(Photonics.com) Physicists at the National Institute of Standards and Technology (NIST) measured and controlled a superconducting qubit using optical fiber, rather than metal electrical wires. The work moves toward a universal quantum computer capable of solving the most difficult equations, which is estimated to require about 1 million qubits.
Superconducting circuits, a leading technology in the creation of quantum computers given their reliability and their ease of mass producibility, must operate at cryogenic temperatures. Schemes for wiring them to room-temperature electronics are complex and prone to overheating the qubits. Conventional cryostats — supercold dilution refrigerators — with metal wiring can support only thousands of qubits at the most.
Optical fibers, due to their ability to carry high volumes of signal without conducting heat, are an attractive alternative to metal wiring. However, superconducting quantum computers use microwave pulses to store and process information, which means the light must be converted precisely to microwaves.
To solve this problem, the researchers combined a fiber with additional standard components that convert, convey, and measure light at the photon level — which could then be easily converted into microwaves. The system operated at the same level as metal wiring and maintained the qubits’ fragile quantum states.

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