  Scalable quantum information processing requires that modular gate operations
can be executed in parallel. The presence of crosstalk decreases the individual
addressability, causing erroneous results during simultaneous operations. For
superconducting qubits which operate in the microwave regime, electromagnetic
isolation is often limited due to design constraints, leading to signal
crosstalk that can deteriorate the quality of simultaneous gate operations.
Here, we propose and demonstrate a method based on AC Stark effect for
calibrating the microwave signal crosstalk. The method is suitable for
processors based on fixed-frequency qubits which are known for high coherence
and simple control. The optimal compensation parameters can be reliably
identified from a well-defined interference pattern. We implement the method on
an array of 7 superconducting qubits, and show its effectiveness in removing
the majority of crosstalk errors.
