Deterministic and tunable quantum dots based on bilayer semiconductor heterostructures

Quantum dots are nanoscale structures capable of controllably trapping single electrons. These nanoscale electronic devices exhibit quantum mechanical behaviors which can potentially be used to realize quantum computing devices that offer significant computational advantages over current computing architectures. Furthermore, these trapped electrons can act as quantum light sources, which would help enable quantum devices that are secure against cyber-attacks.

Over the past 20-years, optically driven quantum dots have been pursued in a variety of semiconductor systems and have been shown to exhibit many of the necessary properties that are required for quantum computing architectures. However, previous quantum dot architectures have not been able to reliably scale up to a large number of quantum dots with sufficient control to be used for quantum devices.

In this project, a new type of quantum dot will be engineered based on two-dimensional materials which are only a few atomic layers thick. The proposed quantum dot consists of two semiconductor monolayers stacked together to realize electrons whose energies can be tuned electrically. Using nanofabrication techniques, small holes will be patterned onto the device, which will form the quantum dot.

The quantum properties of the quantum dot will be measured using state-of-the-art optical techniques. This new quantum dot architecture has the potential to overcome previous limitations because it offers control over the quantum dot position and energy. This research aligns with the NSF Big Idea of the Quantum Leap: Leading the Next Quantum Revolution by developing material systems that have the potential to enable these new quantum information technologies.

Furthermore, the project strengthens the STEM workforce both directly and indirectly by training and mentoring graduate, undergraduate, and high school students through the proposed research, and by encouraging interest in STEM at the high school level in southern Arizona.

The overarching project objective is to achieve deterministic, scalable, and tunable quantum information devices based on optically driven spin-valley electrons in novel two-dimensional (2D) material heterostructures. Specifically, a nano-patterned gate engineering architecture will be explored to realize localized quantum states of single electrons and single excitons in MoSe2-WSe2 heterostructures.

This architecture will enable electrostatic quantum dots (eQDs) that are predicted to exhibit the desired high levels of tunability, spectral stability, and long coherence times necessary for spin-valley qubits with applications in quantum processing and quantum information storage. In solid state systems, QDs can support single photon emitter behavior and, once charged, establish a long-lived, ground-state spin qubit that can be coherently controlled optically and potentially realize long range interactions via entangled photons.

Although other solid-state spin systems (III-V QDs, vacancy centers) have demonstrated the single qubit requirements, scaling these solid-state qubits to large numbers has been limited by inhomogeneity in QDs and photonic integration challenges for vacancy centers. These challenges motivate the development of a new solid-state spin qubit system that is both deterministic and tunable—allowing for control of both the spatial placement and qubit energy.

In this project, novel eQD structures will be engineered and fabricated. The eQD quantum states and coherence properties will be measured using a combination of far-field spectroscopy and near field scanning optical microscopy. Coherent control of single spin-valley qubits will be demonstrated using coherent nonlinear spectroscopy.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.