  Quantum computing is a unique computational approach that promises tremendous
performance that cannot be achieved by classical computers, although several
problems must be resolved to realize a practical quantum computing system for
easy use. Here, we propose a new system and theory for quantum computing that
employs single molecule confinement between electrodes. The striking features
of this system are (i) an individual molecule that exhibits quantum tunneling
can be regarded as a sequence of quantum gates, (ii) the quantum tunneling can
be encoded onto an array of quantum bits and observed without the contraction
of superposition states, and (iii) quantum computing by quantum tunneling can
be performed at room temperature. An adenine molecule is adopted as the single
molecule between electrodes, and conductance data are encoded onto quantum
states including entangled states, depending on the conductance values. As an
application of the new quantum system, molecule identification based on quantum
computing by quantum tunneling is demonstrated.
