For a quantum computer to outdo a classic supercomputer, at least fifty qubits are needed. Likewise, a quantum computer working with light needs at least fifty photons. And what’s more: these photons have to be almost perfectly identical. This is hard to realize, but not impossible, researchers of the University of Twente (UT) have shown.
Currently, any light source for photonic quantum processors produces photons that differ ever so slightly from one another. A filter can be used to make them identical, but that would incur losses, which could derail the quantum calculations just as well. The question is: is it possible to find an acceptable trade-off between indistinguishability and losses?
From a computational complexity point of view, the answer is yes, the UT researchers conclude. By optimizing orientations of crystal structures inside the light source, as well as dividing them up into domains, it’s possible to produce fifty ‘perfect’ photons fit for quantum computations.