Scaling Up a Quantum Computer

A series of sustained quantum operations shows promise for developing a practical device.

Researchers at the National Institute of Standards and Technology (NIST) in Boulder, CO, have demonstrated multiple computing operations on quantum bits--a crucial step toward building a practical quantum computer.

Shine on, ions: Beryllium ions are trapped inside the dark slit on the left side of this chip. When researchers focus lasers on the ions, the ions can be used to perform quantum calculations. Credit: J. Jost at NIST

Quantum computers have the potential to perform calculations far faster than the classical computers used today. This superior computing power comes from the fact that these computers use quantum bits, or qubits, which can represent both a 1 and a 0 at the same time, in contrast to classical bits that can represent only a 1 or a 0. Scientists take a number of different approaches to creating qubits. At NIST, the researchers use beryllium ions stored within so-called ion traps. Lasers are used to control the ions' electronic states, depending on the frequency to which the laser light is tuned. The electronic states of the ions and their interactions determine the quantum operations that the machine performs.

Over the past few decades, researchers have made steady progress toward a quantum computer, for instance, by storing quantum data or performing logic operations on qubits. But the NIST work, which is published online today by the journal Science, pieces together several crucial steps for the first time. The work involved putting an ion into a desired state, storing qubit data in it, performing logical operations on one or two of the qubits, transferring that information among different locations, and finally reading out the qubit result individually. Importantly, the researchers show that they can perform one operation after another in a single experiment.

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"This is the next step in trying to put a quantum computer together," says Dave Wineland, lead researcher on the project. "It's nice to have reached this stage."

The NIST team performed five quantum logic operations and 10 transport operations (meaning they moved the qubit from one part of the system to another) in series, while reliably maintaining the states of their ions--a tricky task because the ions can easily be knocked out of their prepared state. In other words, the researchers had to be careful that they didn't lose quantum combinations of 1s and 0s while they manipulated their ions.