S. J. Boyle

Fast optical preparation, control, and readout of a single quantum dot spin.

We propose and demonstrate the sequential initialization, optical control, and readout of a single spin trapped in a semiconductor quantum dot. Hole spin preparation is achieved through ionization of a resonantly excited electron-hole pair. Optical control is observed as a coherent Rabi rotation between the hole and charged-exciton states, which is conditional on the initial hole spin state. The spin-selective creation of the charged exciton provides a photocurrent readout of the hole spin state.

Phonon-Induced Rabi-Frequency Renormalization of Optically Driven Single InGaAs/GaAs Quantum Dots

We study optically driven Rabi rotations of a quantum dot exciton transition between 5 and 50 K, and for pulse areas of up to 14π. In a high driving field regime, the decay of the Rabi rotations is nonmonotonic, and the period decreases with pulse area and increases with temperature. By comparing the experiments to a weak-coupling model of the exciton-phonon interaction, we demonstrate that the observed renormalization of the Rabi frequency is induced by fluctuations in the bath of longitudinal acoustic phonons, an effect that is a phonon analogy of the Lamb shift.

Two-qubit conditional quantum-logic operation in a single self-assembled quantum dot

The four-level exciton/biexciton system of a single semiconductor quantum dot acts as a two-qubit register. We experimentally demonstrate an exciton-biexciton Rabi rotation conditional on the initial exciton spin in a single InGaAs/GaAs dot. This forms the basis of an optically gated two-qubit controlled rotation (CROT) quantum-logic operation where an arbitrary exciton spin is selected as the target qubit using the polarization of the control laser.

Fast high fidelity hole spin initialization in a single InGaAs quantum dot

A hole spin trapped in a quantum dot is a potential qubit. We demonstrate near unit fidelity initialization of a single hole spin in a InGaAs/GaAs Quantum dot.

Effect of detuning on the phonon induced dephasing of optically driven InGaAs/GaAs quantum dots

Recently, longitudinal acoustic phonons have been identified as the main source of the intensity damping observed in Rabi rotation measurements of the ground-state exciton of a single InAs/GaAs quantum dot. Here we report experiments of intensity damped Rabi rotations in the case of detuned laser pulses. The results have implications for the coherent optical control of both excitons and spins using detuned laser pulses.

Coherent optical control a single hole spin in a quantum dot

We report coherent optical control of a single hole spin confined to an InAs/GaAs quantum dot. The hole spin was initialized by fast dissociation of a spin-polarized electron-hole pair, and controlled by combining coherent rotations about two perpendicular axes: Larmor precession about an external Voigt-geometry magnetic field, and optical rotation caused by the geometric phase shift induced by a picosecond laser pulse.

Inversion recovery measurements of exciton fine-structure beats in a single quantum dot

We present a method for time-resolving the coherent precession of the spin of a single neutral exciton confined to an InAs/GaAs quantum dot. A pair of circularly polarized π pulses are used to pump and probe the exciton spin, rather than a pair of interferometrically stable π/2-pulses in a quantum interference type experiment, faster, technically simpler, measurements of the small 15 μeV exciton fine-structure can be made in the photocurrent regime. A small change in the fine-structure splitting with vertically applied electric-field is observed.

Picosecond coherent control of dressed states in a single quantum dot

We demonstrate picosecond control of dressed states in a single quantum dot. The Rabi oscillations of the dressed states are directly resolved in the time domain through beating of the Autler-Townes doublet.

Controlled-rotation quantum logic gate in a single self-assembled quantum dot

We demonstrate conditional exciton-biexciton Rabi rotations in a single self-assembled InGaAs quantum dot using picosecond optical excitation and photocurrent readout, thereby implementing a two-qubit controlled-rotation (C-rot) quantum logic gate.

Sequential preparation, optical control, and detection of single quantum dot hole spin

We demonstrate a Rabi rotation of the positive trion, which is conditional on the initial spin state.We use photocurrent detection to make picosecond time-resolved measurements of the single quantum dot spin.