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1. Photonic crystal cavities with germanium vacancy color centers in diamond (Conference Presentation)

   https://doi.org/10.1117/12.2507722  

   Akimov, Alexey Alajlan ( March 2019 , Proc. SPIE)

   Development of quantum information processing requires realization of solid state structures able to manipulate light or matter quantum bits. One of the promising candidates for been active elements of such solid-state platform are color centers in diamond. The most famous nitrogen-vacancy color center has number of attractive features and found a lot of applications in sensing and imaging. Still, it has number of considerable disadvantages, among which it sensitivity to the surface damages and thus its incompatibility with nanostructures. On another side implementation of nano- and micro- structures enabled considerable progress in manipulation of light quanta. In particular photonic crystal cavities allowed to realize strong coupling of cavity and spin system. This led to demonstration of efficient light collection and realization of simple quantum gates with artificial or real atoms. Novel color centers such as silicon-vacancy or germanium-vacancy color center due to inversion symmetry of the electron structure are not sensitive to the surface damages and presence of surface nearby. Thus, those are perfect candidates for been combined with photonic crystal structures. Novel technologies enabled growing of the nanodiamonds of ultra-small size having well-defined color center inside. Along with techniques to position those precisely on the nano- and micro structures these achievements opened opportunity to integrate high-fines photonic-crystal cavities with the germanium-vacancy containing nanocrystals thus forming fully solid-state platform for quantum manipulation of light. In my talk I will describe our progress towards realization of this ambitious goal 

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2. A scalable cavity-based spin–photon interface in a photonic integrated circuit

   https://doi.org/10.1364/OPTICAQ.509233  

   Chen, Kevin_C ; Christen, Ian ; Raniwala, Hamza ; Colangelo, Marco ; De_Santis, Lorenzo ; Shtyrkova, Katia ; Starling, David ; Murphy, Ryan ; Li, Linsen ; Berggren, Karl ; et al ( April 2024 , Optica Quantum)

   A central challenge in quantum networking is transferring quantum states between different physical modalities, such as between flying photonic qubits and stationary quantum memories. One implementation entails using spin–photon interfaces that combine solid-state spin qubits, such as color centers in diamond, with photonic nanostructures. However, while high-fidelity spin–photon interactions have been demonstrated on isolated devices, building practical quantum repeaters requires scaling to large numbers of interfaces yet to be realized. Here, we demonstrate integration of nanophotonic cavities containing tin-vacancy (SnV) centers in a photonic integrated circuit (PIC). Out of a six-channel quantum microchiplet (QMC), we find four coupled SnV-cavity devices with an average Purcell factor of ∼7. Based on system analyses and numerical simulations, we find with near-term improvements this multiplexed architecture can enable high-fidelity quantum state transfer, paving the way toward building large-scale quantum repeaters.

    

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3. Polariton creation in coupled cavity arrays with spectrally disordered emitters

   https://doi.org/10.1088/2633-4356/ad3b5d  

   Patton, J. T. ; Norman, V. A. ; Mann, E. C. ; Puri, B. ; Scalettar, R. T. ; Radulaski, M. ( April 2024 , Materials for Quantum Technology)

   Integrated photonics has been a promising platform for analog quantum simulation of condensed matter phenomena in strongly correlated systems. To that end, we explore the implementation of all-photonic quantum simulators in coupled cavity arrays with integrated ensembles of spectrally disordered emitters. Our model is reflective of color center ensembles integrated into photonic crystal cavity arrays. Using the Quantum Master equation and the Effective Hamiltonian approaches, we study energy band formation and wavefunction properties in the open quantum Tavis–Cummings–Hubbard framework. We find conditions for polariton creation and (de)localization under experimentally relevant values of disorder in emitter frequencies, cavity resonance frequencies, and emitter-cavity coupling rates. To quantify these properties, we introduce two metrics, the polaritonic and nodal participation ratios, that characterize the light-matter hybridization and the node delocalization of the wavefunction, respectively. These new metrics combined with the Effective Hamiltonian approach prove to be a powerful toolbox for cavity quantum electrodynamical engineering of solid-state systems.

    

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4. Purcell enhancement of a single T center in a silicon nanophotonic cavity

   Johnston, Adam ; Felix-Rendon, Ulises ; Wong, Yu-En ; Chen, Songtao ( March 2024 , Bulletin of the American Physical Society)

   Optically addressable atomic defects in solids are promising building blocks for future quantum communication technologies. The silicon-on-insulator (SOI) platform is an ideal host for such defects as it benefits from technologically mature silicon photonics and electronics. The novel T center in silicon offers telecommunication O-band optical transitions as well as a doublet ground state spin manifold with a long coherence time, making it a prime candidate for building quantum repeater devices. However, T centers’ weak coherent zero phonon line (ZPL) emission rate stands as an obstacle to their use in quantum networking applications. Here, by integrating single T centers with a low-loss, small mode-volume photonic crystal cavity on SOI, we demonstrate cavity-enhanced fluorescence emission from a single T center with an enhancement factor up to F = 6.89. Leveraging nanophotonic circuits and an angle-polished fiber for light coupling, the system achieves efficient ZPL photon extraction reaching an average outcoupling rate of 73.3 kHz. Lastly, by solving the Lindblad master equation, we extract the T-center-cavity coupling parameters and elucidate the cavity quantum electrodynamics of the coupled system. This work represents a major step towards utilizing single T centers in silicon for quantum information processing and networking applications. 

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5. Hybrid Si-GaAs photonic crystal cavity for lasing and bistability

   https://doi.org/10.1364/OE.496081  

   Rahaman, Mohammad_Habibur ; Lee, Chang-Min ; Atabey_Buyukkaya, Mustafa ; Zhao, Yuqi ; Waks, Edo ( October 2023 , Optics Express)

   The heterogeneous integration of silicon with III-V materials provides a way to overcome silicon’s limited optical properties toward a broad range of photonic applications. Hybrid modes are a promising way to integrate such heterogeneous Si/III-V devices, but it remains unclear how to utilize these modes to achieve photonic crystal cavities. Herein, using 3D finite-difference time-domain simulations, we propose a hybrid Si-GaAs photonic crystal cavity design that operates at telecom wavelengths and can be fabricated without requiring careful alignment. The hybrid cavity consists of a patterned silicon waveguide that is coupled to a wider GaAs slab featuring InAs quantum dots. We show that by changing the width of the silicon cavity waveguide, we can engineer the hybrid modes and control the degree of coupling to the active material in the GaAs slab. This provides the ability to tune the cavity quality factor while balancing the device’s optical gain and nonlinearity. With this design, we demonstrate cavity mode confinement in the GaAs slab without directly patterning it, enabling strong interaction with the embedded quantum dots for applications such as low-power-threshold lasing and optical bistability (156 nW and 18.1µW, respectively). This heterogeneous integration of an active III-V material with silicon via a hybrid cavity design suggests a promising approach for achieving on-chip light generation and low-power nonlinear platforms.

    

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