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Q: Quantenoptik

Q 9: Poster: Quantum Information

Q 9.23: Poster

Tuesday, April 3, 2001, 12:30–15:00, AT2

Squeezed State Entanglement for Free Space Quantum Cryptography — •Stefan Lorenz, Christine Silberhorn, Michael Langer, Natalia Korolkova, and Gerd Leuchs — Zentrum f"ur moderne Optik, Physikalisches Institut, Staudtstr. 7 / B2, D-91058 Erlangen

Quantum key distribution is on the verge of commercial applications as means of establishing secure data transmissions. While most of the existing experiments use single photons, we intend to utilize EPR-entangled multi-photon pulse pairs. They can be generated at a higher repetition rate, leading to decreased key distribution times. The entanglement can be produced by interference of two quadrature squeezed pulses at a beamsplitter. To produce the quadrature squeezed pulses we will use an asymmetric fiber Sagnac interferometer [1].

In contrast to existing experiments, we use a microstructured fiber [2] instead of a standard single mode fiber in the interferometer. This fiber has a very small mode field diameter leading to enhanced nonlinearity. Therefore the fiber length can be reduced, minimizing other noise producing effects such as e.g. guided acoustic wave brillouin scattering. In addition, the zero dispersion wavelength of the fiber lies at about 800nm, giving us the possibility to produce bright entangled pulses at a wavelength which is suited for free space transmission. [1] S. Schmitt et al., Phys. Rev. Lett. 81, 2446 (1998) [2] J.K. Ranka et al., Optics Letters 25, No. 11, 796 (2000)