Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session N1: Quantum Electronics in Silicon |
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Sponsoring Units: DCMP Chair: Xuedong Hu, State University of New York at Buffalo Room: Colorado Convention Center Four Seasons 2-3 |
Wednesday, March 7, 2007 8:00AM - 8:36AM |
N1.00001: Spin Coherence in Silicon Quantum Structures Invited Speaker: |
Wednesday, March 7, 2007 8:36AM - 9:12AM |
N1.00002: Spectroscopy of Few-Electron Quantum Dots in Silicon Invited Speaker: Valley states in Si offer interesting opportunities for new physics through their interaction with spin and orbital states. At the same time, such valleys could in principle create undesired decoherence pathways in quantum devices. Recent advances have allowed new experiments studying these effects. Here we report measurements of few-electron quantum dots in Si quantum wells. Both the Kondo and Fano effects are found in this system. Valley states, if their splitting is small, would produce additional peaks in the non-linear conductance - a feature not observed in the experiments. We propose that their absence is due to enhanced valley splitting in Si quantum dots compared with quantum wells (where measurements have long shown very small splitting). We experimentally confirm such large valley splitting in Si nanostructures by performing measurements of Si quantum point contacts. We find valley splittings of order 1 meV, comparable to the largest predicted theoretical values, and much larger than numerous experiments, by ourselves and others, on laterally unconfined 2DEGs. We offer an explanation based on the role of steps and disorder at the quantum well interface. Finally, building on this understanding of the role of disorder, we discuss recent advances in silicon membranes that offer new ways to create quantum wells with lower disorder. Si membranes with thicknesses as thin as one hundred nanometers and lateral widths as large as a centimeter have been achieved. We discuss their application as hosts for quantum wells and as an enabling technology for the formation of Si/SiO2/Si multilayers in which all Si layers are single crystal. Work performed in collaboration with L.M. McGuire, C. Simmons, N. Shaji, K.A. Slinker, S. Goswami, L.J. Klein, W. Peng, M.M. Roberts, J.O. Chu, R. Joynt, M. Friesen, S.N. Coppersmith, R. Blick, M.G.Lagally, and D.E. Savage. [Preview Abstract] |
Wednesday, March 7, 2007 9:12AM - 9:48AM |
N1.00003: Single-dopant spectroscopy in triple-gate nano MOSFETs Invited Speaker: In this talk we discuss the physics of transport through a single dopant atom in semiconductor matrix to which we have spectroscopic access in a prototype silicon MOSFET. These FinFETs are three dimensional nano-scale devices consisting of a lithographically defined Si nanowire surrounded by a gate. They are fabricated on a Si-on-insulator substrate and have an active region as small as 50x60x35nm$^3$. The electronic states of the dopant appear as resonances in the low temperature conductance at energies below the conduction band edge. We can set the charge on the dopant by means of the gate electrode and observe the single and doubly charged donor state which is under magnetic field successively being occupied by a spin-up and then a spin-down electron. The binding energy of the neutral $D^0$ state is consistent with that of an arsenic donor. The $D^-$ state with two electrons shows a reduced charging energy compared to bulk Si due to the electrostatic coupling with electrodes. The level spectrum of the dopant exhibits a large separation of the ground state from excited states but is not bulk-like. This is also due to the close proximity to the gate which leads to a strong electric field and the formation of a second well close to the interface that overlaps with the donor well. The manipulation of the dopant wavefunction by an electric field (Stark effect) is a key element in Si quantum electronics, {\em e.g.} the solid-state quantum computer. We discuss the level spectrum of this gated $D^0$ system for different field strengths up to 50 MV/m and relate it to theory. At these high fields the charge still remains localized but shows a strongly altered level spectrum.\\ Recent references: H. Sellier {\em et al.}, Transport Spectroscopy of a Single Dopant in a Gated Silicon Nanowire, PRL 97, 206805 (2006) and H. Sellier {\em et al.}, Sub-threshold channels at the edges of nanoscale triple-gate silicon transistors, cond-mat/0603430 [Preview Abstract] |
Wednesday, March 7, 2007 9:48AM - 10:24AM |
N1.00004: Coherent electron spin transport and fault-tolerant semiconductor-based quantum computer architectures. Invited Speaker: The recent progress in single atom fabrication techniques for discrete gated donor systems in semiconductors offer new opportunities for coherent quantum technology applications. We review a new scheme for coherent electron spin transport by adiabatic passage (CTAP) particularly suited to atomic and solid-state systems. In a semiconductor implementation, CTAP based transport is a highly robust mechanism for shuttling electron spin states coherently along pathways defined by ionised donors spaced 20-30 nm apart. Such novel discrete transport of electrons may lead to new applications in semiconductor technology, however, as a transport mechanism for spin-encoded quantum information it is an essential development for the successful design of a strongly scalable quantum computer architecture. Using phosphorous donor electron spins in silicon as a model system, the tunnelling rates, transfer times, and effects of decoherence are calculated. The introduction of electron spin transport leads to a scalable 2D quantum computer architecture for Si:P with spatially separated interaction, storage and readout regions and incorporates non-nearest-neighbour interactions between qubits. The transport rails which provide these non-local interactions, also provide alternative pathways to avoid non-functioning regions. The fault-tolerant operation of such an architecture using CTAP for qubit transport is considered in detail. [Preview Abstract] |
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