Optimal operating conditions of an entangling two-transmon gate

TL;DR

This paper identifies optimal conditions for a two-transmon entangling gate, reducing sensitivity to noise and relaxation effects, using a simple optimization that requires minimal additional control.

Contribution

It introduces a method to optimize a two-transmon gate for minimal noise sensitivity without extra control lines, effective even with relaxation and emission effects.

Findings

Sensitivity to 1/f flux and current noise is suppressed to leading order.

Optimization requires only a preliminary estimate of noise amplitudes.

Method remains effective in presence of relaxation and Purcell effect.

Abstract

We identify optimal operating conditions of an entangling two-qubit gate realized by a capacitive coupling of two superconducting charge qubits in a transmission line resonator (the so called "transmons"). We demonstrate that the sensitivity of the optimized gate to 1/f flux and critical current noise is suppressed to leading order. The procedure only requires a preliminary estimate of the 1/f noise amplitudes. No additional control or bias line beyond those used for the manipulation of individual qubits are needed. The proposed optimization is effective also in the presence of relaxation processes and of spontaneous emission through the resonator (Purcell effect).