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

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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.
SAINT-PETERSBURG, October 17 – 20, 2005 9 Then we can combine outcomes or photocurrents from different biphotons to achieve the desired relationship between the states <strong>of</strong> B photons. This is a gate, that transforms the photon state from one to another. We focus on the next questions: 1/ which is a structure <strong>of</strong> the gates from biphotons, 2/ which <strong>of</strong> operations can be performed. We found that deterministic gates have to include a set <strong>of</strong> retrieval operators to correct the output state when unwanted outcomes arise. It due from the probabilistic nature <strong>of</strong> quantum measurement. We show that the gates are scalable and can perform any operation on given input states, they differ from gates <strong>of</strong> TQC and 1WQC models. In experiment with a pulsed-pump laser biphotons are generated with some probability. Next estimations are true. Let be the laser with pulse <strong>of</strong> 100 fs, repetition rate <strong>of</strong> 100 MHz and the average power 200 mW. Then probability <strong>of</strong> generation <strong>of</strong> pair is about 10 -4 or one biphoton per 10 000 pulses and the rate <strong>of</strong> generation <strong>of</strong> biphotons is 10 4 per second. This is a high rate and it is attractive for real quantum communications. This work was supported in part by Delzell Foundation, Inc. 1. D. Gottesman and I. Chuang. Quantum teleportation as a universal computational primitive. Nature 1999. V. 402. P. 390-393. 2. M. A. Nielsen. Quantum computation by measurement and quantum memory. Phys. Lett. A. 2003. V. 308. P. 96–100. D. W. Leung. Quantum computation by measurements. Int. J. Quant. Inf. 2004 V. 2. P.33-43. D. W. Leung. Two qubit projective measurements are universal for quantum computation. arXiv:quantph/0111122. 2001. 3. R. Raussendorf and H. J. Briegel. A one-way quantum computer. Phys. Rev. Lett. 2001. V. 86. P. 5188–5191. Raussendorf, D. E. Browne, and H. J. Briegel. Measurement-based quantum computation with cluster states. Phys.Rev. A. 2003. V. 68. P.022312. 4. P. Walther, K.J. Resch, T. Rudolph, E. Schenck, H. Weinfurter, V. Vedral, M. Aspelmeyer, .Zeilinger. Experimental One-Way Quantum Computing. arXiv:quantph/0503126. 2005.
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