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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. Triangular quantum photonic devices with integrated detectors in silicon carbide

   https://doi.org/10.1088/2633-4356/acc302  

   Majety, Sridhar ; Strohauer, Stefan ; Saha, Pranta ; Wietschorke, Fabian ; Finley, Jonathan J. ; Müller, Kai ; Radulaski, Marina ( March 2023 , Materials for Quantum Technology)

   Triangular cross-section silicon carbide (SiC) photonic devices have been studied as an efficient and scalable route for integration of color centers into quantum hardware. In this work, we explore efficient collection and detection of color center emission in a triangular cross-section SiC waveguide by introducing a photonic crystal mirror on its one side and a superconducting nanowire single photon detector (SNSPD) on the other. Our modeled triangular cross-section devices with a randomly positioned emitter have a maximum coupling efficiency of 89% into the desired optical mode and a high coupling efficiency ($>$75%) in more than half of the configurations. For the first time, NbTiN thin films were sputtered on 4H-SiC and the electrical and optical properties of the thin films were measured. We found that the transport properties are similar to the case of NbTiN on SiO₂substrates, while the extinction coefficient is up to 50% higher for 1680 nm wavelength. Finally, we performed finite-difference time-domain simulations of triangular cross-section waveguide integrated with an SNSPD to identify optimal nanowire geometries for efficient detection of light from transverse electric and transverse magnetic polarized modes.

    

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3. 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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4. 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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5. 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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