Demonstrate chiral spin currents with nontrivial interactions in superconducting quantum circuit

Quantum many-body systems in which time-reversal symmetry is broken give rise to a wealth of exotic phases,and thus constitute one of the frontiers of modern condensed matter physics.Quantum simulation allows us to better understand many-body systems with huge Hilbert space,where classical simulation is usually inefficient.With superconducting quantum circuit as a platform for quantum simulation,we realize synthetic Abelian gauge fields by using microwave drive and tunable coupling in loop configurations to break the time-reversal symmetry of the system.Based on high-precision manipulation and readout of circuit-QED architecture,we demonstrate the chiral ground spin current of a time-reversal symmetry broken system with nontrivial interactions.Our work is a significant attempt to simulate quantum many-body systems with time-reversal symmetry breaking in multi-qubit superconducting processors.

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).