The technologies of ultrasound detection have a wide range of applications in marine science and industrial manufacturing. With the variation of the environment, the requirements of anti-interference, miniaturization, and ultra-sensitivity are put forward. Optical microcavities are often carefully designed for a variety of ultra-sensitive detections. Using the packaged microsphere cavity, we fabricated an ultrasound sensor that can work in an underwater environment. During practical detection, the optical resonance mode of the cavity can work with real-time response accordingly. The designed structure can work in various complex environments and has advantages in the fields of precision measurement and nano-particle detection.

Photon blockade provides an effective way to realize the single-photon source, which attracts intensive attention in the fields of quantum optics and quantum information. Here in this study, we investigate photon blockade in a non-Hermitian indirectly coupled resonator system, which consists of a dissipative cavity and a Kerr nonlinear resonator coupled to two nano-scatters. We find that by tuning the coupling phase θ between the two resonators, the quantum interference could be induced on one side near the exceptional points (EPs), resulting in the unconventional photon blockade effect. Furthermore, it is noticed that the large Kerr nonlinearity is not always beneficial for unconventional photon blockades. There is an optimal threshold for the intensity of the Kerr nonlinearity and the phase angle θ for the appearance of the unconventional photon blockade effect. We believe the current study has substantial consequences for investigating the physical characteristics close to EPs and presents a novel method for developing integrated on-chip single-photon sources.

The satellite-based measurement-device-independent quantum key distribution can promote the realization of quantum communication networks. Under the condition of the limited data set, it is necessary to optimize all parameters. For communication networks, real-time prediction and optimization are also indispensable. With the development of machine learning, cross-combination with machine learning has also become the mainstream of parameter optimization in various disciplines. This paper discusses the asymmetric MDI-QKD based on the satellite in the case of statistical fluctuations, and uses the local search algorithm to achieve full parameter optimization under the condition of considering the probability of sending the signal. Compared with fixed related parameters, the key rate is increased by an order of magnitude. On this basis, random forest is used to predict the high-precision optimal parameters, thereby eliminating the simulation and iteration required by the search method to meet the real-time optimization of the future QKD network.

We theoretically investigate the strong coupling phenomenon between a quasi-single molecule and a plasmonic cavity based on the blue-detuned trapping system. The trapping system is made up of a metallic nanohole array. A finite-difference time-domain method is employed to simulate the system, and the molecule is treated as a dipole in simulations. By calculating the electromagnetic field distributions, we obtain the best position for trapping a molecule, and we get the strong coupling phenomenon that there are two splitting peaks in the transmission spectrum when the molecule is trapped in the structure, while only one peak is observed in the one without the molecule. We also find that only when the molecule polarization parallels to the incident light wave vector can we observe a strong coupling phenomenon.