Experimental observation of dynamical blockade between transmon qubits via ZZ interaction engineering

TL;DR

This paper demonstrates the experimental realization of strong ZZ coupling between superconducting transmon qubits through capacitive engineering, enabling dynamical blockade and advancing scalable quantum architectures.

Contribution

It introduces a method to achieve strong longitudinal coupling via capacitive design, significantly enhancing inter-qubit interaction strength in superconducting circuits.

Findings

Measured ZZ interaction strengths up to 350 MHz

Observed dynamical blockade effect between qubits

Validated results with circuit simulations and theoretical models

Abstract

We report the experimental realization of strong longitudinal (ZZ) coupling between two superconducting transmon qubits achieved solely through capacitive engineering. By systematically varying the qubit frequency detuning, we measure cross-Kerr inter-qubit interaction strengths ranging from 10 MHz up to 350 MHz, more than an order of magnitude larger than previously observed in similar capacitively coupled systems. In this configuration, the qubits enter a strong-interaction regime in which the excitation of one qubit inhibits that of its neighbor, demonstrating a dynamical blockade mediated entirely by the engineered ZZ coupling. Circuit quantization simulations accurately reproduce the experimental results, while perturbative models confirm the theoretical origin of the energy shift as a hybridization between the computational states and higher-excitation manifolds. We establish a robust and scalable method to access interaction-dominated physics in superconducting circuits, providing a pathway towards solid-state implementations of globally controlled quantum architectures and cooperative many-body dynamics.