreement with our results.
Ponente: Paula Villa Martin. Okinawa Institute of Science and Technology, Biological Complexity Unit.
Fecha y hora: viernes, 9 de octubre de 2020 a las 12:00.
Lugar: Seminario de Física Computacional, planta baja del edificio de Física (junto a las pantallas). Facultad de Ciencias.