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Gaining Nanoscale Control over Quantum Systems

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Scientists at Oak Ridge National Laboratory (ORNL) and Vanderbilt University have developed methods to help control the leaky, dissipative behavior inherent in quantum systems and materials. To do so, they examined the quantum nature of nanostructures. ORNL researcher Eugene Dumitrescu had previously explored the need for precise control over nanoscale energy transfer to enable long-lived entanglement (Physical Review A, doi: 10.1103/PhysRevA.96.053826).

“Our goal is to develop experimental platforms that allow us to probe and control quantum coherent dynamics in materials,” said ORNL researcher Benjamin Lawrie. “To do that, you often have to be able to understand what’s going on at the nanoscale.”  

One project focused on driving nitrogen-vacancy center defects in nanodiamonds with plasmons to investigate the defects for use in entanglement. Working with plasmons allowed researchers to examine electromagnetic fields at the nanoscale.

Electron beam used in studies to enable more control over quantum systems and materials, ORNL and Vanderbilt University.

An electron beam (teal) hits a nanodiamond, exciting plasmons and vibrations in the nanodiamond that interact with the sample’s nitrogen-vacancy center defects. Correlated photons (yellow, left) are emitted from the nanodiamond, while uncorrelated photons (yellow, right) are emitted by a nearby diamond excited by surface plasmons (red). Courtesy of Raphael Pooser/Oak Ridge National Laboratory, U.S. Department of Energy.

Vanderbilt University researchers used a high-energy electron beam to excite nitrogen-vacancy centers in diamond nanoparticles, causing them to emit light. A cathodoluminescence microscope was used to collect the emitted photons and characterize high-speed interactions among nitrogen-vacancy centers, plasmons, and vibrations within the nanodiamond. The photon statistics that were collected could be used to calculate entanglement.

In a separate experiment, a cathodoluminescence microscope was used by ORNL researchers to excite plasmons in gold nanospirals. Researchers investigated how the geometry of the spirals could be harnessed to focus energy in nanoscale systems.

Nanospiral plasmon modes at low energies isolated with cathodoluminescence microscopy. Courtesy of Jordan Hachtel/Oak Ridge National Laboratory, U.S. Department of Energy.


Nanospiral plasmon modes at low energies isolated with cathodoluminescence microscopy. Courtesy of Jordan Hachtel/Oak Ridge National Laboratory, U.S. Department of Energy.

“This work advances our knowledge of how to control light-matter interactions, providing experimental proof of a phenomenon that had previously been described by simulations,” Lawrie said.

Quantum information is considered fragile because it can be lost when the system in which it is encoded interacts with its environment, in a process called dissipation. Closed systems, in which quantum information can be kept away from its surroundings, theoretically can prevent dissipation. But real-world quantum systems are open to numerous influences that can result in information leakage.

ORNL and Vanderbilt University team on exploring ways to control quantum systems and materials.

(From left) Eugene Dumitrescu, Ben Lawrie, Matthew Feldman, and Jordan Hachtel  have conducted investigations aimed at controlling the dissipative nature of quantum systems and materials. The cathodoluminescence microscope used in their work appears at right. Courtesy of Jason Richards/Oak Ridge National Laboratory, U.S. Department of Energy.

“The elephant in the room in discussions of quantum systems is decoherence. If we can model an environment to influence how a quantum system works, we can enable entanglement,” Vanderbilt researcher Matthew Feldman said.

“We know quantum systems will be leaky. One remedy is to drive them. The driving mechanisms we’re exploring cancel out the effects of dissipation,” Dumitrescu said. 

Dumitrescu used the analogy of a musical instrument to explain the researchers' attempts to control quantum systems: “If you pluck a violin string, you get the sound, but it begins to dissipate through the environment, the air. But if you slowly draw the bow across the string, you get a more stable, longer-lasting sound. You’ve brought control to the system.”

The research was published in Physical Review B (doi:10.1103/PhysRevB.97.081404) and in Optics Letters (doi:10.1364/OL.43.000927).

Published: April 2018
Glossary
nano
An SI prefix meaning one billionth (10-9). Nano can also be used to indicate the study of atoms, molecules and other structures and particles on the nanometer scale. Nano-optics (also referred to as nanophotonics), for example, is the study of how light and light-matter interactions behave on the nanometer scale. See nanophotonics.
quantum
The term quantum refers to the fundamental unit or discrete amount of a physical quantity involved in interactions at the atomic and subatomic scales. It originates from quantum theory, a branch of physics that emerged in the early 20th century to explain phenomena observed on very small scales, where classical physics fails to provide accurate explanations. In the context of quantum theory, several key concepts are associated with the term quantum: Quantum mechanics: This is the branch of...
plasmonics
Plasmonics is a field of science and technology that focuses on the interaction between electromagnetic radiation and free electrons in a metal or semiconductor at the nanoscale. Specifically, plasmonics deals with the collective oscillations of these free electrons, known as surface plasmons, which can confine and manipulate light on the nanometer scale. Surface plasmons are formed when incident photons couple with the conduction electrons at the interface between a metal or semiconductor...
nonlinear optics
Nonlinear optics is a branch of optics that studies the optical phenomena that occur when intense light interacts with a material and induces nonlinear responses. In contrast to linear optics, where the response of a material is directly proportional to the intensity of the incident light, nonlinear optics involves optical effects that are not linearly dependent on the input light intensity. These nonlinear effects become significant at high light intensities, such as those produced by...
electron beam
A stream of electrons emitted by a single source that move in the same direction and at the same speed.
nanotechnology
The use of atoms, molecules and molecular-scale structures to enhance existing technology and develop new materials and devices. The goal of this technology is to manipulate atomic and molecular particles to create devices that are thousands of times smaller and faster than those of the current microtechnologies.
nanophotonics
Nanophotonics is a branch of science and technology that explores the behavior of light on the nanometer scale, typically at dimensions smaller than the wavelength of light. It involves the study and manipulation of light using nanoscale structures and materials, often at dimensions comparable to or smaller than the wavelength of the light being manipulated. Aspects and applications of nanophotonics include: Nanoscale optical components: Nanophotonics involves the design and fabrication of...
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