Talks

In this talk, I will focus on the ENSO-Monsoon teleconnection from the perspective of changes in moisture convergence. I will also speak about the performance of some models in capturing global teleconnection to monsoon, mainly when ensemble mean is performed. Finally, a new mode of the southern Pacific Ocean that affects ENSO evolution and global monsoon will be described.

Computing methods on classical computers have dominated the discovery frontline from fundamental physics for several decades now. It is however becoming clear that at least in physics, there are several computational avenues (such as finite density and real-time dynamics) where development can be accelerated via quantum computers. At the same time, improving classical computing techniques using clever analytical insights is essential to provide further inputs to the quantum computing frontier. In this talk, we will discuss the broad ideas behind the novel constructions and selected applications illustrating results for realistic systems in condensed matter and particle physics. Such scenarios are expected to be realized in quantum hardware in the recent future.
 

Certain natural geometric properties of electron wavefunctions in a crystal turn out to explain a vast range of experimentally relevant properties. The original example was the explanation of the integer quantum Hall effect by Thouless and co-workers in terms of the “Berry curvature” derived from Bloch states. We now understand that a kind of gauge field in the Brillouin zone is the key to many equilibrium and linear-response properties, and current work is seeking to generalize these results to nonlinear and non-equilibrium properties as well. This talk reviews the basic concepts of wavefunction geometry starting from basic notions of undergraduate quantum mechanics, then covers more recent applications to new topological states, with a particular focus on effects beyond the standard adiabatic limit.

Quantum error correction (QEC) plays a critical role in preventing information loss in quantum systems and provides a framework for reliable quantum computation. However, implementing protocols for QEC and fault tolerance remains a challenge in the current era of noisy, intermediate-scale quantum (NISQ) processors. Here, we discuss recent progress in identifying resource-efficient strategies for QEC, which are tailored for the dominant noise processes affecting the quantum hardware. We show that such noise-adapted protocols can also provide a route to fault tolerance in near-term quantum devices, under certain assumptions.
 

Atomic and solid-state spin ensembles are promising platforms for implementing quantum technologies, but the unavoidable presence of noise imposes the needs for error correction. Typical quantum error correction (QEC) requires addressing specific qubits, but this is practically challenging in most realistic architectures. In this work, we propose QEC schemes for unresolvable spin ensembles. By using degenerate superpositions of excited states, which are fundamentally mixed, we find codes that can protect against both individual and collective errors, including dephasing, decay, and pumping. We show how information recovery can be achieved with only collective measurement and control, and illustrate its applications in extending memory lifetime. 

Ref: arXiv:2408.11628v1
 

We will discuss some aspects of my recent preprint, joint with Victor Ginzburg, on Kostant-Whittaker reduction, a (deformation) quantization of restriction to a Kostant slice. We will explain how this functor can be used to prove conjectures of Ben-Zvi and Gunningham on parabolic induction, as well as a convolution exactness conjecture of Braverman and Kazhdan in the D-module setting. While this talk will occasionally reference facts from a talk I gave at Perimeter on other aspects of this preprint, the overlap and references will be minimal.

Over the past two decades our understanding of the charge and heat transport properties of graphene has evolved progressively as the quality of the graphene devices improved. A key crossover occurs when the scattering between electrons themselves become more frequent than the scattering between electrons and disorder. In this regime, the electrons gas behaves as a hydrodynamic fluid, whose properties exhibit emergent universalities close to the charge neutrality point. In this talk, I shall present some new experimental result on the electrical and thermal transport measurements in very high-quality graphene devices where electron-electron scattering dominates over the momentum relaxation rate. I shall show that the transport in such graphene devices is unique in multiple ways, ranging from unconventional functional dependence of the dc conductivity on carrier density to giant violation of the Wiedemann-Franz law, where effective Lorenz number varies over six orders of magnitude with carrier density. We find that the transport properties of ultra-clean graphene close to charge neutrality are quantitatively consistent with that of a hydrodynamic Dirac fluid where both charge and heart flow are determined by a single universal transport constant.
 

Common intuition tells us that if one part of an interacting system is continuously cooled, the other parts should also cool down. This intuition can be put on firm grounds for the case of Markovian cooling of a free-fermion "lead" that is locally coupled to a generic quantum system. I will talk about a scenario where the opposite happens, namely, the system heats up toward its most excited state as the lead is cooled (or vice versa), even if other parameters favor sympathetic cooling. This dramatic effect originates from a simple but structured coupling that preserves a U(1) charge, and is realizable as existing setups.