环境热噪声是量子计算走向规模化的一大阻碍，其存在对量子调控过程的鲁棒性和保真度提出了更高要求。采用随机动力学结构分解方法，并根据Kubo-Einstein涨落耗散定理，研究了热噪声环境下量子调控的量子动力学优化问题，即如何提高热噪声环境下量子调控过程的保真度。基于二维球面上的经典路径可完全描述单个量子比特运动这一特性，提出了基于梯度下降算法的变分优化方案，并通过数值模拟证明了该方案的可用性。结果发现，在经典极限下影响量子调控过程保真度的主要因素是热涨落。该方法有望与实验相互验证，进一步指导和评估实验方案，以期实现量子门的高保真度。

The dispersive Fourier transform (DFT) technique opens a fascinating pathway to explore ultrafast non-repetitive events and has been employed to study the build-up process of mode-locked lasers. However, the shutting process for the mode-locked fiber laser seems to be beyond the scope of researchers, and the starting dynamics under near-zero dispersion remains unclear. Here, the complete evolution dynamics (from birth to extinction) of the conventional soliton (CS), stretched pulse (SP), and dissipative soliton (DS) are investigated by using the DFT technique. CS, SP, and DS fiber lasers mode locked by single-walled carbon nanotubes (SWNTs) are implemented via engineering the intracavity dispersion map. The relaxation oscillation can always be observed before the formation of stable pulse operation due to the inherent advantage of SWNT, but it exhibits distinct evolution dynamics in the starting and shutting processes. The shutting processes are dependent on the dispersion condition and turn-off time, which is against common sense. Some critical phenomena are also observed, including transient complex spectrum broadening and frequency-shift interaction of SPs and picosecond pulses. These results will further deepen understanding of the mode-locked fiber laser from a real-time point of view and are helpful for laser design and applications.

The ultrafast fiber laser has attracted a great deal of research interest due to its low cost, high efficiency, and simple maintenance. Optical passive devices are vital parts of a fiber laser. In order to obtain a fiber laser with high quality, optical passive devices with high performance are required. Here, we demonstrate a highly integrated optical device with the combination of a saturable absorber (SA), coupler, isolator, wavelength division multiplexer, and erbium-doped fiber. The built-in SA has a modulation depth of 7% and can withstand high pump power due to the unique structure of the proposed device. The proposed device is applied to an ultracompact fiber laser, which greatly simplifies the laser structure and reduces the size of the proposed laser. The central wavelength, pulse duration, repetition rate, and signal-to-noise ratio of the output soliton are 1560 nm, 1.06 ps, 25.8 MHz, and 50 dB, respectively. The proposed device has great potential for application in high-power and high-frequency fiber lasers. The proposed ultracompact fiber laser has important applications in optical communication, optical sensing, optical frequency combs, and micromachining.

Real-time spectroscopy based on an emerging time-stretch technique can map the spectral information of optical waves into the time domain, opening several fascinating explorations of nonlinear dynamics in mode-locked lasers. However, the self-starting process of mode-locked lasers is quite sensitive to environmental perturbation, which causes the transient behaviors of lasers to deviate from the true buildup process of solitons. We optimize the laser system to improve its stability, which suppresses the Q-switched lasing induced by environmental perturbation. We, therefore, demonstrate the first observation of the entire buildup process of solitons in a mode-locked laser, revealing two possible pathways to generate the temporal solitons. One pathway includes the dynamics of raised relaxation oscillation, quasimode-locking stage, spectral beating behavior, and finally the stable single-soliton mode-locking. The other pathway contains, however, an extra transient bound-state stage before the final single-pulse mode-locking operation. Moreover, we propose a theoretical model to predict the buildup time of solitons, which agrees well with the experimental results. Our findings can bring real-time insights into ultrafast fiber laser design and optimization, as well as promote the application of fiber laser.

We investigate the properties of spatial solitons in the fractional Schr dinger equation (FSE) with parity-time (PT)-symmetric lattice potential supported by the focusing of Kerr nonlinearity. Both one- and two-dimensional solitons can stably propagate in PT-symmetric lattices under noise perturbations. The domains of stability for both one- and two-dimensional solitons strongly depend on the gain/loss strength of the lattice. In the spatial domain, the solitons are rigidly modulated by the lattice potential for the weak diffraction in FSE systems. In the inverse space, due to the periodicity of lattices, the spectra of solitons experience sharp peaks when the values of wavenumbers are even. The transverse power flows induced by the imaginary part of the lattice are also investigated, which can preserve the internal energy balances within the solitons.

Reflective fiber optic sensors have advantages for surface roughness measurements of some special workpieces, but their measuring precision and efficiency need to be improved further. A least-squares support vector machine (LS-SVM)-based surface roughness prediction model is proposed to estimate the surface roughness, Ra, and the coupled simulated annealing (CSA) and standard simplex (SS) methods are combined for the parameter optimization of the mode. Experiments are conducted to test the performance of the proposed model, and the results show that the range of average relative errors is 4.232%–2.5709%. In comparison with the existing models, the LS-SVM-based model has the best performance in prediction precision, stability, and timesaving.