1 Fundamental Problems for Universal Quantum Computers
Several fundamental problems and restrictions for universal quantum computers are pointed out. Firstly, it is shown that the halting of universal quantum computers is incompatible with the constraint of unitarity of the quantum dynamics. Secondly, the consequences of the second law of thermodynamics and the existence of time constants associated with the generation of initial states of quantum systems are shown to impose severe limits on the capabilities of quantum computers.
Using ultrafast optical-pump terahertz-probe spectroscopy, we study the THz dynamics and electronic cooling in few-layer epitaxial and CVD graphene; a microscopic theory of carrier-carrier and carrier-phonon interactions accounts quantitatively for the observed dynamics.