Talks

It is often the case that interaction with a quantum system does not simply occur between an initial point in time and a final one, but rather over many time steps. In such cases, an interaction at a given time step can have an influence on the dynamics of the system at a much later time. Just as quantum channels model dynamics between two time steps, quantum combs model the more general multi-time dynamics described above, and have accordingly found application in such fields as open quantum systems and quantum cryptography. In this talk, we will consider ensembles of combs indexed by a random variable, dubbed classical-quantum combs, and discuss how much can be learnt about said variable through interacting with the system. We characterise the amount of information gain using the comb min-entropy, an extension of the analogous entropic quantity for quantum states. With combs and the min-entropy in our toolbox, we turn to a number of applications largely inspired by Measurement-Based Quantum Computing (MBQC), including the security analysis of a specific Blind Quantum Computing protocol and some comments regarding learning causal structure.

Zoom Link: https://pitp.zoom.us/j/98315660866?pwd=cWU3RzB6SG9DOGIza1BqV1lqNklvQT09

The holographic duality between strongly coupled quantum field theories and weakly coupled gravitational theories in one higher dimension holds, in principle, the promise of understanding strongly coupled systems that occur in condensed matter physics, such as the "strange" metals that appear in materials such as high-Tc cuprates. Unfortunately, the holographic models of metals that have previously been studied have not been successful in capturing even the most basic physics that any realistic model of a metal should obey. In this talk, I will review the essential properties that any metal (strongly coupled or not) must satisfy, and propose a new holographic model that is consistent with these requirements. The new model is based on a radically different approach compared with previous holographic models of metals, and crucially relies on recent work that formulates in a precise way the conditions for an IR effective field theory to be "emergeable" from a UV theory at nonzero charge density. In particular, the holographic model I study is dual to a quantum field theory with a global symmetry group LU(1) -- the "loop group" whose elements are smooth functions from the circle into U(1). I present the results of a solution of the model and argue that its properties are qualitatively consistent with what one should expect to find in a strongly coupled metal.

Zoom Link: TBD