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Researchers at Rice University have made a groundbreaking advance in quantum physics by directly observing a phenomenon known as the superradiant phase transition (SRPT), a prediction that dates back over fifty years. This discovery holds promise for transformative applications in the realms of quantum computing, communication, and sensing.
Superradiant phase transition occurs when two groups of quantum particles synchronize their fluctuations without any external influence, leading to the emergence of a new state of matter. The team achieved this by studying a crystal composed of erbium, iron, and oxygen, which was cooled to an extremely low temperature of minus 457 degrees Fahrenheit and subjected to a high magnetic field of up to 7 tesla—an intensity over 100,000 times greater than Earth’s magnetic field. The findings were published in the journal Science Advances.
Dasom Kim, a doctoral candidate at Rice’s Applied Physics Graduate Program and a lead author of the research, explained, “The SRPT was initially theorized to stem from interactions between quantum vacuum fluctuations—natural quantum light fields in vacuum—and matter fluctuations. However, our approach involved coupling two different magnetic subsystems, specifically the spin fluctuations of iron and erbium ions in the investigated crystal.”
In quantum mechanics, the term “spin” describes the magnetic orientation of particles, likened to a miniature arrow rotating and pointing in a specific direction. When the spins become aligned, they generate magnetic patterns throughout the material. The phenomenon of collective spin excitations, termed magnons, arises when these spin patterns propagate like waves.
Previously, the practical occurrence of an SRPT had been questioned, primarily due to a theoretical limitation known as the “no-go theorem” that applies to light-based systems. However, the Rice scientists successfully initiated the SRPT within a magnetic crystal by leveraging the interactions between two distinct spin subsystems, thereby creating a magnonic manifestation of the effect. In this scenario, the magnons associated with iron ions served the role typically linked to vacuum fluctuations, while the spins of erbium ions represented those of the matter.
Using sophisticated spectroscopic techniques, the researchers detected clear indicators of the superradiant phase transition, characterized by the disappearance of one spin mode’s energy signal and a distinct shift in another. These spectral characteristics align precisely with theoretical predictions pertaining to the transition into a superradiant state, reinforcing their assertion of achieving this long-speculated phenomenon.
“We successfully established an ultrastrong coupling between the two spin systems, allowing us to observe the superradiant phase transition and overcome past experimental limitations,” Kim stated.
The implications of this work extend beyond the validation of a decades-old prediction. The unique characteristics of the collective quantum states at the SRPT could have significant ramifications for the development of next-generation quantum technologies. Kim noted, “Near the quantum critical point of this transition, the system naturally stabilizes quantum-squeezed states, which dramatically reduce quantum noise and enhance measurement precision. This finding has the potential to revolutionize quantum sensors and computing technologies, improving their fidelity, sensitivity, and overall performance.”
Sohail Dasgupta, a fellow graduate student at Rice collaborating with Kaden Hazzard, an associate professor of physics and astronomy, contributed to the theoretical modeling of the SRPT, which was built upon existing models developed by their collaborator Motoaki Bamba from Yokohama National University. Dasgupta remarked, “Although the foundational mathematical model was set, we had to adapt it to incorporate the specific magnetic properties of the material to achieve accurate results. When our theoretical predictions align with experimental findings, it’s an exhilarating moment for any scientist.”
Hazzard emphasized the significance of this research, stating, “This achievement illustrates that principles from quantum optics can be effectively applied to solid materials, opening new avenues for the creation and manipulation of phases of matter through the lens of cavity quantum electrodynamics.”
Additionally, the crystal utilized in this study represents just one type within a broader class of materials, paving the way for further exploration of quantum phenomena in other materials with similar magnetic properties.
“Showing that a superradiant phase transition can be induced entirely through the coupling of two internal matter fluctuations represents a monumental advance in quantum physics,” said Junichiro Kono, the Karl F. Hasselmann Professor in Engineering and a co-author of the study. “This research establishes a new framework for understanding and leveraging intrinsic quantum interactions among materials.”
This groundbreaking study received support from various organizations, including the U.S. Army Research Office, the Gordon and Betty Moore Foundation, and the National Science Foundation, among others. The findings and opinions expressed in the research are solely those of the authors and do not necessarily reflect the views of the funding entities.
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