To capture individual photons, researchers build an interference “wall”


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Photons are the foundation of many next-generation quantum technologies, including ultra-secure quantum communication and potentially breakthrough quantum computers.

Because these light particles can be entangled or superimposed – two quantum states that make quantum technologies possible.

To create these states, however, researchers have to work with extremely non-classical types of light that contain a small number of photons or even just one photon. This can be a difficult task that requires a complicated set-up, as typical light sources (like a laser) create states in which a large number of photons are always possible.

Theorists at the University of Chicago’s Pritzker School of Molecular Engineering (PME) have developed a new scheme for trapping single photons in a cavity. Their mechanism allows two sources to emit the selected number of photons into a cavity before destructive interference cancels both sources, essentially creating a “wall” that prevents further photons from entering.

This new mechanism could provide an easier way to generate quantum light without using the complicated materials and systems normally required.

The study, led by Prof. Aashish Clerk with PhD students Andrew Lingenfelter and David Roberts, was launched on November 26th in. released Scientific advances.

Create a “wall” out of interference

Typical systems for trapping single photons in a cavity involve the use of materials that have extremely large optical non-linearity, which forces the photons in the cavity to strongly interact with one another. In such systems, the resonant frequency of the resonator can be shifted significantly by adding even a single photon. If you then point a laser at the cavity, one photon can enter, but not a second one (because of the frequency shift caused by the first photon).

The problem with this mechanism is that it requires extremely large optical nonlinearities and very low power dissipation, a combination that is extremely difficult, if not impossible, to achieve on most platforms.

The system proposed by Clerk’s research team uses two different sources to simultaneously emit photons into a cavity that has extremely weak nonlinearity (far too weak for conventional approaches). With careful coordination, these sources cancel each other out through destructive interference – creating a “wall” that blocks photons – as soon as the selected number of photons has been captured in the cavity.

The possible uses are diverse. By using destructive interference in this way, the system does not have to use special optically non-linear materials, which opens the door to several different platforms, including as a tool for quantum simulation.

The basic mechanism also applies to all types of electromagnetic radiation, not just visible light. One exciting possibility is to generate and control photons at microwave frequencies in a superconducting circuit. This could open up new ways to store and process quantum information. Clerk’s group is currently working with experimenters to implement this scheme to achieve just that.

He and his colleagues are even investigating the system as a possible method for entangling photons, in which the observation of a photon automatically provides information about the photon with which it is entangled, no matter how far apart they are.

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

For the first time, scientists get photons to interact with atomic pairs

More information:
Andrew Lingenfelter et al., Unconditional Fock State Generation using Arbitrarily Weak Photonic Nonlinearities, Scientific advances (2021). DOI: 10.1126 / sciadv.abj1916

Provided by the University of Chicago

Quote: To capture individual photons, researchers are creating an interference “wall” (2021, December 3), accessed on December 5, 2021 from

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