Modulation of energy spectrum and control of coherent microwave transmission at single-photon level by longitudinal field in a superconducting quantum circuit

We study the effect of longitudinally applied field modulation on a two-level system using superconducting quantum circuits. The presence of the modulation results in additional transitions and changes the magnitude of the resonance peak in the energy spectrum of the qubit. In particular, when the amplitude ,λz and the frequency COl of the modulation field meet certain conditions, the resonance peak of the qubit disappears. Using this effect, we further demonstrate that the longitudinal field modulation of the Xmon qubit coupled to a one-dimensional transmission line could be used to dynamically control the transmission of single-photon level coherent resonance microwave.

Observation of the exceptional point in superconducting qubit with dissipation controlled by parametric modulation

Open physical systems described by the non-Hermitian Hamiltonian with parity-time-reversal(PT)symmetry show peculiar phenomena,such as the presence of an exceptional point(EP)at which the PT symmetry is broken and two resonant modes of the Hamiltonian become degenerate.Near the EP,the system could be more sensitive to external perturbations and this may lead to enhanced sensing.In this paper,we present experimental results on the observation of PT symmetry broken transition and the EP using a tunable superconducting qubit.The quantum system of investigation is formed by the two levels of the qubit and the energy loss of the system to the environment is controlled by a method of parametric modulation of the qubit frequency.This method is simple with no requirements for additional elements or qubit device modifications.We believe it can be easily implemented on multi-qubit devices that would be suitable for further exploration of non-Hermitian physics in more complex and diverse systems.

Rabi oscillations of azimuthons in weakly nonlinear waveguides

Rabi oscillation,an interband oscillation,describes periodic motion between two states that belong to different energy levels,in the presence of an oscillatory driving field.In photonics,Rabi oscillations can be mimicked by applying a weak longitudinal periodic modulation to the refractive index.However,the Rabi oscillations of nonlinear states have yet to be introduced.We report the Rabi oscillations of azimuthons—spatially modulated vortex solitons—in weakly nonlinear waveguides with different symmetries.The period of the Rabi oscillations can be determined by applying the coupled mode theory,which largely depends on the modulation strength.Whether the Rabi oscillations between two states can be obtained or not is determined by the spatial symmetry of the azimuthons and the modulating potential.Our results not only deepen the understanding of the Rabi oscillation phenomena,but also provide a new avenue in the study of pattern formation and spatial field manipulation in nonlinear optical systems.

Output characteristics of Nd:Gd VO_4 crystals laser with dual c-axis orthogonal gains end-pumped by two fibercoupled diode lasers

The output characteristics of neodymium-doped gadolinium vanadate(Nd:GdVO4) crystals laser with dual c-axis orthogonal gains end-pumped by two fiber-coupled diode lasers are investigated. With two 1 W semiconductor diode lasers pumping, the output power of TEM00 laser is 920 m W, and the optical conversion efficiency is close to 46%. By changing the relative orientations of both Nd:Gd VO4 crystals, the polarization characteristics of laser are varied. In particular, by keeping the c-axes of two Nd:Gd VO4 crystals orthogonal to each other and adjusting two diode pump lasers to operate at the same power level, the completely unpolarized light is obtained.