Science & Technology

How to convert vacancies into quantum information

Simulations show that silicon and carbon vacancies pair with two silicon carbide vacancies. Red indicates the void volume at the defect site. Upper left: Cubit. Center: Formation of two pores in the crystal lattice. Right: Simulation result combining MICCoM code.Credit: University of Chicago

The team’s findings may help in the design of industrially relevant quantum materials for sensing, computing, and communications.

“Vacancy” is the sign you want to see when looking for a hotel room on a road trip. When it comes to quantum materials, vacancies are also what you want to see. Scientists create them by removing the atoms of crystalline materials.Such vacancies are qubits or Cubit, The basic unit of quantum technology.

Argonne National Laboratory of the US Department of Energy (DOE) and University of Chicago We have made breakthroughs that should help pave the way for significantly improved control over the formation of pores in the semiconductor silicon carbide.

Semiconductors are the material behind the brains of mobile phones, computers, medical devices, and so on. In these applications, the presence of atomic-scale defects in the form of pores is not desirable as it can hinder performance. However, recent studies have shown that certain types of pores in silicon carbide and other semiconductors are promising for the realization of qubits in quantum devices. Cubit applications may include non-hackable communication networks and ultra-sensitive sensors that can detect individual molecules and cells. In the future, new types of computers will also be available that can solve complex problems beyond the reach of traditional computers.

“We are just getting started. We want to make calculations much faster, simulate more defects, and identify the best defects for different applications.” — Co-appointed with Giulia Galli, Argonne National Laboratory and the University of Chicago

“Scientists already know how to create cubic-worthy vacancies in semiconductors such as silicon carbide and diamond,” said Argonne’s senior scientist in materials science, molecular engineering and chemistry at the University of Chicago. Giulia Galli, a professor at the University of Chicago, said. “But for practical new quantum applications, we need to know more about how to customize these vacancies with the required functionality.”

In silicon carbide semiconductors, the removal of individual silicon and carbon atoms in the crystal lattice results in a single vacancies. Importantly, carbon vacancies can be paired with adjacent silicon vacancies. This pair of pores, called diversity, is an important candidate for a silicon carbide qubit. The problem was that the yield for converting a single vacancy to two vacancy was as low as a few percent. Scientists are competing to develop paths to increase their yields.

“To create a real defect in a sample, we irradiate the sample with a beam of fast electrons, which knocks out individual atoms,” explains Elizabethley, a postdoctoral fellow at the University of Chicago’s Pritzker School of Molecular Engineering. To do. “But that electronic shock also creates unwanted defects.”

Scientists can then repair these defects by processing the sample at very high temperatures above 1,300 degrees Celsius. Fahrenheit, And cool again to room temperature. The secret is to develop a process to retain the required defects and repair the unwanted defects.

“By running computer simulations on an atomic scale using a high-performance computer, we can observe the formation, movement, disappearance, and rotation of defects in the sample over time at different temperatures,” Lee said. .. “This is something that cannot be done experimentally at this time.”

The team’s simulation was assisted by a combination of sophisticated computing tools, tracking individual vacancy pairs into two vacancy. Their efforts have reaped the harvest of crucial discoveries that should pave the way for new quantum devices. One is that the more silicon pores there are compared to the carbon pores at the start of the heat treatment, the more pores there will be afterwards. The other is to create stable pores and determine the optimum temperature for changing their orientation within the crystal structure without destroying them.

Scientists may be able to use the latter finding to align all vacancies in the same direction. This is highly desirable for sensing applications that can operate at many times the resolution of today’s sensors.


The video shows that emptiness turns its direction.Credit: University of Chicago

“A completely unexpected and exciting finding was that vacancies could turn into a whole new type of defect,” Lee added. These newly discovered defects consist of two carbon vacancies paired with what scientists call antisite.That’s where carbon is atom The removal of silicon atoms filled the open holes.

Simulation of the first team of this kind is possible by developing new simulation algorithms and combining computer code developed by the Midwest Computational Materials Integration Center (MICCoM), headquartered in Argonne and funded by Gari. became. Juan de Pablo is a senior scientist in the Department of Materials Science and a professor of molecular engineering at the University of Chicago, developing new algorithms based on the concept of machine learning, a type of artificial intelligence.

“Semiconductor vacancies and defect formation and movement are what we call a rare event,” de Pablo said. “Such events occur on a timescale that is too long to study with traditional molecular simulations, even on the fastest computers on the planet. Without changing the underlying physics, these events occur. It’s important to develop new ways to accelerate the outbreak. That’s what our algorithms do. They make the impossible possible. “

Lee combined various codes based on the work of MICCoM scientists Galli and de Pablo. Over the years, several other scientists have also been involved in code binding, including Francois Gygi at the University of California, Davis and Jonathan Whitmer at the University of Notre Dame. The result is an important and powerful new toolset that combines quantum theory and simulation to investigate the formation and behavior of vacancies. This applies not only to silicon carbide, but also to other promising quantum materials.

“We are just getting started,” Gari said. “We want to be able to perform calculations much faster, simulate more defects, and identify the best defects for different applications.”

See: “Stability and Molecular Pathways for Spin Defect Formation in Silicon Carbide,” Elizabeth MY Lee, Albin You, Juan J. Depablo, Julia Galli, November 3, 2021. Nature Communications..
DOI: 10.1038 / s41467-021-26419-0

The team’s paper, “Stability and Molecular Pathways for Spin Defect Formation in Silicon Carbide,” Nature Communications.. Also contributed by Postdoctoral Fellow Alvin Yu of the University of Chicago. This work was supported by the DOE office of Basic Energy Science. Computational simulations used some high-performance computing resources. Bebop, Computing Resource Center, Argonne National Laboratory. Argonne Leadership Computing Facility (ALCF), a user facility of the DOE Science Bureau. Research Computing Center at the University of Chicago. The team gained access to ALCF computing resources through an innovative and innovative computational impact (INCITE) program on DOE’s theory and experimentation.



How to convert vacancies into quantum information

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