Quantum computers could probe the boundary between classical and quantum physics

The boundary between classical and quantum physics has remained ‘fuzzy’ for a century. New research implies that quantum computers could allow this boundary to be seen clearly for the first time.

A new quantum computing algorithm that offers a clearer understanding of the quantum-to-classical transition, has been developed by researchers at Los Alamos National Laboratory.

The algorithm could provide a method to model systems on the cusp of quantum and classical worlds — such as biological proteins — in the process answering questions about how quantum mechanics applies to large-scale objects.

Patrick Coles of the Physics of Condensed Matter and Complex Systems group at Los Alamos National Laboratory, says: “The quantum-to-classical transition occurs when you add more and more particles to a quantum system, such that the weird quantum effects go away and the system starts to behave more classically.

“For these systems, it’s essentially impossible to use a classical computer to study the quantum-to-classical transition.”

Coles believes his team could study this with the aid of their algorithm and a quantum computer consisting of several hundred qubits. The latter of which, they anticipate will be available in the next few years based on the current progress in the field of quantum computing.

White crosses represent solutions to a simple quantum problem analyzed with a new quantum computer algorithm developed at the Los Alamos National Laboratory. (LNL)

Answering questions about the quantum-to-classical transition have been notoriously difficult for physicists. Despite existing for over a century, researchers still can’t pinpoint at exactly what scale the counter-intuitive phenomena of quantum mechanics yields way to the more familiar physics of the everyday world.

For systems of more than a few atoms, the problem rapidly becomes intractable, with the number of equations growing exponentially with each added atom.

As an example; Proteins, consist of long strings of molecules that may become important biological components or sources of disease, depending on how they fold up.

Even though proteins can be comparatively large molecules, they are small enough that the quantum-to-classical transition, and algorithms that can handle it, become important when trying to understand and predict how folding proceeds.

In order to study aspects of the quantum-to-classical transition on a quantum computer, researchers first need the means to characterize how close a quantum system is to behaving classically.

Quantum objects have characteristics of both particles and waves. In some cases, they interact like tiny billiard balls, in others, they interfere with each other in much the same way that waves on the ocean combine to make larger waves or cancel each other out.

This wave-like interference is a quantum effect. Fortunately, a quantum system can be described using intuitive classical probabilities rather than the more challenging methods of quantum mechanics, when there is no interference.

The LANL group’s algorithm determines how close a quantum system is to behaving classically.

Thus, what emerges is a tool which they can use to search for classicality in quantum systems and understand how quantum systems, may ultimately seem classical to us in our everyday life.