Talks

We show how the extended thermodynamics of hyperbolic black holes in AdS describes features of quantum information measures in quantum field theory, and discuss prospects for making further connections. In particular, the second law of thermodynamics is seen in this context to map to the generalized Zamolodchikov c-theorem, connecting these two firmly for the first time. Some projects for getting further lessons and perhaps new tools from  these connections (perhaps using holographic heat engines) are outlined. 

Clifford V. Johnson is a theoretical physicist passionate about sharing science with the public. He resolved to write a book explaining physics to a lay audience, but he felt that words on a printed page did not fully convey the dynamic, collaborative nature of fundamental research.

What if, he wondered, you could represent multiple voices and points of view? What if one could make the reader feel immersed in scientific discourse, rather than reading the words of an expert sharing a single perspective?

He wanted to write a book that would give readers a fly-on-the-wall experience of the process of fundamental science.

Johnson realized that graphic novels are the unique narrative medium he was searching for. Through the written word and compelling visuals, graphic novels immerse the reader in a sensory world of ideas.

This realization led Johnson to write and draw The Dialogues: Conversations About the Nature of the Universe (MIT Press), which allows readers to eavesdrop on a series of dialogues, set in locations around the world, about cutting-edge scientific topics.

In this public lecture, Johnson will discuss the process of turning complex scientific topics into compelling visual narratives.

Recently, a new formulation of quantum mechanics was suggested which is based on the evolution of classical particles, provided with a sign, rather than standard wave functions. This allows several advantages over other approaches: from a theoretical perspective, it offers a more intuitive framework while, from a numerical point of view, it allows the simulation of complex systems with relatively small computational resources. In this talk, I will first go through the tenets of this new approach. In particular, I will focus on the derivation of such theory and the peculiar view it provides in the passage from the quantum to the classical regime. Then, I will discuss the various applications which have been performed so far, especially for systems of Fermions. Finally, a list of possible future works will be presented and discussed.

Quantum decay of false vacuum states via the nucleation of bubbles may 
have played an important role in the early history of our Universe.  For 
example, in multiverse models that utilize false vacuum eternal 
inflation, the Big Bang of our observable Universe corresponds to one of 
these bubble nucleation events.  Further, our observable Universe may 
have undergone a series of symmetry-breaking first-order phase 
transitions as it cooled, which may have produced a remnant background 
of gravitational waves.

I will present results from a new real-time picture of false vacuum 
decay which, in contrast to existing semiclassical techniques, does not 
rely on classically forbidden tunneling paths.  Lattice simulations are 
used to evolve initial realizations of fluctuations around the false 
vacuum forward in time via the classical equations of motion.  In these 
simulations, we observe the false vacuum decay via the formation and 
subsequent expansion and coalescence of true vacuum bubbles.  By 
sampling initial field realizations, we build up ensembles of these 
decay histories and empirically determine the bubble nucleation rate.  
The rates agree well with standard Euclidean techniques, which cannot 
provide a time-dependent description of the decay.  Some novel 
applications of our new approach include investigation of bubble-bubble 
correlation functions, decay of time-evolving metastable states, decay 
of non-vacuum initial states, and the regime of rapid decays.

In this talk I will set out two new contributions to the study of operational tasks in a relativistic quantum setting. First, I will present a generalisation of the task known as ‘summoning,’ in which an unknown quantum state is supplied to an agent and must be returned at a specified point when a corresponding call is made. I will show that when this task is generalised to allow for more than one call to be made, an apparent paradox arises: the extra freedom makes it strictly harder to complete the task. Second, I will describe a quantum generalisation of the classic cryptographic task known as ‘zero-knowledge-proving.’ I will show that there exists no perfectly secure quantum relativistic protocol for this task, and I will then set out a protocol which is conjectured to be close to optimal in security for this task. These results have practical applications for distributed quantum computing and cryptography and also interesting implications for our understanding of relativistic quantum information and its localisation in spacetime.