Realization of adiabatic and diabatic CZ gates in superconducting qubits coupled with a tunable coupler

High fidelity two-qubit gates are fundamental for scaling up the superconducting qubit number.We use two qubits coupled via a frequency-tunable coupler which can adjust the coupling strength,and demonstrate the CZ gate using two different schemes,adiabatic and diabatic methods.The Clifford based randomized benchmarking(RB) method is used to assess and optimize the CZ gate fidelity.The fidelities of adiabatic and diabatic CZ gates are 99.53(8)% and 98.72(2)%,respectively.We also analyze the errors induced by the decoherence.Comparing to 30 ns duration time of adiabatic CZ gate,the duration time of diabatic CZ gate is 19 ns,revealing lower incoherence error rate r’_(incoherent),int=0.0197(5) compared to r_(incoherent,int)=0.0223(3).

Traveling-wave parametric amplifiere-induced qubit dephasing:analysis and mitigation

The mitigation of dephasing poses a significant challenge toimproving the performance of error-prone superconducting quantum computing systems.Here,the dephasing of a transmon qubit ina dispersive readout regime was investigated by adopting aJosephson traveling-wave parametric amplifier as the preamplifier.Our findings reveal that the potent pump leakage from the preamplifier may lead to severe dephasing.This could be attributed to amixture of measurement-induced dephasing,ac Stark effect,andheating.It is showed that pulse-mode readout is a promising measurement scheme to mitigate qubit dephasing while minimizing theneed for bulky circulators.Our work provides key insights intomitigating decoherence from microwave-pumped preamplifiers,which will be critical for advancing large-scale quantum computers.

Characterizing noise correlation and enhancing coherence via qubit motion

The identification of spacial noise correlation is of critical importance in developing error-corrected quantum devices,but it has barely been studied so far.In this work,we utilize an effective method called qubit motion,to efficiently determine the noise correlations between any pair of qubits in a 7-qubit superconducting quantum system.The noise correlations between the same pairs of qubits are also investigated when the qubits are at distinct operating frequencies.What’s more,in this multi-qubit system with the presence of noise correlations,we demonstrate the enhancing effect of qubit motion on the coherence of logic qubits,and we propose a Motion-CPMG operation sequence to more efficiently protect the logic state from decoherence,which is experimentally demonstrated to extend the coherence time of logic qubits by nearly one order of magnitude.