‘Toggle Switch’ for Quantum Computers

‘Toggle Switch’ for Quantum Computers

Technology News |
By Wisse Hettinga

The novel device could lead to more versatile quantum processors with clearer outputs

What good is a powerful computer if you can’t read its output? Or readily reprogram it to do different jobs? People who design quantum computers face these challenges, and a new device may make them easier to solve.

The device, introduced by a team of scientists at the National Institute of Standards and Technology (NIST), includes two superconducting quantum bits, or qubits, which are a quantum computer’s analogue to the logic bits in a classical computer’s processing chip. The heart of this new strategy relies on a “toggle switch” device that connects the qubits to a circuit called a “readout resonator” that can read the output of the qubits’ calculations.

The photo above shows the central working region of the device. In the lower section, the three large rectangles (light blue) represent the two quantum bits, or qubits, at right and left and the resonator in the center. In the upper, magnified section, driving microwaves through the antenna (large dark-blue rectangle at bottom) induces a magnetic field in the SQUID loop (smaller white square at center, whose sides are about 20 micrometers long). The magnetic field activates the toggle switch. The microwaves’ frequency and magnitude determine the switch’s position and strength of connection among the qubits and resonator.
Credit: K. Cicak and R. Simmonds/NIST

This toggle switch can be flipped into different states to adjust the strength of the connections between the qubits and the readout resonator. When toggled off, all three elements are isolated from each other. When the switch is toggled on to connect the two qubits, they can interact and perform calculations. Once the calculations are complete, the toggle switch can connect either of the qubits and the readout resonator to retrieve the results.

“The goal is to keep the qubits happy so that they can calculate without distractions, while still being able to read them out when we want to,” said Ray Simmonds, a NIST physicist and one of the paper’s authors. “This device architecture helps protect the qubits and promises to improve our ability to make the high-fidelity measurements required to build quantum information processors out of qubits.”

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