Artistic rendering shows two qubits with long coherence time and strong coupling. (Image by Dafei Jin/Argonne National Laboratory and the University of Notre Dame.

A major milestone was achieved in the new quantum computing architecture. A breakthrough was realized for retaining quantum information in a single-electron quantum bit.

Argonne and partners attained a major milestone toward quantum computing based on single-electron qubits: nearly a thousand-fold increase in coherence time and a first demonstration of scale-up.

October 26, 2023 – Coherence stands as a pillar of effective communication, whether it is in writing, speaking, or information processing. This principle extends to quantum bits, or qubits, the building blocks of quantum computing architecture. A quantum computer could one day tackle previously insurmountable challenges in climate prediction, material design, drug discovery, and more.

“Rather than 10 to 100 operations over the coherence times of conventional electron charge qubits, our qubits can perform 10,000 with very high precision and speed.”

Dafei Jin, professor at the University of Notre Dame with a joint appointment at Argonne’s Center for Nanoscale Materials.

In everyday life, 0.1 milliseconds is as fleeting as a blink of an eye. However, in the quantum world, it represents a long enough window for a qubit to perform many thousands of operations.

Unlike classical bits, qubits seemingly can exist in both states, 0 and 1. For any working qubit, maintaining this mixed state for a sufficiently long coherence time is imperative. The challenge is to safeguard the qubit against the constant barrage of disruptive noise from the surrounding environment.

The team’s qubits encode quantum information in the electron’s motional (charge) states. Because of that, they are called charge qubits.

“Among various existing qubits, electron charge qubits are especially attractive because of their simplicity in fabrication and operation, as well as compatibility with existing infrastructures for classical computers,” said Dafei Jin, a professor at the University of Notre Dame with a joint appointment at Argonne and the lead investigator of the project. ​“This simplicity should translate into low cost in building and running large-scale quantum computers.”

Jin is a former staff scientist at the Center for Nanoscale Materials (CNM), a DOE Office of Science user facility at Argonne. While there, he led the discovery of their new type of qubit, reported last year.

The team’s qubit is a single electron trapped on an ultraclean solid-neon surface in a vacuum. The neon is important because it resists disturbance from the surrounding environment. Neon is one of a handful of elements that do not react with other elements. The neon platform keeps the electron qubit protected and inherently guarantees a long coherence time.

“Thanks to the small footprint of single electrons on solid neon, qubits made with them are more compact and promising for scaling up to multiple linked qubits,” said Xu Han, an assistant scientist in CNM with a joint appointment at the Pritzker School of Molecular Engineering at the University of Chicago. ​“These attributes, along with coherence time, make our electron qubit exceptionally compelling.”

Quantum computing architecture Optimization

Following continued experimental optimization, the team not only improved the quality of the neon surface but also significantly reduced disruptive signals. As reported in Nature Physics, their work paid off with a coherence time of 0.1 milliseconds. That is about a thousand-fold increase from the initial 0.1 microseconds.

“The long lifetime of our electron qubit allows us to control and read out the single qubit states with very high fidelity,”

said Xinhao Li, a postdoctoral appointee at Argonne and the co-first author of the paper. This time is well above the requirements for quantum computing architecture.

“Rather than 10 to 100 operations over the coherence times of conventional electron charge qubits, our qubits can perform 10,000 with very high precision and speed,”

Jin said.

Yet another important attribute of a qubit is its scalability to link with many other qubits. The team achieved a significant milestone by showing that two electron qubits can couple to the same superconducting circuit such that information can be transferred between them through the circuit. This marks a pivotal stride toward two-qubit entanglement, a critical aspect of quantum computing architecture.

The team has not yet fully optimized their electron qubit and will continue to work on extending the coherence time even further as well as entangling two or more qubits.

The work was funded by the DOE Office of Basic Energy Sciences, a Laboratory Directed Research and Development award from Argonne, and Q-NEXT, a DOE Energy National Quantum Information Science Research Center headquartered at Argonne. Additional funding came from the Julian Schwinger Foundation for Physics Research and the National Science Foundation.

This research was published in Nature Physics. In addition to Jin, Han, and Li, Argonne contributors include postdocs Xianjing Zhou (co-first author) and Qianfan Chen. Other contributors include co-corresponding author David I. Schuster, a former physics professor at the University of Chicago now at Stanford University, and Xufeng Zhang, a former staff scientist at CNM and now a professor at Northeastern University. Also listed as authors are Gerwin Koolstra, Ge Yang, Brennan Dizdar, Yizhong Huang and Christopher S. Wang.

The collaborating institutions include Lawrence Berkeley National Laboratory, Massachusetts Institute of Technology, Northeastern University, Stanford University, the University of Chicago, and the University of Notre Dame.

About Argonne’s Center for Nanoscale Materials

The Center for Nanoscale Materials is one of the five DOE Nanoscale Science Research Centers, premier national user facilities for interdisciplinary research at the nanoscale supported by the DOE Office of Science. Together, the NSRCs comprise a suite of complementary facilities that provide researchers with state-of-the-art capabilities to fabricate, process, characterize, and model nanoscale materials and constitute the largest infrastructure investment of the National Nanotechnology Initiative. The NSRCs are located at DOE’s Argonne, Brookhaven, Lawrence Berkeley, Oak Ridge, Sandia, and Los Alamos National Laboratories. For more information about the DOE NSRCs.

Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation’s first national laboratory, Argonne, conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state, and municipal agencies to help them solve their specific problems, advance America’s scientific leadership, and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science.

Subscribe to Newsletter !!

Sign up for Newsletter to receive awesome content in your inbox, every week.

We don’t spam! Read our privacy policy for more info.

heshmore logo

Sign up to Newsletter receive Top Technology Stories in your inbox, every week.

We don’t spam! Read our privacy policy for more info.