It is a defining feature of physics — and physicists — to be obsessed with problems at all conceivable scales. One could argue that no other natural science aims so ambitiously to describe objects as minute as quarks and as immense as supermassive black holes or galaxies. This drive to understand the Universe in its entirety has led to the development of experimental methods as varied as the scales they aim to explore. Think, for example, of the dimension range between tabletop optical setups, space-based telescopes, and monumental particle colliders.

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Quantum simulation stands out as a particularly versatile approach within this diverse toolbox. A quantum simulator is a controllable quantum system designed to mimic the behaviour of another — typically more complex or less accessible — system. At first, quantum simulation was developed to tackle moderate-scale problems in condensed-matter physics, such as the study of electron correlations in lattice models. But its scope has expanded radically. Researchers are now using quantum simulators to explore questions that extend into the domains of high-energy physics and cosmology.

This issue of Nature Physics highlights some progress in this direction. In their Review, Jad Halimeh and colleagues discuss the progress in using ultracold atoms to simulate lattice gauge theories. These are discretized versions of continuous gauge theories that describe the interactions between matter and force fields. Continuous gauge theories are notoriously difficult to study because their infinite degrees of freedom make analytical solutions often intractable — especially in strongly interacting regimes where perturbative methods fail. By discretizing spacetime, lattice gauge theories significantly reduce this complexity and make such problems more manageable.

One needs two main ingredients to cook up a lattice gauge theory. The first is a gauge field that mediates the forces between particles, such as photons mediating the electromagnetic interactions. The second is a matter field that represents the actual particles interacting via the gauge field. Simulating these building blocks in a controlled way is where ultracold atoms come into play.

Ultracold atoms can be arranged in optical lattices formed by intersecting laser beams. This naturally provides the discretized spatial structure that lattice gauge theories need. The atoms themselves can represent matter fields, while their mutual interactions emulate gauge fields. Techniques to achieve this kind of control vary, from the use of external magnetic or electric fields to exploiting internal atomic states like spin or hyperfine levels. For example, designing gauge fields that depend on the motion or correlations between atoms allows the simulation of dynamical gauge fields, where the gauge fields evolve in response to the behaviour of the particles — a key feature of real gauge theories.

The Article by Wei-Yong Zhang and co-workers in this issue reports another application of quantum simulation of lattice gauge theories: the study of the confinement–deconfinement transition. Confinement is a phenomenon of particular relevance for quantum chromodynamics, where the attraction between quarks increases with their distance. In the confinement phase, particles are bound together, such as quarks bound by the strong nuclear force to form protons and neutrons. By contrast, the deconfinement phase allows individual particles to exist and move independently, up to certain distances. Deconfinement is typically assumed to occur in extreme, high-energy conditions, such as in quark–gluon plasmas — a state of matter that might have existed in the early Universe.

Zhang and colleagues used a Bose–Hubbard quantum simulator to simulate a one-dimensional lattice gauge theory. By introducing a tuneable topological parameter, known as the θ-angle, they were able to monitor the dynamics of particle–antiparticle pairs and observe the transition from confinement to deconfinement at specific values of this parameter.

The link between deconfinement and extreme conditions in the early Universe brings to mind another recent work where ultracold atoms tackled questions of cosmological scale. In January of last year, Alessandro Zenesini and colleagues observed signatures of false vacuum decay using coupled atomic superfluids (Nat. Phys. 20, 558–563; 2024). False vacuum decay refers to the transition from a metastable quantum state, the false vacuum, into a more stable configuration, the true vacuum. This process is thought to have played a role in the evolution of the early Universe, where quantum fluctuations could have triggered bubbles of true vacuum to form and expand, driving rapid changes in the structure of spacetime.

Zenesini and co-workers engineered a controlled energy landscape to create a metastable state analogous to the false vacuum. To initiate the decay, they tuned the system's parameters to reduce the energy barrier between the metastable and stable states, effectively tilting the landscape. The result was bubbles of true vacuum nucleating spontaneously within the false vacuum and expanding over time.

These studies are just a few examples of the versatility of quantum simulators to address problems that span scales far beyond the laboratory hosting them. These platforms now offer a tabletop complementary probe to experiments performed at large-scale facilities, such as particle colliders and astrophysical observatories. Here at Nature Physics, we’re eager to find out what the journey of quantum simulation into big science might lead to.