Scientists have taken an important step toward using quantum computers to explore extreme versions of quantum electrodynamics (QED). In ordinary conditions QED matches experiments with extraordinary precision, but at very high intensities, known as strong-field QED or SFQED, the behavior becomes much more complex and largely untested. In these regimes, electromagnetic fields trillions of times stronger than those on Earth can cause photons to scatter off each other, create matter from empty space, or produce other unusual effects.
Physicists at the University of Illinois Urbana-Champaign have developed a new method to simulate one such SFQED process, called polarization flip, on a quantum computer. Polarization flip occurs when a photon passing through an intense field splits briefly into an electron and a positron before recombining into a new photon whose polarization, or direction of vibration, has changed. The researchers translated this process into the language of quantum computing by discretizing continuous variables, encoding particles as quantum states, and building a quantum circuit using quantum gates.
To handle the added complexity of this process, they introduced an improved encoding technique that reduces the number of quantum gates needed while managing the larger number of possible particle states. They also applied renormalization to cancel unphysical effects caused by the discretization. Classical simulations of the resulting quantum circuit showed good agreement with exact reference calculations, but the number of gates required remains too high for today’s noisy quantum hardware.
Benchmarking quantum simulations of extreme physics
The work sets a clear performance benchmark and highlights the current limits of quantum computers for strong-field QED. It demonstrates both the challenges, such as excessive noise and gate counts, and the progress made through new algorithmic tools. Future directions include testing different encodings, simulating multi-loop processes, or using spatial lattices instead of momentum lattices. The researchers compare the present stage of quantum computing to the early years of lattice QCD, suggesting that continued development of algorithms could eventually make these simulations practical.
The study, published in Physical Review D, advances the search for a quantum advantage in high-energy physics and prepares theoretical tools for upcoming experiments at facilities like SLAC and DESY.