The research appears in a recent issue of the journal Science . Quantum computation promises greatly advanced speeds for solving certain mathematical problems, including database searching and number factoring. The researchers showed this state's existence using entangled photons, paired particles of light whose conditions are intimately linked. Separate theoretical research has shown that it should be possible to perform quantum computation operations without taking the system out of the decoherence-free subspace, but until now the confirmation of this phenomenon has been lacking. In quantum physics, individual particles have no precise location and can coexist in more than one place at a time.
Polarization is the direction in which the photon's electric field vibrates.
A simplified, classical analogy of the concept of entangled photons is two coins, each equally likely to give heads or tails, that somehow always give the identical result, even if they are very far apart and flipped by different people. The experimentation demonstrating the existence of a decoherence-free subspace was facilitated by work at Los Alamos in developing an improved method for creating entangled photons. In previous research at Los Alamos, these entangled photons have been used for quantum cryptography to create unbreakable cryptographic keys that can be used to lock or unlock encrypted messages. Decoherence is a problem in quantum systems because the fragile quantum superpositions of entangled states are destroyed by unwanted coupling to the environment through which the photons are passing. Decoherence in Kwiat's system is intentionally created by passing the entangled photons through a roughly 10 millimeter piece of quartz.