Room-temperature spinor condensation achieved

A research group including Professor Kenichi Yamashita, Associate Professor Shun Takahashi, and Assistant Professor Daichi Okada of the Faculty of Electrical Engineering and Electronics, Kyoto Institute of Technology, has successfully demonstrated polariton condensation with spin degrees of freedom (spinor condensation) at room temperature within a lead halide perovskite microcavity. Achieving this quantum phenomenon at room temperature, which previously could only be observed under cryogenic conditions, marks a major leap forward for the commercialization of novel optoelectronic quantum devices, including ultrafast optical switches, spin-based logic circuits, and coherent spin transport which all utilize spins. The study was published in Science Advances.

Polaritons, which are formed by the strong coupling of light and matter, possess both a light mass and strong interaction capabilities, making them known for undergoing Bose condensation at relatively high temperatures. In recent years, room-temperature polariton condensation has been reported, drawing significant attention to these particles for next-generation quantum optical devices. Furthermore, because polaritons possess spin degrees of freedom, they have the potential to form a state known as spinor condensation. However, this phenomenon had previously only been confirmed in ultra-low temperature environments below -250℃, leaving room-temperature implementation a major technical hurdle.

The research group successfully achieved this historically low-temperature quantum phenomenon at room temperature by leveraging these special quasi-particles (polaritons) where light and matter are fused as one. When many of these polariton particles condensate, they are relatively likely to align into the same state.

While photons usually behave independently, this study created a condensed state where polaritons are condensed into a unified state. This is conceptually similar to water freezing into ice, where the particles simultaneously align and vibrate cooperatively.

The crucial discovery in this study is that this condensed state exhibits a property where the spins (the rotational orientation of the particles) align. While light can possess rotational properties (polarization) such as right- or left-circular polarization, this experiment revealed that a state where spins align spontaneously emerges due to interactions between the particles (spinor condensation).

Upon closer inspection, the researchers discovered that this phenomenon does not happen all at once. Instead, it exhibits a two-stage phase transition: a standard polariton condensation occurs first, followed by the appearance of the spin-aligned state. This is a novel phenomenon that manifests exclusively due to the strong interactions between the particles.

Previously, such phenomena could only be observed at extremely low temperatures. By utilizing lead halide perovskites, the team successfully realized a spin-polarized condensed state even at room temperature.

Moving forward, these findings are anticipated to drive the realization of new optoelectronic quantum devices, such as ultrafast optical switches, spin-based logic circuits, and coherent spin transport. Furthermore, leveraging the processability and scalability of perovskite materials opens up clear pathways for integration into on-chip optical circuits.

Journal Information
Publication: Science Advances
Title: Room-temperature spinor condensate in halide perovskite microcavity
DOI: 10.1126/sciadv.aeb1521