The development of nonclassical sources of light that rely on the quantum nature of the electromagnetic field has proceeded apace in the past decade. Generically referred to as quiet light, these quantum sources exhibit reduced fluctuations (noise) in comparison with classical sources such as natural light, and light from LEDs and lasers.

A particularly useful quantum source of light is the entangled photon state, which may be generated by spontaneous optical parametric downconversion (SPDC). In this process, a laser beam illuminates an anisotropic nonlinear crystal oriented at the proper angle. A photon from the pump laser (the "mother photon") is split into a pair of twins (the "daughter photons"). The energy and momentum of the mother are shared by the daughters, which share entanglement by virtue of the nonseparability of the quantum state that describes them.

It is the mission of the Quantum Imaging Laboratory to exploit nonclassical light for the purposes of optical imaging, communications, cryptography, teleportation, and computing.

We gratefully acknowledge support from the National Science Foundation, the Center for Subsurface Imaging Systems, a National Science Foundation Engineering Research Center; the National Institute of Standards and Technology, the Office of Naval Research, the Defense Advanced Research Projects Agency; the Boston University Photonics Center; MIT Lincoln Laboratory; the Veridian Corporation; Carl Zeiss Jena GmbH; the David and Lucile Packard Foundation; and the California Institute for Physics and Astrophysics.