Visualization of quantum dots in bilayer graphene using scanning tunneling microscopy and spectroscopy showed three times symmetry. In this three-dimensional image, the peaks represent sites of high amplitude in a wave of trapped electrons. Credit: Zehao G, Frederick Juken and Jero Velasco Jr.
Researchers used a scanning tunneling microscope to look at quantum dots in the bilayer Graphene, An important step towards quantum information technologies.
Trapping and controlling electrons in bilayer graphene quantum dots provides a promising platform for quantum information technologies. Researchers at UC Santa Cruz have now achieved the first direct visualization of quantum dots in bilayer graphene, revealing the shape of the quantum wave function of trapped electrons.
Results published on November 23, 2020 Nano Letters, Provide basic knowledge necessary to develop quantum information technologies based on bilayer graphene quantum points.
“A lot of work has been done to develop this system for quantum information science, but we have lost an understanding of what electrons look like in these quantum dots,” said corresponding author Jero Velasco Jr., an assistant professor of physics. UC Santa Cruz.
When traditional digital techniques encode information in bits represented as 0 or 1, quantum bit or qubit can represent both states at the same time due to quantum superposition. In theory, techniques based on quits would greatly increase computing speed and capacity for certain types of calculations.
Various systems, from diamonds to gallium arsenide, are being explored as platforms for making and manipulating various systems, quits. Blair graphene (two layers of graphene, which is a two-dimensional arrangement of carbon atoms in a hive lattice) is an attractive material because it is easy to produce and work with, and quantum dots in Blair graphene have desirable properties.
“These quantum points are an emerging and promising platform for quantum information technology due to their compressed spin decoherence, appropriate quantum degree of freedom control and tunability with external control voltage.”
It is important to understand the nature of the quantum dot wave function in bilayer graphene as this basic property determines many related features for quantum information processing such as electron energy spectrum, interaction between electrons and the connection of electrons in their environment.
Velasco’s team used a previously developed method to create quantum dots in a monolayer graphene using a scanning tunneling microscope (STM). With the graphene resting on the insulating hexagonal boron nitride crystal, the wide voltage applied along the STM tip generates a charge in the boron nitride that serves to limit the electrons in the boiler graphene.
“The electric field forms a coral like an invisible electric fence, which traps electrons in a quantum dot,” Velasco explained.
The researchers then used a scanning tunneling microscope to image the electronic states inside and outside the coral. Contrary to theoretical predictions, the resulting images showed broken rotational symmetry, with three peaks instead of the expected focal rings.
“We see circular symmetry rings in monolayer graphene, but bilayer graphene has three times symmetry in quantum dot states,” Velasco said. “Peaks represent sites of high amplitude in wave function. Electrons have a dual wave-particle nature, and we will visualize the wave properties of electrons in a quantum dot. “
This function provides critical information, such as the energy radiation spectrum of electrons, which is required to develop quantum devices based on this system. “It is advancing the basic understanding of the system and its potential for quantum information technology,” Velasco said. “It’s a missing part of the puzzle, and taken with the work of others, I think we’re moving in the direction of making this a useful system.”
Reference: “Visualization and Manipulation of Boiler Graphene Quantum Points with Brower Rotational Symmetry and Nontrivial Topology” Zehao G, Frederick Jukan, Ebert Quizada, Diego R. De Costa, John Davenport, Brian Girado, Kenaji Vinoki, Noniji Kobayashi, Tony Lowe and Jero Velasco Jr., 23 November 2020, Nano Letters.
DOI: 10.1021 / acs.nanolett.0c03453
In addition to Velasco, co-authors at the UC Santa Cruz co-authors include Zehao G., Frederick Jucan, and Ebert Cuazada-Lopez, co-authors from the Federal University of Sierra, Brazil, the National Institute for Materials Sciences Japan, the University of Materials Sciences Japan, . The work was funded by the National Science Foundation and Army Research Office Fees.
