The usefulness of most quantum computers is still significantly limited by the low number of qubits that hardware can support. But simple fiber optic cables – just like the ones used for broadband connections – could be the answer.
A team of researchers from the National Institute of Standards and Technology (NIST) found that, with just a few tweaks, optical fiber can be used to communicate with the qubits sitting inside superconducting quantum computers, with the same level of accuracy as existing methods.
Unlike the metal wires currently used, it is easy to multiply the number of fiber optic cables in a single device, which means it is possible to communicate with more qubits. According to NIST, the findings pave the way to packing a million qubits into a quantum computer. Most devices currently support less than a hundred.
Superconducting quantum computers, such as the ones that IBM and Google are building, require qubits to sit on a quantum processor that is cooled to a temperature of 15 milikelvin – colder than outer space – to protect the particles' extremely fragile quantum state.
But whether to control the qubits or measure them, researchers first need to communicate with the processor. This means a connection line must be established between room-temperature electronics and the cryogenic environment of the quantum circuit.
Typically, scientists use microwave pulses to communicate with qubits. With different frequencies and durations, the pulses can influence the state of the qubit; or researchers can look at the amplitude of the reflected microwave signal to "read" qubit-based information.
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