Tailoring Unitary and Dissipative Dynamics in Circuit Quantum Electrodynamics

Chiao-Hsuan Wang

Superconducting qubits and high-quality microwave resonators enable powerful new control methods in circuit QED. I will present two complementary techniques—photon-number-dependent (PND) Hamiltonian engineering and squeezed thermal reservoir engineering—that leverage nonlinearity and dissipation to enhance quantum control and coherence.

The first technique, PND Hamiltonian engineering, uses off-resonant driving of ancilla qubits to create photon-number-dependent interactions in photonic cavities. This engineered Hamiltonian supports fault-tolerant computing with bosonic qubits by enabling precise cancellation of self-Kerr effects, higher-order nonlinearities, and robust gate operations.

The second technique, squeezed thermal reservoir engineering, generates a dissipative environment with reduced fluctuations along specific quadratures by coupling a qubit to a lossy cavity. This engineered squeezed reservoir reduces dephasing and extends the qubit’s coherence time, with potential applications in entanglement stabilization and dissipative squeezing.