CQT Colloquium by Chiara Marletto, University of Oxford

Title: 'The Physics of Can and Can’t': from the universal computer to the universalconstructor
Date/Time: 06-Feb, 04:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15

Abstract:The theory of the universal quantum computer has brought us rapid technologicaldevelopments, together with remarkable improvements in how we understandquantum theory. There are, however, reasons to believe that quantum theory mayultimately have to be modified into a new theory: for instance, it will have tobe merged with general relativity, to incorporate gravity; and some claim thatit may be impossible to have quantum effects beyond a certain macroscopicscale. So what lies ahead of quantum theory, and of the universal quantumcomputer? To shed some light into these questions, we need a shift of logic inthe way things are explained. Specifically, one can adopt the approach wherethe basic assumptions are general principles about possible/impossibletransformations, rather than dynamical laws and initial conditions. Thisapproach is called constructor theory. I will describe its application to a handfulof interconnected problems, within information theory, thermodynamics, and evenquantum gravity. This ‘Physics of Can and Can’t' may be the first step towardsthe ultimate generalisation of the universal quantum computer, which vonNeumann called the 'universal constructor’. 

CQT Talk by Tim Spiller, UK Quantum Communications Hub

Title: The UK National Quantum Technologies Programme and the Quantum Communications Hub
Date/Time: 04-Feb, 04:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15

Abstract: Quantum technologies are new disruptive technologies in which fundamental aspects of quantum physics are instrumental in providing advantages over the conventional technology counterparts. Examples include quantum computing, sensing, imaging and communications. The UK has made a very substantial investment to establish a R&D programme.
I'll give a very brief overview of what is being pursued in the UK National Quantum Technologies Programme, and then expand on the technologies being delivered by the Quantum Communications Hub.

CQT Talk by Marc Olivier Renou, University of Geneva, Genève (UNIGE)

Title: Genuine quantum triangle nonlocality and quantum Finnerinequality
Date/Time: 30-Jan, 02:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15

Abstract: Network nonlocality extends standard Bell nonlocality tonetworks, where several independent sources are distributed to several partiesaccording to the network structure. Contrary to standard Bell Nonlocality, thisproblem is non convex: no efficient systematic way to tackle it is known,either for local or quantum correlations. It is only partially understood forthe simplest scenarios of bilocality (extended to star-locality and nonlocalityon a line). However, for scenarios with loops, e.g. the triangle network,nothing is known except examples directly deduced from the usual form ofquantum nonlocality (via the violation of a standard Bell inequality). This caneven be done without using inputs. The question of finding a genuine quantumviolation of triangle network locality was open the last years.

Inthis talk, we first present a novel example of quantum nonlocality withoutinputs in the triangle network, which we believe represent a new form ofquantum nonlocality, genuine to the triangle network. It involves bothentangled qubit states and joint entangled measurements. We generalize it toqutrits shared states and any odd-cycle networks.

Then,we move to the question of the characterization of local and quantumcorrelations. We derive a bound, the quantum Finner inequality (already knownto hold for local ressources), which we also demonstrate to hold when thesources are arbitrary no-signaling boxes which can be wired together. Wegeneralizes this bound to all networks involving bipartite sources. We discussit as an application for the device-independent characterization of thetopology of a quantum network.

Weconclude with some open questions related to quantum network nonlocality.

Thistalk is based on arXiv:1905.04902 andarXiv:1901.08287