Interference wall captures single photons

28 Jan 2022 Isabelle Dumé

On and off: Better, simpler control of single-photon emissions opens the door to new platforms in quantum research. (Courtesy: art-skvortsova/iStockphoto)

Researchers in the US have devised a new scheme for trapping single photons in a cavity that involves creating a “wall” to prevent additional photons from entering. The technique could provide a simpler way to generate single photons for use in next-generation quantum technologies such as ultra-secure quantum communications and quantum computers.

Devices that emit single photons are crucial for light-based quantum-information systems. Because the quantum state of a photon is what carries the information (in the form of a quantum bit, or qubit), these devices must also emit photons that are in the same quantum state, and therefore indistinguishable from each other.

Creating single photons in such Fock states (as they are known) is no easy matter, however. Conventional light sources such as lasers generate states containing large numbers of photons, so researchers need alternatives that allow them to manipulate non-classical, or non-linear, light. This typically requires complicated optical set-ups involving materials with an extremely large optical nonlinearity, which are difficult to create.

Preventing further photons from entering the cavity

The new scheme, developed Aashish Clerk and colleagues at the University of Chicago’s Pritzker School of Molecular Engineering, is very different from conventional “blockade” systems that use such nonlinear materials to trap single photons in a cavity. In these systems, the materials force photons in the cavity to interact strongly with each other in a way that causes the cavity’s resonance frequency to shift in the presence of even one single extra photon.

In contrast, Clerk and colleagues developed a system using only weakly nonlinear materials that allows two sources of light to emit a selected number of photons into a cavity. “Once the desired number of photons has entered the cavity, the two sources destructively interfere, which cancels out both sources and creates a ‘wall’ that prevents further photons from entering the cavity,” Clerk tells Physics World.READ MORE

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Expanding the potential of light-based quantum technologies

The researchers say their approach could be applied to wavelengths of electromagnetic radiation other than visible light. One possibility would be to use it to create and control microwave-frequency photons in a superconducting circuit, they explain. Such a system could make it possible to store and process quantum information.

“We think this scheme could work in a lot of different systems,” Clerk says. “If you don’t need special materials, it really expands the potential of light-based quantum technologies.”

The research is detailed in Science Advances.

Isabelle Dumé is a contributing editor to Physics World

FROM PHYSICSWORLD.COM      30/1/2022