  We propose a new type of molecular transistor, the Quantum Interference
Effect Transistor (QuIET), based on tunable current suppression due to quantum
interference. We show that any aromatic hydrocarbon ring has two-lead
configurations for which current at small voltages is suppressed by destructive
interference. A transistor can be created by providing phase relaxation or
decoherence at a site on the ring. We propose several molecules which could
tunably introduce the necessary dephasing or decoherence, as well as a proof of
principle using a scanning tunneling microscope tip. Within the self-consistent
Hartree-Fock approximation, the QuIET is shown to have characteristics
strikingly similar to those of conventional field effect and bipolar junction
transistors.
