Control of spin dynamics with laser pulses: Generation of entangled states of donor-bound electrons in a Cd1-xMnxTe quantum well

TL;DR

This paper demonstrates the creation and control of spin entangled states in donor-bound electrons within a Cd1-xMnxTe quantum well using ultrafast laser pulses, advancing quantum information processing capabilities.

Contribution

It introduces a novel optical method to generate and manipulate multi-electron spin entanglement in a semiconductor quantum well, with potential scalability to many electrons.

Findings

Observation of overtones of donor spin-flips indicating entanglement

Enhanced entanglement signatures with above-gap excitation

Generation of coherent excitations of Mn pairs and phonons

Abstract

A quantum-mechanical many-particle system may exhibit non-local behavior in that measurements performed on one of the particles can affect a second one that is far apart. These so-called entangled states are crucial for the implementation of quantum information protocols and gates for quantum computation. Here, we use ultrafast optical pulses and coherent pump-probe techniques to create and control spin entangled states in an ensemble of up to three non-interacting electrons bound to donors in a Cd1-xMnxTe quantum well. Our method, relying on the exchange interaction between optically-excited excitons and the paramagnetic impurities, can in principle be applied to entangle an arbitrarily large number of electrons. A microscopic theory of impulsive stimulated Raman scattering and a model for multi-spin entanglement are presented. The signature of entanglement is the observation of overtones of donor spin-flips in the differential reflectivity of the probe pulse. Results are shown for resonant excitation of localized excitons below the gap, and above the gap where the signatures of entanglement are significantly enhanced. Data is also presented on the generation of coherent excitations of antiferromagnetically-coupled manganese pairs, folded acoustic phonons, exciton Zeeman beats and entanglement involving two Mn2+ ions.