Powerful Atomic-Level Interactions Unleashed by Revolutionary Quantum Computer Algorithm

Figure 1: An illustration showing the two states of a cuprate high-temperature superconductor. A new protocol for constructing quantum circuits could help with calculations on quantum materials such as superconductors. Credit: US Department of Energy

RIKEN researchers have developed a novel protocol for quantum computers to reproduce the complex dynamics of quantum materials. This hybrid quantum-computational algorithm enables the efficient calculation of atomic-level interactions in complex materials using smaller quantum computers or conventional computers. This breakthrough paves the way for new discoveries in condensed-matter physics and quantum chemistry.

The potential of quantum computers lies in their enhanced number-crunching power, giving them the ability to solve problems beyond the reach of conventional computers. Qubits, the building blocks of quantum computers, are tiny systems governed by the laws of quantum physics. Unlike bits used in conventional computers, qubits can hold multiple values simultaneously, providing an advantage in terms of speed.

In order to tackle problems too difficult for conventional computers, new perspectives on how to efficiently process data are required. One example of this is the time-evolution operator, which are huge grids of numbers describing the complex behaviors of quantum materials. These operators are crucial for quantum computers to better understand quantum chemistry and the physics of solids.

Current quantum computers use Trotterization, a relatively simple technique to achieve time-evolution operators. However, this method proves inadequate for the quantum computers of the future, requiring an excessive number of quantum gates and substantial computational time. Therefore, researchers have been developing quantum algorithms for accurate quantum simulations using fewer quantum gates.

Mizuta and his team proposed a more efficient and practical algorithm, a hybrid of quantum and classical methods, which can compile time-evolution operators at a lower computational cost, allowing it to be executed on small quantum computers or even conventional ones.

“By combining small quantum algorithms with the fundamental laws of quantum dynamics, our protocol succeeds in designing quantum circuits for replicating large-scale quantum materials, but with simpler quantum computers,” says Mizuta. The team aims to clarify how the time-evolution operators optimized by their method can be applied to various quantum algorithms that can calculate the properties of quantum materials.

Their research on "Local Variational Quantum Compilation of Large-Scale Hamiltonian Dynamics" has been published in PRX Quantum.

Reference: “Local Variational Quantum Compilation of Large-Scale Hamiltonian Dynamics” by Kaoru Mizuta, Yuya O. Nakagawa, Kosuke Mitarai and Keisuke Fujii, 5 October 2022, PRX Quantum. DOI: 10.1103/PRXQuantum.3.040302