Artistic rendering of a chemically modified carbon nanotube hosting a spinning electron as a qubit. Image: Argonne National Laboratory.
Artistic rendering of a chemically modified carbon nanotube hosting a spinning electron as a qubit. Image: Argonne National Laboratory.

Scientists are vigorously competing to transform the counterintuitive discoveries about the quantum realm from a century past into technologies of the future. The building block in these technologies is the quantum bit, or qubit. Several different kinds are under development, including ones that use defects within the symmetrical structures of diamond and silicon. They may one day transform computing, accelerate drug discovery, generate unhackable networks and more.

Working with researchers from several universities, scientists at the US Department of Energy (DOE)’s Argonne National Laboratory have discovered a novel method for introducing spinning electrons as qubits in a host nanomaterial. Their test results, reported in a paper in Nature Communications, revealed record-long coherence times — the key property for any practical qubit because it defines the number of quantum operations that can be performed in the lifetime of the qubit.

Electrons have a property analogous to the spin of a top, with a key difference. When tops spin in place, they can rotate either to the right or left. Electrons can behave as though they were rotating in both directions at the same time. This is a quantum feature called superposition.

Being in two states at the same time makes electrons good candidates for spin qubits. But spin qubits need a suitable material to house, control and detect them, as well as read out information in them. With that in mind, the team chose to investigate a nanomaterial that is made only from carbon atoms, has a hollow tubular shape and a thickness of only about 1nm – a carbon nanotube.

“These carbon nanotubes are typically a few micrometers long,” said Argonne’s Xuedan Ma. “They are mostly free of fluctuating nuclear spins that would interfere with the spin of the electron and reduce its coherence time.”

Ma is a scientist in Argonne’s Center for Nanoscale Materials (CNM), a DOE Office of Science user facility. She also holds appointments at the Pritzker School of Molecular Engineering at the University of Chicago and the Northwestern-Argonne Institute of Science and Engineering at Northwestern University.

The problem the team faced is that carbon nanotubes by themselves cannot maintain a spinning electron at one site. It moves about the nanotube. Past researchers have inserted electrodes nanometers apart to confine a spinning electron between them. But this arrangement is bulky, expensive and challenging to scale up.

The current team devised a way to eliminate the need for electrodes or other nanoscale devices for confining the electron. Instead, they chemically alter the atomic structure of a carbon nanotube in a way that traps a spinning electron in one location.

“Much to our gratification, our chemical modification method creates an incredibly stable spin qubit in a carbon nanotube,” said chemist Jia-Shiang Chen, who is a member of both CNM and a postdoctoral scholar in the Center for Molecular Quantum Transduction at Northwestern University.

The team’s test results revealed record-long coherence times compared with qubit systems made by other means – 10 microseconds.

Given its small size, the team’s spin-qubit platform can be more easily integrated into quantum devices and permits many possible ways to read out the quantum information. Also, the carbon tubes are very flexible and their vibrations can be used to store information from the qubit.

“It is a long way from our spin qubit in a carbon nanotube to practical technologies, but this is a large early step in that direction,” Ma said.

This story is adapted from material from Argonne National Laboratory, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.