Quantum Information Processing, Vol. 3, Nos. 1–5, October 2004 (© 2004)
Towards Scalable Linear-Optical Quantum Computers
J. P. Dowling,
J. D. Franson,
and G. J. Milburn
Received February 4, 2004; accepted April 1, 2004
Scalable quantum computation with linear optics was considered to be impossible
due to the lack of efﬁcient two-qubit logic gates, despite the ease of implementa-
tion of one-qubit gates. Two-qubit gates necessarily need a non-linear interaction
between the two photons, and the efﬁciency of this non-linear interaction is typi-
cally very small in bulk materials. However, it has recently been shown that this
barrier can be circumvented with effective non-linearities produced by projective
measurements, and with this work linear-optical quantum computing becomes a
new avenue towards scalable quantum computation. We review several issues con-
cerning the principles and requirements of this scheme.
KEY WORDS: Linear optics, Logic gates, Single photon, Quantum memory,
PACS: 03.67.Lx, 03.67.Pp, 42.50.Dv, 42.65.Lm.
There are three key principles in the Knill, Laﬂamme, and Milburn
for efﬁcient and scalable linear-optical quantum infor-
mation processing (QIP):
(1) Conditional non-linear gates for two photon states.
(2) Teleportation to achieve high efﬁciency.
(3) Error correction to achieve scalability.
Quantum Computing Technologies Group, Section 367, Jet Propulsion Laboratory,
MS 126-347 and California Institute of Technology, 4800 Oak Grove Drive, CA 91109,
Applied Physics Laboratory, Johns Hopkins University, Laurel, MD 20723, USA.
Centre for Quantum Computer Technology, University of Queensland, QLD 4072,
To whom correspondence should be addressed.
Department of Physics, Louisiana State University, Baton Rouge, LA 70803, USA.
1570-0755/04/1000-0205/0 © 2004 Springer Science+Business Media, Inc.