Factoring integers with Young's N-slit interferometer
  We show that a Young's N slit interferometer can be used to factor the integer N. The device could factor four- or five-digit numbers in a practical fashion. This work shows how number theory may arise in physical problems, and may provide some insight as to how quantum computers can carry out factoring problems by interferometric means. 
John F. Clauser and Jonathan P. Dowling