## Our colleagues who came to visit us

# Seungbeom Chin

University, South Korea -- ICTQT, Gdańsk, Poland.

Independent Researcher: Nov 2021 to present

I study quantum resource theory, quantum simulation, and the entanglement of identical particles.

# Maria Stasinou

University of Oxford, UK -- ICTQT, Gdańsk, Poland.

Independent Researcher: Jul 2021 to Oct 2021

I study Causality in quantum process theories and beyond, the role of time in quantum theory, functorial quantum field theory, algebraic quantum field theory, and quantum cellular automata.

# Giovanni Scala

Istituto Nazionale di Fisica Nucleare, Italy -- ICTQT, Gdańsk, Poland.

Independent Researcher: Jan 2021 to June 2021

I study entanglement detection, contextuality scenarios, and Bell’s inequalities.

# Robert Pisarczyk

University of Oxford, UK.

Visit: 24.02.2020 to 28.02.2020

**Seminar title: Causal limit on quantum communication**

Abstract: The capacity of a channel is known to be equivalent to the highest rate at which it can generate entanglement. Analogous to entanglement, the notion of a causality measure characterizes the temporal aspect of quantum correlations. Despite holding an equally fundamental role in physics, temporal quantum correlations have yet to find their operational significance in quantum communication. Here we uncover a connection between quantum causality and channel capacity. We show the amount of temporal correlations between two ends of the noisy quantum channel, as quantified by a causality measure, implies a general upper bound on its channel capacity. The expression of this new bound is simpler to evaluate than most previously known bounds. We demonstrate the utility of this bound by applying it to a class of shifted depolarizing channels, which results in improvement over previously known bounds for this class of channels.

# Dominic Horsman

Université Grenoble Alpes, France.

Visit: 03.02.2020 to 14.02.2020

**Seminar title: Quantum compilation using the ZX-calculus**

Abstract: In this talk I will give an introduction to the use of the ZX calculus of observables as a compilation language for quantum computing. ZX calculus diagrams comprise a formal re-write language that allows purely diagrammatic equational reasoning for qubit quantum mechanics. I will give a basic introduction to the diagrams (no category theory required), and show how the calculus is especially suited to acting as an 'intermediate representation' for quantum compilers. This entails mediating between high-level user workloads/algorithms and qubit-level device specifications. I will go over recent work (both academic and commercial) on circuit optimisation using the calculus, and on its function as a design, verification, and optimisation language for error correction. I will finish by discussing insights the use of ZX gives into possible new models of quantum computation.