Talks

In order to understand many Quantum information aspects of the Ads/CFT correspondence, tensor network toy models of holography have been a useful and concrete tool. However, these models traditionally lack many features of their continuum counterparts, limiting their applicability in arguments about gravity. In this talk, I present a natural extension of the tensor network holography paradigm which rectifies some of these issues. Its direct inspiration originates in Loop Quantum Gravity, which allows not only lifting existing limitations of tensor networks, but also firmly grounds the models in the context of nonperturbative canonical quantum gravity.

In recent years, ‘measurement-induced phase transitions’ (MIPT), have led to a new paradigm for dynamical phase transitions in quantum many-body systems. I will discuss a model of continuously monitored or weakly measured arrays of Josephson junctions (JJAs) with feedback. Using a variational self-consistent harmonic approximation, as well as analysis in the semiclassical limit, strong feedback and measurement limit, and weak coupling perturbative renormalization group, I will show that the model undergoes re-entrant superconductor-insulator MIPTs in its long-time non-equilibrium steady state as a function of measurement and feedback strength. I will contrast the phase diagram of monitored JJA with the well-studied case of dissipative JJA.
 

We discuss the entanglement between two critical spin chains induced by the Bell-state measurements, when each chain was independently in the ground state before the measurement. This corresponds to a many-body version of “entanglement swapping”. We employ a boundary conformal field theory (CFT) approach and describe the measurements as conformal boundary conditions in the replicated field theory. We show that the swapped entanglement exhibits a logarithmic scaling, whose coefficient takes a universal value determined by the scaling dimension of the boundary condition changing operator. We apply our framework to the critical spin-1/2 XXZ chain and determine the universal coefficient by the boundary CFT analysis, which is verified by a numerical calculation.

This talk is based on M. Hoshino, M. O., and Y. Ashida, arXiv:2406.12377
 

Measurement induced phase transitions (MIPT) occur when the natural entangling dynamics in many-body systems is overcome by persistent but random single particle measurements. The entanglement originates from two-qubit gates, and we consider circuits when this is fixed and the one qubit operations are random unitaries. This talk discusses how the entangling power and other local unitary invariants of special two-qubit gates modify the phase transition parameters with much more robust circuits possible than with typical gates. Apart from the usual bipartite entanglement, the possible relevance of some other characterizations of local entanglement structure in MIPT are also discussed. Entangling power, gate typicality and Measurement-induced Phase Transitions,

Based on: Sourav Manna, Vaibhav Madhok, Arul Lakshminarayan, arXiv:2407.17776
 

Climate Scientists are increasingly turning to Machine Learning to answer various questions in their domain. In this talk, we will discuss a few typical problems related to Indian Monsoon, and discuss ML-based approaches for them. Specifically, we will focus on multi-scale forecasting, downscaling, and attribution to large-scale drivers.