Quantum Computational Research First Project Selected for Strategic Applications Program (SAP)

By Herbert Morgan, NCSA

An investigation into the potential role of electron spin in the development of quantum devices has been selected as one of NCSA's Strategic Applications Program (SAP) projects. The project, "High Performance Algorithms for Scalable Spin-Qubit Circuits with Quantum Dots," seeks to understand what it takes to create new opportunities for making high-performance devices based on the manipulation of the electron spin to define a qubit in quantum dots for quantum information processing. A qubit is the basic unit of information in a quantum computer.

This project is ideal for SAP because it involves a small research group that has large computational needs. The research group will also benefit by collaborating with the NCSA staff, which can assist with code optimization, data management, and visualization.

The Scientific Goals of This Project

The PI, Jean-Pierre Leburton, a professor in the Department of Electrical and Computer Engineering, worked with SAP Coordinator Nahil Sobh to prepare a brief description of the project in terms of its scientific objectives. The goals of this project are summarized here; a full description of the project is available from the SAP Web site.

"One of the greatest scientific and engineering challenges of this decade is the realization of a quantum computer. In this context, a solid-state system is highly desirable because of its compactness, scalability and compatibility with existing semiconductor technology. For this purpose, the use of spin states (S) rather than charge-states as qubits in semiconductor materials is relatively appealing because of their relative insensitivity to electric noise in the device environment.

"For single-spin operations, carrier confinement is a major issue... [several developments have] placed this objective within experimental reach. The ability to manipulate the spin S of electrons by combining gate electrodes and magnetic fields provides the necessary ingredients for controlling spin-qubit operations in nanoscale devices. This scenario has the advantage of relying on established semiconductor fabrication techniques, while semiconductor materials enjoy long spin coherence times, which is of utmost importance for preserving quantum information during many qubit operations.

"Consequently, there is a need for comprehensive high-performance computer tools capable of simulating quantum operation within the device environment while describing the microscopic reality of quantum effects in nanostructures."

The Road to SAP

How was this project identified as a potential SAP project? "First of all," said Sobh, "I was trying to find someone on campus who does computations, but who was unaware of the potential benefits of working with NCSA..." During his search, Sobh found Leburton, who was conducting research on quantum devices.

"He was asking what kind of resources we have and support we can provide," said Sobh, "and he got very interested when I told him what was available." Leburton and his team were running their codes on workstations and came to the conclusion that the single-processor machines did not meet the challenges of their research, which required simulating subtle many-body effects in quantum dots and quantum wires.

Sobh said that because researchers are so intently focused on their work and getting to results, they may not be aware, in the beginning, of the resources and logistic support provided by NCSA. But once they reap the rewards, they want to explore more and on a larger scale.

Working with the NCSA's Allocations team, Leburton received 10,000 hours to run his project. It was soon discovered that the linear solver within the algebra portion of their code was too slow for their self-consistent scheme. Sobh, who is also the manager of the Performance Engineering and Computational Methods (PECM) group, proposed using PETSc (Portable, Extensible Toolkit for Scientific Computation). PETSc is a suite of data structures and routines for the uni- and parallel-processor solution of large-scale scientific application problems modeled by partial differential equations. It worked, and the next step, according to Sobh is to let PETSc communicate with their code.

Generally, SAP projects last six months, but may be extended. Prior to this project's acceptance in SAP, two months were spent learning what Leburton's team was doing, looking at their code, understanding how their application works, and evaluating their needs. "Getting to know what they have; it's like getting married," said Sobh.

John Fettig, a graduate research assistant at NCSA, will work with Leburton's team and Sobh on this project.