Mitigation of readout errors in near-term quantum devices
Quantum Universes on a computer - the CDT approach
Causal Dynamical Triangulations (CDT) is an attempt to quantize gravity via lattice regularization, where 4-dimensional tetrahedra play the role of the building blocks of space-time. The mathematical basis of CDT is a mixture of Regge calculus and Feynman path integral formulation. Numerical simulations show that CDT has a well defined semiclassical limit as the classical solution emerges in the form of the de-Sitter space-time. The Einstein-Hilbert action has a very simple form, with three bare coupling constants. The space of couplings reveals a rich phase structure of four phases with first and higher order phase transitions. In the recent years two different spatial boundary conditions were analyzed and no significant difference was found between sphere and torus. The most recent research is focused on implementing scalar fields, massive particles and applying RG methods. During my talk I will give a review about the current state of the field.
New results supporting the existence of the X17 particle
Recently, we have got experimental data for a new hypothetical boson with mass about 17 MeV/c2, called later on X17 in the literature. There are plenty theoretical explanations already in the literature, which may be connected also to dark matter. Recently we studied the characteristics of the two-body decay of X17 to electron positron pair, which also supports the existence of such hypothetical particle.
Pásztázó alagútmikroszkóp szimulációja első elvekből
Mándi Gábor (BME) PhD házivédése
Kivonat: "Feltalálása óta a pásztázó alagútmikroszkóp (STM) nagyban hozzájárult a nanotechnológia és nanotudomány gyors fejlődéséhez és a mai napig aktívan használt eszköz az anyagtudomány számos ágában a legkülönfélébb felületek vizsgálatára. Kutatásaim során olyan gyors és hatékony elektron alagút modelleket fejlesztettem és implementáltam, amelyek alkalmasak nagy felbontású STM és spinpolarizált STM képek szimulációjára. Ezek a modellek első elvekből származó elektronszerkezet-számításokon alapulnak és képesek tetszőleges tűorientáció modellezésére. Kutatásaim hozzájárulnak a kísérleti STM képek értelmezésének meglehetősen komplex feladatához."
Neural network wave functions and the sign problem
Neural quantum states (NQS) are a promising approach to study many-body quantum physics. However, they face a major challenge when applied to lattice models: Convolutional networks struggle to converge to ground states with a nontrivial sign structure. We tackle this problem by proposing a neural network architecture with a simple, explicit, and interpretable phase ansatz, which can robustly represent such states and achieve state-of-the-art variational energies for both conventional and frustrated antiferromagnets. In the latter case, our approach uncovers low-energy states that exhibit the Marshall sign rule and are therefore inconsistent with the expected ground state. Such states are the likely cause of the obstruction for NQS-based variational Monte Carlo to access the true ground states of these systems. We discuss the implications of this observation and suggest potential strategies to overcome the problem. (https://arxiv.org/abs/2002.04613)
Microwave Cavity Quantum Electrodynamics with superconductor-semiconductor hybrid technology
A New Window to the Universe: Gravitational Waves
According to Albert Einstein’s theory of general relativity, gravitational waves (GWs) are wavelike distortions in the fabric of space-time created by accelerating masses, and propagating at the speed of light. Although there had been several experimental attempts throughout the 20th century to detect GWs, the first direct detection was achieved in September 2015 by the LIGO-Virgo Collaboration (LVC) using the two LIGO detectors. As members of the LVC since 2007, the LIGO group at Eötvös University had the privilege of being involved in and contributing to this major scientific achievement. The ongoing common detections of GW signals have already started to revolutionize astronomy, astrophysics, and cosmology, by providing a new and previously unaccessible window to the universe. In my talk I will give an overview of the most recent results and developments in GW astronomy, and the contributions of Eötvös University's LIGO group to the international LIGO project and its discoveries.
Schrödinger's Cats remain afraid of gravity!
Magnetic anisotropy and spin reorientation transition in thin films - the metadynamics method
 B. Nagyfalusi, L. Udvardi, and L. Szunyogh, Physical Review B 100, 174429 (2019)