Xiu-Ping Xie

A laser on a lithium niobate crystal comes to life with a current of 40 milliamps. Its light splits into two streams, each passing through a six-millimeter waveguide, where twin photon pairs are born. One stream rotates the polarization of its twins, after which both flows merge into a common channel.

Infrared light with a wavelength of about three micrometers is the working range for identifying molecules: each molecule absorbs light at its own characteristic frequencies, leaving behind "fingerprints." But until now, instruments for this range could not simultaneously provide broad frequency coverage, sufficient power, and…

Ordinary messages can be intercepted without anyone noticing. Physicists have come up with a way to create a shared secret that instantly breaks if someone so much as glances at it. Instead of paper, they use single particles of light. This quantum communication exploits a rule: any measurement changes a quantum object.