The physics of Light and Sound: Examining the Quantum Nature of Nanostructures – Putting Quantum Scientists in the Driver’s Seat


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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 (yellow) photons are emitted from the nanodiamond, while uncorrelated (yellow) photons are emitted by a nearby diamond excited by surface plasmons (red).
Credit: Raphael Pooser/Oak Ridge National Laboratory, US Department of Energy

Scientists at the Department of Energy’s Oak Ridge National Laboratory are conducting fundamental physics research that will lead to more control over mercurial quantum systems and materials. Their studies will enable advancements in quantum computing, sensing, simulation, and materials development.

The researchers’ experimental results were recently published in Physical Review B Rapid Communication and Optics Letters.

Quantum information is considered fragile because it can be lost when the system in which it is encoded interacts with its environment, a process called dissipation. Scientists with ORNL’s Computing and Computational Sciences and Physical Sciences directorates and Vanderbilt University have collaborated to develop methods that will help them control — or drive — the “leaky,” dissipative behavior inherent in quantum systems.

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

Bringing perspectives from quantum information science, nanoscience and electron microscopy, the scientists exploit existing knowledge of matter and the physics of light and sound to examine the quantum nature of nanostructures — structures that measure about one-billionth of a meter.

One project focused on driving nitrogen vacancy center defects in nanodiamonds with plasmons. The naturally occurring defects are created when a nitrogen atom forms in place of the typical carbon atom, adjacent to an atomless vacancy. The defects are being investigated for use in tests of entanglement, a state that will allow substantially more information to be encoded in a quantum system than can be accomplished with classical computing.

Electrons generate an electric field. When an electron beam is applied to a material, the material’s electrons are spurred to motion — a state called excitation — creating a magnetic field that can then be detected as light. Working with plasmons, electron excitations that couple easily with light, allows scientists to examine electromagnetic fields at the nanoscale.

Matthew Feldman, a Vanderbilt University graduate student conducting doctoral research at ORNL through the National Defense Science and Engineering Graduate Fellowship program and a member of the Quantum Sensing Team, used a high-energy electron beam to excite nitrogen vacancy centers in diamond nanoparticles, causing them to emit light. He then used a cathodoluminescence microscope owned by ORNL’s Materials Science and Technology Division, which measures the visible-spectrum luminescence in irradiated materials, to collect the emitted photons and characterize high-speed interactions among nitrogen vacancy centers, plasmons and vibrations within the nanodiamond.

In other research, Jordan Hachtel, a postdoctoral fellow with ORNL’s Center for Nanophase Materials Sciences, used the cathodoluminescence microscope to excite plasmons in gold nanospirals. He explored how the geometry of the spirals could be harnessed to focus energy in nanoscale systems. Andy Lupini served the project as a microscopy consultant, providing expertise regarding equipment optimization and troubleshooting.

Precise control over nanoscale energy transfer is required to enable long-lived entanglement in a model explored by Eugene Dumitrescu, a research scientist in ORNL’s Quantum Information Science Group. Dumitrescu’s research, published in Physical Review A in late 2017, showed that the photon statistics Feldman collected could be used in calculations to show entanglement.

“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.

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 result in information leakage.

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

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

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,” he said. “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.”

Feldman thinks these are fascinating times for quantum physicists because the field of quantum computing is at the same phase classical computing was in the mid-20th century. “What excites me most is how current research could change our understanding of quantum systems and materials,” he said.

Story Source:

Materials provided by DOE/Oak Ridge National LaboratoryNote: Content may be edited for style and length.


Journal Reference:

  1. Matthew A. Feldman, Eugene F. Dumitrescu, Denzel Bridges, Matthew F. Chisholm, Roderick B. Davidson, Philip G. Evans, Jordan A. Hachtel, Anming Hu, Raphael C. Pooser, Richard F. Haglund, Benjamin J. Lawrie. Colossal photon bunching in quasiparticle-mediated nanodiamond cathodoluminescencePhysical Review B, 2018; 97 (8) DOI: 10.1103/PhysRevB.97.081404
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Max Planck ~ Father-Founder-Messiah(?) of Quantum Physics ~ Do You Quantum?



If physicists wrote history, we would now be in the second century of our era, specifically the year 116 of Planck, the German physicist who changed our view of the world when he laid the cornerstone of quantum theory in the year 1900 (of the Christian era.) And incredibly, some of his professors had recommended that he devote himself to mathematics, as physics had no future.



