Photonics

Quantum entanglement lies at the heart of numerous quantum technologies, yet macroscopic entanglement remains a long-standing challenge to achieve. Here, we theoretically investigate stationary entanglement between a Laguerre–Gaussian (LG) cavity mode and a macroscopic rotating mirror in a double LG cavity optomechanical system with a non-degenerate optical parametric amplifier (NOPA). The two LG cavity modes interact with each other via a NOPA, and one of them is coupled with a rotating mirror through radiation torque. We employ logarithmic negativity to quantify optomechanical entanglement. We analyze the effects of the gain and phase of the NOPA, the pump powers of the two LG cavity modes, the topological charge and cavity detuning of the LG cavity mode coupled with the rotating mirror, and the environmental temperature affect optomechanical entanglement. We find that the presence of the NOPA can significantly enhance optomechanical entanglement and make it more robust against thermal noise. Our results provide a feasible approach for generating robust macroscopic optomechanical entanglement, which may find applications in quantum sensing and quantum networks.

We propose an amplitude–phase-asymmetric hyperbolic-chirped double-ring Airy–Gaussian vortex beam (AHC-DRAGVB). Oppositely signed radial chirps are imposed on the inner and outer rings, respectively, while a hyperbolic-cosine amplitude modulation is applied only to the outer ring. A vectorial tight-focusing model based on Richards–Wolf diffraction is used to examine the effects of the scale factor G, vortex displacement, optical distribution factor b, hyperbolic modulation coefficient κ, and radial-chirp coefficients. The scale factor jointly controls the focal position, depth of focus, and longitudinal peak-intensity ratio. Off-axis vortex displacement modifies the focal distribution and reshapes the focal-plane spin density and polarization ellipses. Increasing b changes the relative Gouy phase and the associated local phase slopes and thereby reconstructs the axial spin texture. Increasing κ enhances longitudinal peak weighting, accompanied by changes in focal widths and competing transverse peaks. Radial chirp further shifts the focal region and modifies the local field, although excessive chirp degrades the intensity balance between foci. Rayleigh-force calculations are complemented by three-dimensional force directions and coordinate cuts to examine the local restoring response for b = 0.3.

The avalanche photodiode (APD) is an optoelectronic detector with superior sensitivity that typically requires a high operating voltage. Reducing the avalanche region size could lower the breakdown voltage, but at the cost of increased excess noise. In this work, a scattering-engineered APD (SE APD) is proposed to reduce the operating voltage while maintaining a low excess noise merit. In SE APD, a special staggered-finger doping profile is used to spatially separate the electron-ionization path and the hole-transport path via scattering mechanisms, thereby enabling electron unipolar ionization. In SE APD, avalanche occurs at a very low reverse bias of ~2 V in the current–gain–voltage test; an extremely low ionization coefficient ratio (k-value) of 0.003 @ gain = 40 is verified by the noise power spectral density test. A low temperature-dependent breakdown drift coefficient of ~10 mV/K is obtained, indicating good thermal stability. Through comparative experiments, it is demonstrated that the SE APD can increase the gain–bandwidth product by fivefold when compared with the traditional APD structure. Furthermore, the width of the electron ionization multiplication path should be moderate, allowing holes to scatter into the transport path while retaining more electrons within the multiplication path.