Using quantum computers for innovative materials simulation

Since 2021, IBM has been operating one of the world's most powerful quantum computers for the Fraunhofer-Gesellschaft in Ehningen near Stuttgart. As part of the Quantum BW network, the Baden-Württemberg Ministry of Economic Affairs, Labor and Tourism is funding joint projects with the aim of making quantum computing usable for applications. The Fraunhofer IWM's "Material Modeling" group is involved in two projects.

Pairing classic computers with Quantum hardware

In principle, a quantum computer, due to its mode of operation, offers ideal prerequisites for mapping quantum chemical processes in complex functional materials. However, the currently available hardware is still inferior to the mathematically ideal performance of a quantum computer. In particular, the decoherence of the system, i.e. the loss of quantum properties due to interference during the calculation time, is a serious problem. This severely limits the universal applicability of a quantum computer at present. The technology is developing rapidly, however, so that in a few years' time, much more powerful and fault-tolerant systems will be available.

We are researching how best to use the quantum hardware available today to address material modeling issues in the most effective manner and are developing specific expertise for hybrid simulation methods. In these hybrid methods those aspects that can be reliably calculated on conventional computers are treated with established methods of density functional theory.

The part of the problem, which classically is the most demanding to solve in terms of computational resources, is mapped to an effective auxiliary model and calculated using the quantum computer. An iteration loop between the two computer systems then provides the overall solution (Figure 1). The aim of our research work is to develop these type of effective models that can be implemented on today's quantum computers.

Our findings form a basis for future software with transferable quantum algorithms.

Materials simulation for batteries and fuel cells

The successful expansion of electromobility requires small and lightweight energy storage systems with high energy densities and performance as well as efficient energy converters. The material and structure of the electrodes determine the electrical function of batteries and fuel cells and ultimately their service life.

In the joint project "Quantum computer material design for electrochemical energy storage and conversion with innovative simulation techniques" (QuESt), we are working with project partners at the German Aerospace Center (DLR) to test new approaches to material design. Using the IBM quantum computer, we are investigating the interactions between atoms and electrons of battery electrodes and in fuel cell catalysts. Such functional materials usually contain chemical elements with strongly correlated electrons, in particular transition metals. Their physically correct description requires numerically complex procedures. These provide an optimal testbed for the development of the hybrid simulation methods described above, using currently available quantum hardware. Within the scope of QuESt, we are investigating in particular the phase, defect and reaction properties of oxide compounds containing manganese, iron, cobalt and nickel with perovskite crystal structure types.

Alternative technology for quantum registers

The IBM quantum computers use superconductor-based circuits as elementary qubits. Shielding these as well as possible against external interference requires a great deal of technological effort. The quantum processor chip is therefore cooled to temperatures close to absolute zero and shielded against electric and magnetic fields. An alternative approach to the realization of qubits, technologically still in its infancy, involves the use of certain isolated crystal defects in solids. The most promising candidate for this is the nitrogen-vacancy center (NV center) in the diamond crystal, which exhibits its quantum properties even at room temperature for an astonishingly long time.

In the joint project "Modeling and simulation of qubit registers from chains of NV centers on dislocations in diamond" (SiQuRe), we are working together with partners at the Albert-Ludwigs-University of Freiburg and the University of Ulm on the modeling and simulation of solid-state defect-based qubit registers. The research project deals with models and computer simulation methods concerning theoretical quantum physics and deals with the question to what extent qubits addressable NV centers in diamond are periodically arranged along linear structural defects and can be used for the construction of future quantum computers.

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