Optical Preparation and Manipulation of Entangled Spin States in Quantum Dot Molecules

Ohio University, Athens OH

Investigators

Abstract

****NON-TECHNICAL ABSTRACT**** An electron possesses a property known as spin, behaving in many ways like a tiny magnet. However, unlike familiar bar magnets, when the electron's spin is measured it points in only one of two directions, sometimes referred to as 'up' or 'down' or like a computer bit "1" or "0". In addition to this binary nature, the spin can also be in a state where it is 'pointing' in both directions 'up' and 'down' at the same time. A set of spins in such a state would contain all possible combinations of a classical set of bits. The capacity for a set of quantum bits to hold such an enormous amount of information would provide an exponential increase in computing power. Therefore, the ability to measure and control these spin properties has the potential to lead to transformative new technologies such as spintronics and quantum information processing. The goal of the research is to prepare and measure spin states through optical methods in a special type of semiconductor nanostructures known as coupled quantum dots (CQD). The ability to produce a robust initial state for quantum information operations is difficult; however, the CQD system may naturally be in desirable states after relaxation and emission of a photon. This research will characterize and use the emission from the CQD itself as a trigger indicating the spins are in the necessary configuration. The research provides students with training in various aspects of optics, photonics, spectroscopy, and basic semiconductor processing and characterization while participating in timely and technologically relevant research. One of the important broader impacts of the proposal is to recruit undergraduate students to engage in advanced research providing hands-on involvement in the operation of the laboratory. ****TECHNICAL ABSTRACT**** Robust control of spin in nanostructures will have broad scientific impacts, from advances in technology to probing fundamental quantum mechanics. The goal of the research is to prepare and measure entangled spin states through optical excitation in coupled quantum dots. Implementing quantum information processing requires the ability to identify, manipulate, and measure coupled quantum states. This program will impact the field by pursuing the use of excited state properties in coupled quantum dots (CQD) for spin preparation and measurement. These results will provide a natural route to spin manipulation through the use of pulsed laser techniques. The research will specifically address the excited state spectra through the use of optical polarization signatures and photon correlation measurements. Polarization signatures can offer a clear identification of specific charge and spin states, yet, a study of these signatures in the field of CQDs is still lacking. Similarly, selective excitation into higher energy states may provide a pathway for the preparation and coherent manipulation of coupled spins. Combining these techniques with photon correlation measurements will provide a straightforward method to select and study prepared spin states in CQDs. The research provides students with training in various aspects of optics, photonics, spectroscopy, and basic semiconductor processing and characterization while participating in timely and technologically relevant research. One of the important broader impacts of the proposal is to recruit undergraduate students to engage in advanced research providing hands-on involvement in the operation of the laboratory.