Upcoming seminars

We consider the most general (finite-dimensional) quantum mechanical information source, which is given by a quantum system

$A$ that is correlated with a reference system $R$. The task is to compress $A$ in such a way as to reproduce the joint source state

$\rho^{AR}$ at the decoder with asymptotically high fidelity. This includes Schumacher's original quantum source coding problem of a

pure state ensemble and that of a single pure entangled state, as well as general mixed state ensembles.

Steady technological advances are paving the way for the implementation of the quantum internet, a network of locations interconnected by quantum channels. In this talk I will describe a model to simulate a quantum internet based on optical fibers and employ network-theory techniques to characterize the statistical properties of the photonic networks it generates. This model predicts (i) a phase transition between a disconnected and a highly-connected phase, (ii) that the typical photonic networks do not present the small world property, but that (iii) they are highly aggregated.

We propose a general-purpose quantum algorithm for preparing ground states of quantum Hamiltonians from a given trial state. The algorithm is based on techniques recently developed in the context of solving the quantum linear systems problem [Childs, Kothari, Somma'15]. We show that, compared to algorithms based on phase estimation, the runtime of our algorithm is exponentially better as a function of the allowed error, and at least quadratically better as a function of the overlap with the trial state.

The recently established resource theory of quantum thermodynamics offers a framework to determine the ultimate possibilities and limitations in the manipulation of quantum states and in the implementation of nanoscale thermal machines. A core endeavour of this programme is to determine under which conditions can a nonequilibrium quantum state be converted into another using thermal operations. Here we settle this question in the important case of Gaussian quantum states and channels.