Based on solid-state neon, scientists have developed new qubit platforms

Recently, the U.S. Department of Energy's (DOE) Argonne National Laboratory announced that its team has developed a new qubit platform based on solid-state neon.

New qubit platform: Electrons from the top heating filament fall onto a solid neon (red block), and individual electrons (blue for wave function) are captured and manipulated by a chip of superconducting quantum circuits at the bottom, image from Argonne National Laboratory

At present, scientists around the world are competing to develop quantum computers. As the unit of operation of quantum computing, qubits can represent the superposition of two states, 0 and 1. In the future, quantum computers could solve specific complex problems that any classical supercomputer cannot.

This time, the research team led by Argonne National Laboratory, in collaboration with The Wei Guo team of Associate Professor of Mechanical Engineering at the FAMU-FSU School of Engineering (a joint college of engineering at Florida A&M University and Florida State University), built a new qubit platform that demonstrates the potential of developing quantum computers. The results were recently published in Nature.

Image from Nature

Participants in the study also included scientists from the University of Chicago, Washington University in St. Louis, lawrence Berkeley National Laboratory (LBNL) and the Massachusetts Institute of Technology.

"Through this research, we believe that an important breakthrough has been made that will make great strides in the manufacture of qubits, helping to realize the potential of this technology." Wei Guo, co-author of the paper, said.

The team made new qubits by freezing neon gas into a solid at very low temperatures, spraying electrons from a heated filament in a bulb onto the solid, and capturing individual electrons. When neon cools to about minus 248.6 degrees Celsius and the pressure exceeds 0.42 atmospheres, it freezes into a solid.

Experimental related devices, pictures from the paper

While there are many types of qubits, the team chose the simplest one, a single electron. Heating a simple filament in a light bulb seen every day can easily emit unlimited electrons.

An important property of the qubit is that it is able to maintain a state of 0 or 1 at the same time for a long time, and is called "coherence time". But coherence time is limited, and this limitation is determined by the way the qubits interact with the environment. Defects in qubit systems can greatly reduce coherence time.

For these reasons, the team chose to trap electrons in a vacuum on an ultrapure solid-state neon surface. Neon is currently one of only six inert elements, which means it does not react with other elements.

Previous studies have used liquid helium as a medium for preserving electrons. Although liquid helium is easy to manufacture, solid neon is a material that is virtually defective and does not vibrate like liquid helium. Vibration can easily disturb the electronic state, which affects qubit performance.

"Because of this inertia, solid neon can act as the purest solid in a vacuum to carry and protect any qubits from interference." Dafei Jin, a scientist at Argonne National Laboratory and principal investigator of the project, said.

By using a chip-scale superconducting resonator, the electrodes in the microchip can keep electrons trapped on the solid neon in place for more than two months. Using the microwave emitted by the superconducting microwave resonator, the team manipulated the captured electrons, enabling them to read and store information from qubits for application to future quantum computers.

The superconducting microwave resonator (gold) can use microwaves (light blue beams) to help control an isolated electron (orange wave function) trapped on a solid piece of neon (green), pictured from Argonne National Laboratory

After building the aforementioned qubit platform, the team used microwave photons to perform qubit real-time manipulation of the captured electrons and described their quantum properties. Experimental tests have shown that solid-state neon provides a stable environment for electrons with very low electronic noise interference. At the same time, the coherence time of this qubit in the quantum state is more competitive than other qubits.

"Based on this platform, we have for the first time achieved strong coupling between individual microwave photons in a single electron and resonator in a near-vacuum environment," said Xianjing Zhou, a postdoc at Argonne National Laboratory and first author of the paper, "which opens up the possibility of using microwave photons to control each electron qubit and connect multiple qubits in a quantum processor." ”

Scientists believe that practical qubits need to have three key qualities: first, they can exhibit long-term consistency, that is, they remain superimposed for a long period of time, ideally more than one second; second, they can quickly transition from one state to another to help perform operations quickly, ideally about one billionth of a second; and third, through a quantum mechanical phenomenon called entanglement, they can be scaled up and connected with many other qubits to achieve parallel work.

The above experiments show that after optimization, the new qubits can maintain a superposition of 220 nanoseconds, and it takes only a few nanoseconds to change the state (1 nanosecond is one billionth of a second), which is better than the charge-based qubits that have been studied for 20 years.

The researchers believe that by developing qubits based on electron spins rather than charge, it is more likely to develop qubits with a coherence time of more than 1 second. At the same time, the device is relatively simple and easier to manufacture at low cost.

For now, researchers don't know how scalable the new system will be. "This is still a problem common to all qubit platforms," Dafei Jin said, "and it's not easy to achieve hundreds of qubits in the short term." ”

In the future, the team also plans to entangle two qubits based on electron spin and charge to achieve the goal of making dozens of qubits on the same chip.