Not all light is the same. For example, a light bulb emits countless numbers of light particles, or photons, in all directions at any given moment, making it useful for lighting a room. In contrast, laser light emits controllable numbers of photons in controllable directions, enabling it to weld metal, read DVDs or perform eye surgery.
While not yet as common, the use of individual photons separated in space and time could find applications in secure communications and incredibly quick database searches. This is because single photons, being fundamental quantum particles, have features that set them apart from other kinds of light.
For one thing, a single photon is indivisible. If information is encoded in individual photons and sent from one party to another, an eavesdropper cannot simply intercept a small portion of the light to learn what is being transmitted without the other parties knowing. This “all or nothing” constraint enables unbreakable internet security.
Furthermore, single photons can exist in a quantum superposition. This allows a single photon to be two or more things simultaneously until it is detected; it could be both red and blue in colour, or even in different locations. Being in more than one state at the same time can allow single photons to examine multiple entries in a database simultaneously.
