An international team of researchers, spearheaded by North Carolina State University, has made a groundbreaking discovery in the field of quantum materials, demonstrating both the mechanism and the necessary material conditions for superfluorescence to occur at room temperature.
This pivotal work, published in Nature, offers a long-sought-after blueprint for designing advanced materials capable of exhibiting exotic quantum states – such as superconductivity, superfluidity, or superfluorescence – at high temperatures, potentially revolutionizing fields from quantum computing to energy transmission.
Superfluorescence is a collective quantum optical phenomenon where a group of atoms or molecules spontaneously emit light in a highly coordinated, coherent manner. It occurs when many atoms are initially prepared in an excited state and then emit photons together as a synchronized ensemble, rather than independently.
Unlike normal fluorescence where individual atoms emit light randomly and independently, superfluorescence involves many atoms acting as a single quantum system. The atoms become correlated through their interaction with the shared electromagnetic field.
Superfluorescence was first predicted theoretically by Robert Dicke in 1954 (sometimes called “Dicke superradiance”) and has since been observed in various systems including atomic gases, quantum dots, and organic molecules.
It has potential applications in quantum optics, precision timing, and could be relevant for developing new types of coherent light sources.
Historically, the tantalizing promise of macroscopic quantum coherence – where groups of quantum particles act in unison like a single, giant quantum entity – has been hampered by the absolute necessity for super-cold, or cryogenic, conditions.
The “thermal noise” inherent at higher temperatures typically disrupts the delicate synchronization required for these exotic quantum phase transitions.
“In this work, we show both experimental and theoretical reasons behind macroscopic quantum coherence at high temperature,” explains Kenan Gundogdu, professor of physics at NC State and corresponding author of the study.
“In other words, we can finally explain how and why some materials will work better than others in applications that require exotic quantum states at ambient temperatures.”
Previous research by Gundogdu and his colleagues had hinted that the unique atomic structure of certain hybrid perovskites offered a protective shield, allowing quantum particles to maintain their coherence against thermal interference.
Specifically, they observed the formation of “large polarons” – groups of atoms bound to electrons – which insulated light-emitting dipoles, enabling superfluorescence.
The new study delves deeper, uncovering how this insulating effect functions.
By exciting electrons within the hybrid perovskite using a laser, the researchers witnessed a remarkable phenomenon: large groups of polarons coalescing into an ordered formation, a collective unit they termed a “soliton.”
Gundogdu vividly illustrates the concept: “Picture the atomic lattice as a fine cloth stretched between two points. If you place solid balls – which represent excitons – on the cloth, each ball deforms the cloth locally. To get an exotic state like superfluorescence you need all the excitons, or balls, to form a coherent group and interact with the lattice as a unit, but at high temperatures thermal noise prevents this.”
He continues, “The ball and its local deformation together form a polaron. When these polarons transition from a random distribution to an ordered formation in the lattice, they make a soliton, or coherent unit. The soliton formation process dampens the thermal disturbances, which otherwise impede quantum effects.”
This crucial “soliton” formation isn’t haphazard.
“A soliton only forms when there is enough density of polarons excited in the material,” notes Mustafa Türe, an NC State Ph.D. student and co-first author of the paper.
“Our theory shows that if the density of polarons is low, the system has only free incoherent polarons, whereas beyond a threshold density, polarons evolve into solitons.”
The experimental validation of this theory was a significant breakthrough.
“In our experiments we directly measured the evolution of a group of polarons from an incoherent uncorrelated phase to an ordered phase,” adds Melike Biliroglu, a postdoctoral researcher at NC State and co-first author of the work.
“This is one of the first direct observations of macroscopic quantum state formation.”
To further solidify their findings, the team collaborated with Volker Blum at Duke University to calculate the lattice oscillations responsible for thermal interference, and with Vasily Temnov at CNRS and Ecole Polytechnique to simulate the recombination dynamics of the soliton in the presence of thermal noise.
These collaborations confirmed the experimental results and verified the intrinsic coherence of the soliton.
This research marks a significant leap forward in understanding the elusive behavior of quantum materials at higher temperatures.
“This work shows a quantitative theory and backs it up with experimental results,” Gundogdu said.
The study was supported by the Department of Energy, Office of Science. Collaborating institutions included Duke University, Boston University, and the Institut Polytechnique de Paris.
