Photon Entanglement - Applications

Applications

An important area where entanglement can be applied is in computer microchips. Normally, the size of a microchip is restricted by the wavelength of the photon carving the chip, being able to carve at one-half of the wavelength in accordance with the Rayleigh criterion. However, entangled photons can be separated and then rejoined together, and since they have exactly the same position the constructive interference doubles the energy so that it can carve as low as 1/4 of the original wavelength and thus make microelectronic devices half the size of what was previously possible. Entangling more than one photon can lead to even greater energies, hitting 1/6 and theoretically even 1/8 the original wavelength.

Instantaneous communication by means of quantum entanglement is actually impossible because neither side can manipulate the state of the entangled particles, they can only measure it (see No-communication theorem). This fact means that if you measure one particle you cannot infer anything meaningful about the observers measuring the other particle, except you know what state they will measure, or have already measured. Thus causality is preserved.

Photon entanglement may soon be used as a Covert channel if not already. This is due to it being impossible to eavesdrop on the channel, at least for now. Although it may be possible to entangle additional photons and thus observe the communication or tamper with it in the future, this would most likely require physical access to the photons. See the No cloning theorem for additional information.

It may soon be possible to mass produce entangled photons since scientists have discovered a way to produce these photons using a simple semi-conductor. This approach is not only simpler then the previous nonlinear optical crystals such as beta barium borate (BBO) or Potassium titanyl phosphate (KTP), but also produces them on demand as opposed to the one in ten billion being downconverted into entangled photons within the crystal. The semiconductor is made from gallium arsenide used in optoelectronics, and dots made from indium arsenide mere nanometers in size; this compound is convenient since it self-organizes into dots. Currently it has to be produced at low temperatures to produce infrared light, but some companies predict that it can be produced at room temperature soon.