Quantum Disappointment to Quantum Reserection

In theory, quantum cryptography enables two or more people to communicate with one another in complete secrecy. In practice, eavesdroppers can exploit weaknesses in the equipment used to send and receive secret keys.

Researchers in Singapore have now shown how practice can be brought closer to theory—by inserting a fairly simple passive device to prevent eavesdropping attacks involving bright light (Phys. Rev. X, doi: 10.1103/PRXQuantum.2.030304). They reckon their solution could be widely adopted in future, having shown that it can be applied to a number of popular cryptographic schemes...

Here is how it works.
Don't worry if you don't get it.
Just pretend Dr. Emilio Lizardo is doing the explaining.

Their device exploits an acrylic prism with a negative thermo-optical coefficient. Incoming light generates a gradient in temperature, and therefore in refractive-index, inside the prism that turns the acrylic into a concave lens. A small aperture placed behind the prism blocks most of the resulting diverged light beam, diminishing the beam power. more