Based on the broken spatial symmetry, we propose a scheme for engineering a unidirectional photonic reflector using a one-dimensional atomic lattice with defective cells that have been specifically designed to be vacant. By trapping three-level atoms and driving them into the regime of electromagnetically induced transparency, and through the skillful design of the number and position of vacant cells in the lattice, numerical simulations demonstrate that a broad and high unidirectional reflection region can be realized within the EIT window. This proposed unidirectional reflector scheme provides a new platform for achieving optical nonreciprocity and has potential applications for designing optical circuits and devices of nonreciprocity at extremely low energy levels. Published by the American Physical Society 2024
Based on the broken spatial symmetry, we propose a scheme for engineering a unidirectional photonic reflector using a one-dimensional atomic lattice with defective cells that have been specifically designed to be vacant. By trapping three-level atoms and driving them into the regime of electromagnetically induced transparency, and through the skillful design of the number and position of vacant cells in the lattice, numerical simulations demonstrate that a broad and high unidirectional reflection region can be realized within the EIT window. This proposed unidirectional reflector scheme provides a new platform for achieving optical nonreciprocity and has potential applications for designing optical circuits and devices of nonreciprocity at extremely low energy levels. Published by the American Physical Society 2024
In order to further investigate the non-reciprocity of light propagation in the defective atomic lattices, and due to its effective application in designing novel photonic devices, such as all-optical diodes and isolators, which are powerful tools for information processing and quantum simulation, we innovatively propose to use the Fibonacci sequence to modulate the arrangement of empty lattice cells that form a quasi periodic defective atomic lattices. In the electromagnetically induced transparency window, the probe light is almost not absorbed under the control of a strong coupling field (see Fig. 1). The numerical simulation indicates that a wide nonreciprocal reflection band can be achieved by modulating the number of filled lattice cells, Fibonacci sequence, the period number in a single quasi period (see Fig. 2). These results provide more degrees of freedom for regulating nonreciprocal reflection with wide bandwidth and high contrast, and have potential applications in quantum computing and information processing.
We extend a recent theoretical work [ Phys. Rev. A 101 , 053856 ( 2020 ) 10.1103/PhysRevA.101.053856 ] by replacing disorders characterized by varied atomic densities with defects characterized by vacant lattice cells to evaluate again three-color reflection in a one-dimensional optical lattice filled with cold 87Rb atoms. This is based on the consideration that trapped atoms may escape from some lattice cells and effects of vacant cells on light propagation are of major importance from both fundamental and applied research viewpoints. We consider two types of defective atomic lattices where vacant cells are randomly or continuously distributed among filled cells. Numerical results show that the wider reflection band in a large detuning region of negligible off-resonance absorption is quite sensitive to, while the narrower reflection bands in two near-resonant regions of electromagnetically induced transparency are rather robust against, the number of random vacant cells. In contrast, all three reflection bands exhibit strong robustness against the number of continuous vacant cells. Note, however, that both narrower reflection bands may become widened and exhibit a blue shift when continuous vacant cells appear in the front of our atomic lattice due to the joint contributions of Bragg scattering and quantum interference.
Based on spatial symmetry breaking, we propose a tunable unidirectional zero-reflection scheme in a one-dimensional single-defect atomic lattice. Reflection suppression stems from destructive interference between the direct-reflection and multiple-scattering components, whose amplitudes and phases are co-modulated by coherent atomic response, Bragg scattering, and structural asymmetry. The system supports both broadband and narrowband asymmetric-reflection regions, each containing a unidirectional zero-reflection point, with the minimum reflectivity reaching below 10 −6 in one incident direction while remaining above 0.93 in the reverse direction. External coherent fields tune the UZR frequency, and the vacant-region length modulates phase and scattering amplitudes for zero-reflection at discrete incident angles. Boasting robustness against atom number density fluctuations, this work provides an intuitive theoretical framework for directional scattering, promising tunable optical switches, low-back-reflection photonic structures, and asymmetric light-control devices.
Simultaneously realizing nonreciprocity and signal amplification in the same physical system cannot only greatly enhance the efficiency of nonreciprocal photonic devices but also facilitate their integration. We propose a scheme to achieve gain-assisted nonreciprocal or even unidirectional reflection amplification by exploring spontaneously generated coherence (SGC) activated by a weak incoherent pump in a defective atomic lattice. The numerical results show that the monochromatic to two-color nonreciprocal reflection amplification (the maximum of reflectivities R l ≃ 10 4 and R r ≃ 10 2 ), and even unidirectional reflection amplification ( R l ≃ 10 2 and R r ≃ 10 −4 ) can be modulated freely by adjusting the relative phase ϕ , the dipole moment angle θ and the parameters of defective atomic lattice, e.g., the number and period of vacant lattice cells, the period of filled lattice cells, and so on. This indicates that nonreciprocal reflection amplification can be enhanced and modulated via the SGC effect and multiple reflections within the atomic lattice. Such efficient nonreciprocal amplification can be effectively applied to integrated chips, thereby advancing the development of quantum information technology.
Improving the performance of non-reciprocal photonic devices is one of the key factors for promoting the development of quantum networks. To achieve this goal, we propose a scheme to realize multicolored unidirectional reflection amplification in the defective atomic lattice, with all atoms trapped in each filled lattice cell being driven into a four-level diamond-type coherent gain atomic system by two coupling fields and two probe fields. Therefore, this scheme simultaneously achieves light amplification (resulting from the joint effect of the coherent gain atomic system and the distributed feedback mechanism of the atomic lattice) and non-reciprocity (arising from the symmetry-breaking effect of the defective atomic lattice) in a single physical system. Furthermore, we propose a reasonable scheme for obtaining equivalent results by reducing the energy level structure, and through numerical simulations and calculations, it is concluded that perfect unidirectional reflection amplification requires that the two-photon resonance is not only located in the gain region, but also satisfies the Bragg condition. This scheme can be used to design non-reciprocal photonic devices that are easily integrable, high-efficiency, and capable of flexible multi-channel manipulation.
Unidirectional lasing is highly desirable for practical high-performance quantum information processing platforms, while most existing schemes still rely on the combination of resonant cavities and nonreciprocal mechanisms. Here, we propose a cavity-free scheme for achieving the onset of narrowband unidirectional reflection lasing (URL) in a single physical system by introducing a coherent gain atomic medium into a one-dimensional defective atomic lattice, where the former amplifies the probe field and the latter provides spatial symmetry breaking and a distributed-feedback mechanism. We show that the threshold condition for URL, characterized by λ + −1 ≃ λ − −1 →0, can be tuned from single-mode to dual-mode by varying the microwave field and the lattice structure. Its underlying mechanism lies in the constructive or destructive interference between the reflections from both sides under distinct Bragg conditions.