Improved Superconducting Qubit State Readout by Path Interference

High fidelity single shot qubit state readout is essential for many quantum information processing protocols. In superconducting quantum circuit, the qubit state is usually determined by detecting the dispersive frequency shift of a microwave cavity from either transmission or reflection. We demonstrate the use of constructive interference between the transmitted and reflected signal to optimize the qubit state readout, with which we find a better resolved state discrimination and an improved qubit readout fidelity. As a simple and convenient approach, our scheme can be combined with other qubit readout methods based on the discrimination of cavity photon states to further improve the qubit state readout.

Optimization of extreme ultraviolet vortex beam based on high harmonic generation

In high harmonic generation(HHG),Laguerre–Gaussian(LG) beams are used to generate extreme ultraviolet(XUV)vortices with well-defined orbital angular momentum(OAM),which have potential applications in fields such as microscopy and spectroscopy.An experimental study on the HHG driven by vortex and Gaussian beams is conducted in this work.It is found that the intensity of vortex harmonics is positively correlated with the laser energy and gas pressure.The structure and intensity distribution of the vortex harmonics exhibit significant dependence on the relative position between the gas jet and the laser focus.The ring-like structures observed in the vortex harmonics,and the interference of quantum paths provide an explanation for the distinct structural characteristics.Moreover,by adjusting the relative position between the jet and laser focus,it is possible to discern the contributions from different quantum paths.The optimization of the HH vortex field is applicable to the XUV,which opens up a new way for exploiting the potential in optical spin or manipulating electrons by using the photon with tunable orbital angular momentum.

Study on moving target detection to passive radar based on FM broadcast transmitter

Target detection by a noncooperative illuminator is a topic of general interest in the electronic warfare field. First of all, direct-path interference （DPI） suppression which is the technique of bottleneck of moving target detection by a noncooperative frequency modulation（FM） broadcast transmitter is analyzed in this article; Secondly, a space-time-frequency domain synthetic solution to this problem is introduced： Adaptive nulling array processing is considered in the space domain, DPI cancellation based on adaptive fractional delay interpolation （AFDI） technique is used in planned time domain, and long-time coherent integration is utilized in the frequency domain; Finaily, an experimental system is planned by considering FM broadcast transmitter as a noncooperative illuminator, Simulation results by real collected data show that the proposed method has a better performance of moving target detection.

Towards simultaneous observation of path and interference of a single photon in a modified Mach–Zehnder interferometer

Classical wisdom of wave-particle duality regulates that a quantum object shows either the particle or wave nature but never both.Consequently,it would be impossible to observe simultaneously the complete wave and particle nature of the quantum object.Mathematically the principle requests that the interference visibility V and whichpath distinguishability D satisfy an orthodox limit of V^2+D^2≤1.The present work reports a new waveparticle duality test experiment using single photons in a modified Mach-Zehnder interferometer to demonstrate the possibility of breaking the limit.The key element of the interferometer is a weakly scattering total internal reflection prism surface,which exhibits a pronounced single-photon interference with a visibility of up to 0.97and simultaneously provides a path distinguishability of 0.83.Apparently,the result of V^2+D^2≈1.63 exceeds the orthodox limit set by the classical principle of wave-particle duality for single photons.We expect that more delicate experiments in the future should be able to demonstrate the ultimate limit of V^2+D^2≈2 and shed new light on the foundations of con temporary quantum mechanics.