Prof. Jacob Olshansky, Amherst College, "Harnessing spin polarization in photoexcited quantum dots"

Generating spin polarization is useful for both quantum computing and quantum sensing technologies. This talk will highlight two systems that harness spin polarization in quantum dots in different ways.

In the first system, a series of tunable quantum dot–organic molecule conjugates that can host photogenerated spin-based qubit pairs (SQPs) are presented. The photogenerated qubit pairs, composed of a spin-correlated radical pair (SCRP), are particularly intriguing since they can be initialized in well-defined, non-thermally populated, quantum states.

The materials underlying this system are an organic molecular chromophore electron donor and a quantum dot acceptor composed of ZnO. A series of quantum dot–molecule conjugates are prepared that possess variable geometries.

Photoexcited charge separation generates long-lived charge-separated radical pairs that are probed with light-induced time-resolved electron paramagnetic resonance (TR-EPR) spectroscopy. Notably, the EPR spectra of the radical pairs are dependent on the geometry of this highly tunable system.

Overall, this work demonstrates the power of synthetic tunability in adjusting the spin specific addressability, satisfying a key requirement of functional qubit systems. In the second system, the synthesis and photophysics of manganese-doped indium phosphide quantum dots are presented.

The spin configuration of manganese allows for exciton storage in the quantum dots for milliseconds. We use time-resolved temperature-dependent photoluminescence spectroscopy to show that there is a thermal equilibrium between the quantum dot excitonic state and the localized excited dopant.

At room temperature, these materials display exciton emission that is delayed by more than a millisecond. Work is ongoing to measure the magnetic field effect in these materials.