Q-Cryptography

Now that you have learned about the fundamentals of Q-Mechanics, we will talk about Q-Cryptography. The curious story of its first application began in the 70s, when a Ph.D. candidate, Stephen Wiesner, from Columbia University had an idea. He invented a special kind of money that (theoretically) couldn't be counterfeited: quantum money. Wiesner's quantum money mostly relied on quantum physics regarding photons.

Suppose that we have a group of photons traveling all in the same direction on a predetermined axis. Moving in space, a photon has a vibration known as the polarization of the photon. The following diagram shows what we are talking about:

Figure 8.7 — Photon polarization

As you can see, photons spin their polarization in all directions. Still, if we place a filter, called a polaroid, oriented vertically, we will see that photons oriented vertically will pass across the filter 100% of the time. However, most of...