Natalia Berloff
Department of Applied Mathematics and Theoretical Physic, University of Cambridge, UK
Non-Hermitian Gain-Based Computing with Coupled Light-Matter Systems
When: 12:00-13:00 CET, November 7th (Thursday), 2024
Where: Sala de Seminarios (182), ICMM-CSIC, Campus de Cantoblanco, Madrid
Gain-based computing utilizing non-Hermitian dynamics in light-matter interactions presents a novel approach to physics-based hardware and physics-inspired algorithms. By encoding complex optimization problems into the gain and loss rates of driven-dissipative systems, we leverage non-Hermiticity to destabilize non-optimal states and guide the system toward the global minimum. The incorporation of prior knowledge about ground state energies into the complex part of the energy enhances the system’s ability to navigate complex energy landscapes.
In this paradigm, the system undergoes symmetry-breaking transitions on a dynamically changing loss landscape, selecting modes that minimise losses and manifesting the optimal solutions to the original problems. This approach enables solving significant combinatorial optimization problems via mapping to Ising, XY, and k-local Hamiltonians, applicable across various physical platforms, including photonic, electronic, and atomic systems.
Despite advancements, critical questions remain regarding scalability, the impact of phase space structures on system performance, and the identification of problems best suited for these unconventional computing architectures. I will address these challenges in my talk by understanding the dynamic behaviour during symmetry-breaking transitions, optimizing trajectories toward global minima, quantifying error probabilities, and using dissipation and nonlinearities to correct errors.
Hugo Aramberri
Luxembourg Institute of Science and Technology (LIST)
Brownian electric bubble quasiparticles and topological phase transitions in frustrated ferroelectrics
When: 12:00-13:00 CET, November 14th (Thursday), 2024
Where: Sala de Juntas, ICMM-CSIC, Campus de Cantoblanco, Madrid
Electrostically frustrated ferroelectrics have become an exciting playground for new physics. In these systems, the delicate balance between electrostatic, elastic and domain wall energies can make the system highly responsive, and can give rise to diverse dipole topologies. A notable breakthrough was the recent realization of electric skyrmion bubbles in ferroelectric/dielectric superlattices (PbTiO3/SrTiO3)[1]. Interestingly, the topology of the dipole field can be manipulated through external stimuli like temperature and electric fields[2], and also by tuning heterojunction design parameters like layer thicknesses and epitaxial strain.
In this talk I will present our recent contributions to this field. First, I will discuss a temperature-driven topological phase transition of the dipolar order that mirrors the two-step melting process seen in some liquid crystals[3]. Second, I will introduce our recent prediction that electric bubble domains behave as Brownian particles, exhibiting thermally activated diffusive motion[4], similar to magnetic skyrmions. I will also share our latest calculations on bubble manipulation and outline our ongoing efforts to understand their dynamical behaviour.
[1] S. Das et al., Nature 568, 368 (2019).
[2] J. Junquera et al., Rev. Mod. Phys. 95, 025001 (2023).
[3] F. Gómez-Ortiz, M. Graf, J. Junquera, J. Íñiguez-González, H. Aramberri, Phys. Rev. Lett. 133, 066801 (2024).
[4] H. Aramberri & J. Íñiguez-González, Phys. Rev. Lett. 132, 136801 (2024).