Quantum simulations reveal spin transport in 1D materials

Researchers from the Department of Energy's Quantum Science Center (QSC) headquartered at Oak Ridge National Laboratory (ORNL) have achieved a significant milestone by demonstrating the first digital quantum simulations of how spin currents change over time in a 1-D model of a quantum spin material. The results, now published in Physical Review Letters, establish a new, programmable way to use quantum computers to study the transport of spin - a fundamental quantum variable - in materials.

Spin transport measurements are a cornerstone of condensed matter physics, providing important insight into how quantum materials carry energy and information. In this work, QSC researchers, led by Purdue University's Arnab Banerjee, demonstrated how a quantum computer can simulate spin transport behavior across ballistic, diffusive and superdiffusive - meaning a faster and farther spread than typical diffusion - motion. These different cases of spin transport represent fundamental changes in how the material responds to experimental probes. The simulation results make a direct comparison with experimental materials and opens new avenues for understanding complex quantum phenomena such as coherence and energy flow in quantum materials.

The simulations provide the researchers with a real-space dynamical picture that shows how spin evolves at a microscopic level. The QSC team is now able to watch spin currents form and move across the model system, rather than inferring this behavior indirectly from measurements. By revealing how transfer emerges from simple quantum interactions, the method provides a clear picture of how energy and information - encoded in the spins - flow through low-dimensional quantum materials.

"This achievement shows how quantum computing can move beyond proof-of-concept demonstrations to address real, experimentally relevant questions in materials physics," said Banerjee. "By simulating spin transport on an IBM quantum computer, we are creating tools that complement laboratory measurements and extend our ability to explore quantum materials that are otherwise difficult to study."

The collaborative effort, led by QSC members at Purdue University and IBM, with collaborators from the University of Illinois Urbana-Champaign (UIUC), used a 40-qubit simulation of a 1-D Heisenberg quantum model, run on IBM Heron, a quantum processor (the "chip" inside a quantum computer) developed by IBM. The Heisenberg model is a powerful approach to describing a wide variety of spin materials that are usually too complex to simulate with classical numerical methods at large scales. The team used a step-by-step digital simulation method to model how a realistic material system described by a 1-D Heisenberg model evolves over time, showing that current quantum computers can help study real spin transport problems.

A key advance in this work is the use of a novel algorithm that avoids the computational inefficiency of previous approaches, explained co-author and UIUC graduate student Yi-Ting Lee. By using carefully designed mid-circuit measurements, the team demonstrated an efficient way to track spin-current behavior that makes the simulations possible with today's quantum computers.

To validate the quantum simulations, the researchers compare their simulation results directly with experimental data of real materials, such as the often-studied quantum magnet potassium copper fluoride (KCuF₃), by using spin Seebeck effect measurements, complementary numerical calculations, and - going forward - inelastic neutron scattering. The strong agreement between the quantum simulation and numerical calculations shows that quantum computers are a promising tool for simulating quantum spin transport.

"This work highlights the strength of the QSC's collaborative approach to advancing quantum computing," said Travis Humble, director of the QSC at ORNL. "By bringing together quantum computing hardware, algorithm development, and experimental validation, the team has delivered a result that highlights the QSC's mission to use quantum computers for real-world scientific applications in the DOE mission space"

The cascading impact of these simulations

Beyond spin transport, the team showed that the same measurement approach can be used to study a wider range of quantum effects. These include how spins interact over time and how quantum materials respond to dynamic changes. These suite of new capabilities offers a flexible tool for simulating the spin dynamics of quantum materials.

The research findings represent an important step toward simulating more complex phenomena in quantum materials, including thermal transport, or how heat moves through a material at the atomic level. Currently, the team has used numerical simulations to validate their results, but continued advances in quantum computing hardware and error-reduction techniques are expected to scale these simulations of transport to problems that are beyond reach of current approaches. This includes applying these techniques to 2-D spin systems, which are central to understanding other exotic phenomena in quantum materials and their applications in energy technologies.

"This research is a fantastic example of how quantum computers can tackle dynamic problems that pose challenges for classical supercomputers," said Jerry Chow, Chief Technology Officer of Quantum-Centric Supercomputing, IBM. "Alongside the Quantum Science Center at Oak Ridge National Laboratory, we look forward to exploring more complex spin transport phenomena as quantum computers evolve into a core engine driving the future of computing."

Additional contributors that made this work possible include Jeffrey Cohn from IBM and André Schleife from the IBM-Illinois Discovery Accelerator Institute at UIUC.

The QSC, a DOE National Quantum Information Science Research Centers led by ORNL, is building the first national scientific ecosystem for quantum-accelerated high-performance computing (QHPC). By uniting national laboratories, academic institutions and industry partners, the QSC endeavors to advance American innovation and global leadership by enhancing the computational robustness, algorithmic scalability and simulation accuracy of quantum computing systems. The QSC's efforts to validate QHPC methods against state-of-the-art experiments is positioning the United States at the forefront of quantum-accelerated computing, benefiting science and technology worldwide. For more information, visit qscience.org.

UT-Battelle manages ORNL for DOE's Office of Science. The single largest supporter of basic research in the physical sciences in the United States, the Office of Science is working to address some of the most pressing challenges of our time. For more information, please visit energy.gov/science.