Quantum computers get a light alternative

17 Jun 2002

US scientists have developed a light-based computer that could challenge quantum computing.

Ian Walmsley and colleagues at Rochester University, US, have devised a simple optical system that performs a database search in a similar way to quantum computers. Rather than harnessing the phenomenon of quantum interference and its associated technical difficulties, Walmsley and his colleagues used light-wave interference.

"We've shown that if you have a quantum computer entirely based on quantum interference, we can build you [an alternative] based on light interference that is equally efficient," said Walmsley.

The researcher's device consists of a database that is based on an acousto-optic modulator fabricated from transparent tellurium dioxide. A vibrating transducer, pressed against the modulator, propagates acoustic waves through the modulator to create a wave pattern in which information can be stored.

To search the database, the team produced a single pulse of light. They knew that each color of the spectrum could be used to "carry" a bit of information, so before passing the light through the modulator they split it into two beams and passed one of the beams through a prism to separate it into its different frequencies. They then directed this beam through the modulator, which shifted the phases of certain light frequencies relative to others. By recombining the beam with its unaltered "other half", the researchers were able to detect the distorted frequency and use this to determine the location of a bit of information in the database.

"If [the team] shines 50 frequencies of light through the modulator and the 20th frequency is altered," explained a spokesman for Rochester University, "they know that the bit of information they were searching for is located at position 20 in the database."

The researchers' device can search a database that contains up to 50 items, which, they claim, is the largest search performed using wave interference. They now expect their work to expand the power of "wave computing" to between that of classical and quantum computing.