
 NIST Ion Storage Group (Site not responding. Last check: 20071020) 
  In a quantum computer, data can be stored in qubits, each of which is a twolevel quantum mechanical system, with basis states 0> and 1> (for example). 
  However, there is a drawback to this sort of computation: according to quantum mechanics, whenever we read the state of a quantum register, we effectively collapse the superposition to one particular value and immediately destroy the parallelism. 
  A quantum logic gate is a fundamental building block of a quantum computer, just as conventional logic gates (AND, OR, ExclusiveOR, etc.) are the building blocks for traditional digital logic. 
 tf.nist.gov /ion/qucomp/quan_log.htm (992 words) 
