New Fast Forward Algorithm Could Unleash the Power of Quantum Computers

Fast-forward quantum computations are exceeding the time limits imposed by decoherence, which plagues today’s machines.

A new algorithm that speeds up simulations could bring greater usability to current and short-term quantum computers, paving the way for applications to run beyond strict time limits that hinder many quantum computations.

“Quantum computers have a limited time to perform calculations before their useful quantum nature, which we call coherence, collapses,” said Andrew Sornborger of the Computer, Computational and Statistical Sciences Division at Los Alamos National Laboratory. , and lead author of an article announcing the research. “With a new algorithm that we have developed and tested, we will be able to rapidly advance quantum simulations to solve problems that were previously out of reach.”

Computers made up of quantum components, called qubits, can potentially solve extremely difficult problems that are beyond the capabilities of even the most powerful modern supercomputers. Applications include faster analysis of large datasets, drug development, and uncovering the mysteries of superconductivity, to name just a few of the 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 would take the best conventional computing millennia to complete. The challenge remains, however, to ensure that a quantum computer can run meaningful simulations before quantum coherence breaks down.

“We’re using machine learning to create a quantum circuit that can approximate a large number of quantum simulation operations at a time,” Sornborger said. “The result is a quantum simulator that replaces a sequence of calculations with a single, fast operation that can complete before quantum coherence breaks down.”

The Variational Fast Forwarding (VFF) algorithm that Los Alamos researchers have developed is a hybrid combining classical aspects and quantum computing. Although well-established theorems rule out the potential for general rapid advance with absolute fidelity for arbitrary quantum simulations, researchers work around the problem by tolerating small computational errors for split times in order to provide useful, albeit slightly, predictions. imperfect.

In principle, the approach allows scientists to mechanically simulate a system for as long as they want. In practice, the errors that accumulate as simulation times increase limit potential calculations. Yet the algorithm allows for simulations far beyond the timescales quantum computers can achieve without the VFF algorithm.

A quirk of the process is that it takes twice as many qubits to fast forward a calculation than the fast forward quantum computer would. In the recently published paper, for example, the research group confirmed their approach by implementing a VFF algorithm on a two-qubit computer to rapidly advance the calculations that would be done in a one-qubit quantum simulation.

In future work, Los Alamos researchers plan to explore the limits of the VFF algorithm by increasing the number of qubits that they advance rapidly and by checking how fast they can advance systems. The research was published on September 18, 2020 in the journal Quantum information NPj.

Reference: “Variational Fast Forwarding for Quantum Simulation Beyond the Coherence Time” by Cristina Cîrstoiu, Zoë Holmes, Joseph Iosue, Lukasz Cincio, Patrick J. Coles and Andrew Sornborger, September 18, 2020, Quantum information NPj.
DOI: 10.1038 / s41534-020-00302-0

The research was supported by funding from the Los Alamos National Laboratory Information Science & Technology Institute, the Department of Energy Advanced Scientific Computing Beyond Moore’s Law program, and the Los Alamos National Laboratory Directed Research and Development program.