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Controlling quantum particle states through structural phase transition of crystals

A research team has successfully fine-tuned the Rabi oscillation of polaritons, quantum composite particles, by leveraging changes in electrical properties induced by crystal structure transformation. in Advanced Science, this study demonstrates that the properties of quantum particles can be controlled without the need for complex external devices, which is expected to greatly enhance the feasibility of practical quantum technology. The team was led by Professor Chang-Hee Cho from the Department of �鶹��Ժics and Chemistry at DGIST.

Quantum technology enables much faster and more precise information processing than conventional electronic devices and is gaining attention as a key driver of future industries, including quantum computing, communications, and sensors. At the core of this technology lies the ability to accurately generate and control quantum states. In particular, recent research has been actively exploring light-based quantum devices, with polaritons at the center of this field.

Polaritons are composite quasiparticles formed through the hybridization of photons and excitons—bound states arising from the motion of electrons. These quasiparticles travel at the speed of light while retaining the ability to interact with other particles, much like electrons.

Notably, the Rabi oscillation of polaritons is directly linked to the operation of quantum information processing, and the ability to control this oscillation precisely is essential for realizing quantum devices. However, freely controlling the Rabi oscillation frequency has remained a challenge until now.

To overcome this limitation, the DGIST research team focused on a special semiconductor material called perovskite (MAPbBr₃). Just as water changes its state into ice or vapor depending on temperature, this material features a phase transition property, meaning its crystal structure can transform in response to external conditions.

In particular, in certain structural phases, it exhibits spontaneous polarization without any external electric field—a phenomenon known as ferroelectricity. This unique electrical behavior can alter the properties of excitons, which, in turn, influences the quantum characteristics of polaritons.

The research team designed a microcavity structure using perovskite and experimentally demonstrated that phase-transition-induced structural changes influence the oscillation of polaritons (Rabi oscillation). The results showed that controlling the crystal phase allowed the frequency of polariton oscillations to be tuned by up to 20%, while the oscillator strength, representing the coupling intensity between light and matter, varied by up to 44%. Notably, the team identified ferroelectricity, observed in the asymmetric crystal structure, as the key factor driving these changes.

The ferroelectric-based control technology developed in this study presents a new approach to enhancing both the flexibility and precision of quantum device design using polaritons. In particular, it can serve as a key factor in improving both the operating speed and stability of various quantum information applications, including quantum computing, quantum communication, photonic AI chips, and ultrafast sensors.

Furthermore, since the control is achieved simply by tuning the crystal phase, this approach holds strong potential for realizing practical and cost-effective quantum devices that can operate at room temperature.

Professor Cho stated, "This study goes beyond simply generating polaritons; it demonstrates that their intensity and properties can be controlled through ferroelectricity, a practical approach. As control technologies for quantum devices continue to advance, the practical implementation of various quantum-based technologies, such as quantum computers and communication systems, could be accelerated."

This study was led by Hyeon-Seo Choi, a Ph.D. candidate in the Department of �鶹��Ժics and Chemistry at DGIST, as the first author.