An international team of researchers has reported a major advance in understanding quantum dynamics in semiconductor materials. They directly observed how excitons and phonons evolve together in perovskite nanocrystals, revealing a fully coherent quantum dance between light-induced electronic excitations and crystal lattice vibrations. They published their findings in Nature Communications.
An exciton is created when light excites an electron inside a semiconductor. The electron absorbs energy and leaves behind a positively charged “hole”; the two bind together and move through the crystal as a single quantum object. A phonon is a different kind of quantum object, as it is a quantum of crystal lattice vibration. Though being fundamentally different objects, in perovskites they are strongly linked and evolve together as a coupled quantum system.
Perovskite nanocrystals are miniature crystals only a few nanometers in size, a thousand times smaller than a hair thickness. Each crystal forms a nanoscale “box” that traps both excitons and phonons. This confinement makes the interaction between them especially strong: an exciton inside the nanocrystal is tightly coupled to vibrations of the surrounding crystal lattice. When an exciton is created by a short laser pulse, it also slightly distorts the surrounding crystal lattice, creating phonons. The electronic excitation and the lattice vibration then form a joint quantum state known as an exciton-polaron.
In most solids, the interaction with the crystal lattice quickly destroys the fragile quantum states. The motion of many atoms acts like noise, washing out the quantum coherence. However, the researchers found a striking exception in lead-halide perovskite nanocrystals. At low temperature of 2 Kelvin, the crystal vibrations remain well defined, allowing the quantum state to evolve coherently for about 10 picoseconds, corresponding to many oscillations and thus many turns of the quantum dance.
Using very short laser pulses lasting for about hundred femtoseconds, the experimental team from TU Dortmund University directly tracked this evolution and observed pronounced quantum beats . These beats appear when a system exists in a coherent superposition of different quantum states at the same time. Since each state evolves with a slightly different energy, their quantum waves interfere with each other. This interference produces a rhythmic oscillation, a quantum beat. In the examined nanocrystals, these oscillations revealed how excitons and crystal vibrations exchange energy and evolve together on ultrafast timescales.
What makes the result especially remarkable is the exceptionally strong amplitude of quantum beats and their long coherence. This regime remained experimentally inaccessible in other solid systems. In close collaboration with theory teams from Condensed Matter Theory at TU Dortmund University and Jackson State University in the USA, the researchers demonstrated that the effect can be tuned simply by changing the nanocrystal size: Excitons in smaller nanocrystals couple stronger to lattice vibrations, while in larger ones the oscillations are preserved for longer times. This opens a practical way to engineer and control the quantum dynamics of this system.
The findings identify perovskite nanocrystals as a promising platform for future quantum devices. The ability to control coherent exciton-phonon dynamics could enable new approaches for semiconductor quantum information processing, quantum light sources, and the generation of single phonons - individual packets of crystal vibration. More broadly, the work shows that crystal vibrations, often viewed as a source of decoherence, can instead become a useful quantum resource.
Nature Communications
Experimental study
Not applicable
Quantum beats of exciton-polarons in CsPbI3 perovskite nanocrystals
26-May-2026