# Calibration of the cross-resonance two-qubit gate between directly-coupled transmons

## TL;DR

This paper presents a practical calibration method for a high-fidelity cross-resonance two-qubit gate in superconducting transmon qubits, crucial for scalable quantum computing.

## Contribution

It introduces a combined calibration procedure using Hamiltonian tomography and error reduction, achieving a 97% fidelity for the gate.

## Key findings

- Achieved a 97.0(7)% fidelity for the _{-/2} gate.
- Demonstrated a calibration method combining continuous tomography and error correction.
- Showed the method's applicability in an architecture suitable for larger quantum circuits.

## Abstract

Quantum computation requires the precise control of the evolution of a quantum system, typically through application of discrete quantum logic gates on a set of qubits. Here, we use the cross-resonance interaction to implement a gate between two superconducting transmon qubits with a direct static dispersive coupling. We demonstrate a practical calibration procedure for the optimization of the gate, combining continuous and repeated-gate Hamiltonian tomography with step-wise reduction of dominant two-qubit coherent errors through mapping to microwave control parameters. We show experimentally that this procedure can enable a $\hat{ZX}_{-\pi/2}$ gate with a fidelity $F=97.0(7)\%$, measured with interleaved randomized benchmarking. We show this in a architecture with out-of-plane control and readout that is readily extensible to larger scale quantum circuits.