Nonreciprocal single-photon scattering mediated by a driven Λ-type three-level giant atom

Waveguide-QED with giant atoms, which is capable of accessing various limits of a small one, provides a new paradigm to study photon scatterings. Thus, how to achieve nonreciprocal photon transmissions via such giant atom setup is highly desirable. In this work, the nonreciprocal single-photon scattering characteristics of a double driven Λ-type three-level giant atom, where one of the transition couples to a one-dimensional waveguide at two separate points, and the other one is driven by two coherent driving fields, are investigated. It is found that a frequency tunable single photon diode with ideal contrast ratio can be achieved by properly manipulating the local coupling phases between the giant atom and the waveguide, the accumulation phase between the two waveguide coupling points, the Rabi frequencies and phase difference of the two driven fields. Compared to the previous single driving schemes, on the one hand, the presence of the second driving field can provide more tunable parameters to manipulate the nonreciprocal single-photon scattering behaviors. On the other hand, here perfect nonreciprocal transmission for photons with arbitrary frequencies is achievable by tuning the driving phases while the two driving fields keep turning on, which provides an alternative way to control the nonreciprocal single photon scattering. Furthermore, the results reveal that both the locations and width of each optimal nonreciprocal transmission windows are also sensitive to the driving detuning, and single photon diode with wide or narrow bandwidth can be realized based on demand. These results may be beneficial for designing nonreciprocal single photon devices based on a double driven giant atom setup.