(SciTechDaily) The secret to building superconducting quantum computers with massive processing power may be an ordinary telecommunications technology — optical fiber.
Physicists at the National Institute of Standards and Technology (NIST) have measured and controlled a superconducting quantum bit (qubit) using light-conducting fiber instead of metal electrical wires, paving the way to packing a million qubits into a quantum computer rather than just a few thousand.
Optical fiber, the backbone of telecommunications networks, has a glass or plastic core that can carry a high volume of light signals without conducting heat. But superconducting quantum computers use microwave pulses to store and process information. So the light needs to be converted precisely to microwaves.
To solve this problem, NIST researchers combined the fiber with a few other standard components that convert, convey and measure light at the level of single particles, or photons, which could then be easily converted into microwaves. The system worked as well as metal wiring and maintained the qubit’s fragile quantum states.
“I think this advance will have high impact because it combines two totally different technologies, photonics and superconducting qubits, to solve a very important problem,” NIST physicist John Teufel said. “Optical fiber can also carry far more data in a much smaller volume than conventional cable.”
The NIST team conducted two types of experiments, using the photonic link to generate microwave pulses that either measured or controlled the quantum state of the qubit. The method is based on two relationships: The frequency at which microwaves naturally bounce back and forth in the cavity, called the resonance frequency, depends on the qubit state. And the frequency at which the qubit switches states depends on the number of photons in the cavity.
The researchers envision a quantum processor in which light in optical fibers transmits signals to and from the qubits, with each fiber having the capacity to carry thousands of signals to and from the qubit.