A group of researchers from Stanford and from the University of California Santa Barbara have made a critical breakthrough on the road to quantum computing. The main advance that the group achieved was an interaction among light particles called photons. The researchers were able to do this by placing and indium arsenide quantum dot within the cavity of a photonic crystal. The photonic crystal was a chip of gallium arsenide with precisely drilled holes. The holes give it the ability to trap photons so they can interact with the quantum dot. With the device, the researchers were able to demonstrate controlled phase and amplitude modulation between two modes of light at the single photon level. The device produced phase shifts. The larger control powers produced greater phase shifts. They were able to produce a 45 degree phase shift at larger control powers.
Two photon beams were focused on a quantum dot. One of the photon beams is called a control beam. If the control beam gets to the quantom dot first, the difference in the amount of time in the cavity of the two photon beams corresponds to its phase shift. Phase shifts of 180 degrees are required for a quantum logic gate, the building block of a theorized quantum computer. The researchers believe this could be accomplished with a series of such devices. The results of the research have been published in the May 9, 2008, issue of the journal, Science. Related Article Abstract