Multidimensional synthetic chiral-tube lattices via nonlinear frequency conversion

Geometrical dimensionality plays a fundamentally important role in the topological effects arising in discrete lattices.Although direct experiments are limited by three spatial dimensions,the research topic of synthetic dimensions implemented by the frequency degree of freedom in photonics is rapidly advancing.The manipulation of light in these artificial lattices is typically realized through electro-optic modulation;yet,their operating bandwidth imposes practical constraints on the range of interactions between different frequency components.Here we propose and experimentally realize all-optical synthetic dimensions involving specially tailored simultaneous short-and long-range interactions between discrete spectral lines mediated by frequency conversion in a nonlinear waveguide.We realize triangular chiral-tube lattices in three-dimensional space and explore their four-dimensional generalization.We implement a synthetic gauge field with nonzero magnetic flux and observe the associated multidimensional dynamics of frequency combs,all within one physical spatial port.We anticipate that our method will provide a new means for the fundamental study of high-dimensional physics and act as an important step towards using topological effects in optical devices operating in the time and frequency domains.

Photon-pair generation in a quadratically nonlinear parity-time symmetric coupler

Integrated nonlinear waveguide structures enable generation of quantum entangled photons. We describe theoretically the effects of spatially inhomogeneous loss on the creation of photon pairs through spontaneous parametric down-conversion in quadratically nonlinear directional couplers, where photons experience effective parity-time(PT) symmetric potential due to the presence of optical loss in one of the waveguides. We show that for losses below the PT-breaking threshold, the quantum photon states can be flexibly tuned similarly to conservative couplers, whereas for stronger losses, the correlations between two waveguide modes are suppressed. We also formulate a quantum-classical correspondence with sum-frequency generation for fast evaluation of device performance.These results can be applied for the design of quantum plasmonic circuits.

Topologically protecting squeezed light on a photonic chip

Squeezed light is a critical resource in quantum sensing and information processing. Due to the inherently weak optical nonlinearity and limited interaction volume, considerable pump power is typically needed to obtain efficient interactions to generate squeezed light in bulk crystals. Integrated photonics offers an elegant way to increase the nonlinearity by confining light strictly inside the waveguide. For the construction of large-scale quantum systems performing many-photon operations, it is essential to integrate various functional modules on a chip. However, fabrication imperfections and transmission cross talk may add unwanted diffraction and coupling to other photonic elements, reducing the quality of squeezing. Here, by introducing the topological phase, we experimentally demonstrate the topologically protected nonlinear process of four-wave mixing, enabling the generation of squeezed light on a silica chip. We measure the cross-correlations at different evolution distances for various topological sites and verify the nonclassical features with high fidelity. The squeezing parameters are measured to certify the protection of cavity-free, strongly squeezed states. The demonstration of topological protection for squeezed light on a chip brings new opportunities for quantum integrated photonics,opening novel approaches for the design of advanced multi-photon circuits.