A new platform of qubits: electrons with heated light filament (above) land on solid neon (red block), where one electron (represented as a wave function in blue) is captured and manipulated by a superconducting quantum chain (lower sample chip). Credit: Provided by Dafei Jin / Argon National Laboratory

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

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

In an article published May 4, 2022 in the journal Nature, a team led by the U.S. Department of Energy’s Argonne National Laboratory (DOE) announced the creation of a new qubit platform formed by freezing neon gas into solids at very low temperatures, spraying electrons from a light bulb filament, and capturing one electron there. This system can be developed into the perfect building blocks for future quantum computers.

“It would seem the perfect qubit might be on the horizon. Due to the relative simplicity of the electron-on-neon platform, it should be easy to produce at a low price ”. – Dafei Jin, an Argon scientist at the Center for Nanoscale Materials

To implement a useful quantum computer, the quality requirements of qubits are very demanding. Although there are different forms of qubits today, none of them are optimal.

What would make a perfect qubit? According to Dafei Gina, an Argon scientist and chief researcher of the project, he possesses at least three outstanding qualities.

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

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

Third, the qubit can be easily linked to many other qubits so that they can work in parallel with each other. Scholars refer to this connection as confusion.

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 pursuing technological advancement and commercialization.

“Our ambitious goal is not to compete with these companies, but to open and build a fundamentally new system of qubits, which could lead to an ideal platform,” said Gene.

Although there are many variants of qubit types, the team chose the simplest – one electron. Heating a simple light thread that you can find in a baby toy can easily release an endless supply of electrons.

One of the problems for any qubit, including for an electron, is that it is very sensitive to shocks from its surroundings. So the team decided to hold the electron on a superficial solid neon surface in a vacuum.

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

A key component of the team’s qubit platform is a chip-scale microwave resonator made from a superconductor. (A much larger home microwave oven is also a microwave resonator.) Superconductors – metals without electrical resistance – allow electrons and photons to interact together at close to[{” 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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