Events

Localization, which is typically induced by disorder, is an exotic phenomenon where a quantum state fails to spread over the entire Hilbert space. Recently, measurement is utilized as another mechanism to localize a quantum state in nonunitary quantum circuits and continuously monitored systems, which exhibit novel quantum phenomena dubbed measurement-induced phase transitions (MIPTs). However, while both the disorder and the measurement localize the wave function and suppress the entanglement spreading, it is still not clear whether they exhibit the same localization properties.

In the last few years there has been great interest in the dynamics of monitored quantum many-body systems. The interplay between unitary evolution and dissipative dynamics leads to many effects, including measurement induced phase transitions of the entanglement scaling. While earlier works all considered Markovian dissipative processes, lately there has been growing interest in non-Markovian dissipation and the effect of memory on entanglement transitions.I will present recent results and developments on the study of entanglement in non-Markovian systems. In particular, I will focus on a free fermions ladder model, where one of the chains is the system of interest and the other chain (bath chain) is subjected to Markovian projective measurements. The global dynamics is Markovian and can be studied through standard Montecarlo quantum jumps methods, but because of the internal dynamics of the bath chains, the reduced dynamics on the system chain is non-Markovian. The introduction of this ancillary chain allows to study the entanglement transition in the presence of memory effects. The studied model exhibits a variety of phases, including transition a from area-law to CFT phase and different regimes where the monogamy of entanglement produces strong counter-intuitive effects.

Ta2NiSe5 has long been considered as a prominent candidate for realization of the excitonic condensation that was invoked to explain the opening of the gap in the photoemission and to rationalize the existence of short time scales in pump-probe experiments. A structural transition that coincides with the putative excitonic transition leads to eternal chicken-egg debate addressing the dominant mechanism of the transition. We consider a realistic 6 orbital model and discuss its instabilities in Hartree-Fock calculations including the relevant B2g Raman active phonon. The model realizes excitonic transition with experimentally expected symmetry only provided the electron-phonon coupling is taken into account. From time-dependent calculations we evaluate also two-particle response corresponding to Raman and optical spectra. The key feature of the calculated response is a prominent phase mode, and the extent to which it survives in the structurally distorted ground state may help settling the debate.

Excitons are correlated electron-hole pairs in multi-band electron systems, which can condense and form ordered phases of matter called excitonic insulators. These are expected to display novel and technologically highly relevant features like superfluid energy transport. While it is experimentally challenging to identify real materials hosting equilibrium excitonic order, out-of-equilibrium protocols open up an independent route to stabilize excitonic condensates.Ma et.al. proposed a gated semiconductor bilayer architecture, in which an applied voltage bias allows for the continuous creation of interlayer excitons by means of an induced electrical current. We model the setup starting from the quasi-stationary situation within the static Hartree-Fock and second order Born approximations. We compare results from dynamical mean-field theory to simulations in one spatial dimension to shed light on the strong impact of dimensionality on the formation of the excitonic state. To go beyond the quasi-stationary case, we discuss results of time-dependent simulations of a driven four-band model in one spatial dimension, which is coupled to a bosonic bath.

We introduce and discuss dynamical universality of charge fluctuations in charged single-file systems. The full counting statistics of such systems out of equilibrium generically undergoes first and second order dynamical phase transitions, while equilibrium typical fluctuations are non-Gaussian and given by a universal distribution. Similar phenomenology of dynamical criticality is observed in equilibrium in the easy axis and isotropic regimes of an integrable spin chain. While the easy axis regime does not satisfy a single-file kinetic constraint, it nevertheless supports the non-Gaussian distribution of the charged single-file universality class. Fluctuations at the isotropic point are also anomalous and distinct from those of the Kardar-Parisi-Zhang universality class.

We propose the correlated random anisotropy model that describes thin ferromagnetic films hybridized with organic molecular layers. The asymmetry of the molecules leads to the random in-plane anisotropy induced at the surface of the magnetic film. We show that this strongly modifies the magnetic anisotropy of the whole cobalt layer which magnitude critically depends on the correlation radius of random anisotropy (fig. a). When this radius is small even strong induced anisotropy can be neglected. However, with the increase of correlation radius, the effect of molecules starts to dominate the magnetic properties. It results in the colossal increase of the coercive field, modification of the hysteresis loop shape (fig. b), and breaking of the Raleigh law at low fields.