Optimal Control in Large Open Quantum Systems: The Case of Transmon Readout and Reset

Area of Science:

• Quantum Information Science
• Quantum Control Engineering
• Computational Physics

Background:

• Optimizing quantum control for large open quantum systems is computationally challenging.
• Dissipative operations like dispersive readout and qubit reset in superconducting circuits often have suboptimal fidelity and duration.
• Existing methods struggle with scalability and efficiency for complex quantum systems.

Purpose of the Study:

• To present a novel framework for solving large-scale open-system quantum control problems.
• To optimize inherently dissipative operations in superconducting qubits, specifically dispersive readout and qubit reset.
• To enhance the fidelity and reduce the duration of these critical quantum operations.

Main Methods:

• Combined the adjoint-state method with reverse-time backpropagation for efficient optimization.
• Developed a framework applicable to large open quantum systems described by Lindblad master equations.
• Applied the method to optimize dispersive readout and all-microwave reset protocols for transmon qubits.

Main Results:

• Demonstrated a scalable, computationally efficient, and low-memory footprint framework.
• Achieved a 2x improvement in fidelity and duration for transmon qubit reset through pulse shaping.
• Showed that adding a transmon drive during dispersive readout can yield 2x improvements in fidelity and duration.

Conclusions:

• The developed framework significantly enhances the performance of dissipative quantum operations.
• Pulse shaping and additional drives offer substantial improvements for superconducting qubit control.
• The approach is broadly applicable to various quantum control applications, including error correction and reservoir engineering.