Operator spreading, often characterized by out-of-time-order correlators (OTOCs), is one of the central concepts in quantum many-body physics. However, measuring OTOCs is experimentallychallenging due to the requirement of reversing the time evolution of the system. Here we apply Floquet engineering to investigate operator spreading in a superconducting 10-qubit chain. Floquet engineering provides an effective way to tune the coupling strength between nearby qubits, which is used to demonstrate quantum walks with tunable coupling, dynamic localization, reversed time evolution, and the measurement of OTOCs. A clear light-cone-like operator propagation is observed in the system with multiphoton excitations, and the corresponding spreading velocity is equal to that of quantum walk. Our results indicate that the method has a high potential for simulating a variety of quantum many-body systems and their dynamics, which is also scalable to more qubits and higher dimensional circuits.
Stimulated Raman adiabatic passage (STIRAP) offers significant advantages for coherent population transfer between un- or weakly-coupled states and has the potential of realizing efficientquantum gate, qubit entanglement, and quantum information transfer. Here we report on the realization of STIRAP in a superconducting phase qutrit – a ladder-type system in which the ground state population is coherently transferred to the second-excited state via the dark state subspace. The result agrees well with the numerical simulation of the master equation, which further demonstrates that with the state-of-the-art superconducting qutrits the transfer efficiency readily exceeds 99% while keeping the population in the first-excited state below 1%. We show that population transfer via STIRAP is significantly more robust against variations of the experimental parameters compared to that via the conventional resonant π pulse method. Our work opens up a new venue for exploring STIRAP for quantum information processing using the superconducting artificial atoms.