Todays computers are built using transistors fabricated in the semiconductor silicon. Improvements in these kinds of transistors are slowing, and will come to an end in the next few years. Quantum computing is a new way of doing computation that breaks with the way computing is currently done. This approach, using quantum mechanical elements called qubits, requires new materials and approaches. These qubits and their interactions are very fragile, so protection from quantum errors is critical in creating a quantum computer. This project will investigate the formation of very robust quantum mechanical elements (quantum gates) using an effect known as topological protection. Topological protection implies using composite fermions vortexes in a p-wave superconductor which obey non-Abelian quantum statistics and are known as non-Abelian anyons. A physical realization of topological quantum gate implies the use of solid-state platforms providing a set of localized non-Abelian anyons combined with a "tweezer" to perform their braiding and fusion, and a phase detector. The project involves a collaboration of groups at the University of Notre Dame, the Tyndall National Institute in the Republic of Ireland, and Queen's University Belfast in Northern Ireland, to develop and investigate a new material system for a topological quantum gate, based on In(Ga)P/GaInP quantum Hall puddles. The goal is to produce deterministic quantum Hall puddles, containing a set of localized non-Abelian anyons, that can be used in large scale quantum computing. This project also helps in the development of human resources by providing research and training experience to undergraduate and graduate students in the areas of materials processing and characterization, nanofabrication and experimental measurements.
Protection from quantum errors is a critical point in the realization of quantum computing. One line of research in the scientific community is based on the expectation that strong protection for quantum operations will occur in quantum computation systems based on qubits built from topological states. An efficient platform for the realization of such fault tolerant topological quantum computing could be built using strongly correlated electron systems supporting the so-called Majorana zero modes (MZMs), having non-Abelian quantum statistics. Such topological quantum states were first detected in the quantum Hall effect, and they are represented by vortex composite fermion quasiparticles, known as anyons, composed of magnetic flux quanta attached to electrons/holes or defects in one and two-dimensional p-wave superconductors. Several composite fermion systems are known which supports MZMs, but routes to their implementation in a quantum processor are not well defined, primarily due to difficulties in implementing the control of qubits based on these quasiparticles. This international collaborative project aims to develop and investigate a novel system to realize MZMs: a quantum Hall puddles. Composite fermions were observed in preliminary experiments with quantum Hall puddles using near-field scanning optical microscopy. This opens the possibility for creating localized MZMs, with a number of non-trivial advantages, such as a relatively high operating temperature, zero external magnetic fields, and electrostatic "tweezers" to perform braiding and fusion. The goal is to produce deterministic quantum Hall puddles to support "large scale" development of localized MZMs using selective area epitaxy in the In(Ga)P/GaInP systems and development of scanning charge probe techniques for their characterization. Production of these quantum Hall puddles is an important step in the development of a scalable approach to quantum computers. The grown structures are studied by using structural characterization, optical spectroscopy, and nanoelectronic charge measurements, and used to fabricate candidate quantum gates.
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.
