The upcoming Modern Optics and Spectroscopy Seminar on December 7 is of special interest to the Physics of Computation community: Tuesday, 7 December 1993 11:00 -- 12:00 AM Room 37-252 (Marlar Lounge) "Towards Perfect Ciphers --- Quantum Cryptography." Artur K. Ekert Oxford University Cryptography has, for a long period of time, been regarded as a part of mathematics, with computational difficulty as a safeguard of information. Unfortunately, faster computers and better algorithms have step by step cracked the protection barriers of even the most sophisticated codes. The quest for unbreakable ciphers had to venture outside mathematics, and surprisingly, towards quantum physics [1]. I will discuss the overlap between different theoretical and experimental techniques developed independently by research groups working in secure communication and quantum physics. In particular I will present a method in which the security of the so-called key distribution and also the key storing processes in cryptography relies on quantum correlations [2]. The proposed scheme is based on Bohm's well-known version of the Einstein-Podolsky-Rosen gedankenexperiment and has been currently implemented using the Mach-Zehnder interferometer [3]. REFERENCES [1] For a simple introduction to quantum cryptography see BENNET_CH, BRASSARD_G, EKERT_AK "Quantum Cryptography" SCIENTIFIC AMERICAN 1992 OCTOBER PP.50-59; EKERT_AK "Quantum Keys for Keeping Secrets" NEW SCIENTIST 16 JANUARY 1993 PP.24-28. [2] EKERT_AK "Quantum Cryptography Based on Bell's Theorem" PHYSICAL REVIEW LETTERS 1992 VOL.67 PP.661-663. [3] EKERT_AK, RARITY_JG, TAPSTER_PR, PALMA_GM "Practical Quantum Cryptography Based on 2-Photon Interferometry" PHYSICAL REVIEW LETTERS 1992 VOL.69 NO.9 PP.1293-1295.