December 23, 2019
Randomness governs many things, from the growth of cell colonies and the agglomeration of polymers to the shapes of tendrils that form when you pour cream into a cup of coffee.Since as early as 1905, scientists have described these seemingly unrelated phenomena in a unified way: as random walks. By imagining that individual particles or molecules are constantly taking steps in a random direction, researchers have successfully modeled many of the complexities of classical physics.More recently, scientists have brought the idea of a random walk to the quantum world, where the “walkers” can exhibit nonclassical behaviors like quantum superposition and entanglement. These quantum random walks can simulate quantum systems and may eventually be used to implement speedy quantum computing algorithms. However, this will require the walker to move in multiple dimensions (2D and higher), which has been difficult to achieve in a manner that is both practical and scalable.Quantum walks that use photons—the quantum particles of light—are particularly promising, since photons can travel long distances as energy in wave form. However, photons don’t carry an electric charge, which makes it difficult to fully control their motion. In particular, photons won’t respond to magnetic fields—an important tool for manipulating other particles like atoms or electrons. To address these shortcomings, researchers at the Joint Quantum Institute (JQI) have adopted a scalable method for orchestrating 2D quantum random walks of photons—results that were recently published in the journal Physical Review Letters. The research team, led by JQI Fellows Edo Waks and Mohammad Hafezi, developed synthetic magnetic fields in this platform that interact with photons and affect the movement of photonic quantum walkers.