Summary
As monolayers, transition metal dichalcogenides (TMDCs) – such as tungsten diselenide (WSe2) – become direct-bandgap semiconductors capable of emitting light. Compared to conventional direct-bandgap semiconductors, such as III-V semiconductors like GaAs, excitons (quasiparticles made of an electron hole bound with an electron) and single-layer TMDCs (SL-TMDCs) have much stronger binding energy. Excitons and SL-TMDCS also have an extra degree of freedom called “k-valley index” or “pseudospin”, which couples with their spin in the presence of light. Due to the way the spin and valley degrees of freedom couple together, excitons in SL-TMDCs can act as a two-level quantum system, whose quantum state can be initialized and controlled with photons of specific polarization, either collectively or as individual excitons confined in quantum dots. To utilize these two-level quantum systems as solid-state qubits in a quantum device, the spectral and temporal dynamics of SL-TMDC excitons in the presence of electric and optical fields needs to be investigated. However, some of the exciton processes in SL-TMDCs happen at timescales that are beyond the resolution of streak cameras used for studies of excitons in conventional semiconductors. To overcome this problem, this research will use femtosecond photoluminescence up-conversion (fsPLupC). This technique relies on sum frequency generation that arises when the photoluminescence signal overlaps with a reference femtosecond (fs) pulse inside a non-linear crystal. It can reveal both temporal and spectral information about the studied processes, potentially with a resolution better than 100 fs. This work will provide a greater fundamental understanding of TMDC monolayers and explore their potential use as ‘valleytronic’ based quantum devices.
Figure 1. Bloch sphere depiction of the optical addressability of bright excitons in a Single-Layer TMDC. Bright excitons with pseudospin ├ |↑⟩ or ├ |↓⟩ are created (annihilated) via absorption (emission) of a right-handed or a left-handed circularly polarized photon (red and blue arrows, respectively). The equator corresponds to equal superpositions of bright excitons in the two valleys and are therefore generated by absorption of linearly polarized photons denoted by green arrows.
Related Content
Extensible Technology for a Medium-Scale Superconducting Quantum Processor
Summary Superconducting quantum bits, or qubits, use circuits made from superconducting materials to harness quantum mechanical states. These devices contain many atoms, but can behave as simple, controllable qubits. We are building technologies for the control and measurement of superconducting qubits to enable the first demonstration of an extensible, medium-scale quantum processor. Our approach […]
November 28, 2016
Engineering and Characterizing Programmable Interaction Graphs in a Trapped Ion Quantum Simulator
Summary Quantum simulators have the potential to bring unprecedented capabilities in areas such as the discovery of new materials and drugs. Engineering precise and programmable interaction graphs between qubits or spins forms the backbone of simulator applications. The trapped ion system is unique in that the interaction graph between qubits can be programmed, in […]
July 24, 2018
Spin-transfer Torque Magnetic Random Access Memory for On-chip Spin Information Storage
Summary Leakage power in semiconductor memories, such as Dynamic Random Access Memory (DRAM) and Static Random Access Memory (SRAM), can be substantial and is one of the limits for scalability of classical electronics. This is attributed to the fact that the information stored is volatile, requiring constant refreshing, as well as reprogramming upon powering […]
August 6, 2018
Magnetoelectric Coupling in New Composite Multiferroic Nanostructures as High-Density Quantum Multistate Memory Elements
Summary Magnetoelectric multiferroics are materials that exhibit correlated ferroelectric and ferromagnetic properties (i.e., a magnetoelectric effect). The resulting ability of these materials to simultaneously store data in electric polarization and magnetic moment could increase data storage density and data processing speed while reducing energy consumption. This project aims to design and fabricate new composite multiferroic […]
February 1, 2023