Quantum computing and quantum cryptography

The manipulation of subatomic particles at the quantum level has raised eyebrows in computer science research departments lately -- so much so that several approaches to incorporating quantum mechanics into computing have been launched to varying degrees of success.
The most advanced field of research is quantum cryptography, a bit of a misnomer given that it doesn't rely on anything resembling traditional codes or ciphers. Instead of locking up data in a mathematical safe, the technique encodes messages in the clear by tweaking the quantum properties of photons -- a 1 may transform into a photon with "left" spin; a 0, into a photon with "right" spin.
The technique offers security because it is believed to be impossible to detect the spin of a photon without destroying or significantly altering it. So any eavesdropper would annihilate the message or change it enough for the recipient to notice. Two leaders in the field, IBM and Los Alamos National Laboratory, have built working devices and have demonstrated the transmission of photon streams through fiber optics and even the air.
Another technology based on the principles of quantum mechanics, quantum computing, attempts to model computation with quantum states. The field has produced tantalizing theoretical results that show how such a computer instantly could solve some of the most complicated problems such as factoring exceedingly large numbers.
Quantum computing is much further from having an impact in the lab or the enterprise than quantum cryptography. No one has built a particularly useful quantum computer yet, although some researchers have built machines that work with one or two bits. One group recently announced it is building machines that work with problems that take around 1,000 bits to describe.
--Jayant