Seminars from 2026

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Comenzamos el ciclo de seminarios de los departamentos del IEM para este año 2026 con el del “Departamento de Departamento de Química y Física Teóricas”. Para ello os invitamos al primer seminario del ciclo que tendrá lugar en la Sala de Conferencias del CFMAC (Serrano, 121) el próximo jueves 5 de Marzo a las 12.00h. Será impartido por el Dr. Juan Ramón Muñoz de Nova que es la reciente incorporación Ramón y Cajal 2026 en el IEM cuyo título es: Interdisciplinary Quantum Field Theory: Hawking effect, Quantum time, Quantum Information in High-Energy Physic.

Quantum networks are the most promising proposal to scale quantum computers in what is known as distributed quantum computation. Superconducting waveguide QED networks have shown to be very effective for distributing quantum information based on the exchange of photons between the nodes of the networks. However, fabrication imperfections of nodes require additional techniques to compensate for the frequency differences, leading to reduced scalability and efficiencies. We present a novel approach to emit and absorb arbitrality detuned photons, allowing for an on-demand and deterministic exchange of quantum information. It leverages the large and good controllability of the light-matter couplings that superconducting circuits provide. Then, we propose a protocol for entanglement distribution between the nodes of the network via emission of fractional photons. Numerical solutions support the feasibility and high-fidelity of both protocols, indicating the new possibilities that detuned single photons bring to quantum networks. Warning: I wanted to use the seminar as an opportunity to practice for the defence of my bachelor thesis. Since the evaluating professors need not be related to physics, it will be less technical than many of you would like. Nevertheless, you are all invited to come, and after the presentation, I’ll try to answer as best as possible any related questions.

In this talk, I discuss the many-body physics of interacting waveguide QED systems, where photons in a coupled-cavity array are strongly coupled to atomic impurities and interact via local Kerr nonlinearities. After introducing the model and its relevance to nanophotonic crystals, circuit QED lattices, and ultracold atomic systems, I briefly review the striking consequences that additional photon-photon interactions can have on the collective emission dynamics of atomic emitters. I then focus on the ground-state properties of this system, which are governed by the competition between attractive Jaynes-Cummings-mediated binding and intrinsic photon-photon repulsion. This interplay drives the formation of localized few-photon bound states and results in a rich phase diagram featuring Mott-like insulating states as well as superfluid phases characterized by long-range correlations mediated by photons detached from impurity sites.

In this talk, I will present flow topology as a practical route to classify dynamical phases in driven dissipative nonlinear systems, distinct from band-topology approaches in Hermitian and non Hermitian periodic settings. The key idea is to extract global information from the semiclassical phase-space flow pattern across all initial conditions, beyond local order parameters. Using parametrically driven nonlinear resonators as an example, I will introduce a graph-based topological invariant which captures all dynamical phase transitions as drive and detuning are varied, including both local changes, such as local instabilities, and global ones, such as how regions of initial conditions connect to different long-time behaviors. I will show how these predictions are directly confirmed experimentally in a nonlinear electromechanical resonator [1]. I will then show how flow topology also appears in the quantum steady state probability distributions and in asymmetries of their linear responses [2]. Finally, I will extend the framework to limit-cycle phases with persistent oscillations in the steady state. An extension of the graph-invariant above will capture more complex phase transitions, including mergers of limit cycles and the formation of forbidden regions in phase space. In the quantum regime, these flow-topology changes reflect dynamical phase transitions in the transient evolution, even when they are not directly reflected in standard indicators such as the Liouvillian spectral gap [3]. References [1] Villa et al., Topological classification of driven-dissipative nonlinear systems, Sci. Adv.11, eadt9311 (2025) [2] Seibold et al., Manifestations of flow topology in a quantum driven-dissipative system, arXiv:2508.16486 (2025). [3] Gómez and del Pino, Quantum Dynamical Signatures of Topological Flow Transitions in Limit Cycle Phases, arXiv:2512.11747 (2025).

