This work focuses on the study of phase coherent properties of low-dimensional tunnel junctions and tunable semiconductor quantum dots. These systems juxtapose competing zero-, one- and two-dimensional states separated by a precise, nanometer-scale barriers. Quantum tunneling mixes and enhances the coupling between the degenerate ground states, leading to potential development of long-lived quantum coherence in nanometer scale devices. Precise control and detection of quantum states within solid-state environment remain important challenges in condensed matter physics today. The development of macroscopic quantum coherence in these systems arises from quantum phase transitions that break the underlying symmetry. The underlying physics of phase coherent systems in nanostructured environment is largely unexplored, the dominant decoherent mechanisms unknown, and no detailed theoretical model is currently available. A series of electrical, tunneling, and dynamical measurements to study the quantum coherent transport of electrons in nanometer-scale semiconductor devices is proposed. An important feature of the work is fabrication and characterization of tunnel junctions with barriers down to few lattice spacings. Undergraduate and graduate students involved in the project will receive training in the state of art fabrication and characterization techniques. This training is intended to prepare them for careers in academe, industry or government.
This research is centered on the study of quantum coherent phenomena arising from quantum mechanical interplay of electrons in nanometer-scale semiconductor devices. Quantum mechanical coherence is normally difficult to sustain for extended period of time because of coupling to the external perturbations and presence of imperfections. The quantum coherence in these systems derives from recent advances in fabrication of semiconductor nanostructures. In these unprecedentedly clean systems, theories predict quantum phase transitions into novel collective states that can sustain exceptionally long-lived excitations. Electrical and high frequency measurements designed to probe and characterize the postulated quantum states are proposed. Control and manipulation of quantum states can be exploited for applications in quantum information processing, a field of increasing technological importance. Potential applications include quantum computation, quantum cryptography, and test of Einstein-Podolsky-Rosen (EPR) paradox within a solid state environment. Undergraduate and graduate students participating in this research receive broad training in the state of art fabrication and characterization techniques and can pursue careers in industrial or fundamental research.
