Quantum Computing using Linear Optics
  Quantum computers are expected to be able to solve mathematical problems that cannot be solved using conventional computers. Many of these problems are of practical importance, especially in the areas of cryptography and secure communications. APL is developing an optical approach to quantum computing in which the bits, or "qubits", are represented by single photons. Our approach allows the use of ordinary (linear) optical elements that are available for the most part as off-the-shelf components. Recent experimental demonstrations of a variety of logic gates for single photons, a prototype memory device, and other devices will be described. 
T.B. Pittman, B.C. Jacobs, and J.D. Franson