Tuneable hopping and nonlinear cross-Kerr interactions in a high-coherence superconducting circuit

TL;DR

This paper introduces a superconducting circuit with tunable photon hopping and nonlinear cross-Kerr interactions, enabling advanced quantum simulations and potential quantum computing applications with high-coherence transmons.

Contribution

It presents a novel superconducting circuit with in situ tunable interactions mediated by a nonlinear coupler, enhancing quantum simulation capabilities.

Findings

Demonstrated tunable photon hopping and cross-Kerr interactions.

Achieved high coherence times of 15 to 40 microseconds.

Validated the system with theoretical modeling and experimental characterization.

Abstract

Analog quantum simulations offer rich opportunities for exploring complex quantum systems and phenomena through the use of specially engineered, well-controlled quantum systems. A critical element, increasing the scope and flexibility of such experimental platforms, is the ability to access and tune in situ different interaction regimes. Here, we present a superconducting circuit building block of two highly coherent transmons featuring in situ tuneable photon hopping and nonlinear cross-Kerr couplings. The interactions are mediated via a nonlinear coupler, consisting of a large capacitor in parallel with a tuneable superconducting quantum interference device (SQUID). We demonstrate the working principle by experimentally characterising the system in the single- and two-excitation manifolds, and derive a full theoretical model that accurately describes our measurements. Both qubits have high coherence properties, with typical relaxation times in the range of 15 to 40 microseconds at all bias points of the coupler. Our device could be used as a scalable building block in analog quantum simulators of extended Bose-Hubbard and Heisenberg XXZ models, and may also have applications in quantum computing such as realising fast two-qubit gates and perfect state transfer protocols.