A circuit of four superconducting qubits. Scientists have succeeded in entangling three of these. Yale work published in Nature
NY Times reports that I.B.M. has reconstituted what had recently been a relatively low-level research effort in quantum computing. I.B.M. is responding to advances made in the past year at Yale University and the University of California, Santa Barbara, that suggest the possibility of quantum computing based on standard microelectronics manufacturing technologies. Both groups layer a superconducting material, either rhenium or niobium, on a semiconductor surface, which when cooled to near absolute zero exhibits quantum behavior. IBM has assembled a large research group at its Thomas J. Watson Research Center in Yorktown Heights, N.Y., that includes alumni from the Santa Barbara and Yale laboratories and has now begun a five-year research project.
D-Wave Systems, a Canadian computer maker has built an adiabatic quantum computer system [different approach than the IBM effort] with more than 50 [128 qubits] quantum bits, but it has been greeted skeptically by many researchers who believe that it has not proved true entanglement. Nevertheless, Hartmut Neven, an artificial-intelligence researcher at Google, said the company had received a proposal from D-Wave and NASA’s Jet Propulsion Laboratory to develop a quantum computing facility for Google next year based on the D-Wave technology.
The quantum processors built by D-Wave Systems are a perfect example of specialized animals, and give an insightful look into some of the ideas behind co-design. The D-Wave machines don’t look much like regular computers. They require complex refrigeration equipment and magnetic shielding. They use superconducting electronics rather than semiconducting transistors. They are, at first inspection, very unusual indeed. But they are carefully designed and built in a way that allows an intimate match between the hardware and the software algorithm that they run.
Santa Barbara researchers are currently designing a quantum device with four qubits, and five resonators,” the standard microelectronic components that are used to force quantum entanglement. “If all goes well, we hope to increase this to eight qubits and nine resonators in a year or so.”
Competing quantum computer technological approaches are also being pursued. One approach involves building qubits from ions, or charged atomic particles, trapped in electromagnetic fields. Lasers are used to entangle the ions. To date, systems as large as eight qubits have been created using this method, and researchers believe that they have design ideas that will make much larger systems possible. Currently more than 20 university and corporate research laboratories are pursuing this design.
In June, researchers at Toshiba Research Europe and Cambridge University reported in Nature that they had fabricated light-emitting diodes coupled with a custom-formed quantum dot, which functioned as a light source for entangled photons. The researchers are now building more complex systems and say they can see a path to useful quantum computers.