Chronological feed of everything captured from Jeremy O'Brien.
Silica-on-silicon waveguides form directional couplers and interferometers for photonic quantum circuits meeting quantum information requirements. A spectrally tuned photon source generates near-identical photon pairs to test circuit performance. Demonstrated non-classical two-photon interference and a two-photon entangling logic gate with near-unit fidelity advance scalable photonic quantum systems.
Superconducting single-photon detectors (SSPDs) integrated with silica-on-silicon quantum waveguide circuits achieve 92.3±1.0% two-photon interference visibility in a directional coupler at 804 nm, surpassing silicon detectors (89.9±0.3%). This enables operation of controlled-NOT gates and quantum metrology circuits with superior infrared sensitivity, low dark counts, and picosecond timing. The approach paves the way for telecom-wavelength scalable quantum information processing on chip.
Photonic cluster states encoded in polarization can be expanded by deterministically entangling additional path-encoded qubits using a polarization-path controlled-phase gate. This gate is realized stably with a Sagnac interferometer on single photons, enabling precise phase control for measurement basis adjustment. The approach is experimentally validated with a 2-photon, 3-qubit cluster state demonstrating measurement-based quantum computing properties.
Commercial quantum key distribution systems, the first quantum technology, use photons to encode information with detectable eavesdropping. Future quantum technologies will include secure networks, enhanced metrology, lithography, and information processors offering exponential computational advantages. Photonics is central due to photons' high-speed transmission and low-noise properties, leveraging single photons, squeezed laser states, or both alongside photonic advances.
Proposes a QKD protocol using entangled qubit pairs that operates securely in environments with unknown, slowly varying reference frames, requiring only particle delivery direction while tolerating unknown computational basis phases. Achieves asymptotic secret key rate matching the six-state protocol under white noise for two-qubit sources. Extends to higher-dimensional systems like qutrits with detailed physical implementation, enabling applications in earth-to-satellite links and photonic waveguides.