Noisy quantum gases can stay perfectly ordered and break a fundamental rule of matter.
April 20, 2026
Original Paper
Observation of Strong-to-Weak Spontaneous Symmetry Breaking in a Dephased Fermi Gas
arXiv · 2604.16137
The Takeaway
Landau’s paradigm of symmetry states that structured patterns in matter should fall apart when things get too noisy or decoherent. This experiment used a quantum gas microscope to watch a Fermi gas as it was exposed to environmental interference. The gas actually transitioned into a new state where it maintained weak symmetry even after the strong symmetry was gone. This is the first time this specific type of phase transition has ever been seen in a lab. It proves that quantum systems are more resilient to noise than we previously believed. This opens up new possibilities for building stable quantum materials that survive in real-world conditions.
From the abstract
Symmetry-based classification of quantum phases of matter is one of the most foundational organizing principles in physics; however, an analogous framework for mixed, decohered quantum states has only begun to emerge. A central new concept is strong-to-weak spontaneous symmetry breaking (SW-SSB), a sharp transition in mixed quantum states that is invisible to any observable linear in the density matrix and that has since been predicted across a broad class of open and monitored quantum systems.