> are we sure we will not need exponentially more energy or time to get the result of computation The minimum free energy that must be expended to operate a co

> are we sure we will not need exponentially more energy or time to get the result of computation The minimum free energy that must be expended to operate a computer is theoretically very close to zero, since it is not strictly necessary to use irreversible primitives[0], such as NAND gates, which is something that we do in traditional computers. For irreversible elements the theoretical requirement is about kT*ln(2) at temperature T. DNA uses about 100 kT per bit copied. I really recommend that you take a look at Feynman's introduction to quantum computing[1]. [0] http://www.cs.princeton.edu/courses/archive/fall04/cos576/papers/bennett73.html http://www.cs.princeton.edu/courses/archive/fall04/cos576/pa... [1] http://www.cs.princeton.edu/courses/archive/fall05/frs119/papers/feynman85_optics_letters.pdf http://www.cs.princeton.edu/courses/archive/fall05/frs119/pa...