Browsing by Author "Chen, Songtao"

Now showing 1 - 5 of 5
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    An Optical Lattice for Ultracold Strontium
    (2022-10-11) Wang, Chuanyu; Killian, Thomas C.; Pu, Han; Chen, Songtao
    Strongly interacting many-body systems are of great interest in many areas of physics. Ultracold atoms in optical lattices are a powerful tool for creating and studying such systems. In this thesis, the construction and characterization of an 3D optical lattice for a ultra-cold Strontium apparatus is described. A 1064nm fiber amplified laser system is used to create three orthogonal pairs of standing waves that together form the 3D lattice. By delivering 4W of power to each arm of the lattice and focusing the beams to a beam radius of about 250 microns at the location of the atoms, we can create a 3D lattice with a maximum trap depth around 70 photon recoils.
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    Cavity-coupled telecom atomic source in silicon
    (Springer Nature, 2024) Johnston, Adam; Felix-Rendon, Ulises; Wong, Yu-En; Chen, Songtao; Smalley-Curl Institute
    Novel T centers in silicon hold great promise for quantum networking applications due to their telecom band optical transitions and the long-lived ground state electronic spins. An open challenge for advancing the T center platform is to enhance its weak and slow zero phonon line (ZPL) emission. In this work, by integrating single T centers with a low-loss, small mode-volume silicon photonic crystal cavity, we demonstrate an enhancement of the fluorescence decay rate by a factor of F = 6.89. Efficient photon extraction enables the system to achieve an average ZPL photon outcoupling rate of 73.3 kHz under saturation, which is about two orders of magnitude larger than the previously reported value. The dynamics of the coupled system is well modeled by solving the Lindblad master equation. These results represent a significant step towards building efficient T center spin-photon interfaces for quantum information processing and networking applications.
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    Cavity-enhanced telecom atomic source in silicon
    (2024-07-31) Felix Rendon, Ulises; Chen, Songtao
    Quantum networks represent one of the most promising technologies for the future development of quantum information science (QIS), with broad applications that range from secure communication and distributed quantum computing to enhanced sensing. Solid-state platforms are ideal candidates for the implementation of such quantum networks, since they offer easy accessibility to device integration and spin-photon interfaces capable of processing and storing qubits, as well as connecting remote network nodes by sending photons through optical fibers. In this thesis, we focus on single T centers, which are a novel type of color centers in silicon. This quantum defect stands out as a promising candidate for quantum networking applications due to its telecom optical transition, superior spin performance, and its compatibility with the technologically mature silicon platform. Here, we present our initial studies on single T centers, including the design and fabrication of nanophotonic devices in a silicon-on-insulator (SOI) sample with integrated T centers, and the cavity-enhanced fluorescence emission of single T centers, which have achieved the highest Purcell factor (Pt = 43) to date. Moreover, our experimental and numerical results allow us to determine a lower bound to the T center quantum efficiency of η = 23.4%, which is a key optical parameter for T centers that is largely overlooked in the community. Additionally, we present preliminary bulk spectroscopy work on ensemble T centers. The same setup will be exploited towards the exploration of novel quantum defects in silicon, including the boron-carbon (B-C) complex defect and the Ti+ defect, which are expected to have similar or better optical properties than the T center.
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    Purcell Enhancement of a single T center in a silicon nanophotonic cavity
    (2024-07-25) Johnston, Adam; Chen, Songtao
    Implementation of large-scale quantum networks have the potential to augment the capabilities of existing quantum information technologies. By linking quantum processors over photonic channels, future quantum networks could enable applications such as remote quantum sensing, distributed quantum computing, and secure quantum communication. Atomic defects in solids are readily integrated with photonic structures, making them promising candidates for use in quantum networking devices. In particular, the silicon material platform holds great promise due to the technologically mature silicon electronic and photonic industries. The T center defects in silicon possess telecom O-band optical transitions, as well as long-lived electronic and nuclear spins, making it the focus of particular interest. These spin and optical properties of single T centers, together with their accessibility to the existing integrated electronic and photonic technologies, opening the door to modular long-distance quantum networking technologies built on the T center platform. This work outlines the integration of single T centers with a silicon photonic crystal cavity; we observe cavity-enhanced fluorescence emission, resulting in a decay rate enhancement factor of F = 6.89 compared to the bulk emission rate. Through the use of silicon photonic circuits and an angle-polished fiber for light coupling, we achieve a maximum zero phonon line photon outcoupling rate of 73.3 kHz. The design and fabrication of the nanophotonic cavity used in experiment is detailed. This work represents a major step towards use of the silicon T center as a telecom spin-photon interface in future quantum networking applications.
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    Topological Photonic Devices in the UV-visible Spectrum Based on the III-N Wide Bandgap Semiconductor Platform
    (2024-04-19) Li, Tao; Zhao, Yuji; Huang, Shengxi; Chen, Songtao
    Topological photonics, renowned for the edge/interface states resistant to local defects and back-scattering, can be a promising solution for ensuring the stability in integrated photonic platforms and has already found applications in lasers and quantum photonic circuits. However, existing topological photonic demonstrations have primarily operated in the microwave or near-infrared spectrum due to material and nanofabrication limitations. In this thesis, we break through this wavelength barrier and extend the limit into UV-visible spectrum by implementing topological photonics on the III-N wide bandgap semiconductor platform. In the first part of the thesis, we devise a 1D topological photonic cavity fabricated from a gallium nitride on silicon (GaN-on-Si) wafer. The designed cavity has a single resonance mode around the wavelength of 800 nm and shows a simulated quality factor (Q) around 1600. Based on the non-zero second-order susceptibility of the GaN, we further demonstrate the second harmonic generation (SHG) from the 1D topological photonic cavity and reveal the power dependence and polarization dependence of the cavity-based SHG. The second part of the thesis focuses on the design of topological photonic routing devices in the visible spectrum based on 2D photonic crystals (PC) made of hexagonal boron nitride (h-BN). Interfacing 2D h-BN PCs with distinct topological phases gives rise to topological edge states supporting polarization-resolved unidirectional propagation. Through meticulous design of the interfaces’ shape, we demonstrate ultra-compact topological photonic routers. These routers feature 6 input/output ports within a 10 µm × 10 µm footprint and showcase a simulated crosstalk extinction ratio exceeding 15 dB. The results from this thesis underpin the UV-visible topological photonics based on the III-N wide bandgap semiconductor platform and can potentially benefit the design of high-performance integrated photonic devices in the UV-visible spectrum by leveraging the unique properties of photonic topology.