The fundamental building blocks of a quantum computer are quantum bits, or qubits. Some of the most common examples of qubits are based on the different energy states of single electrons.

In a recent Nature paper, a team led by the U.S. Department of Energy (DOE)'s Argonne National Laboratory has announced the creation of a new qubit platform formed by freezing neon gas into a solid at very low temperatures, spraying electrons from a light bulb's filament onto the solid and trapping a single electron there. This system shows great promise to be developed into ideal building blocks for future quantum computers.

Kater Murch, professor of physics in Arts and Sciences at Washington University in St. Louis, is a senior co-author of the paper. He explains some of the science behind the discovery in this short video animation: https://www.youtube.com/watch?v=yvlDUIcOL4A&ab_channel=WashingtonUniversityinSt.Louis

A key component in the team's new qubit platform is a chip-scale microwave resonator made out of a superconductor. (The much larger home microwave oven is also a microwave resonator.) Superconductors - metals with no electrical resistance - allow electrons and photons to interact together at near to absolute zero with minimal loss of energy or information.

"The microwave resonator crucially provides a way to read out the state of the qubit," Murch said. "It concentrates the interaction between the qubit and microwave signal. This allows us to make measurements telling how well the qubit works."

To realize a useful quantum computer, the quality requirements for qubits are extremely demanding. While there are various forms of qubits today, none of them is ideal. But the new neon system described in this paper is very good, the co-authors said in a news release shared by the DOE, and they plan to continue optimizing and improving its coherence times.

As part of Washington University's new Center for Quantum Leaps, Murch and members of his research group use nano-fabrication techniques to construct superconducting quantum circuits that allow them to probe fundamental questions in quantum mechanics.

Physics graduate student Kaiwen Zheng is working with Murch to build on work initiated at Argonne National Laboratory, developing the capabilities to trap electrons on neon in the group's facilities housed in Crow Hall on the Danforth Campus. They have developed technologies to deposit neon thin film in selective locations at cryogenic temperatures and patterned the trapping electrodes. Now, they are looking at ways to mitigate decoherence in new qubit systems, thus improving its longevity.

"At the moment, the qubit we have is based on the motion of the electron," Murch said. "We call this a charge qubit, but one of the exciting future prospects will be to convert this into a spin qubit, relating to the spin of the electron. This should make the qubit much less sensitive to its environment, increasing the quality of the qubit by orders of magnitude."

Building a better quantum bit: New qubit breakthrough could transform quantum computing
Tallahassee FL (SPX) May 05 - You are no doubt viewing this article on a digital device whose basic unit of information is the bit, either 0 or 1. Scientists worldwide are racing to develop a new kind of computer based on the use of quantum bits, or qubits, which can simultaneously be 0 and 1 and could one day solve complex problems beyond any classical supercomputers.

A team led by researchers at the U.S. Department of Energy's (DOE) Argonne National Laboratory, in close collaboration with FAMU-FSU College of Engineering Associate Professor of Mechanical Engineering Wei Guo, has announced the creation of a new qubit platform that shows great promise to be developed into future quantum computers. Their work is published in Nature.

"Quantum computers could be a revolutionary tool for performing calculations that are practically impossible for classical computers, but there is still work to do to make them reality," said Guo, a paper co-author. "With this research, we think we have a breakthrough that goes a long way toward making qubits that help realize this technology's potential."

The team created its qubit by freezing neon gas into a solid at very low temperatures, spraying electrons from a light bulb onto the solid and trapping a single electron there.

While there are many choices of qubit types, the team chose the simplest one - a single electron. Heating up a simple light filament such as you might find in a child's toy can easily shoot out a boundless supply of electrons.

One important quality for qubits is their ability to remain in a simultaneous 0 or 1 state for a long time, known as its "coherence time." That time is limited, and the limit is determined by the way qubits interact with their environment. Defects in the qubit system can significantly reduce the coherence time.

For that reason, the team chose to trap an electron on an ultrapure solid neon surface in a vacuum. Neon is one of only six inert elements, meaning it does not react with other elements.

"Because of this inertness, solid neon can serve as the cleanest possible solid in a vacuum to host and protect any qubits from being disrupted," said Dafei Jin, an Argonne scientist and the principal investigator of the project.

By using a chip-scale superconducting resonator - like a miniature microwave oven - the team was able to manipulate the trapped electrons, allowing them to read and store information from the qubit, thus making it useful for use in future quantum computers.

Previous research used liquid helium as the medium for holding electrons. That material was easy to make free of defects, but vibrations of the liquid-free surface could easily disturb the electron state and hence compromise the performance of the qubit.

Solid neon offers a material with few defects that doesn't vibrate like liquid helium. After building their platform, the team performed real-time qubit operations using microwave photons on a trapped electron and characterized its quantum properties. These tests demonstrated that solid neon provided a robust environment for the electron with very low electric noise to disturb it. Most importantly, the qubit attained coherence times in the quantum state competitive with other state-of-the-art qubits.

The simplicity of the qubit platform should also lend itself to simple, low-cost manufacturing, Jin said.

The promise of quantum computing lies in the ability of this next-generation technology to calculate certain problems much faster than classical computers. Researchers aim to combine long coherence times with the ability of multiple qubits to link together - known as entanglement. Quantum computers thereby could find the answers to problems that would take a classical computer many years to resolve.

Consider a problem where researchers want to find the lowest energy configuration of a protein made of many amino acids. These amino acids can fold in trillions of ways that no classical computer has the memory to handle. With quantum computing, one can use entangled qubits to create a superposition of all folding configurations - providing the ability to check all possible answers at the same time and solve the problem more efficiently.

"Researchers would just need to do one calculation, instead of trying trillions of possible configurations," Guo said.

The team published its findings in a Nature article titled "Single electrons on solid neon as a solid-state qubit platform." In addition to Jin, Argonne contributors include first author Xianjing Zhou, Xufeng Zhang, Xu Han, Xinhao Li and Ralu Divan. Contributors from the University of Chicago were David Schuster and Brennan Dizdar. Other co-authors were Kater Murch of Washington University in St. Louis, Gerwin Koolstra of Lawrence Berkeley National Laboratory and Ge Yang of Massachusetts Institute of Technology.

Funding for the Argonne research primarily came from the DOE Office of Basic Energy Sciences, Argonne's Laboratory Directed Research and Development program and the Julian Schwinger Foundation for Physics Research. Guo is supported by the National Science Foundation and the National High Magnetic Field Laboratory.

Research Report:Single electrons on solid neon as a solid-state qubit platform

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The quest for an ideal quantum bit
Lemont IL (SPX) May 05, 2022
New qubit platform could transform quantum information science and technology. You are no doubt viewing this article on a digital device whose basic unit of information is the bit, either 0 or 1. Scientists worldwide are racing to develop a new kind of computer based on use of quantum bits, or qubits. In a recent Nature paper, a team led by the U.S. Department of Energy's (DOE) Argonne National Laboratory has announced the creation of a new qubit platform formed by freezing neon gas into a s ... read more