EPJ Quantum Technol. (2014) 1: 13
https://doi.org/10.1140/epjqt13

Research

Minimal ancilla mediated quantum computation

¹ School of Physics and Astronomy, University of Leeds, E C Stoner Building, Leeds, LS2 9JT, UK
² Department of Physics, Durham University, South Road, Durham, DH1 3LE, UK

^* e-mail: py08tjp@leeds.ac.uk

Received: 10 April 2014
Accepted: 13 August 2014
Published online: 4 September 2014

Abstract

Schemes of universal quantum computation in which the interactions between the computational elements, in a computational register, are mediated by some ancillary system are of interest due to their relevance to the physical implementation of a quantum computer. Furthermore, reducing the level of control required over both the ancillary and register systems has the potential to simplify any experimental implementation. In this paper we consider how to minimise the control needed to implement universal quantum computation in an ancilla-mediated fashion. Considering computational schemes which require no measurements and hence evolve by unitary dynamics for the global system, we show that when employing an ancilla qubit there are certain fixed-time ancilla-register interactions which, along with ancilla initialisation in the computational basis, are universal for quantum computation with no additional control of either the ancilla or the register. We develop two distinct models based on locally inequivalent interactions and we then discuss the relationship between these unitary models and the measurement-based ancilla-mediated models known as ancilla-driven quantum computation.