Feb 25 2020
With quantum technologies as a basis for the future, spaceships and planes could be driven by the momentum of light. Quantum computers will be able to solve complex problems in fields ranging from chemistry to cryptography, with higher energy efficiency and speed compared to present-day processors.
Researchers studied a material capable of emitting bright quantum light. Materials like this could someday enable the creation of quantum computers, which would be much faster and more efficient than current computers. Image Credit: Getty Images.
However, in order to near this future, the availability of on-demand, bright, predictable quantum light sources will be incredibly important.
For this purpose, a group of material scientists, engineers, and physicists from Stanford University collaborated with labs at the University of Technology Sydney and Harvard University to examine hexagonal boron nitride, a material with the ability to emit bright light as a single photon, a quantum unit of light, at an instance. Moreover, it can emit such light even at room temperature, rendering it simpler to use than alternative quantum sources.
Sadly, there is a major disadvantage of hexagonal boron nitride: it emits light in a rainbow of distinct hues.
While this emission is beautiful, the color currently can’t be controlled. We wanted to know the source of the multi-color emission, with the ultimate goal of gaining control over emission.
Fariah Hayee, Study Lead Author and Graduate Student, Jennifer Dionne’s Lab, Stanford University
Jennifer Dionne is an associate professor of materials science and engineering at Stanford University.
The researchers used a combination of microscopic techniques to successfully trace the colorful emission of the material with respect to particular atomic defects. A team headed by Prineha Narang, study co-author and assistant professor of computational materials science at Harvard University, also proposed a new theory to predict the color of defects by describing how electrons, light, and heat interact within the material.
“We needed to know how these defects couple to the environment and if that could be used as a fingerprint to identify and control them,” stated Christopher Ciccarino, co-author of the study and a graduate student in the NarangLab at Harvard University.
The scientists have explained their technique and various categories of defects in a paper published in the Nature Materials journal.
Multiscale Microscopy
Finding the defects that cause quantum emission is somewhat similar to looking for a friend in a crowded city without a cellphone. It is known that they are there, but the entire city will have to be scanned to determine their exact location.
The researchers extended the capabilities of a unique, modified electron microscope created by the Dionne lab and used it to match hexagonal boron nitride’s local, atomic-scale structure with its exclusive color emission.
While performing hundreds of experiments, the material was bombarded with visible light and electrons, and the light emission pattern was recorded. In addition, the effect of the periodic arrangement of atoms in hexagonal boron nitride on the emission color was also analyzed.
The challenge was to tease out the results from what can seem to be a very messy quantum system. Just one measurement doesn’t tell the whole picture. But taken together, and combined with theory, the data is very rich and provides a clear classification of quantum defects in this material.
Fariah Hayee, Study Lead Author and Graduate Student, Jennifer Dionne’s Lab, Stanford University
Apart from their particular findings related to the types of defect emissions in hexagonal boron nitride, the process devised by the researchers to collect and classify these quantum spectra could, by itself, be transformative for a wide array of quantum materials.
“Materials can be made with near atomic-scale precision, but we still don’t fully understand how different atomic arrangements influence their opto-electronic properties,” said Dionne, who is also director of the Photonics at Thermodynamic Limits Energy Frontier Research Center (PTL-EFRC). “Our team’s approach reveals light emission at the atomic-scale, en route to a host of exciting quantum optical technologies.”
A Superposition of Disciplines
Currently, the focus of the group is to understand which types of defects cause specific colors of quantum emission. However, the ultimate goal is to manipulate their properties. For instance, the researchers visualize the tactical positioning of quantum emitters and switching their emission on and off for future quantum computers.
Studies in this field require a cross-disciplinary approach. This study gathered together materials scientists, electrical engineers, and both theoretical and experimental physicists. The team included Tony Heinz, professor of applied physics at Stanford’s School of Humanities and Sciences and of photon science at the SLAC National Accelerator Laboratory, and Jelena Vučković, the Jensen Huang Professor in Global Leadership in the School of Engineering.
We were able to lay the groundwork for creating quantum sources with controllable properties, such as color, intensity and position. Our ability to study this problem from several different angles demonstrates the advantages of an interdisciplinary approach.
Jennifer Dionne, Director, Photonics at Thermodynamic Limits Energy Frontier Research Center (PTL-EFRC), Stanford University
Leo Yu, a postdoctoral scholar in the Heinz lab, and Jingyuan Linda Zhang, who was a graduate student in the Ginzton Laboratory during this study, are the additional Stanford co-authors of this paper. Researchers from the University of Technology Sydney in Australia are the other co-authors of the study.
Dionne is also a member of Stanford Bio-X, an affiliate of the Precourt Institute for Energy, and a member of the Wu Tsai Neurosciences Institute at Stanford. Vučković is also a professor of electrical engineering and a member of Stanford Bio-X and of the Wu Tsai Neurosciences Institute.
The Department of Energy, Stanford’s Diversifying Academia, Recruiting Excellence Doctoral Fellowship Program, the National Science Foundation, and the Betty and Gordon Moore Foundation financially supported this study.