Control and tomography of a three level superconducting artificial atom

Area of Science:

• Quantum Computing
• Superconducting Circuits
• Quantum Information Science

Background:

• Superconducting qubits like the transmon have low anharmonicity, enabling access to higher energy levels.
• Short control pulses can unintentionally excite qubits to unwanted higher levels, complicating quantum operations.

Purpose of the Study:

• To demonstrate the preparation of arbitrary three-level superposition states in a transmon qubit using optimal control.
• To characterize the coherence properties of the excited states of a three-level transmon system (qutrit).
• To perform quantum state tomography and evaluate the fidelity of prepared qutrit states.

Main Methods:

• Utilized optimal control techniques to precisely manipulate the transmon qubit.
• Employed dispersive readout to measure the populations of all three energy levels.
• Conducted full quantum state tomography to reconstruct the quantum states.

Main Results:

• Successfully prepared arbitrary three-level superposition states in the transmon.
• Extracted and analyzed the populations of the ground, first, and second excited states.
• Achieved an average fidelity of 95% for the prepared qutrit states.
• Investigated the coherence of the excited states.

Conclusions:

• Optimal control techniques enable precise preparation of multi-level superposition states in superconducting transmons.
• Dispersive readout and quantum state tomography are effective tools for characterizing qutrit states.
• High fidelities achieved pave the way for advanced applications in quantum information processing.