Tiny imperfections with dramatic impacts in quantum systems

Delft University of Technology

Researchers at Delft University of Technology have demonstrated for the first time that even realistic, small amounts of disorder in modern quantum simulators can cause the system to exhibit completely different physical behaviour. Quantum simulators play a central role in the development of future quantum technologies, including quantum computers and advanced materials design. For these technologies to work reliably, we must understand how sensitive they are to imperfections. The reseachers Jose Soto-Garcia and Natalia Chepiga show that very small positional errors can have dramatic consequences. This insight is crucial for designing more robust quantum devices. More broadly, this work contributes to the fundamental understanding of how complex quantum systems behave in realistic conditions. The research is published in Physical Review Letters (PRL).

Quantum simulators based on chains of laser-trapped Rydberg atoms are widely used to explore quantum phase transitions and exotic states of matter. The researchers show that unavoidable tiny imperfections in these experiments, specifically small variations in atomic positions caused by optical tweezers, can fundamentally change the physics that quantum simulators are meant to reproduce.

Large-scale numerical simulations

Using large-scale numerical simulations, two key results are demonstrated. First, a well-known type of quantum phase transition, the Ising transition, does not behave as previously expected when these small imperfections are present. Instead, it crosses over into a regime dominated by extreme randomness, where the standard theoretical rules no longer apply. Second, an exotic state of matter called a floating phase, which is characterized by the absence of long-range order and long-range correlations, is destroyed by disorder. Although some of its features remain, the long-range correlations become localized.

Compare it to an orchestra

For a better understanding: think of an orchestra preparing to perform a masterpiece. If every musician begins at exactly the right moment, following the conductor’s cue with perfect timing, the result is a wonderful masterpiece. Every instrument blend into the collective rhythm. The composition emerges exactly as intended. But now imagine that each musician starts playing just a fraction of a second too early or too late. This will cause small, almost invisible timing errors. Those tiny shifts make the entire performance collapse and instead of music the audience will hear noise. Even tiny deviations can completely change what the orchestra produces.

Importance

Rydberg atom arrays in optical tweezers are considered one of the most promising platforms for quantum simulation. They are designed to emulate complex quantum many-body systems with high precision.

Rather than being a setback, this work helps the field mature. It clarifies what current quantum simulators are realising in practice and highlights what must be improved, such as trapping precision or interaction control, to reach the intended regimes. In addition, the findings open a new research direction: instead of avoiding disorder, experiments could deliberately explore these randomness-dominated quantum regimes, which are fascinating and not yet fully understood.