Max Planck portrait, circa 1930. Credit: Smithsonian Libraries

 When Max Planck (1858-1947) entered university, it seemed that in the field of physics everything had already been discovered. By the end of the nineteenth century physicists understood movement, matter, energy, heat, electromagnetism and light very well when they were considered separately, but how they related to each other was less clear. 

For example, physicists had trouble explaining the way in which hot bodies radiate energy.
Although the human body emits infrared radiation, it is not hot enough to emit visible light; however, the Sun or a red-hot nail certainly is. If the nail is heated even more, its light will be predominantly orange, yellow, green, blue and violet. 

This was no way to fit this observation with any formula constructed according to the rules of classical physics, and thus, at age 42, Planck decided to skip over these rules and pulled from his sleeve a fixed number containing 34 zeros, which he introduced between the unknowns in his equations. 

At the beginning, he used this tiny number only because it enabled him to solve the problem, but months later he realized what it meant. He had discovered that radiation was not a steady stream of energy, but rather that energy is radiated and absorbed in small indivisible portions, which he called quanta. 

That sounded as ridiculous as if someone pressing a key on an organ keyboard heard an intermittent, choppy sound.

Planck was a good musician. The concerts that he gave at his home in Berlin served as a peaceful meeting place for dedicated scientists, theologians, philosophers and linguists. 

Turning this intellectual world upside down was the furthest thing from his mind; in fact, Planck was the first to distrust his quantum theory and he tried very hard to rid himself of that tiny number (and from its revolutionary implications), which we now call Planck’s constant. 



But he failed and his theory changed physics forever, for which he received the Nobel Prize in 1918. Nor could he stop the Nazis, who came to power in the 1930s, from controlling and using the German Society of Science for their bellicose interests, an organization chaired by Planck. 

Therefore he resigned. He endured living in Germany until the end of World War II, despite losing all his scientific notes in a bombing and having his son executed, accused of plotting to assassinate Hitler.


Nernst, Einstein, Planck, Millikan and von Laue at a dinner in Berlin in 1931. Author: Unknown

Despite some initial resistance, first Einstein and then many other scientists adopted Planck’s quantum ideas to explain that light waves sometimes behave like a stream of particles, and that the electrons that revolve around atoms are simultaneously particles and waves; or to discover that there are more ways to produce light than by burning something or heating a metal. The benefits were enormous: fluorescent tubes, lasers, electronics…




Thanks to Planck and his quantum theory, physics could now be applied to the infinitely small, but in exchange it became something beyond our imagination; an electron occupies all points of its orbit simultaneously, can jump to another orbit without passing through any intermediate point and its path is unpredictable, unlike that of a moving object, such as a bullet. 
At least classical physics continued to be useful for the things we can see with our own eyes. 


As Niels Bohr, the first to use quantum theory to describe the atom, famously said: “If none of this seems shocking to you, then you have not understood it.”

It’s ALL in Our Heads ~ Studying the Consciousness to Better Understand …


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The physical brain and the conceptual mind are linked in ways that we don’t fully understand. A new collaboration is getting us closer.

How does the brain give rise to the mind? This question lies at the interface between philosophy and biology. Researchers are starting to zero in on how brain activity translates into consciousness and how we experience the world around us. The results have broad implications for cognition, brain health, human nature, and artificial intelligence.

The Azrieli Program in Brain, Mind & Consciousness is a collaboration started by the Canadian Institute for Advanced Research, bringing together a team of neuroscientists to answer these big questions.

Watch the Video

 

 

But how is it possible to probe something like consciousness? Professors Adrian Owen, Melvyn Goodale, and Lisa Saksida are all fellows of the Azrieli Program working at Western University, and they look at brain activity at the boundaries between health and dysfunction.

Owen studies patients who are losing consciousness. Communicating with patients who will soon be in a vegetative state, Owen takes functional magnetic resonance imaging (fMRI) scans to observe transitions in the brain as they lose awareness, allowing a better understanding what types of brain activity are preserved or lost.

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Along similar lines, Goodale looks at how brain damage impacts cognition, memory, sensory processing, and motor control. These insights illuminate how the brain solves problems and controls complex movement, which have implications not only in health, but also in computer science and artificial intelligence, says Goodale.

Saksida wants to understand how brain circuits are altered in Alzheimer’s Disease. Drug treatment for Alzheimer’s only treats symptoms. There is still no proven therapy that stops or reverses progression of Alzheimer’s. Saksida believes the key to effective treatments is to better understand the brain circuits involved so that they can be targeted to improve cognition.

While the mind remains a bit of a mystery, these studies are working to fill in the gaps. This understanding allows researchers to better understand how the mind emerges, how it can be damaged, and perhaps one day, how it can be imitated or repaired.