his proposal was received in response to NSE, NSF01-157. Quantum computing offers the prospect of computational power far beyond that which could be obtained merely by scaling current technologies to ever-smaller scales. However, recent "proof-of-principle" realizations of quantum computers do not appear to be amenable to large-scale integration, like current solid-state technology. One of the outstanding unsolved problems in materials theory is understanding the feasibility of a solid-state quantum bit (qubit), the fundamental building block of a quantum computer. The proposed research will study the possibility to use a pair of extremely small semiconducting islands (with diameters less than 20 nanometers) as a solid-state qubit. The dynamics of quantum control in this system will be investigated theoretically, including the coupling to the environment, which tends to "collapse the wavefunction" of the qubit. This problem is an example of a very general problem in quantum mechanics, that of tunneling in the presence of a dissipative environment. It is closely related to an analogous problem in nuclear physics, the decay of a superdeformed nucleus. Progress in understanding the proposed mathematical model is thus likely to impact not only nanoscience and quantum computing, but also nuclear physics (femtoscience).
As a testbed for the solid-state qubit, it is proposed that such a double quantum dot can be operated as an electron pump with a quantized electrical current. Because the operating frequency of the proposed electron pump would be much greater than that of previous quantized current sources, it could be significant for metrology. The accuracy of the current quantization in this set-up is a measure of the fidelity of the qubit under repeated logical manipulations. This research is cofunded by the Divisions of Materials Research and Physics.
