Quantum Process Tomography of a Room-Temperature Alkali-Metal Vapor

Abstract: Quantum process tomography (QPT) is a technique for reconstructing the dynamics of open quantum systems under the Born-Markov approximation, as described by a Liouvillian superoperator, capturing both coherent and dissipative processes. While QPT is well established for qubits, it presents significant experimental challenges in multi-level qudits. In room-temperature atomic vapors, these difficulties arise from complex interactions, residual fields present in the system, environmental noise, and inhomogeneities in the medium. Overcoming these limitations is essential for accurate modeling and precise control of such systems--a critical step toward practical usage of the QPT. We present a QPT method that we experimentally validate on a room-temperature $^{87}$Rb vapor ensemble, achieving high-fidelity reconstruction of qutrit Liouvillians. Our approach establishes a computationally efficient framework for characterizing open quantum systems, enabling the study of non-unitary dynamics, efficient benchmarking of quantum sensors, and data-driven identification of environmental noise correlations.