Simplifying quantum logic using higher-dimensional Hilbert spaces

Benjamin P. Lanyon (1) , Marco Barbieri (2, 1) , M.P. Almeida (1) , Thomas Jennewein (1, 3) , Timothy C. Ralph (1) , Kevin J. Resch (1, 4, 5) , Geoff J. Pryde (1, 6) , Jeremy L. O'Brien (1, 7) , Alexei Gilchrist (1, 8) , Andrew G. White (1)

1 Department of Physics and Centre for Quantum Computer Technology
2 Laboratoire Charles Fabry de l'Institut d'Optique / Optique quantique
3 Institute for Quantum Optics and Quantum Information
4 IQC - Institute for Quantum Computing [Waterloo]
5 Department of Physics and Astronomy [Waterloo]
6 Centre for Quantum Dynamics
7 Centre for Quantum Photonics
8 Physics Department

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.

Domains: Physics [physics]; Quantum Physics [quant-ph]

Benjamin P. Lanyon, Marco Barbieri, M.P. Almeida, Thomas Jennewein, Timothy C. Ralph, et al.. Simplifying quantum logic using higher-dimensional Hilbert spaces. Nature Physics, 2009, 5, pp.134 - 140. ⟨10.1038/nphys1150⟩. ⟨hal-00569583⟩