Argonne National Laboratory develops a new type of quantum bit

Produced by Photon Box Research Institute

Qubits, or qubits, rely on the exotic properties of quantum physics, which suggest that electrons, atoms, and other particles of the universe can exist in a state called "superposition," where they spin in two opposite directions at essentially the same time, or at the same time. exist in two or more places. By placing many qubits in a superposition state, a quantum computer could theoretically perform an incredible number of calculations simultaneously.

Today, Amazon, Google, IBM, and many other companies are racing to create practical quantum computers from various qubit platforms, such as superconducting circuits, trapped ions, and spin within silicon. However, all qubits are very vulnerable to external disturbances.

A research team led by the U.S. Department of Energy's (DOE) Argonne National Laboratory collaborated with Wei Guo, associate professor of mechanical engineering in the FAMU-FSU School of Engineering (a joint engineering school of Florida A&M University and Florida State University) to create a new qubit platform that The platform shows great promise for development into the quantum computer of the future. The related work was published in the journal "Nature" under the title "Single Electron on Solid Neon as a Solid-State Qubit Platform".

Associate Professor of Mechanical Engineering, FAMU-FSU School of Engineering: Wei Guo

"Quantum computers may be a revolutionary tool for performing calculations that are nearly impossible for classical computers, but there is still work to be done to make them a reality," said Wei Guo, co-author of the paper. "Through this study, We have a breakthrough: we have a long way to go in making qubits that help realize the potential of this technology."

The team created qubits by trapping individual electrons by freezing neon gas into a solid at very low temperatures, and then electrons from the heated filament land on the solid neon and emit electrons there.

A new qubit platform: Electrons from a heated filament (top) fall on solid neon (red blocks), where individual electrons (represented as wavefunctions in blue) are trapped by a superconducting quantum circuit (bottom patterned chip) Capture and manipulate.

An important quality of qubits is their ability to simultaneously remain in the 0 or 1 state for long periods of time, known as "coherence time." This time is limited and determined by the way the qubit interacts with its environment. Defects in qubit systems can dramatically shorten coherence times.

 For this reason, the research team chose to trap electrons 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; when cooled below about minus 248.6 degrees Celsius, neon freezes into a solid and exerts a pressure of more than 0.42 atmospheres.

 "Solid neon can act as the cleanest solid in a vacuum to hold and protect any qubit from destruction," said Argonne scientist Dafei Jin, principal investigator on the project.

The researchers chose one of the simplest qubits for their design -- a single electron, and by using a chip-scale superconducting resonator, the team was able to manipulate the trapped electrons, allowing them to read and store information from the qubit, enabling It can be used in future quantum computers.

A superconducting microwave resonator (gold) can use microwaves (light blue beam) to help control individual isolated electrons (orange waves) trapped on solid neon (green blocks).

After building the solid-neon platform, the team used microwave photons to perform real-time qubit manipulations on the trapped electrons and characterize their quantum properties. These tests show that solid neon provides a robust environment for electrons with very low electrical noise to interfere with it. Most importantly, the qubits achieve coherence times in quantum states that compete with other state-of-the-art qubits.

 "When you bring electrons close to the solid neon surface, the electrons in the neon atom rearrange a little bit and are repelled by the electrons, because it's like the charge repulsion, but because Neon is neutral, and this slight repulsion of electrons leaves a slightly positive charge that attracts the electrons to the surface; however, this electron cannot penetrate the surface of neon because all of its electrons' energy levels are filled Instead, this electron is repelled from the actual contact surface." Electrodes in the microchip can keep electrons trapped on solid neon in place for more than two months. Superconducting microwave resonators on the chip emit microwaves to concentrate the interaction between the qubits and the microwave signal to help control and read the qubits.

"With this platform, we have, for the first time ever, achieved strong coupling between a single electron in a near-vacuum environment and a single microwave photon in a resonator," said Xianjing Zhou, an Argonne postdoc and the paper's first author. This opens up the possibility of using microwave photons to control each electron qubit and link many of these electrons in a quantum processor."

The team's experiments show that, in optimization, the new qubit can already stay in a superposition state for 220 nanoseconds and change state in just a few nanoseconds, outperforming what scientists have been studying for 20 years. Charge-based qubits. "We will continue to improve the coherence time. And because this qubit platform operates so fast, in nanoseconds, the promise of scaling it to many entangled qubits is significant." University of Chicago professor of physics and senior co-author of the paper Author David Schuster said.

 Lead researcher Dafei Jin said that by developing qubits based on an electron's spin rather than its charge, they could develop qubits with coherence times greater than 1 second. The simplicity of the new qubit platform also lends itself to simple, low-cost fabrication.

Reference link:

[1]https://www.nature.com/articles/s41586-022-04539-x

[2]https://news.fsu.edu/news/science-technology/2022/05/04/building-a-better-quantum-bit-new-qubit-breakthrough-could-transform-quantum-computing/

[3]https://spectrum.ieee.org/neon-qubit