Among the most promising approaches to building a quantum computer is using superconducting circuits as quantum bits, or qubits. But controlling the qubit without destroying the information tucked inside it is a major challenge.
Andrew Houck, an assistant professor of electrical engineering, developed a superconducting qubit called a transmon that helps keep quantum information intact.
The data in a qubit–0, 1, or a quantum superposition of the two–is represented using different energy and phase states in the circuit, but stray electrical fields can easily destroy these states during readout. Instead of targeting the source of interference, as other researchers have, Houck armored the qubit, adding a capacitor that makes it difficult for stray electrons to interfere.
Getting data from the transmon is the next hurdle. Usually the qubit is read directly, by measuring changes in charge, but that’s not possible with the transmon. So Houck coupled it to a microwave photon, which interacts differently with the qubit depending on its state. By measuring the photon, it’s possible to infer the qubit’s state and thus extract its information.
While the quantum data in transmons lasts a few microseconds–an order of magnitude longer than in previous qubits–there’s still a way to go before millions of qubits can be used to make a large-scale quantum computer. –Anne-Marie Corley