分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： The novel physics of twisted bilayer graphene has motivated extensive studies of magic-angle flat bands hosted by moir\'e structures in electronic, photonic and acoustic systems. On the other hand, bound states in the continuum (BICs) have also attracted great attention in recent years because of their potential applications in the field of designing superior optical devices. Here, we combine these two independent concepts to construct a new optical state in a twisted bilayer photonic crystal slab, which is called as moir\'e quasi-BIC, and numerically demonstrate that such an exotic optical state possesses dual characteristics of moir\'e flat bands and quasi-BICs. To illustrate the mechanism for the formation of moir\'e flat bands, we develop an effective model at the center of the Brillouin zone and show that moir\'e flat bands could be fulfilled by balancing the interlayer coupling strength and the twist angle around the band edge above the light line. Moreover, by decreasing the twist angle of moir\'e photonic crystal slabs with flat bands, it is shown that the moir\'e flat-band mode at the Brillouin center gradually approaches a perfect BIC, where the total radiation loss from all diffraction channels is significantly suppressed. To clarify the advantage of moir\'e quasi-BICs, enhanced second-harmonic generation (SHG) is numerically proven with a wide-angle optical source. The efficiency of SHG assisted by designed moir\'e quasi-BICs can be greatly improved compared with that based on dispersive quasi-BICs with similar quality factors.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Locally chiral light (LCL) is a promising tool for probing and controlling molecular chirality. The pioneering tricolor LCLs' degrees of chirality (DOCs) change periodically in space and vanish by integrating over the whole spatial period, making them cease to be globally effective (i.e., globally achiral). Locally and globally chiral light (LGCL) is a type of more efficient LCL whose DOCs survive by integrating but still change periodically in space. Here, we propose a scheme to generate a new type of LCL called uniformly locally chiral light (ULCL). ULCLs are globally chiral and have spatially uniform DOCs, which makes them superior to current types of LCLs in studies of chiral molecules. By applying the ULCLs in an optical molecular-chirality switch, the racemic mixtures can be converted to enantiopure samples without size restrictions, where the perfect control of molecular chirality with a global efficiency of $100\%$ is predicted, which is twice that of LGCLs. Our work potentially constitutes the starting point for developing more efficient chiroptical techniques for probing and controlling molecular chirality.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Integrated quantum memories are a scalable solution to synchronize a large number of quantum computers, which are essential to build a quantum network to boost their capabilities on information processing. Rather than expecting to find a specific kind of atoms to meet all the requirements of a good quantum memory, as other protocols usually do, we propose that assigning the memory requirements on coherence property and control property to rare earth ions and lithium niobate crystal, respectively. In particular, optical quantum states are stored into erbium doped lithium niobate (Er$^{3+}$:LiNbO$_3$) micro-cavity by utilizing the electro-optic effect of LiNbO$_3$. The Er$^{3+}$:LiNbO$_3$ cavity frequency can be shifted by an external electric field, which is used to control the photon-echo emission by changing the resonance condition between micro-cavity and collective atomic excitation. According to calculations, high efficiency and low noise storage can be achieved. Benefiting from the host lithium-niobate thin film, such a device can be controlled by on-chip electrodes and is easy to be integrated with modern photonic devices, paving way of integrated quantum chips.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： As an important imaging technique, holography has been realized with different physical dimensions of light,including polarization, wavelength, and time. Recently, quantum holography has been realized by utilizing polarization entangled state with the advantages of high robustness and enhanced spatial resolution, comparing with classical one. However, the polarization is only a two-dimensional degree of freedom, which greatly limits the capacity of quantum holography. Here, we propose a method to realize high-dimensional quantum holography by using high-dimensional orbital angular momentum (OAM) entanglement. A high capacity OAM-encoded quantum holographic system can be obtained by multiplexing a wide range of OAM-dependent holographic images. Proof-of-principle experiments with four- and six-dimensional OAM entangled states have been implemented and verify the feasibility of our idea. Our experimental results also demonstrate that the high-dimensional quantum holography shows a high robustness to classical noise. Furthermore, OAMselective holographic scheme for quantum encryption is proposed and demonstrated. Comparing with the previous schemes, the level of security of holographic imaging encryption system can be greatly improved in our high-dimensional quantum holography.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： The realization of all-optical integration and optical computing has always been our goal. One of the most significant challenges is to make integrated all-optical logic devices as small as possible. Here, we report the implementation of ultra-compact all-optical logic devices and integrated chips on silicon photonic platforms by topology optimization. The footprint for the fabricated all-optical logic gates with XOR and OR functions is only 1.3*1.3 {\mu}m2 (~0.84{\lambda}*0.84{\lambda}), that are the smallest all-optical dielectric logic devices ever verified in experiments in the optical communication range. The ultra-low loss of the optical signal is also demonstrated experimentally (-0.96dB). Furthermore, an integrated chip containing seven major logic gates (AND, OR, NOT, NAND, NOR, XOR, and XNOR) and a half adder is fabricated, where the associated footprint is only 1.3*4.5 {\mu}m2. Our work opens up a new path towards practical all-optical integration and optical computing.
点击量
待评议
点击量
下载量
评论
