The Economist profiles the progress in quantum computing coming from John Martinis' lab


A series of reports from the annual meeting of the American Association for the Advancement of Science kicks off with new developments in quantum computing

Feb 25th 2012 | vancouver | from the print edition

QUANTUM effects are vital to modern electronics. They can also be a damnable nuisance. Make a transistor too small, for example, and electrons within it can simply vanish from one place and reappear in another because their location is quantumly indeterminate. Currents thus leak away, and signals are degraded.

Other people, though, see opportunity instead. Some of the weird things that go on at the quantum scale afford the possibility of doing computing in a new and faster way, and of sending messages that—in theory at least—cannot be intercepted. Several groups of such enthusiasts hope to build quantum computers capable of solving some of the problems which stump today’s machines, such as finding prime factors of numbers with hundreds of digits or trawling through large databases. They gave a progress report to the annual meeting of the American Association for the Advancement of Science (AAAS) in Vancouver.


John Martinis and his colleagues at the University of California, Santa Barbara (UCSB), meanwhile, have been trying to forge qubits from superconducting circuits. In a superconductor, electrons do not travel solo. Instead, for complicated quantum-mechanical reasons, they pair up (for the same reasons, the pairs feel no electrical resistance). When they do so, the pairs start behaving like a single particle, superposing proclivities and all. This superparticle can, for instance, in effect be moving in two directions at once. As electrons move, they create a magnetic field. Make a closed loop of superconducting wire, then, and you get a magnetic field which can be facing up and down at the same time. You have yourself a superconducting qubit—or five, the number Dr Martinis has so far managed to entangle.

He has another clever trick up his sleeve. Using a device called a resonator he has been able to transfer information from the circuit to a single photon and trap it in a cavity for a few microseconds. He has, in other words, created a quantum memory. A few microseconds may not sound much, but it is just about enough to perform some basic operations.


John Martinis