Zhichuan Niu

We report InAs/AlSb triple-barrier resonant tunneling diodes (TB-RTDs) exhibiting one-sided negative differential conductance (NDC) and pronounced zero-bias nonlinearity at room temperature. A peak current of 320.1 µ A is obtained at a negative collector bias of −0.34 V, with a peak-to-valley current ratio of 6.61. The observed polarity-selective transport is interpreted in terms of a resonance channel involving the first quasi-bound state (QBS) in the collector-side well and the second QBS in the emitter-side well. An absolute curvature coefficient of 23.14 V ⁻¹ is obtained at zero bias, indicating strong intrinsic rectification behavior. These results identify mixed-order quasi-bound-state coupling in asymmetric InAs/AlSb TB-RTDs as a viable route to polarity-selective NDC and strong zero-bias nonlinear response.

Charged quantum dots (QD) coupled to micropillar cavities are key platforms for studying photon-spin interactions. However, most research involves quantum dots charged via external excitation, resulting in short charge lifetimes. We demonstrate a device where a quantum dot confines an extra electron through δ -doping and couples to a high Q -factor (about 11 000) micropillar cavity mode (CM). We propose a precise calibration process for the micropillar cavity to achieve coupling between the negatively charged exciton (X−) transitions and CM at low temperatures. Micro-photoluminescence ( μ PL) spectroscopy confirms X− transitions and their coupling with CM at 7 K, with the coupled emission intensity enhanced about tenfold relative to the uncoupled state. The X− transitions and CM both show low spectral fluctuations at the change of polarization of incident light (X− 2.66 μ eV, CM 3 μ eV).

Polarized single-photon sources (SPSs) are valuable for quantum information applications and can be implemented by exploiting an elliptical or birefringent cavity that provide polarization-selective Purcell enhancement. However, current designs suffer from similar quality (Q) factors of split cavity modes, requiring both high Purcell factor and substantial mode splitting for ideal polarization performance. Here, we report a low-Purcell anisotropic Dirac cavity that supports orthogonally polarized modes with significantly distinct Q factors (1032 vs 98). When coupled to a single quantum dot, this cavity enables single-photon emission [g^{(2)}(0)=0.028] with >99% degree of linear polarization (DoLP). The high DoLP is tolerant to emission wavelength, originating from suppression of competing radiative channels. Lifetime measurements demonstrate a 1.72-fold enhancement at cavity resonance and a 3.47-fold inhibition in a photonic band gap. Additionally, the anisotropic Dirac cavity exhibits vertical directionality with simulated collection efficiency up to 92.7%. Our results offer a novel strategy toward ideal solid-state polarized SPSs.

Resonance fluorescence from a two-level emitter is a standard route to single-photon generation, where the emitter produces only one photon at a time, and multiphoton emission or scattering is inherently suppressed. In this study, we challenge this paradigm in the weak-excitation limit, where coherent scattering dominates. Using a single quantum dot in a microcavity, we show that the incoherent component exhibits pronounced superbunching, revealing simultaneous multiphoton scattering from a single emitter. In contrast, the total reflected field—comprising the reflected driving field and incoherent scattering—displays perfect antibunching, arising from quantum interference that cancels two-photon probability amplitudes. By spectrally filtering the reflected field, we tune the relative contributions of coherent and incoherent components, observing transitions in photon statistics from antibunching to superbunching, or to Poissonian light. Supported by master-equation simulations and an interference-based model, these results uncover the hidden but fundamental role of multiphoton dynamics in resonance fluorescence, and open avenues for generating nonclassical light in cavity and waveguide quantum electrodynamics.

Entangled photon sources (EPSs) are essential for quantum science and technology. Despite advancements in integrated optical platforms like thin-film lithium niobate, a scalable, high-performance, chip-scale EPS has remained elusive. We address this by demonstrating an electrically pumped, post-selection-free polarization EPS, achieved through hybrid integration of a distributed feedback laser with a thin-film lithium niobate chip, which integrates periodically poled lithium niobate waveguides, a beam splitter, and a polarization rotator combiner. By injecting current into the chip, we realize a high-performance EPS with a bandwidth of 73 nm and an entanglement pair generation rate of 4.5×10^{10} pairs/s/mW. The polarization entanglement shows Bell-state fidelities above 96% across frequency-correlated modes. This compact, integrated EPS enables key applications, including high-speed quantum key distribution via wavelength division multiplexing, satellite-based quantum communication, and entanglement-based quantum metrology.

Two-photon interference (TPI) underpins many photonic quantum technologies and is commonly regarded as a quantum effect requiring indistinguishable photons. Here, we demonstrate TPI between single photons with ultralong coherence time and an independent continuous-wave laser. The measurements reveal a sharp antibunching dip, governed by the single-photon correlation time, together with a broad Hong-Ou-Mandel dip whose half-width is set by the mutual coherence time of the two sources. We achieve a maximum TPI visibility of 72 ± 2 % , well above the 50 % classical limit, thereby confirming the quantum nature of TPI. At the same time, we observe a broad visibility background and a beat visibility below 50 % , signatures of classical interference. Both quantum and classical visibility features remain unchanged for frequency separations up to 10 4 times the linewidth of the single photons, showing no distinction between distinguishable and indistinguishable photons. By applying both general wave superposition theory and a quantum field approach, we derive the same cross-correlation functions that quantitatively reproduce the data. Our results show that quantum and classical features of TPI originate from the same underlying fourth-order interference process arising from second-order interference within the mutual coherence time. Photon indistinguishability is a sufficient condition for TPI to occur, but not a necessary one. This insight offers different perspectives for the development of quantum photonic technologies based on independent photons.

We demonstrate a high-power and broad-spectrum GaSb-based superluminescent diode (SLD) emitting around 2.1 μm with an advanced cascade cavity suppression (ACCS) waveguide geometry, where the most appropriate combination of the ACCS waveguide geometry was identified through optimizing the mode distribution overlap integral of different curved radii and tilt angles of SLD's waveguide geometry. The SLD performs an exceptional single-transverse-mode optical output power of up to 300 mW at room temperature (RT) under the continuous wave (CW) operation and a broad spectrum with a full width at half maximum (FWHM) of 90 nm and a 15°FWHM divergence angle. The emitting structure, grown by molecular beam epitaxy (MBE) technique, consists of two compressively strained InGaSb/AlGaAsSb type-I quantum wells, which ensures superior optical output power. An ultra-low antireflection (UAR) coating was employed with the ACCS waveguide to achieve its amplified spontaneous emission (ASE) and prevent the potential of lasing. Above all, the high power, broad spectrum, and high-quality light source can satisfy demands for mid-wave infrared (MWIR) heterogeneous integration with photonic integrated circuits for spectroscopic sensing and address the need for coupling to external cavity elements with silicon waveguides to achieve further applications.

An extended-wavelength InGaAsSb focal plane array (FPA) with a 15 μm pixel pitch, 640 × 512 format, and a cutoff wavelength of 3.22 μm is demonstrated. Through the atomic layer deposition Al₂O₃ passivation technology, the natural oxide leakage channel is reduced and the leakage current of the device is well suppressed. The optoelectronic performance of the FPA is close to that of the large-scale test unit. At 180 K, the quantum efficiency of the FPA is 45.6% and the dark current is about 2.76 × 10⁻⁵ A/cm². Laboratory imaging shows potential for applications at temperatures above 200 K.