New qubit platform: Electrons from a heated light filament (top) land on solid neon (red block), where an electron (represented as a wave function in blue) is captured and manipulated by a superconducting quantum circuit (lower color chip). Credit: Courtesy of Dafei Jin / Argonne National Laboratory

A new qubit platform can transform quantum information science and technology.

No doubt you are looking at this article on a digital device whose basic unit of information is the bit, 0 or 1. Scientists around the world are vying to develop a new type of computer based on the use of quantum bits or qubits.

In an article published on May 4, 2022 in the journal nature, a team led by the US Department of Energy’s National Argon Laboratory (DOE) announced the creation of a new qubit platform formed by freezing neon gas in solids at very low temperatures, scattering electrons from an incandescent light bulb on a solid substance and capturing a single electron there. This system has the potential to be developed into perfect building blocks for future quantum computers.

“It seems that the ideal qubit may be on the horizon. Due to the relative simplicity of the electron-on-neon platform, it must be easy to produce at a low cost. – Dafei Jin, an Argon scientist at the Center for Nanoscale Materials

In order to realize a useful quantum computer, the quality requirements of qubits are extremely demanding. Although there are different forms of qubits today, none of them are optimal.

What would make an ideal qubit? According to Dafei Jin, an Argon scientist and chief researcher of the project, he has at least three excellent qualities.

It can stay in both 0 and 1 conditions (remember the cat!) For a long time. Scientists call this long “coherence.” Ideally, this time would be about a second, a time step that we can take on a home clock in our daily lives.

Second, the qubit can be changed from one state to another in a short time. Ideally, this time would be about one billionth of a second (nanosecond), a step in the time of a classic computer clock.

Third, the qubit can be easily connected to many other qubits so that they can work in parallel with each other. Scientists call this connection entanglement.

Although currently well-known qubits are not perfect, companies such as IBM, Intel, Google, Honeywell and many startups have chosen their favorite. They are aggressively striving for technological improvement and commercialization.

“Our ambitious goal is not to compete with these companies, but to discover and build a fundamentally new qubit system that can lead to an ideal platform,” said Gene.

Although there are many options for choosing qubit types, the team chose the simplest – a single electron. Heating a simple light thread that you can find in a toy can easily launch an endless supply of electrons.

One of the challenges for every qubit, including the electron, is that it is very sensitive to disturbances from its surroundings. So the team chose to capture an electron on a super-pure solid neon surface in a vacuum.

Neon is one of a handful of inert elements that do not react with other elements. “Because of this inertia, solid neon can serve as the cleanest possible solid in a vacuum to receive and protect all qubits from disturbance,” said Gene.

A key component in the team’s qubit platform is a microwave resonator with a chip made of superconductor. (The much larger home microwave oven is also a microwave resonator.) Superconductors – metals without electrical resistance – allow electrons and photons to interact at close range.[{” attribute=””>absolute zero with minimal loss of energy or information.

“The microwave resonator crucially provides a way to read out the state of the qubit,” said Kater Murch, physics professor at the Washington University in St. Louis and a senior co-author of the paper. “It concentrates the interaction between the qubit and microwave signal. This allows us to make measurements telling how well the qubit works.”

“With this platform, we achieved, for the first time ever, strong coupling between a single electron in a near-vacuum environment and a single microwave photon in the resonator,” said Xianjing Zhou, a postdoctoral appointee at Argonne and the first author of the paper. “This opens up the possibility to use microwave photons to control each electron qubit and link many of them in a quantum processor,” Zhou added.

“Our qubits are actually as good as ones that people have been developing for 20 years.” — David Schuster, physics professor at the University of Chicago and a senior co-author of the paper

The team tested the platform in a scientific instrument called a dilution refrigerator, which can reach temperatures as low as a mere 10 millidegrees above absolute zero. This instrument is one of many quantum capabilities in Argonne’s Center for Nanoscale Materials, a DOE Office of Science user facility.

The team performed real-time operations to an electron qubit and characterized its quantum properties. These tests demonstrated that the solid neon provides 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 state-of-the-art qubits.

“Our qubits are actually as good as ones that people have been developing for 20 years,” said David Schuster, physics professor at the University of Chicago and a senior co-author of the paper. “This is only our first series of experiments. Our qubit platform is nowhere near optimized. We will continue improving the coherence times. And because the operation speed of this qubit platform is extremely fast, only several nanoseconds, the promise to scale it up to many entangled qubits is significant.”

There is yet one more advantage to this remarkable qubit platform.“Thanks to the relative simplicity of the electron-on-neon platform, it should lend itself to easy manufacture at low cost,” Jin said. “It would appear an ideal qubit may be on the horizon.”

Reference: “Single electrons on solid neon as a solid-state qubit platform” by Xianjing Zhou, Gerwin Koolstra, Xufeng Zhang, Ge Yang, Xu Han, Brennan Dizdar, Xinhao Li, Ralu Divan, Wei Guo, Kater W. Murch, David I. Schuster and Dafei Jin, 4 May 2022, Nature.
DOI: 10.1038/s41586-022-04539-x

The team published their findings in a Nature article titled “Single electrons on solid neon as a solid-state qubit platform.” In addition to Jin and Zhou, Argonne contributors include Xufeng Zhang, Xu Han, Xinhao Li and Ralu Divan. In addition to David Schuster, the University of Chicago contributors also include Brennan Dizdar. In addition to Kater Murch of Washington University in St. Louis, other researchers include Wei Guo of Florida State University, 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.

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