This manuscript gathers and subsumes a long series of works on using QW to simulate transport phenomena. Quantum Walks (QWs) consist of single and isolated quantum systems, evolving in discrete or continuous time steps according to a causal, shift-invariant unitary evolution in discrete space. We start reminding some necessary fundamentals of linear algebra, including the definitions of Hilbert space, tensor state, the definition of linear operator and then we briefly present the principles of quantum mechanics on which this thesis is grounded. After having reviewed the literature of QWs and the main historical approaches to their study, we then move on to consider a new property of QWs, the plasticity. Plastic QWs are those ones admitting both continuous time-discrete space and continuous spacetime time limit. We show that such QWs can be used to quantum simulate a large class of physical phenomena described by transport equations. We investigate this new family of QWs in one and two spatial dimensions, showing that in two dimensions, the PDEs we can simulate are more general and include dispersive terms. We show that the above results do not need to rely on the grid and we prove that such QW-based quantum simulators can be defined on 2-complex simplicia, i.e. triangular lattices. Finally, we extend the above result to any arbitrary triangulation, proving that such QWs coincide in the continuous limit to a transport equation on a general curved surface, including the curved Dirac equation in 2+1 spacetime dimensions.
Collaborations and publications• Chapter 4 introduce the notion of Plasticity for QW on the infinite line and is only partially resulting from the paper A quantum walk with both a continuous-time limit and a continuous-spacetime limit, co-authored with Pablo Arrighi (AMU), see [25].• Chapter 5 extends the Plastic QW to the grid and refers to the paper Continuous Time Limit of the DTQW in 2D+ 1 and Plasticity, coauthored with Michael Manighalam (University of Boston) and recently accepted in QINP, see [58]. • Sections in Chapter 6 are results from the paper Dirac equation as a quantum walk over the honeycomb and triangular lattices, co-authored with Ivan Marquez, Armando Perez (Universidad de Valencia) and Pablo Arrighi, see [13]. • Section 7.2 generalises results obtained in the paper From curved spacetime to spacetime-dependent local unitaries over the honeycomb and triangular Quantum Walks, co-authored with Ivan Marquez, Armando Perez and Pablo Arrighi, see [14]. • Section 7.3 refers to a recent result obtained in the paper Dynamical Triangulation Induced by Quantum Walk, co-authored with Quentin Aristote (ENS Paris) and Nathanael Eon, see [4]. • Section 7.3 refers to the paper Grover Search as a Naturally Occurring Phenomenon, co-authored with Mathieu Roget (ENS Lyon), Stephan Guillet (ENS Lyon) and Pablo Arrighi, see [70].