Jin Liu

Cavity quantum electrodynamics (cQED) harnesses light-matter interactions to produce nonclassical light states. However, a fundamental challenge lies in simultaneously achieving Purcell enhancement and tailored wave front control within a single cavity, due to conflicting resonator requirements. Here, we overcome this limitation by demonstrating triggered single-photon emission with customizable wave fronts from semiconductor quantum dots embedded in geometric-phase metacavities. These monolithic devices-only 200 nm thick-deliver Purcell-enhanced emission alongside spin-momentum-locked radiation, vortex beams, and holographic patterns depending on the design. The meta-atom lattice provides high-Q optical confinement, while spatially modulated orientations of the elliptical holes enable efficient outcoupling of photons with designed states. This Letter establishes a new paradigm for intrinsically multiplexing metasurface-based wave front shaping with cQED, enabling high-performance quantum light sources from subwavelength-scale monolithic platforms.

A promising pathway towards scalable quantum photonic processors involves the simultaneous integration of deterministic single-photon sources, low-loss photonic circuitry, and fast reconfigurability. Thin-film lithium tantalate on insulator (LTOI) offers an exceptional electro-optic response and low optical loss at 900 nm wavelength band, yet its lack of efficient quantum emitters has hindered progress toward fully integrated quantum technologies. Here, we demonstrate heterogeneous integration of indium arsenide quantum dots (QDs) with low-loss reconfigurable LTOI waveguides (0.30 ± 0.04 dB/cm) using micro-transfer printing. By directly butt-coupling tapered gallium arsenide waveguides with inversely tapered LTOI waveguides, we achieve robust and alignment-tolerant inter-waveguide coupling. The hybrid chip operates at cryogenic temperatures, enabling deterministic routing of successively emitted single photons from the QDs with a half-wave voltage-length product ( ~ 1.9 V·cm at 4 K), confirming the cryogenic stability of LTOI’s electro-optic coefficient. These results establish demonstration of high-speed on-chip routing of single photons with hybrid QD-LTOI circuits, providing a scalable pathway toward integrated quantum photonic processors.

The ultimate non-classic light sources for modern photonic quantum technology require on-demand generation of indistinguishable quantum light with high brightness and flexible engineering of quantum emission in multiple degrees of freedom. In this work, we present monolithic microcavity-metalens interfaces consisting of quantum-dot-micropillar single-photon sources and ultra-thin metalenses accurately aligned on opposite sides of an III-V compound semiconductor chip. The pronounced cavity quantum electrodynamics effect enabled by the micropillar cavity facilitates single-photon emission from quantum dots with simultaneous high degrees of single-photon purity, source brightness and photon indistinguishability while the multi-functional metalenses concurrently tailor quantum emission in multiple physical degrees of freedom including radiation divergence, emission directionality, polarization state and orbital angular momentum (OAM). Furthermore, high-fidelity polarization-OAM entanglement and single photons with local spin topologies are successfully generated in our integrated device. In particular, we demonstrate stable propagations of single-photon skrymions in atmospheric turbulence and reveal their topological advantages over the conventional structured quantum light. Our work advances the research fields of integrated quantum photonics and meta-optics, providing integrated high-dimensional quantum light sources for advanced photonic quantum science and technology.

Reconfigurable interfaces between confined optical modes in integrated photonic chips and structured light in free space would benefit fundamental optical science and photonic technologies. Here we exploit the anisotropic nonlinear susceptibility tensors associated with thin-film lithium niobate to construct nanophotonic chip-space interfaces capable of generating and multidimensionally engineering structured light via injections of photons to on-chip waveguides. Harnessing the nonlinear Čerenkov radiation in integrated nonlinear microring resonators, we tailor the spatial profile, polarization state, emission wavelength, topological charge and temporal wave packet of structured optical vortices, exhibiting reconfigurability and tunability. To showcase the capabilities of our platform, we use continuous-wave excitation to generate tunable optical skyrmions via the spin-orbit coupling and multistate integrated vortex microcombs in the short near-infrared range via synergistic χ⁽²⁾ and χ⁽³⁾ nonlinear optical processes. Our work bridges the research fields of structured light and integrated nonlinear optics, providing opportunities for spatiotemporal light generation and on-chip multidimensional nonlinear optics.

Exceptional points (EPs) are singularities in non-Hermitian systems where at least two eigenstates coalesce. They provide additional control over light–matter interactions and can, for example, enhance radiation from ensembles of photonic emitters. Advanced control over the characteristics of single quantum emitters via EPs remains, however, elusive. Here we engineer the quantum vacuum, the lowest energy state of the electromagnetic field, via a chiral EP to shape the spontaneous emission of a single quantum emitter. We develop a heterogeneously integrated lithium niobate-GaAs photonic circuit comprising high-quality quantum emitters, low-loss photonic circuits, electro-optic modulators and piezoelectric actuators. We dynamically tune the clockwise–counterclockwise mode coupling to access EPs, thereby inducing anomalous spontaneous emission dynamics with a sevenfold lifetime modulation (120–850 ps) and tunable chirality. Furthermore, we shape the emission spectra at the single-photon level via an EP-controlled local density of states, generating squared-Lorentzian, Fano-asymmetric and EP-induced transparency emissions. The latter manifests as a suppression of photon emission at zero detuning, arising from the non-Lorentzian optical response characteristics inherent to EP systems. This work unveils uncommon cavity quantum electrodynamics unique to EPs and exemplifies how the concept of non-Hermitian quantum photonics may contribute towards high-performance topological quantum light sources.

Bound states in the continuum (BICs) provide a route to strong, long-range photonic coupling with dynamic tunability. Recent advances demonstrate that BIC metasurfaces enable reconfigurable two-dimensional coupling between arbitrarily positioned resonators, with the added capability of ultrafast all-optical control.

Hybrid integrated quantum photonics offers a scalable route to chip-based quantum networks by combining solid-state quantum dots (QDs) with low-loss and reconfigurable photonic circuits. However, limited integration scalability, spectral inhomogeneity of QD emissions and the challenge of achieving quantum interference between independent sources have impeded progress towards this goal. Here we demonstrate a hybrid lithium niobate photonic platform integrating arrays of QD-containing waveguides with 20 deterministic single-photon sources. Leveraging the piezoelectric properties of thin-film lithium niobate, we develop a circuit-compatible local strain-tuning technique that enables on-chip spectral tuning of individual QDs by up to 7.7 meV. This capability allows quantum interference with a visibility of 0.73 between two spatially separated waveguide-coupled QD single-photon sources, thereby establishing a functional on-chip quantum network. The large-scale integration of tunable and interconnected QD-based single-photon sources within low-loss lithium niobate circuits paves the way for realizing compact and scalable quantum networks on a photonic chip.