Talks

Traditionally, quantum many-body theory has focussed on ground states and equilibrium properties of spatially extended systems, such as electrons and spins in crystalline solids. In recent years “noisy intermediate scale quantum computers” (NISQ) have emerged, providing new opportunities for controllable non-equilibrium many-body systems. In such dynamical quantum systems the inexorable growth of non-local quantum entanglement is expected, but monitoring (by making projective measurements) can compete against entanglement growth. In this talk I will overview theoretical work exploring the behavior of “monitored” quantum circuits, which can exhibit a novel quantum dynamical phase transition between a weak measurement phase and a quantum Zeno phase, the former which we characterize in detail. Accessing such physics in the lab is challenged by the need for post-selection, which might be circumnavigated by decoding using active error correction, conditioned on the measurement outcomes, as will be described in systems with Z2 symmetry.

Zoom Link: https://pitp.zoom.us/meeting/register/tJcqc-ihqzMvHdW-YBm7mYd_XP9Amhypv5vO

I will discuss the dynamical friction experienced by black holes moving through scalar or “wave-like” dark matter. This has been studied analytically and numerically in the non relativistic case, which is applicable to its effect in “fuzzy dark matter” halos where the scalar wavelength is on galactic scales. On smaller scales, dynamical friction from dark matter clouds formed from accretion or superradiance may cause a dephasing in the gravitational wave signal in LISA EMRIs. I will discuss our recent numerical work (https://arxiv.org/abs/2106.08280) to extend the description of dynamical friction to relativistic scalars, in order to treat this case.

Zoom Link: https://pitp.zoom.us/j/98815587081?pwd=a3FvcUtTaWFUejBpR1Q3QUhRRzF4dz09

The information loss paradox is usually stated as an incompatibility between general relativity and quantum mechanics. However, the assumptions leading to the problem are often overlooked and, in fact, a careful inspection of the main hypothesises suggests a radical reformulation of the problem. Indeed, I will present a thought experiment that shows the existence of an incompatibility between (i) the validity of the laws of general relativity to describe infalling matter far from the Planckian regime, and (ii) the so-called central dogma which states that as seen from an outside observer a black hole behaves like a quantum system whose number of degrees of freedom is proportional to the horizon area. We critically revise the standard arguments in support of the central dogma, and argue that they cannot hold true unless some new physics is invoked even before reaching Planck scales. This leads to the counterintuitive result that the information loss problem, in its current formulation, is not necessarily related to any loss of information or lack of unitarity. Semiclassical general relativity and quantum mechanics can be perfectly compatible before reaching the final stage of the black hole evaporation where, instead, a consistent theory of quantum gravity is needed to make any prediction.

Zoom Link: https://pitp.zoom.us/j/94637978136?pwd=VmlWa1BJU3I1UGVRNjliMEpUTlo2dz09