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Photons can interact with magnetic fields!!

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Making photons interact with a magnetic field

Researchers in the US have synthesized an artificial magnetic field for photons for the first time in a device known as an Aharonov–Bohm ring. Being able to make such fields is one of the prerequisites for creating exotic phases of matter that arise from the interplay of particles among themselves and their interaction with external fields. The new work could help make experimental platforms for engineering quantum phases of strongly interacting photons in which the fundamental properties of some of the most complicated states of quantum matter could be studied.
The Aharonov–Bohm ring for photons
The Aharonov–Bohm ring for photons
The Aharonov–Bohm effect is a quantum mechanical phenomenon in which the wavefunction of an electrically charged particle, like an electron, couples to an electromagnetic potential in a confined space (widely known as an Aharonov–Bohm ring). However, unlike electrons, photons do not carry an electric charge and so do not interact with magnetic fields. This means that they cannot be studied using such rings.
A team led by John Martinisof Google Inc. in Santa Barbara and the University of California at Santa Barbara has now overcome this problem by coupling photons to an engineered magnetic field produced in an Aharonov–Bohm device containing three superconducting Josephson junctions in a loop. Each junction comprises two superconductors that are coupled both capacitively and through quantum tunnelling. Superconducting currents flow back and forth between the superconductors, so creating confined oscillations of electric and magnetic fields.
“When one photon wants to jump from one junction to the next, it effectively sees this field,” explains team member and lead author of the study Pedram Roushan.

Controlling the three-state ring

The researchers can control their three-state ring with remarkable precision and can measure and tune how the photons interact with each other and how the sites couple. They can also control the amount of effective magnetic flux passing through the device.
The team loaded the ring with either one or two photons and found that they behave as a charged quantum particle would in an Aharonov–Bohm ring – that is, the ground state energy of a photon depends periodically on the effective flux running though the ring. Another finding was that the wavefunction of the photon is symmetric when there is no magnetic flux but has a preferred direction in the presence of a flux. This means that the photon is behaving as a charged particle.
“Being able to control a quantum system in this way is challenging and our work is now state-of-the-art in this area of research,” Roushan tells nanotechweb.org. “Our particular experiments posed some challenges and mastering these was instrumental in advancing our technical capabilities and learning to take them to the next step.

Engineering exotic phenomena

“In the future, we would like to scale up our experiment to try and engineer exotic phenomena such as the fractional quantum Hall effect in a Bosonic platform made of strongly interacting photons. If we succeed in making this platform, we could use it to study some of the most exciting and complicated states of quantum matter.”
Doing this will not be without challenges though, he admits, since the ring we made is a closed 1D lattice, while the fractional quantum Hall effect is inherently 2D.
The research is detailed in Nature Physics

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