Rig fires more photon pairs

November 5/12, 2003

Many groups of researchers are working on quantum communications systems, which use attributes of individual photons to carry information.

Such systems are potentially very powerful because photons can be entangled, or connected so that attributes like polarization remain linked regardless of the distance between them.

Massachusetts Institute of Technology researchers have moved the field forward with entangled photon beams that contain specific wavelengths of light and are relatively bright.

Firing a laser into a certain type of crystal causes some single photons to become a pair of lower-energy entangled photons. The researchers generated 12,000 photon pairs per second per milliwatt of laser power by using a continuous split laser beam that hit the crystal from two directions.

The method produces relatively many entangled pairs of photons because it skips the filtering step usually required to remove unentangled photons, according to the researchers. The researchers produced entangled-photon beams at wavelengths of 795 nanometers, which is appropriate for quantum memory, and 1,600 nanometers, which be transmitted down a standard telecom fiber.

The researchers' next step is to make a brighter beam by adding an optical cavity, which amplifies light, to the device.

The project is part of a five-year program to transmit information over long distances using entanglement. The researchers presented the work at the Frontiers in Optics meeting of the Optical Society of America (OSA) in Tucson, Arizona October 5 to 9.

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