A team led by Yale researchers has created the first rudimentary solid-state quantum processor, a major step in the quest to build a quantum computer.
They also used the two-qubit superconducting chip to successfully run elementary algorithms such as a simple search, demonstrating quantum information processing with a solid-state device for the first time.
"Our processor can perform only a few very simple quantum tasks, which have been demonstrated before with single nuclei, atoms and photons," said Robert Schoelkopf, the William A Norton Professor of Applied Physics & Physics at Yale. "But this is the first time they've been possible in an all-electronic device that looks and feels much more like a regular microprocessor."
The team manufactured two artificial atoms, or qubits (quantum bits) - made up of a billion aluminum atoms, but acting like single atoms that can occupy two different energy states like the 'on' and 'off' states of regular bits employed by conventional computers. But because of the counterintuitive laws of quantum mechanics, scientists can effectively place qubits in a 'superposition' of multiple states at the same time, allowing for greater information storage and processing power.
These sorts of computations, though simple, haven't been possible using solid-state qubits until now, partly because scientists couldn't get the qubits to last longer than about a nanosecond. Schoelkopf and his team are now able to maintain theirs for a microsecond — enough to run the simple algorithms.
To perform their operations, the qubits communicate with one another using a 'quantum bus' — photons that transmit information through wires connecting the qubits — previously developed by the Yale group.
The key that made the two-qubit processor possible was getting the qubits to switch 'on' and 'off' abruptly, so that they exchanged information quickly and only when the researchers wanted them to.
Next, the team will work to increase the amount of time the qubits maintain their quantum states so they can run more complex algorithms. They will also work to connect more qubits to the quantum bus. The processing power increases exponentially with each qubit added, Schoelkopf said, so the potential for more advanced quantum computing is enormous. But he cautions it will still be some time before quantum computers can be used to solve complex problems.
Their findings will appear in Nature's online publication.