Fast and High-Fidelity State Preparation and Measurement in Triple-Quantum-Dot Spin Qubits

High-fidelity gates in quantum dot spin qubits.

Several logical qubits and quantum gates have been proposed for semiconductor quantum dots controlled by voltages applied to top gates. The different schemes can be difficult to compare meaningfully. Here we develop a theoretical framework to evaluate disparate qubit-gating schemes on an equal footing. We apply the procedure to two types of double-dot qubits: the singlet-triplet and the semicon...

Quantum-dot spin-state preparation with near-unity fidelity.

We have demonstrated laser cooling of a single electron spin trapped in a semiconductor quantum dot. Optical coupling of electronic spin states was achieved using resonant excitation of the charged quantum dot (trion) transitions along with the heavy-light hole mixing, which leads to weak yet finite rates for spin-flip Raman scattering. With this mechanism, the electron spin can be cooled from ...

Weak measurement of quantum dot spin qubits

The theory of weak quantum measurements is developed for quantum dot spin qubits. Building on recent experiments, we propose a control cycle to prepare, manipulate, weakly measure, and perform quantum state tomography. This is accomplished using a combination of the physics of electron spin resonance, spin blockade, and Coulomb blockade, resulting in a charge transport process. We investigate t...

High-fidelity initialization of long-lived quantum dot hole spin qubits by reduced fine-structure splitting

Fast, High Fidelity Quantum Dot Spin Initialization without a Strong Magnetic Field by Two-Photon Processes

Recent demonstrations of cavity quantum electrodynamics (QED) effects with semiconductor quantum dots (QDs) coupled to microcavities [1, 2, 3, 4, 5] show that these systems are robust and scalable platforms for quantum information science. The QD-cavity QED experiments performed so far treat each QD as a two-level quantum system consisting of a ground state and the single exciton excited state....