Synopsis: Quantum Signals Outpace Classical Ones

New theoretical work shows how much faster quantum information can travel through a system than classical information.
Synopsis figure
APS/Alan Stonebraker/P. Arrighi et al., Phys. Rev. A (2017)

Rumors and bad news spread quickly, but they could travel even faster if they were quantized. A new theoretical work explores the limits of this quantum speedup in a model system based on computational grids called cellular automata. The authors show that quantum signals can initially travel much faster through the grids than classical signals. However, for time-symmetric cases (when forward signal speed equals backward speed), the quantum advantage eventually disappears.

A well-known example of quantum speedup is in random walks. In the classical case, the walker travels, on average, a distance proportional to the square root of the time elapsed. A quantum walker, by contrast, benefits from the phenomenon of quantum superposition that allows it to travel at a faster rate (the distance grows linearly with time).

Researchers from France and Germany investigated the quantum speedup for nonrandom systems. As a representative case, they chose cellular automata grids, which evolve based on well-defined rules and can model hydrodynamical and other physical systems. Each cell in the grid has a value, which is computed during each time step using the values of cells in a local neighborhood. The size of this neighborhood determines the speed with which information (concerning a change in the value of one cell, for example) travels through the grid. The researchers showed that such signals can travel faster if cells are allowed to be in quantum superpositions—effectively increasing their neighborhood size. This speedup is most prominent in the initial steps. As time wears on, the quantum speed approaches a limit that depends on how fast classical signals travel backwards in time.

This research is published in Physical Review A.

–Michael Schirber

Michael Schirber is a Corresponding Editor for Physics based in Lyon, France.


Features

More Features »

Announcements

More Announcements »

Subject Areas

Quantum Information

Previous Synopsis

Topological Insulators

The Trouble with Smooth Edges

Read More »

Next Synopsis

Quantum Information

Superdense Coding over Optical Fiber

Read More »

Related Articles

Synopsis: Fish Eye Lens Could Entangle Atoms
Optics

Synopsis: Fish Eye Lens Could Entangle Atoms

An optical design called Maxwell’s fish eye lens could produce quantum entanglement between atoms separated by an arbitrary distance, new calculations show. Read More »

Synopsis: Quantum Walk in a Bose-Einstein Condensate
Quantum Physics

Synopsis: Quantum Walk in a Bose-Einstein Condensate

By manipulating the momenta of ultracold atoms, researchers demonstrate a quantum walk—a potential ingredient for quantum search algorithms. Read More »

Synopsis: A Classical Machine Learning Algorithm Goes Quantum
Quantum Information

Synopsis: A Classical Machine Learning Algorithm Goes Quantum

Researchers have mathematically proven that a powerful classical machine learning algorithm should work on quantum computers. Read More »

More Articles