Simplifying quantum logic using higher-dimensional Hilbert spaces

Author(s): B. P. Lanyon, A. Gilchrist, J. L. O'Brien, G. J. Pryde, K. J. Resch, T. Ralph, T. Jennewein, M. P. Almeida, M. Barbieri, A. G. White

Journal: Nature Physics

Volume: 5

Page(s): 134 - 140

Year: 2008

DOI Number: 10.1038/nphys1150

Link: Link to publication

Abstract:

Quantum computation promises to solve fundamental, yet otherwise intractable, problems across a range of active fields of research. Recently, universal quantum logic-gate sets—the elemental building blocks for a quantum computer—have been demonstrated in several physical architectures. A serious obstacle to a full-scale implementation is the large number of these gates required to build even small quantum circuits. Here, we present and demonstrate a general technique that harnesses multi-level information carriers to significantly reduce this number, enabling the construction of key quantum circuits with existing technology. We present implementations of two key quantum circuits: the three-qubit Toffoli gate and the general two-qubit controlled-unitary gate. Although our experiment is carried out in a photonic architecture, the technique is independent of the particular physical encoding of quantum information, and has the potential for wider application.