Manipulation of superconducting qubit with direct digital synthesis

We investigate the XY control and manipulation of the superconducting qubit state using direct digital synthesis(DDS)for the microwave pulse signal generation.The decoherence time, gate fidelity, and other qubit properties are measured and carefully characterized, and compared with the results obtained by using the traditional mixing technique for the microwave pulse generation.In particular, the qubit performance in the state manipulation with respect to the sampling rate of DDS is studied.Our results demonstrate that the present technique provides a simple and effective method for the XY control and manipulation of the superconducting qubit state.Realistic applications of the technique for the possible future scalable superconducting quantum computation are discussed.

Fabrication of microresonators by using photoresist developer as etchant

In superconducting circuit,microwave resonators and capacitors are crucial components,and their quality has a strong impact on circuit performance.Here we develop a novel wet etching process to define these two components using common photoresist developer as etchant.This method reduces subsequent steps and can be completed immediately after development.By measuring the internal quality factor of resonators,we show that it is possible to achieve similar or better performance when compared with samples made by standard etching processes.This easy-to-implement method may boost the yield hence providing an alternative fabrication process for microwave resonators and capacitors.

Universal quantum control based on parametric modulation in superconducting circuits

As superconducting quantum circuits are scaling up rapidly towards the noisy intermediate-scale quantum(NISQ)era,the demand for electronic control equipment has increased significantly.To fully control a quantum chip of N qubits,the common method based on up-conversion technology costs at least 2×N digital-to-analog converters(DACs)and N IQ mixers.The expenses and complicate mixer calibration have become a hinderance for intermediate-scale quantum control.Here we propose a universal control scheme for superconducting circuits,fully based on parametric modulation.To control N qubits on a chip,our scheme only requires N DACs and no IQ mixer,which significantly reduces the expenses.One key idea in the control scheme is to introduce a global pump signal for single-qubit gates.We theoretically explain how the universal gates are constructed using parametric modulation.The fidelity analysis shows that parametric single-qubit(two-qubit)gates in the proposed scheme can achieve low error rates of 10^(4),with a gate time of about 60 ns(100 ns).

Integrated superconducting circuit for qubit and resonator protection

A semi-infinite waveguide acts as a mirror and helps protect the qubit in front of it from decoherence.Here,we investigate the interference effect in an open waveguide consisting of resonators with different decay rates.We find that a lossy resonator works as a mirror and changes the effective decay rate of the other.The spontaneous radiation of qubit is related to its environment,and we can control it by arranging the lossy resonator's position or frequency.Our approach helps improving the qubit performance,as well as the quantum gate fidelities.