Sami Amasha

Energy-Dependent Tunneling in a Quantum Dot

We present measurements of the rates for an electron to tunnel on and off a quantum dot, obtained using a quantum point contact charge sensor. The tunnel rates show exponential dependence on drain-source bias and plunger gate voltages. The tunneling process is shown to be elastic, and a model describing tunneling in terms of the dot energy relative to the height of the tunnel barrier quantitatively describes the measurements.

Spin-dependent tunneling of single electrons into an empty quantum dot

Using real-time charge sensing and gate pulsing techniques we measure the ratio of the rates for tunneling into the excited and ground spin states of a single-electron quantum dot at an AlGaAs/GaAs interface in a magnetic field parallel to the interface. We find that the ratio decreases with increasing magnetic field until tunneling into the excited spin state is completely suppressed. However, we find that by adjusting the voltages on the surface gates to change the orbital configuration of the dot, we can restore tunneling into the excited spin state and that the ratio reaches a maximum when the dot is symmetric.

Toward the manipulation of a single spin in an AlGaAs/GaAs single-electron transistor

Single-electron transistors (SETs) are attractive candidates for spin qubits. An AlGaAs/GaAs SET consists of a confined two-dimensional droplet of electrons, called an artificial atom or quantum dot, coupled by tunnel barriers to two conducting leads. Controlling the voltages on the lithographic gates that define the quantum dot allows us to confine a single electron in the dot, as well as to adjust the tunnel barriers to the leads. By applying a magnetic field, we can split the spin-up and spin-down states of the electron by an energy |g|μBB; the goal is to utilize coherent superpositions of these spin states to construct a qubit. We will discuss our attempts to observe electron spin resonance (ESR) in this system by applying magnetic fields at microwave frequencies. Observation of ESR would demonstrate that we can manipulate a single spin and allow us to measure the decoherence time T2*.

Surface-gated quantum Hall effect in an InAs heterostructure

We demonstrate low leakage surface gating of an indium arsenide heterostructure with the two-dimensional electron gas close to the surface. Gating is made possible by growing an aluminum oxide layer on top of the device. We find that the depletion point can be changed by applying a positive gate voltage and we see hysteresis when the voltage is swept below depletion.