Proceedings of Topical Meeting on Optoinformatics (pdf-format, 1.21 ...

8 OPTOINFORMATICS’05
OPTOELECTRONIC GATES ON BIPHOTONS
Yu. A. Asikritova, I.D. Balatsky, V.N. Gorbachev, A.I Trubilko
Nor'Westerly Institute <strong>of</strong> Printing <strong>of</strong> St.-Petersburg State
University <strong>of</strong> Technology and Design 13, Djambula, St.-Petersburg,
191180, Russia Tel: (+7 812) 164-6556 Fax: (+7 812) 164-6556
Laboratory <strong>of</strong> Quantum Information and Computation, St.-Petersburg
State University <strong>of</strong> AeroSpace Instrumentation, 67, Bolshaya
Morskaya, St.-Petersburg, 190000
E-mail: vn@vg3025.spb.edu
A set <strong>of</strong> the measurement-based gates exploiting bipartite entanglement is
considered. These gates allow to perform any operations on given input states
and can be implemented from biphotons.
Biphotons or pairs <strong>of</strong> strong correlated photons are well known in quantum optics
and there is a significant progress in their generating and manipulating. Because <strong>of</strong> nonclassical
correlation between photons their state is entangled and known as EPR (Einstein-
Podolsky-Rosen) pair, that is a main resource <strong>of</strong> quantum information processing. In our
work we exploit the correlation to achieve a set <strong>of</strong> logical gates with optical input and
output. The gates proceed via measurement on the photons, when the measurement
outcomes or photocurrent <strong>of</strong> detectors carry out the gate operation.
Our gates belong to the class <strong>of</strong> the measurement based circuits, that perform
computations using quantum measurement as primitive. This idea has been introduced by
Gottesman and Chuang [1] and developed by many authors. In fact, any gate changes the
input state by transforming it into output. The state <strong>of</strong> the physical system can be changed
by two ways. First is an unitary evolution due from interaction between physical systems,
second is quantum projective measurement. Now there are two models <strong>of</strong> the measurement
based computation. First is teleportation quantum computation (TQC) [1,2] with gates based
on teleportation. Second is one-way quantum computer (1WQC) introduced Briegel [3] in
which computation proceeds via local single-qubit measurements on the multiparticle
entangled states, known as cluster or graph states. An experimental implementations <strong>of</strong>
1WQC using four-qubit optical cluster states have been demonstrated by Zeilinger [4] .
We consider a version <strong>of</strong> the measurement based gates using biphotons. The key idea
is a strong correlation between pair <strong>of</strong> photons A and B from biphoton. Let photon A is
measured, then the remainder photon B is projected into a state dependent from the
measurement outcome. Therefore there is a strong correlation between the quantum state <strong>of</strong>
B photon and the measurement outcomes (or photocurrent <strong>of</strong> detector) which are nice
electronic replica <strong>of</strong> B.