Purdue Researchers Advance Silicon Nitride Platform for Photon Control

Photons offer stable operation at room temperature, reducing energy consumption and minimizing data transfer delays by moving through circuits at the speed of light.

The team’s silicon nitride platform emits exact single photons from dozens of locations each time a laser beam passes through it. These photons originate from intentionally created atomic defects within the silicon nitride. Embedding them within nanosized pillars on the platform allows for more uniform manufacturing.

Controlling photon interactions has historically hindered on-chip switches because single photons do not readily interact. The Purdue team adapted an existing industry technique of using light to modulate light, refining it to operate at the single-photon level.

The apparatus employs an off-the-shelf single-photon avalanche diode to spot the incoming photon and verify the switching process. This configuration allows a single photon to control a more powerful beam.

Researchers also addressed decoherence. A certain pattern can be recognized.

Individual rubidium atoms are held in an array of optical tweezers acting as tiny traps. The array is placed inside an optical cavity consisting of two highly reflective mirrors facing each other. Thousands of reflections occur as a photon traverses the cavity, making countless passes across the atoms.

The team excited atoms to Rydberg states where they interact strongly with their neighbors. Combining cavities and Rydberg states is difficult because they react strongly to stray electric fields arising from piezoelectric elements.

Piezoelectric elements are tiny electrically driven actuators needed to keep cavity mirrors precisely aligned. The researchers bypassed this difficulty by housing these components within a titanium substrate that acts as a protective shield for the atoms.

The electric field experienced by the atoms dropped over tenfold. Dependable Rydberg excitation became possible even during active cavity tuning.

“Optical tweezers, optical cavities and Rydberg atoms have each driven remarkable progress in quantum science over the past decade. Bringing them together in a single platform lets us control the interface between light and matter at an entirely new level. We see this as a stepping stone toward quantum processors that talk to each other through light, and toward new ways of creating and shaping entangled states of light and matter,” said Johannes Zeiher, who supervised the experiment.

Atoms couple strongly to the cavity so that a single atom measurably shifts the cavity’s resonance. Groups of up to four atoms exhibit a collective behavior known as Rydberg blockade where one excited atom prevents its neighbors from excitation.