Talks

Introduction to path integrals and the semi-classical limit

https://drive.google.com/drive/folders/1L6a1YCdB9EejAUmZ52oLDAeB6oosjwhU?usp=sharing

https://www.dropbox.com/sh/sprq2u40e3leoso/AADhyov350QS9TEDdgtErekCa?dl=0

https://github.com/gsellaroli/pi-summer-school-2020

Overview/definition of symmetry, elements of group theory
https://drive.google.com/drive/folders/1L6a1YCdB9EejAUmZ52oLDAeB6oosjwhU?usp=sharing

https://www.dropbox.com/sh/sprq2u40e3leoso/AADhyov350QS9TEDdgtErekCa?dl=0

https://github.com/gsellaroli/pi-summer-school-2020

Foundations of Quantum Statistical Mechanics - Entanglement

https://drive.google.com/drive/folders/1L6a1YCdB9EejAUmZ52oLDAeB6oosjwhU?usp=sharing

https://www.dropbox.com/sh/sprq2u40e3leoso/AADhyov350QS9TEDdgtErekCa?dl=0

https://github.com/gsellaroli/pi-summer-school-2020

Harlow and Hayden [arXiv:1301.4504] argued that distilling information out of Hawking radiation is computationally hard despite the fact that the quantum state of the black hole and its radiation is relatively un-complex. I will trace this computational difficulty to a geometric obstruction in the Einstein-Rosen bridge connecting the black hole and its radiation. Inspired by tensor network models, I will present a conjecture that relates the computational hardness of distilling information to geometric features of the wormhole - specifically to the exponential of the difference in generalized entropies between the two non-minimal quantum extremal surfaces that constitute the obstruction. Due to its shape, this obstruction was dubbed "Python's Lunch", in analogy to the reptile's postprandial bulge.

Using a definition of bulk diff-invariant observables, we go into the bulk of 2d Jackiw-Teitelboim gravity. By mapping the computation to a Schwarzian path integral, we study exact bulk correlation functions and discuss their physical implications. We describe how the black hole thermal atmosphere gets modified by quantum gravitational corrections. Finally, we will discuss how higher topological effects further modify the spectral density and detector response in the Unruh heat bath. 

Given the large push by academia and industry (e.g., IBM and Google), quantum computers with hundred(s) of qubits are at the brink of existence with the promise of outperforming any classical computer. Demonstration of computational advantages of noisy near-term quantum computers over classical computers is an imperative near-term goal. The foremost candidate task for showing this is Random Circuit Sampling (RCS), which is the task of sampling from the output distribution of a random circuit. This is exactly the task that recently Google experimentally performed on 53-qubits.

Stockmeyer's theorem implies that efficient sampling allows for estimation of probability amplitudes. Therefore, hardness of probability estimation implies hardness of sampling. We prove that estimating probabilities to within small errors is #P-hard on average (i.e. for random circuits), and put the results in the context of previous works.

Some ingredients that are developed to make this proof possible are construction of the Cayley path as a rational function valued unitary path that interpolate between two arbitrary unitaries, an extension of Berlekamp-Welch algorithm that efficiently and exactly interpolates rational functions, and construction of probability distributions over unitaries that are arbitrarily close to the Haar measure.

I will give an overview of holographic cosmology and discuss recent results and work in progress.

In holographic cosmology time evolution is mapped to inverse RG flow of the dual QFT. As such this framework naturally explains the arrow of time via the

monotonicity of RG flows. Properties of the RG flow are also responsible for the holographic resolution of the classic puzzles of hot big bang cosmology, such as the horizon problem, the flatness problem and the relic problem.

The holographic framework includes qualitatively new models describing a non-geometric  very early Universe, and such models provide an excellent fit to CMB data.  In the last part of the talk I will present on-going work with lattice gauge theorists aiming to compute on the lattice the QFT observables(the 2-point function of stress energy tensor) needed to compute holographically the cosmological  power spectrum in the regime where the dual QFT is non-perturbative.

The discovery of the Higgs boson has revealed that the quartic Higgs self-coupling becomes small at very high energy scales. Guided by this observation, I introduce Higgs Parity, which is a spontaneously broken symmetry exchanging the standard model Higgs with its parity partner. In addition to explaining the small Higgs quartic coupling, Higgs Parity can provide a dark matter candidate, solve the strong CP problem, and arise from an SO(10) grand unified gauge symmetry. I will show that the Higgs Parity symmetry breaking scale is determined by standard model parameters and predicts experimental signals such as the proton decay rate and the warmness of dark matter. As a result, Higgs Parity provides a tight correlation between future precision measurements of standard model parameters and these experimental signals.

Hawking famously observed that the formation and evaporation of black holes appears to violate the unitary evolution of quantum mechanics. Nonetheless, it has been recently discovered that a signature of unitarity, namely the "Page curve" describing the evolution of entropy, can be recovered from semiclassical gravity. This result relies on "replica wormholes" appearing in the gravitational path integral, which are examples of spacetime wormholes studied more than 30 years ago and related to interactions with closed "baby" universes. I will discuss the connection between these new and old ideas and the consequences for the black hole information problem. A central lesson is that a Hilbert space in quantum gravity can be dramatically modified by nonperturbative topology-changing processes.