The world's first single photon machine

Nanotechnologists at the University of Southern California (USC) are building a device dubbed the Einstein Emitter which will deliver a single photon produced by a single electron. Coupled with a detector, this will be the the first real-world photon computer system.

Nanotechnologists at the University of Southern California (USC) are building a device dubbed the Einstein Emitter which will deliver a single photon produced by a single electron. At the same time, other researchers at the University of Texas/Austin are developing the detector for this single photon. Together, they are assembling the first real-world photon computer system. These photon machines will first be used in cryptographic devices. But later, these photonic systems might lead to smaller and faster general purpose computers.

Why such photon machines would be used for cryptography?

John O'Brien of the Viterbi School’s electrical engineering department, principal investigator in the project, says that theory, and particularly a classic paper by mathematician Peter Shor, indicate that a computational device using quantum phenomena to represent information should be able to perform certain tasks, particularly securely encrypting and decrypting messages, far faster than traditional chips.

Recent studies have suggested that devices that can both create and detect single photons could be used to perform these encrypting and decrypting tasks. But building single photon emitters is not that easy.

Below is a picture of the USC's Einstein Emitter under electron microsope (Credit: USC).

The Einstein Emitter

So, if this is difficult, how did they build this emitter? Here are some theoretical explanations to start with.

The "quantum dots" that the USC team will use to generate single photons, one at a time, are ultra-small ("nanoscale") devices that perform the photoelectric process Einstein explained in reverse. The dots are minute particles of a highly engineered semiconductor material. Classic photoelectric materials produce electric current -- electrons -- when struck by sufficiently energetic photons, in a mechanism Einstein explained. The same mechanism, working in reverse, sends out a single photon when energized by an electron.

And now, let's look at more practical explanations about how these scientists built arrays of microscopic photonic crystals.

Creating the crystal is only the first step. To activate it in a useful way, an elaborate electronic control system is needed, which will feed a single electron of precisely the correct electric potential into the system at precisely the right time. This potential is so minute that, to avoid introduction of potentially stray electrons into the system, the electronics will function at extremely low temperature -- 10 Kelvin, (-441 Fahrenheit, -263 Celsius).
Using resonance effects, the group hopes to speed up the rate of production of single photons, so that the process happens in 100 picoseconds -- ten times faster than existing devices.

While these preliminary results look promising, I doubt we'll see practical applications anytime soon. Even the researchers don't know when such devices will be fully functioning in their labs.

General purpose computers using this embryonic technology are probably more than a decade away.

Sources: USC Viterbi School of Engineering, September 2, 2005; and various web sites

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