The search for the optimal quantum bit

 

A new qubit platform has the potential to revolutionise quantum information science and technology.

You are most likely reading this on a digital device whose basic unit of information is the bit, which may be either 0 or 1. Scientists all around the world are racing to create a new type of computer based on the usage of quantum bits, or qubits.

A team led by the U.S. Department of Energy's (DOE) Argonne National Laboratory announced the creation of a new qubit platform in a recent Nature paper 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 has the potential to be perfect building blocks for future quantum computers.

The quality criteria for the qubits are quite rigorous in order to build a practical quantum computer. While there are several types of qubits available today, none of them are optimal.

What would constitute a perfect qubit? According to Dafei Jin, the project's chief investigator and an Argonne scientist, it possesses at least three remarkable properties.

It can persist in a simultaneous 0 and 1 state for an extended period of time (remember the cat!). This length is referred to by scientists as "coherence." That time would ideally be roughly a second, a time step that we can sense on a house clock in our everyday lives.

Second, the qubit may be quickly switched from one state to another. That time would ideally be roughly a billionth of a second (nanosecond), a time step of a traditional computer clock.

Third, the qubit can be readily coupled with numerous other qubits, allowing them to function in parallel. Entanglement is the scientific term for this connecting.

Although the well-known qubits are not optimal at the moment, firms like as IBM, Intel, Google, Honeywell, and many startups have chosen their favourite. They are working hard to enhance technology and commercialise it.

"Our lofty objective is not to compete with those firms, but to find and build a fundamentally new qubit technology that might lead to an ideal platform," Jin explained.

While there are many other sorts of qubits, the team picked the simplest one: a single electron. Heating up a basic light filament found in a child's toy may simply provide an infinite supply of electrons.

One of the difficulties for any qubit, including the electron, is that it is extremely susceptible to external disturbances. As a result, the researchers decided to trap one electron in a vacuum on an ultrapure solid neon surface.

Neon is one of a few inert elements, meaning it does not react with other elements. "Because of its inertness," Jin explained, "solid neon may serve as the cleanest conceivable material in a vacuum to host and safeguard any qubits from being disturbed."

A chip-scale microwave resonator built of a superconductor is an important component of the team's qubit platform. (A microwave resonator is also found in the considerably bigger household microwave oven.) Superconductors, which are metals with no electrical resistance, allow electrons and photons to interact with each other at temperatures close to absolute zero with no loss of energy or information.

"The microwave resonator is critical in reading out the state of the qubit," said Kater Murch, a physics professor at Washington University in St. Louis and a senior co-author on the work. "It focuses the interaction of the qubit and microwave signal. This enables us to take measurements that indicate how effectively the qubit functions."

"With this technology, we established significant coupling between a single electron in a near-vacuum environment and a single microwave photon in the resonator for the first time ever," said Xianjing Zhou, an Argonne postdoctoral appointee and the paper's first author. ? "This opens the door to using microwave photons to control each electron qubit and connect many of them in a quantum processor," Zhou noted.

The platform was tested in a scientific device known as a dilution refrigerator, which can achieve temperatures as low as 10 millidegrees above absolute zero. This device is one of several quantum capabilities available at Argonne's Center for Nanoscale Materials, which is a DOE Office of Science user facility.

The researchers used real-time procedures to quantify an electron qubit's quantum characteristics. These investigations proved that solid neon provides a stable habitat for the electron with very low electric noise. Most crucially, the qubit achieved quantum coherence times competitive with state-of-the-art qubits.

"Our qubits are actually as excellent as ones that others have been building for 20 years," said David Schuster, a senior co-author of the research and a physics professor at the University of Chicago. "This is merely the beginning of our research. Our qubit platform is far from optimal. We will be working to improve the coherence times. And, because this qubit platform's operating speed is exceedingly rapid, only a few nanoseconds, the prospect of scaling it up to many entangled qubits is substantial."

This extraordinary qubit platform has one additional benefit. "Because of the relative simplicity of the electron-on-neon platform," Jin explained, "it should lend itself to easy fabrication at a cheap cost." "It appears like an ideal qubit is on the horizon."

The findings were reported in the journal Nature under the headline "Single electrons on solid neon as a solid-state qubit platform." Argonne contributions include Xufeng Zhang, Xu Han, Xinhao Li, and Ralu Divan, in addition to Jin and Zhou. Brennan Dizdar and David Schuster are among the University of Chicago contributors. Other researchers include Wei Guo of Florida State University, Gerwin Koolstra of Lawrence Berkeley National Laboratory, and Ge Yang of Massachusetts Institute of Technology, in addition to Kater Murch of Washington University in St. Louis.

The DOE Office of Basic Energy Sciences, Argonne's Laboratory Directed Project and Development programme, and the Julian Schwinger Foundation for Physics Research provided the majority of funding for the Argonne research.