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MIT and Ghent University integrate single photon emitters onto photonic chips

09 Oct 2019

New approach points towards scalable quantum photonic components.

A collaboration between MIT and the Imec-affiliated Photonics Research Group at Ghent University has successfully integrated single photon emitters (SPEs) in 2D layered materials with a silicon nitride photonic chip.

This approach could allow the design of photonic integrated circuit (PIC) platforms without the need for additional processing in the SPE host material, a step towards scalable quantum photonic chips. The work was published in Nature Communications.

SPEs are a key resource for a number of developing quantum technologies in computation, metrology and communications, and developing suitable SPE sources as alternatives to using coherent laser pulses has been a focus of research for these applications. SPEs embedded in 2D transition metal structures can achieve high light extraction efficiencies and are likely to be particularly appealing for large-scale integration.

The MIT group's research into SPEs has already included the use of a dual optical cavity design as a way to increase the number of optically identical photons produced; and a frequency-locking technique based on micro-ring resonators that monitors and corrects frequency variations.

In its new published paper, the research group notes that 2D-SPEs mainly emit in the visible, meaning that the standard silicon-on-insulator PIC platform cannot be used because it is not transparent for these wavelengths, and integration of these structures with a PIC has not been achieved until now.

The breakthrough involved the integration of a tungsten diselenide monolayer emitter onto a silicon nitride (SiN) chip, and the coupling of the 2D-based single photon source with the guided mode of a SiN waveguide.

Scaling up of quantum photonic devices

Such architectures, with integrated cavity-emitter systems evanescently coupled to a waveguide, should optimize single photon extraction and allow the full potential of a high quality and CMOS-compatible PIC platform to be exploited without the need for stringent processing in the host material itself.

"2D-based SPEs can be easily interfaced with PICs and stacked together to create complex heterostructures," commented the project. "Due to their thinness, and the absence of total internal reflection, they enable very high light extraction efficiencies without the need of any additional processing, allowing efficient single photon transfer between the host and the underlying PIC. And 2D materials grown with high wafer-scale uniformity are becoming more readily available."

In trials, second-order correlation measurements on the spectrally isolated quantum emitter confirmed that single photons were emitted with a waveguide-coupled saturation count rate of 100 kHz. The project also found that even for moderate quantum yields, dielectric cavities can be designed such that the single photon extraction into the guided mode reaches unity.

The findings suggest a route to larger quantum photonic circuits, by exploiting recent progress in wafer-scale growth and patterning of identical devices, alongside waveguide-coupled 2D-SPEs.

"These results provide a crucial step in scaling up quantum photonic devices using 2D-based integrated single photon sources," said project leader Frédéric Peyskens.

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