Resolving Fock states near the Kerr-free point of a superconducting resonator

TL;DR

This paper presents a tunable superconducting resonator with suppressed Kerr nonlinearity, enabling precise control of photon states for quantum processing, demonstrated through photon-number-dependent spectral shifts.

Contribution

The authors design a SNAIL-based resonator with a Kerr-free point, allowing enhanced photon control and characterization using a transmon qubit.

Findings

Photon-number-dependent frequency shifts nine times larger than qubit linewidth.

Demonstration of a compact platform for continuous-variable quantum processing.

Suppression of Kerr interaction at the sweet spot.

Abstract

We have designed a tunable nonlinear resonator terminated by a SNAIL (Superconducting Nonlinear Asymmetric Inductive eLement). Such a device possesses a sweet spot in which the external magnetic flux allows to suppress the Kerr interaction. We have excited photons near this Kerr-free point and characterized the device using a transmon qubit. The excitation spectrum of the qubit allows to observe photon-number-dependent frequency shifts about nine times larger than the qubit linewidth. Our study demonstrates a compact integrated platform for continuous-variable quantum processing that combines large couplings, considerable relaxation times and excellent control over the photon mode structure in the microwave domain.