Complete state tomography of a quantum dot confined spin qubit

TL;DR

This paper introduces a new all-optical method for full quantum state tomography of spin qubits in quantum dots, enabling high-fidelity measurement of various electronic spin configurations using polarized light and time-resolved photon detection.

Contribution

The authors develop a novel optical technique for complete spin state tomography in quantum dots, applicable to multiple spin configurations, with demonstrated high fidelity.

Findings

Achieved 0.94 fidelity in dark exciton spin state tomography

Method applicable to conduction-band electrons, valence-band holes, and electron-hole pairs

Utilized polarized optical pulses and time-resolved polarization measurements

Abstract

Semiconductor quantum dots are probably the preferred choice for interfacing anchored, matter spin qubits and flying photonic qubits. While full tomography of a flying qubit or light polarization is in general straightforward, matter spin tomography is a challenging and resource-consuming task. Here we present a novel all-optical method for conducting full tomography of quantum-dot-confined spins. Our method is applicable for electronic spin configurations such as the conduction-band electron, the valence-band hole, and for electron-hole pairs such as the bright and the dark exciton. We excite the spin qubit using short resonantly tuned, polarized optical pulse, which coherently converts the qubit to an excited qubit that decays by emitting a polarized single-photon. We perform the tomography by using two different orthogonal, linearly polarized excitations, followed by time-resolved measurements of the degree of circular polarization of the emitted light from the decaying excited qubit. We demonstrate our method on the dark exciton spin state with fidelity of 0.94, mainly limited by the accuracy of our polarization analyzers.