Xinan Xu

Ultralow power all-optical diode in photonic crystal heterostructures with broken spatial inversion symmetry

We experimentally realize an all-optical diode in a photonic crystal heterostructure with broken spatial inversion symmetry. The physical mechanism is attributed to bandgaps only for certain wavevectors and the transition between different electromagnetic Bloch modes, without any nonlinearity and high power requirement. An ultralow photon intensity of 50 kW/cm2 and an ultrahigh transmission contrast of over 103 are reached simultaneously. Compared with previous reported all-optical diodes, the operating power is reduced by seven orders of magnitude, while the transmission contrast is enlarged by two orders of magnitude. This approach may open a way for the study of integrated photonic devices.

Strongly coupled slow-light polaritons in one-dimensional disordered localized states

Cavity quantum electrodynamics advances the coherent control of a single quantum emitter with a quantized radiation field mode, typically piecewise engineered for the highest finesse and confinement in the cavity field. This enables the possibility of strong coupling for chip-scale quantum processing, but till now is limited to few research groups that can achieve the precision and deterministic requirements for these polariton states. Here we observe for the first time coherent polariton states of strong coupled single quantum dot excitons in inherently disordered one-dimensional localized modes in slow-light photonic crystals. Large vacuum Rabi splittings up to 311 μeV are observed, one of the largest avoided crossings in the solid-state. Our tight-binding models with quantum impurities detail these strong localized polaritons, spanning different disorder strengths, complementary to model-extracted pure dephasing and incoherent pumping rates. Such disorder-induced slow-light polaritons provide a platform towards coherent control, collective interactions, and quantum information processing.

Photonic realization of topologically protected bound states in domain-wall waveguide arrays

We present an analytical theory of 2D topologically protected guided photonic modes for continuous periodic dielectric structures, modulated by a domain wall. We then numerically corroborate the applicability of this theory for 3D structures.

Near-infrared Hong-Ou-Mandel interference on a silicon quantum photonic chip

Near-infrared Hong-Ou-Mandel quantum interference is observed in silicon nanophotonic directional couplers with raw visibilities on-chip at 90.5%. Spectrally-bright 1557-nm two-photon states are generated in a periodically-poled KTiOPO₄ waveguide chip, serving as the entangled photon source and pumped with a self-injection locked laser, for the photon statistical measurements. Efficient four-port coupling in the communications C-band and in the high-index-contrast silicon photonics platform is demonstrated, with matching theoretical predictions of the quantum interference visibility. Constituents for the residual quantum visibility imperfection are examined, supported with theoretical analysis of the sequentially-triggered multipair biphoton, towards scalable high-bitrate quantum information processing and communications. The on-chip HOM interference is useful towards scalable high-bitrate quantum information processing and communications.