Quantum Computers Now Calculate Material Properties Without Exponential Slowdowns
Gian Gentinetta and colleagues at the Institute of Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), in a collaboration between EPFL, IBM Quantum, IBM T.J. Watson Research Centre, and others, present the Quantum Finite Temperature Lanczos Method (QFTLM). The new method uses quantum computers to compute thermal expectation values, enabling calculations beyond the limitations of classical approaches. Applying it to the transverse-field Ising model demonstrates QFTLM as a potentially key set of tools for finite-temperature quantum simulation and opens avenues for exploring previously inaccessible quantum phenomena. Quantum computation extends thermal modelling of many-body systems beyond classical limits Accurate modelling of quantum many-body systems at temperatures where classical simulations become intractable is now possible by circumventing the exponential computational scaling that previously limited progress. The computational challenge arises because, in quantum mechanics, describing a system at finite temperature requires averaging over an exponentially large number of possible quantum states, a task that quickly overwhelms classical computers. The Quantum Finite Temperature Lanczos Method (QFTLM) extends the finite-temperature Lanczos method to quantum computers, utilising trace estimation to calculate thermal expectation values, representing properties at specific temperatures. The Lanczos method is an iterative algorithm used to find the eigenvalues and eigenvectors of a matrix, and its adaptation to the quantum realm allows for efficient computation of thermal properties. The transverse-field Ising model was used in numerical experiments to demonstrate QFTLM’s ability to reproduce thermal observables across a broad temperature range, paving the way for exploring previously inaccessible quantum phenomena and advancing our understanding of materials at varying temperatures. Magnetisation, a key property indicating the alignment of atomic spins, and s
