Researchers are exploring both analog and digital quantum simulators to replicate the complex behavior of quantum fields, aiming to better understand the universe at the quantum level.
A team led by Ringbauer developed a quantum computer using qudits—five-level quantum units—rather than traditional qubits with two states. This approach allows each particle to store more information, reducing circuit complexity. When Muschik converted her simulation to qudit logic, the circuits shrank by a factor of ten, speeding execution and reducing errors. Their initial 2016 experiment demonstrated a one-dimensional simulation of the electromagnetic field.
Nearly a decade later, the team scaled this to two dimensions, simulating a richer electromagnetic system using five calcium-40 ions arranged in a square lattice. Each ion represents a qudit with five energy states. Despite these states lasting only about a second, the simulation completed its 10–20 millisecond sequence swiftly enough to observe quantum phenomena such as particle pair creation and annihilation. This work, published in Nature Physics in March, marks the first 2D quantum simulation of particles and their quantum force field using qudits.
Meanwhile, physicists like Jad Halimeh at Ludwig Maximilian University of Munich are advancing analog quantum simulators. These devices map complex quantum systems onto analogous, easier-to-study lab systems, often involving ultracold atoms that naturally evolve over time. In 2020, Halimeh and colleagues used a 71-atom array to simulate one-dimensional quantum electrodynamics analogously. Recently, a two-dimensional simulation of string breaking—a phenomenon where the electric field between particles snaps to create new particle pairs—was demonstrated, though it omitted some magnetic dynamics.
The ultimate goal is to simulate quantum chromodynamics (QCD), the theory behind the strong force binding quarks and gluons into protons and neutrons. QCD’s complexity far exceeds that of electromagnetism and remains largely beyond current computational reach. Some researchers believe qudit-based digital simulations offer the best path forward. A recent proposal by Halimeh, Ringbauer, and collaborators outlines a qudit algorithm to simulate hadron collisions, revealing processes from the early universe.
Conversely, analog simulations may better handle large systems typical in quark-gluon interactions. Bing Yang’s team has employed analog simulators to study quark-gluon plasma transitions reflecting conditions soon after the Big Bang.
Emerging hybrid approaches combine analog and digital methods on the same hardware. For example, a 2024 study on Google’s quantum computer integrated both techniques to leverage their respective strengths.
“They’re all studying different aspects in a different way. It’s quite an interesting time. But it’s also quite early.” — Mikhail Lukin, Harvard University