Southwest Quantum Information and Technology

Quantum optimal control of superconducting circuits

Presenting Author: Christiane Koch, Kassel

Quantum optimal control has grown into a versatile tool for quantum technology. Its key application is to identify performance bounds, for tasks such as state preparation or quantum gate implementation, within a given architecture. One such bound is the quantum speed limit, which determines the shortest possible duration to carry out the task at hand. Typical examples include the creation of entanglement or quantum error correction. To date, these tasks have been optimized for known, fixed parameters of the system. I will show that a fully numerical quantum optimal control approach can go even further and, using the most advanced control techniques, map out the entire parameter landscape for two superconducting transmon qubits. This allows to determine the global quantum speed limit for a universal set of gates with gate errors limited solely by the qubit lifetimes. While the interaction of qubits with their environment is typically regarded as detrimental, this does not need to be the case. I will show that the back-flow of amplitude and phase encountered in non-Markovian dynamics can be exploited to carry out quantum control tasks for a superconducting circuit that could not be realized if the system was isolated. The control is facilitated by a few strongly coupled, sufficiently isolated environmental modes. These can be found in a variety of solid-state devices other than superconducting circuits, for example in color centers in nanodiamonds or nanomechanical oscillators.

(Session 2 : Thursday from 10:30am - 11:15am)