Observation of Bloch Oscillations and Wannier-Stark Localization on a Superconducting Processor

TL;DR

This paper demonstrates the simulation of Bloch oscillations and Wannier-Stark localization using a 5-qubit superconducting processor, revealing suppressed spin propagation and blocked thermal transport under a linear potential.

Contribution

First experimental observation of BOs and WSL in a superconducting qubit system with a programmable Hamiltonian.

Findings

Spin propagation is suppressed near initial positions.

Wannier-Stark localization length inversely correlates with potential gradient.

Thermal transport is blocked under linear potential.

Abstract

The Bloch oscillation (BO) and Wannier-Stark localization (WSL) are fundamental concepts about metal-insulator transitions in condensed matter physics. These phenomena have also been observed in semiconductor superlattices and simulated in platforms such as photonic waveguide arrays and cold atoms. Here, we report experimental investigation of BOs and WSL simulated with a 5-qubit programmable superconducting processor, of which the effective Hamiltonian is an isotropic $XY$ spin chain. When applying a linear potential to the system by properly tuning all individual qubits, we observe that the propagation of a single spin on the chain is suppressed. It tends to oscillate near the neighborhood of their initial positions, which demonstrates the characteristics of BOs and WSL. We verify that the WSL length is inversely correlated to the potential gradient. Benefiting from the precise single-shot simultaneous readout of all qubits in our experiments, we can also investigate the thermal transport, which requires the joint measurement of more than one qubits. The experimental results show that, as an essential characteristic for BOs and WSL, the thermal transport is also blocked under a linear potential. Our experiment would be scalable to more superconducting qubits for simulating various of out-of-equilibrium problems in quantum many-body systems.