September 26, 2007

Quantum computing photon qubit communication advances

Two major steps toward putting quantum computers into real practice — sending a photon signal on demand from a qubit onto wires and transmitting the signal to a second, distant qubit — have been brought about by a team of scientists at Yale.

They report that superconducting qubits, or artificial atoms, have been able to communicate information not only to their nearest neighbor, but also to a distant qubit on the chip. This research now moves [this type of] quantum computing from “having information” to “communicating information.”

The first breakthrough reported is the ability to produce on demand — and control — single, discrete microwave photons as the carriers of encoded quantum information.

They added a second qubit and used the photon to transfer a quantum state from one qubit to another. This was possible because the microwave photon could be guided on wires — similarly to the way fiber optics can guide visible light — and carried directly to the target qubit. “A novel feature of this experiment is that the photon used is only virtual,” said Majer and Chow, “winking into existence for only the briefest instant before disappearing.”

Together the new Yale research constitutes the first demonstration of a “quantum bus” for a solid-state electronic system. This approach can in principle be extended to multiple qubits, and to connecting the parts of a future, more complex quantum computer.

There are many competing methods for making quantum computers. This approach is to down to the level of precisely manipulating single photons. Other approaches like adiabatic quantum computers could succeed with a lower degree of physical control and precision. This approach could ultimately have higher potential especially if molecular nanotechnology helps enable the high levels of precision and control.