Ability to harness quantum speed gains now within sight after researchers solve massive simulation problem in a heartbeat

Quantum technologies like quantum computers are built from quantum materials. These types of materials exhibit quantum properties when exposed to the right conditions. Curiously, engineers can also trigger quantum behaviour by manipulating a material’s structure, for example by stacking layers of graphene on top of each other and twisting them to create a moiré pattern, which suddenly turns them into a superconductor. 

The layers can be arranged in increasingly complex ways all the way to quasicrystals and super-moiré materials. The fundamental problem is that scientists must first calculate the properties of potential new materials to predict if they could be useful. Quasicrystals, for example, are so complex they can require processing more than a quadrillion numbers — far beyond the capacity of the world’s most powerful supercomputers.

Now researchers at Aalto University’s Department of Applied Physics have shown how a quantum-inspired algorithm makes solving these colossal, non-periodic quantum materials possible in a heartbeat.  It is also an early showcase of a positive quantum technology feedback loop, explains Assistant Professor Jose Lado.

‘Crucially, these new quantum algorithms can enable the development of new quantum materials to build new paradigms of quantum computers, creating a productive two-way feedback loop between quantum materials and quantum computers,’ he explains.

Their discovery paves the way for building dissipationless electronics, which could, for example, help mitigate the heat impact of AI-powering data centres.

The team, led by Lado, included doctoral researcher Tiago Antão, main author of the work; QDOC doctoral researcher Yitao Sun, and Academy Research Fellow Adolfo Fumega. The paper was recently published in Physical Review Letters as an Editor’s suggestion: https://journals.aps.org/prl/abstract/10.1103/hhdf-xpwg.

Scattered across an already complex shape

In the study, the team focused on topological quasicrystals, which feature unconventional quantum excitations. Harnessing their power is important as they protect the electric conductivity of the quantum material from fatal noise and interference, yet they are scattered unevenly throughout the quasicrystal. Instead of trying to compute the enormous shape of the quasicrystal, the team translated the problem into the same language that quantum computers speak.

‘Quantum computers work in exponentially large computational spaces, so we used a special family of algorithms to encode those spaces, known as tensor networks, to compute a quasicrystal with over 268 million sites. Our algorithm shows how colossal problems in quantum materials can be directly solved with the exponential speed-up that comes from encoding the problem  as a quantum many-body system’, Antão says.

The algorithm is a theoretical computation run on a simulation, but experimental confirmation and potential future steps are in sight.

‘The quantum-inspired algorithm we demonstrated enables us to create super-moiré quasicrystals several orders of magnitude above the capabilities of conventional methods. That is an instrumental step towards designing topological qubits with super-moiré materials for use in quantum computers, for example,’ Lado says.

Towards an early use-case for quantum computers

According to Lado, the team’s algorithm could be adapted to be injected into a quantum computer.

‘Our method can be adapted to run on real quantum computers, once they reach necessary scale and fidelity. In particular, the new AaltoQ20 and the Finnish Quantum Computing Infrastructure can play a significant role for future demonstrations,’ Lado says.

The results demonstrate that understanding and designing exotic quantum materials is one of the first potential real uses of quantum algorithms and quantum computers—something for which Lado has already paved the way.

The study brings together two major directions in quantum technology in Finland: quantum materials and quantum algorithms. It is part of Lado’s ERC Consolidator grant ULTRATWISTROICS that aims to design topological qubits using van der Waals materials, and the Center of Excellence in Quantum Materials QMAT whose mission is to power the quantum technology of coming decades.