&Cartridge; physics 14, s111
A new quantum simulator uses microwave photons in a superconducting cavity to simulate particles on a lattice similar to those in superconductors or atomic nuclei.
A quantum simulator is a limited-use quantum computer: a machine that can be programmed to emulate the behavior of a particular quantum system that is too complex to be simulated using classical methods. Because of their comparative simplicity, many researchers believe that quantum simulators could provide useful applications sooner than universal quantum computers. With this goal in mind, Christopher Wilson of the University of Waterloo in Canada and colleagues used a chip-based superconducting cavity to build a quantum simulator that can simulate quantum particles on a grid  . Such particle-lattice systems can be used as models for the behavior of high-temperature superconductors or of the particles inside an atomic nucleus.
The superconducting cavity demonstrated by Wilson and colleagues contains microwave radiation with specific frequencies or modes that are determined by the size of the cavity. The researchers change the effective size of the cavity by delaying the propagation of photons at one end by a variable interval. When the cavity contains multiple microwave photons, tuning its effective length causes the various cavity modes to interact with one another.
The team used this setup to create what is known as a bosonic Creutz ladder – a simple model of particles moving on a grid of four nodes. In their implementation of the model, Wilson and colleagues constructed the cavity-mode interactions so that each mode of the cavity corresponded to a node on the lattice. They also showed that the quantum simulator can be programmed on site by introducing microwaves of different frequencies into the cavity. The technique can be scaled to simulate more complex quantum systems by placing multiple superconducting cavities on the chip.
Sophia Chen is a freelance science writer based in Columbus, Ohio.
- JSC Hung et al., “Quantum simulation of the bosonic Creutz ladder with parametric cavity”, Phys. Rev. Lett.127, 100503 (2021).