Universal MBQC with generalised parity-phase interactions and pauli measurements

Abstract

We introduce a new family of models for measurement-based quantum computation which are deterministic and approximately universal. The resource states which play the role of graph states are prepared via 2-qubit gates of the form exp(−i2πn Z Z). When n = 2, these are equivalent, up to local Clifford unitaries, to graph states. However, when n > 2, their behaviour diverges in two important ways. First, multiple applications of the entangling gate to a single pair of qubits produces non-trivial entanglement, and hence multiple parallel edges between nodes play an important role in these generalised graph states. Second, such a state can be used to realise deterministic, approximately universal computation using only Pauli Z and X measurements and feed-forward. Even though, for n > 2, the relevant resource states are no longer stabiliser states, they admit a straightforward, graphical representation using the ZX-calculus. Using this representation, we are able to provide a simple, graphical proof of universality. We furthermore show that for every n > 2 this family is capable of producing all Clifford gates and all diagonal gates in the n-th level of the Clifford hierarchy.