Quantum Dots Arindam Ghosh Physics research on quantum dots What are the active areas • • • • Understand nanoscale transport Materials Self-assembly of nano-structures Paradigm shift in functional electronics? Singlenanostructured Organization Effect New of electron quantum of large number offor mechanics materials transistors nanostructures Confinement transistors: Carbon for next Beyond and – scalabilityforce Coulomb silicon? generation? Utilize Nanowires New Spin architecture? effects natural for and forces Organic,magnetism intrinsic interconnects Electronics inorganic with or active and biological–systems Disorder elements nanomachines? error optimization New Ferromagnetic dielectrics: and logic high-k modeling and devices? low-k Quantum computation Single electron transistors (SET) – Operation of atomic switches Quantum Dot Gate Source Drain VSD Particle in a small box ~ 10 – 100 nm Energy-levels are quantized DE ~ 1/L2 Quantum effects only when DE>>kT VSD current current Drain current Source -Vg VSD Gate voltage (Vg) Source-drain voltage (VSD) The top-down approach Materials Plus Plus Creates Plan/Information Tools Product The bottom-up approach Self-Assembled Product Creates Plus Tools Materials with stored information New materials and protocols for SET 1. High-mobility two-dimensional electron gas 2. Nano-engineering with silicon 3. Semiconductor nanoparticles and nanowires 4. Carbon electronics with nanotubes and graphene 5. Molecules and DNA The two-dimensional electron gas in semiconductor heterostructures Si atoms Aluminum Gallium Arsenide 2D electrons Gallium Arsenide Extremely versatile Expensive Incompatible to Silicon technology Carbon nanotubes The Carbon nanotube single electron transistor Source Drain Gate Single electron transistor with nanotube rope Structures of Quantum dot Transport in single quantum dots Constant interaction model Coulomb blockade oscillations The magic numbers The Fock-Darwin Spectrum Experiment Excitation spectrum Quantum dot in quantum computation 1. Spin qubit in single quantum dot 2. Charge qubit in double quantum dots 3. Varying readout schemes Spin measurement in a quantum dot “Spin to charge” conversion Nature 2004 The protocol (1) Empty, (2) inject and wait, (3) measure Measuring spin Experiment 2D Artificial Atoms