Researchers at the University of Michigan, U.S. Naval Research Laboratory, and the University of California at San Diego recently demonstrated the fastest quantum computer bit that exploits the main advantage of the qubit over the conventional bit. The scientists used lasers to create an initialized quantum state of this solid-state qubit at rates of about a gigahertz, or a billion times per second. A conventional bit can be a 0 or a 1. A quantum bit, or qubit, can be both at the same time. The problem, until now, was that scientists could not stabilize that duality.
Physics professor Duncan Steel, doctoral student Xiaodong Xu, and their colleagues used lasers to coherently, or stably, trap the spin of one electron confined in a single semiconductor quantum dot. A quantum dot is like a transistor in a conventional computer. The scientists trapped the spin in a dark state in which they can arbitrarily adjust the amount of 0 and 1 the qubit represents. They call this state "dark" because it does not absorb light, which destabilizes the qubit.
Spin is an intrinsic property of the electron that isn't a real rotation. Steel compares it to the magnetic poles. Electrons are said to have spin up or down. In quantum computing, the up and down directions represent the 0s and 1s of conventional computing. Steel's approach to developing a quantum computer is to use ultrafast lasers to manipulate arrays of semiconductor quantum dots, each containing one electron. Quantum logic gates are formed by quantum mechanical interactions between the dots.
