# New “Fast Forward” Algorithm May Unleash Quantum Computer Power

Quantum calculations of acceleration pass the time limit determined by decoherence, which interferes with the current machine.

New algorithms that speed up simulations could bring greater use capabilities to current and short-term quantum computers, paving the way for applications to walk past tight time limits that inhibit many quantum calculations.

“Quantum computers have limited time to calculate before their useful quantum properties, which we call coherence, break down,” said Andrew Sornborger of the division of Computer Science, Computing, and Statistics at Los Alamos National Laboratory, and senior author on the paper. announced the research. “With the new algorithms we have developed and tested, we will be able to accelerate quantum simulations to solve previously unaffordable problems.”

Computers built from quantum components, known as qubits, can potentially solve extremely difficult problems that exceed even the capabilities of even the most powerful modern supercomputers. Applications include faster analysis of large data sets, drug development, and unraveling the mysteries of superconductivity, to name a few possibilities that could lead to major technological and scientific breakthroughs in the near future.

Recent experiments have demonstrated the potential of quantum computers to solve problems in seconds that will take thousands of years for the best conventional computers to solve. The challenge remains, however, to ensure quantum computers can run meaningful simulations before quantum coherence breaks down.

“We use machine learning to create quantum circuits that can approach a large number of quantum simulation operations at once,” Sornborger said. The result is a quantum simulator that replaces the sequence of calculations with a single, fast operation that can be completed before quantum coherence breaks down.

The Variational Fast Forwarding (VFF) algorithm developed by los alamos researchers is a combination of classical computing and quantum computing aspects. Although established theorems exclude the potential for general rapid forwarding with absolute precision for arbitrary quantum simulations, the researchers addressed the problem by tolerating small miscalculations for middle time to provide useful, if slightly imperfect, predictions.

In principle, such approaches allow scientists to simulate quantum systems mechanically for as long as they like. Practically speaking, errors that accumulate over time limit simulation potential calculations. However, the algorithm allows simulations far beyond the time scale that quantum computers can achieve without VFF algorithms.

One peculiarity of this process is that it takes twice as many qubits to speed up calculations than it would make quantum computers forward quickly. In a newly published paper, for example, a group of researchers confirmed their approach by applying a VFF algorithm on a two-qubit computer to speed up calculations to be performed in a single qubit quantum simulation.

In future work, the Los Alamos researchers plan to explore the limits of VFF algorithms by increasing the number of qubits they accelerate forward, and examine the extent to which they can speed up the system. The study was published on September 18, 2020 in the npj journal Quantum Information.