Coherent optical writing and reading of the exciton spin state in single quantum dots

TL;DR

This paper demonstrates a method to coherently encode and decode the exciton spin state in single quantum dots using polarized light pulses, enabling precise optical control and readout of quantum information.

Contribution

It introduces a technique for direct optical writing and reading of exciton spin states in quantum dots via polarization-controlled laser pulses, establishing a one-to-one correspondence with light polarization states.

Findings

Successful mapping between light polarization and exciton spin states.

Real-time optical control of exciton spins in quantum dots.

Potential for quantum information applications using optical spin manipulation.

Abstract

We demonstrate a one to one correspondence between the polarization state of a light pulse tuned to neutral exciton resonances of single semiconductor quantum dots and the spin state of the exciton that it photogenerates. This is accomplished using two variably polarized and independently tuned picosecond laser pulses. The first "writes" the spin state of the resonantly excited exciton. The second is tuned to biexcitonic resonances, and its absorption is used to "read" the exciton spin state. The absorption of the second pulse depends on its polarization relative to the exciton spin direction. Changes in the exciton spin result in corresponding changes in the intensity of the photoluminescence from the biexciton lines which we monitor, obtaining thus a one to one mapping between any point on the Poincare sphere of the light polarization to a point on the Bloch sphere of the exciton spin.