NIST Physicists Harness Microwave Source to Facilitate Ion-Trap Quantum Supercomputers

For the first time, physicists at the National Institute of Standards and Technology (NIST) have linked the quantum properties of two separated ions (electrically charged atoms) by manipulating them with microwaves instead of the usual laser beams. Thus suggesting that it may be possible to replace an exotic room-sized quantum computing laser park with compact commercial microwave technology used in smartphones.

According to the physicists, microwaves have been used in past experiments to manipulate single ions. But the NIST group is the first to position microwaves sources close enough to the ions—just 30 micrometers away—and create the conditions enabling entanglement, a quantum phenomenon expected to be crucial for transporting information and correcting errors in quantum computers, said the developers.

In this experiment, which is described in the August 11 issue of Nature magazine, the wiring for microwave sources is integrated directly on a chip-sized ion trap with a desktop-scale table of lasers, mirrors and lenses. A pair of ions (electrically charged atoms) are trapped by electric fields and manipulated with microwaves inside a glass chamber at the center of the apparatus. The chamber is illuminated by a green light-emitting diode (LED) for visual effect and an ultraviolet laser beam is used to cool the ions.

Compared to complex, expensive laser sources, microwave components could be expanded and upgraded more easily to build practical systems of thousands of ions for quantum computing and simulations, the researchers said.

“It's conceivable a modest-sized quantum computer could eventually look like a smartphone combined with a laser pointer-like device, while sophisticated machines might have an overall footprint comparable to a regular desktop PC,” said NIST physicist Dietrich Leibfried, a co-author of the paper published in Nature.

He added, “Although quantum computers are not thought of as convenience devices that everybody wants to carry around, they could use microwave electronics similar to what is used in smartphones. These components are well developed for a mass market to support innovation and reduce costs. The prospect excites us.”

A nearer-term goal is to design quantum simulations of important scientific problems, to explore quantum mysteries such as high-temperature superconductivity, the disappearance of electrical resistance in certain materials when sufficiently chilled.

In the latest experiments, the NIST team used microwaves to rotate the “spins” of individual magnesium ions and entangle the spins of a pair of ions. This is a “universal” set of quantum logic operations because rotations and entanglement can be combined in sequence to perform any calculation allowed by quantum mechanics, Leibfried noted.

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