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1. Ultra-low loss quantum photonic circuits integrated with single quantum emitters

   https://doi.org/10.1038/s41467-022-35332-z  

   Chanana, Ashish; Larocque, Hugo; Moreira, Renan; Carolan, Jacques; Guha, Biswarup; Melo, Emerson G.; Anant, Vikas; Song, Jindong; Englund, Dirk; Blumenthal, Daniel J.; et al (December 2022, Nature Communications)

   Abstract The scaling of many photonic quantum information processing systems is ultimately limited by the flux of quantum light throughout an integrated photonic circuit. Source brightness and waveguide loss set basic limits on the on-chip photon flux. While substantial progress has been made, separately, towards ultra-low loss chip-scale photonic circuits and high brightness single-photon sources, integration of these technologies has remained elusive. Here, we report the integration of a quantum emitter single-photon source with a wafer-scale, ultra-low loss silicon nitride photonic circuit. We demonstrate triggered and pure single-photon emission into a Si₃N₄photonic circuit with ≈ 1 dB/m propagation loss at a wavelength of ≈ 930 nm. We also observe resonance fluorescence in the strong drive regime, showing promise towards coherent control of quantum emitters. These results are a step forward towards scaled chip-integrated photonic quantum information systems in which storing, time-demultiplexing or buffering of deterministically generated single-photons is critical. 

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2. Indistinguishable photons from an artificial atom in silicon photonics

   https://doi.org/10.1038/s41467-024-51265-1  

   Komza, Lukasz; Samutpraphoot, Polnop; Odeh, Mutasem; Tang, Yu-Lung; Mathew, Milena; Chang, Jiu; Song, Hanbin; Kim, Myung-Ki; Xiong, Yihuang; Hautier, Geoffroy; et al (August 2024, Nature Communications)

   Abstract Silicon is the ideal material for building electronic and photonic circuits at scale. Integrated photonic quantum technologies in silicon offer a promising path to scaling by leveraging advanced semiconductor manufacturing and integration capabilities. However, the lack of deterministic quantum light sources and strong photon-photon interactions in silicon poses a challenge to scalability. In this work, we demonstrate an indistinguishable photon source in silicon photonics based on an artificial atom. We show that a G center in a silicon waveguide can generate high-purity telecom-band single photons. We perform high-resolution spectroscopy and time-delayed two-photon interference to demonstrate the indistinguishability of single photons emitted from a G center in a silicon waveguide. Our results show that artificial atoms in silicon photonics can source single photons suitable for photonic quantum networks and processors. 

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3. High-speed programmable photonic circuits in a cryogenically compatible, visible–near-infrared 200 mm CMOS architecture

   https://doi.org/10.1038/s41566-021-00903-x  

   Dong, Mark; Clark, Genevieve; Leenheer, Andrew J.; Zimmermann, Matthew; Dominguez, Daniel; Menssen, Adrian J.; Heim, David; Gilbert, Gerald; Englund, Dirk; Eichenfield, Matt (December 2021, Nature Photonics)

   Abstract Recent advances in photonic integrated circuits have enabled a new generation of programmable Mach–Zehnder meshes (MZMs) realized by using cascaded Mach–Zehnder interferometers capable of universal linear-optical transformations on N input/output optical modes. MZMs serve critical functions in photonic quantum information processing, quantum-enhanced sensor networks, machine learning and other applications. However, MZM implementations reported to date rely on thermo-optic phase shifters, which limit applications due to slow response times and high power consumption. Here we introduce a large-scale MZM platform made in a 200 mm complementary metal–oxide–semiconductor foundry, which uses aluminium nitride piezo-optomechanical actuators coupled to silicon nitride waveguides, enabling low-loss propagation with phase modulation at greater than 100 MHz in the visible–near-infrared wavelengths. Moreover, the vanishingly low hold-power consumption of the piezo-actuators enables these photonic integrated circuits to operate at cryogenic temperatures, paving the way for a fully integrated device architecture for a range of quantum applications. 

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4. Room-temperature single-photon emitters in silicon nitride

   https://doi.org/10.1126/sciadv.abj0627  

   Senichev, Alexander; Martin, Zachariah O.; Peana, Samuel; Sychev, Demid; Xu, Xiaohui; Lagutchev, Alexei S.; Boltasseva, Alexandra; Shalaev, Vladimir M. (December 2021, Science Advances)

   Single-photon emitters are essential in enabling several emerging applications in quantum information technology, quantum sensing, and quantum communication. Scalable photonic platforms capable of hosting intrinsic or embedded sources of single-photon emission are of particular interest for the realization of integrated quantum photonic circuits. Here, we report on the observation of room-temperature single-photon emitters in silicon nitride (SiN) films grown on silicon dioxide substrates. Photophysical analysis reveals bright (>10 5 counts/s), stable, linearly polarized, and pure quantum emitters in SiN films with a second-order autocorrelation function value at zero time delay g (2) (0) below 0.2 at room temperature. We suggest that the emission originates from a specific defect center in SiN because of the narrow wavelength distribution of the observed luminescence peak. Single-photon emitters in SiN have the potential to enable direct, scalable, and low-loss integration of quantum light sources with a well-established photonic on-chip platform. 

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5. Entangled photon pair generation in an integrated SiC platform

   https://doi.org/10.1038/s41377-024-01443-z  

   Rahmouni, Anouar; Wang, Ruixuan; Li, Jingwei; Tang, Xiao; Gerrits, Thomas; Slattery, Oliver; Li, Qing; Ma, Lijun (December 2024, Light: Science & Applications)

   Abstract Entanglement plays a vital role in quantum information processing. Owing to its unique material properties, silicon carbide recently emerged as a promising candidate for the scalable implementation of advanced quantum information processing capabilities. To date, however, only entanglement of nuclear spins has been reported in silicon carbide, while an entangled photon source, whether it is based on bulk or chip-scale technologies, has remained elusive. Here, we report the demonstration of an entangled photon source in an integrated silicon carbide platform for the first time. Specifically, strongly correlated photon pairs are efficiently generated at the telecom C-band wavelength through implementing spontaneous four-wave mixing in a compact microring resonator in the 4H-silicon-carbide-on-insulator platform. The maximum coincidence-to-accidental ratio exceeds 600 at a pump power of 0.17 mW, corresponding to a pair generation rate of (9 ± 1) × 10³pairs/s. Energy-time entanglement is created and verified for such signal-idler photon pairs, with the two-photon interference fringes exhibiting a visibility larger than 99%. The heralded single-photon properties are also measured, with the heraldedg⁽²⁾(0) on the order of 10⁻³, demonstrating the SiC platform as a prospective fully integrated, complementary metal-oxide-semiconductor compatible single-photon source for quantum applications. 

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