A new hybrid platform for quantum simulation of magnetism (opens in new tab)

Google Quantum AI researchers have developed a hybrid quantum simulation platform that combines the flexibility of digital gates with the high-speed entanglement growth of analog dynamics. Using a 69-qubit Sycamore processor, the team demonstrated high-precision simulations of quantum magnetism that are estimated to be over a million years beyond the reach of the world’s fastest supercomputers. This approach allows for the study of complex physical systems before environmental noise can degrade the quantum state.

The Hybrid Analog-Digital Approach

• Digital simulation provides high flexibility by breaking operations into sequential logical gates, but it is relatively slow because qubits only interact in pairs.
• Analog simulation activates all qubit couplers in parallel to mimic continuous, real-world dynamics, enabling much faster growth of quantum entanglement.
• The hybrid model uses digital gates for initial state preparation and final characterization, while utilizing analog evolution for the core simulation phase.
• This combination minimizes the time the system is exposed to noise while maintaining the ability to target specific, complex problems.

High-Precision Calibration and Benchmarking

• The team overcame the "interference" problem of analog simulation—where simultaneous coupler activation creates unpredictable results—by developing a new calibration scheme and precise hardware modeling.
• The system achieved a high level of accuracy, with an error rate of only 0.1% each time a quantum excitation moves between qubits.
• Benchmarking via random circuit sampling showed the platform can reach chaotic, highly entangled states significantly faster than purely digital methods.
• Researchers estimate that reproducing these results with the same accuracy on the Frontier supercomputer would take more than one million years.

Discovery in Quantum Magnetism

• The researchers used the platform to study the XXZ model, a foundational paradigm in quantum magnetism, across a 69-qubit array.
• The experiment investigated how quantum systems reach thermal equilibrium, focusing on the Eigenstate Thermalization Hypothesis (ETH).
• The simulation revealed a surprising exception to standard physics theories: a specific parameter regime where the system resisted thermalization and remained in a non-equilibrium state.
• This finding challenges the "Generalized Gibbs Ensemble," a widely used theory for predicting the behavior of isolated quantum systems.

This hybrid platform establishes a new standard for using current-generation quantum hardware to conduct meaningful scientific research. By integrating analog speed with digital control, the approach provides a viable roadmap for exploring many-body physics and finding practical applications in the NISQ (Noisy Intermediate-Scale Quantum) era.