RESUMEN
Single-photon devices such as switches, beam splitters, and circulators are fundamental components to construct photonic integrated quantum networks. In this paper, two V-type three-level atoms coupled to a waveguide are proposed to simultaneously realize these functions as a multifunctional and reconfigurable single-photon device. When both the two atoms are driven by the external coherent fields, the difference in the phases of the coherent driving induces the photonic Aharonov-Bohm effect. Based on the photonic Aharonov-Bohm effect and setting the two-atom distance to match the constructive or destructive interference conditions among photons travelling along different paths, a single-photon switch is achieved since the incident single photon can be controlled from complete transmission to complete reflection by adjusting the amplitudes and phases of the driving fields. When properly changing the amplitudes and phases of the driving fields, the incident photons are split equally into multiple components as a beam splitter operated with different frequencies. Meanwhile, the single-photon circulator with reconfigurable circulation directions can also be obtained.
RESUMEN
An external mirror coupling to a cavity with a two-level atom inside is put forward to control the photon transport along a one-dimensional waveguide. Using a full quantum theory of photon transport in real space, it is shown that the Rabi splittings of the photonic transmission spectra can be controlled by the cavity-mirror couplings; the splittings could still be observed even when the cavity-atom system works in the weak coupling regime, and the transmission probability of the resonant photon can be modulated from 0 to 100%. Additionally, our numerical results show that the appearance of Fano resonance is related to the strengths of the cavity-mirror coupling and the dissipations of the system. An experimental demonstration of the proposal with the current photonic crystal waveguide technique is suggested.
RESUMEN
Quantum coherent transport through open mesoscopic Aharonov-Bohm rings (driven by static fluxes) have been studied extensively. Here, by using quantum waveguide theory and the Floquet theorem we investigate the quantum transport of electrons along an open mesoscopic ring threaded by a time-periodic magnetic flux. We predicate that current density waves could be excited along such an open ring. As a consequence, a net current could be generated along the lead with only one reservoir, if the lead additionally connects to such a normal-metal loop driven by the time-dependent flux. These phenomena could be explained by photon-assisted processes, due to the interaction between the transported electrons and the applied oscillating external fields. We also discuss how the time-average currents (along the ring and the lead) depend on the amplitude and frequency of the applied oscillating fluxes.
RESUMEN
Aharonov-Bohm (AB) effects in mesoscopic metal rings have been extensively studied. In this paper, we investigate these effects on the persistent currents (PCs) in a closed graphene ring with broken time-reversal symmetry. A hard boundary condition is introduced to describe the Dirac electrons moving along such a ring-shaped configuration, and then the induced persistent currents are numerically calculated. Differing from the properties of PCs revealed in the metal AB rings, we show that the present PCs neither show the regular saw-tooth-like features nor present the odd-even symmetry of the electron number. More interestingly, we show that the energy difference between the two valleys and the amplitude of the oscillating PCs increase with the decrease (increase) of the radius (width) of the graphene ring. Our results imply that the AB effect and size-dependent PCs in ring-shaped microstructures could be tested at room temperature.