Coherent optical control of a quantum-dot spin-qubit in a waveguide-based spin-photon interface

TL;DR

This paper demonstrates polarization-controlled coherent manipulation of a quantum-dot spin in a waveguide-based interface, achieving Ramsey interference with a dephasing time comparable to bulk media, advancing integrated quantum photonics.

Contribution

It presents the first demonstration of polarization-controlled spin control in a waveguide-based quantum-dot system with detailed analysis of coherence and limitations.

Findings

Achieved coherent control of a quantum-dot spin via polarization in a waveguide.

Measured a pure dephasing time of 2.2 ns, similar to bulk media.

Identified mechanisms limiting spin initialization fidelity and Ramsey contrast.

Abstract

Waveguide-based spin-photon interfaces on the GaAs platform have emerged as a promising system for a variety of quantum information applications directly integrated into planar photonic circuits. The coherent control of spin states in a quantum dot can be achieved by applying circularly polarized laser pulses that may be coupled into the planar waveguide vertically through radiation modes. However, proper control of the laser polarization is challenging since the polarization is modified through the transformation from the far field to the exact position of the quantum dot in the nanostructure. Here we demonstrate polarization-controlled excitation of a quantum-dot electron spin and use that to perform coherent control in a Ramsey interferometry experiment. The Ramsey interference reveals a pure dephasing time of $ 2.2\pm0.1 $ ns, which is comparable to the values so far only obtained in bulk media. We analyze the experimental limitations in spin initialization fidelity and Ramsey contrast and identify the underlying mechanisms.