Meet the Quadruplon: Scientists Discover a New Four-Body Quantum Particle

By Light Publishing Center, Changchun Institute of Optics, Fine Mechanics And Physics, CAS April 19, 2025
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A research team has discovered the first experimental evidence of a genuine four-body quasi-particle, called a quadruplon, in a semiconductor made of monolayer Molybdenum Ditelluride. Using a combination of optical pump-probe techniques and advanced theoretical modeling, they confirmed the unique spectral signatures of this irreducible four-particle state. (Artist’s concept.)

Scientists have discovered a new four-body quasi-particle, the quadruplon, in a 2D semiconductor. Using laser experiments and advanced theory, they identified unique spectral features unexplained by existing models, confirming the quadruplon’s existence.


A central goal of physics is to understand why different materials exhibit specific properties, such as electrical, optical, thermal, or magnetic behavior. These properties are fundamental to nearly all technological applications. Modern quantum theory explains them through various types of “elementary excitations,” commonly referred to as quasi-particles.

Well-known quasi-particles include phonons (quantized lattice vibrations in a crystal), electrons and holes influenced by the crystal lattice in semiconductors, and polarons, electrons or holes further modified by their interaction with phonons. More complex examples include excitons, which are bound electron-hole pairs resembling hydrogen atoms. Two excitons can bind together to form a molecular-like structure known as a biexciton, analogous to a hydrogen molecule.

Although a biexciton consists of four particles (two electrons and two holes), it is typically treated as a system composed of two interacting excitons, effectively a reducible, two-body system. In contrast, physicists have proposed the existence of genuine four-body quasi-particles that cannot be reduced to combinations of two-body entities. However, experimental evidence for such irreducible four-body states is extremely limited, and none has been confirmed in semiconductors to date.

First Evidence of a Genuine Four-Body Quasi-Particle

In a new paper published in eLight, a team of scientist led by Professor Cun-Zheng Ning from College of Integrated Circuits and Optoelectronic Chips, Shenzhen Technology University and Electronic Engineering Department, Tsinghua University, China, reported experimental results and supporting theory that show first evidence of the existence of a genuine four-body quasi-particle called quadruplon in a semiconductor of a mono-molecular thickness, the so-called two-dimensional material, Molybdenum Ditelluride.

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