I will present our recent work exploring a bosonic analogue of the Dicke model of superradiance. Specifically, we study a system of bosonic modes subject to fully symmetric collective decay and a uniform on-site interaction, which is naturally realised in waveguide-coupled transmon arrays. Exploiting the permutation symmetry of the problem, we combine perturbative arguments with large-scale numerical simulations to analyse the collective emission dynamics in the weak- and strong-interaction limits. In both regimes, we find that the dynamics are well captured by rate equations closely analogous to those of standard Dicke superradiance. Building on this understanding, I will present evidence for a crossover in the scaling of the peak emission rate with system size, from sub-quadratic to quadratic. If time permits, I will also discuss the dynamics of different initial states with no counterparts in the case of two-level emitters.

As we have have a couple of new members, especially younger ones, I wanted to take the time and briefly introduce Tensor Networks as a state-of-the-art numerical method and advertise its benefits and use. I will briefly introduce Matrix Product States (MPS) and the DMRG algorithm. Then I will discuss the findings of https://doi.org/10.21468/SciPostPhys.18.4.142; the puzzling features of the MPS transfer matrix spectrum at a critical point. We set up an effective field theory formulation for the renormalization flow of MPS with finite bond dimension, focusing on systems exhibiting finite-entanglement scaling close to a conformally invariant critical fixed point. We show that the finite MPS bond dimension χ is equivalent to introducing a perturbation by a relevant operator to the fixed-point Hamiltonian. This phenomenon defines a renormalization group self-congruent point, where the relevant coupling constant ceases to flow due to a balance of two effects; When increasing χ, the infrared scale, set by the correlation length ξ(χ), increases, while the strength of the perturbation at the lattice scale decreases

This seminar presents a comprehensive overview of the research initiatives in Quantum Technologies and Metrology led by the Universidad Nacional de Colombia, together with a detailed analysis of recent advancements in the engineering of Photonic Crystals (PhCs) for nanoscale light manipulation. The first part of the seminar outlines the strategic initiatives developed under a nationally funded project on Quantum Metrology and Technologies. It presents the experimental milestones enabled by advanced instrumentation acquired through this grant, covering key research pillars such as quantum metrology, high-resolution spectroscopy, quantum information and computing, and quantum materials. Furthermore, the socio-economic and scientific impact of these developments is highlighted, emphasizing their role in fostering technological sovereignty and innovation within the Colombian scientific landscape. The second part of the presentation provides a technical review of fundamental developments in PhC research, including: All-optical logic gates and waveguides: Design and optimization of PhC-based architectures for optical signal processing. Cavity–emitter interactions: Analysis of the coupling between quantum emitters and localized modes in PhC cavities to enhance light–matter interactions. Topological and chiral photonics: Exploration of symmetry-protected states and non-reciprocal light propagation in periodic dielectric structures. Coupled cavity systems: Study of modal coupling and energy transfer in multicavity arrays. Finally, specific contributions from the research group are showcased, including original designs for high-sensitivity sensors, optimized waveguides, and structured environments for emitters in PhC slabs. These results illustrate the potential for synergy and collaborative research between Colombian institutions and international partners, particularly with the Instituto de Física Fundamental (IFF-CSIC).

We study the directed transport of bosons along a one dimensional lattice in a dissipative setting, where the hopping is only facilitated by coupling to a Markovian reservoir. By combining numerical simulations with a field-theoretic analysis, we investigate the current fluctuations for this process and determine its asymptotic behavior. These findings demonstrate that dissipative bosonic transport belongs to the Kardar-Parisi-Zhang universality class and therefore, in spite of the drastic difference in the underlying particle statistics, it features the same coarse-grained behavior as the corresponding asymmetric simple exclusion process for fermions. However, crucial differences between the two processes emerge when focusing on the full counting statistics of current fluctuations. By mapping both models to the physics of fluctuating interfaces, we find that dissipative transport of bosons and fermions can be understood as surface growth and erosion processes, respectively. Within this unified description, both the similarities and discrepancies between the full counting statistics of the transport are reconciled. Beyond purely theoretical interest, these findings are relevant for experiments with cold atoms or long-lived quasiparticles in nanophotonic lattices, where such transport scenarios can be realized.

Lattice gauge theories are very complicated models, capturing a variety of interesting physics, but like most quantum many-body models, their study involves several challenges, both analytical and numerical. In my talk I will discuss an analogy between them and PEPS (projected entangled pair states), a high dimensional tensor network construction, and show how it can be used for studying such models while overcoming long standing bottlenecks.