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.
Chiral Quantum Antenna Based on Multilayer Metasurface
Summary Individual atoms can act as stationary qubits and thus serve as nodes in quantum computing networks or as memories for quantum repeaters. However, to successfully use qubits based on single atoms suspended in free space, photons emitted by a single atom need to be efficiently collected. Conventionally, this can be done with high […]
September 20, 2018
Development of Terahertz Polariton Lasers
Theoretical and experimental results show that the polariton lasing mechanism is a promising basis for a compact, efficient source of terahertz radiation.
July 1, 2017
Two-Dimensional Quantum Materials and Heterostructures
Two-dimensional (2D) layers just one atom thick can be stripped from certain materials, such as graphene.
June 1, 2017
Developing Tools for Quantum Characterization and Validation
Summary Coherence is essential for quantum computation; yet it introduces a unique sensitivity to any imperfections in hardware design, control systems, and the operating environment. Overcoming these sensitivities requires a hierarchy of strategies, ranging from optimization of the hardware architecture to software solutions including quantum error correction. Randomized Benchmarking Protocols are an important family of […]
October 3, 2017