Why Quantum Computation?

There are several reasons why quantum computers should be studied. First, quantum computation soon will become a revolutionary new technology. Quantum computers will be extremely faster than the classical computers of our time. New technologies always offer new perspectives, not only economically. They bind the best intellectual resources of a society and are the key for sustained growth of wealth and science.

One of the most important consequences of runnable quantum computers with a register of about 1 kq (1000 qubit) will be that all current public key systems will be cracked!¹ OK, this may last one or more decades from now, but quantum computation is a problem (as well as a solution, by the way, since it offers new cryptography!) coming with certainty to e-commerce firms and intelligence services. It is an economical and a political factor of high relevance.

Another reason concerns scientific and theoretical aspects. Quantum registers are among the simplest many-particle quantum systems, being describable as “spinors.” So, quantum computers could serve as laboratories to investigate quantum effects. Especially one feature can be studied extensively, because quantum computation is based mainly upon it: “quantum entanglement.” Sloppily said, two distinguished particles can be brought into a common superposition state called entanglement which has the following strange property. If an attribute of one of the particles is measured (e.g., its spin), then the other particle has the opposite value, no matter how far they are apart; but until the measurement, the value of the property might be completely undetermined, only afterwards they are anticorrelated. This phenomenon had been rather controversial since it discovery by Einstein and his coworkers Podolsky and Rosen [1], although they thought to have found an impossible consequence of quantum mechanics and thus a counterexample to falsify this theory. However, complex as Nature is, the phenomenon could be demonstrated experimentally in the 1980's. Nowadays, nearly no one doubts the reality of entanglement, but the philosophical implications are still not clear.