Enlarge / Like this, but for photons. (credit: US Consumer Product Safety Commission )
As happened in the past with classical computers, researchers are still searching for a good way to implement quantum computers.
It isn’t so much that researchers don’t know what they want to build; it’s more of a question of searching for the right materials to create a scalable quantum computer.

The current leader in the field—although I’m sure many would dispute this—uses the currents in loops of superconducting material.

This has the advantage of being based on very traditional manufacturing processes.

And because it is manufactured, many properties are under design control.
This has led to quite rapid progress, but there has been one limitation: long-distance communication. Quantum computers need to be able to communicate with other quantum computers, even with other parts of the same quantum computer.

But superconducting loops all speak to each other in the tones of microwaves, which are low energy and easily disrupted. Now, however, a path to using visible light to transfer quantum information between qubits has opened up.

This could revolutionize the development of quantum computers based on superconducting currents.
Loopy qubits
The fundamental unit of information in a quantum computer is a qubit.
It’s not quite analogous to a bit, which has one of two possible values: a one or a zero. While a qubit has two quantum states that we label as a one and a zero, it is incorrect to think of the qubit storing a one or a zero.
It is more correct to think of it as holding a one and a zero.
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