Transport approach to two-qubit quantum state tomography

Abstract: Quantum state tomography (QST) is a central task for quantum information processing, enabling quantum cryptography, computation, and state certification. Traditional QST relies on projective measurements of single- and two-qubit Pauli operators, requiring qubits to be isolated from environmental dissipation. In this work, we demonstrate that measuring currents and associated transport quantities flowing through a two-qubit system between two terminals biased in temperature or voltage are sufficient to perform complete QST of the open quantum system. This transport approach requires minimal knowledge of the system-environment couplings and of the parameters setting the system's dynamics, accessible in state-of-the-art solid-state experiments via spectroscopic measurements for instance. Our findings are analytical, offering comprehensive insights into the underlying processes. As a direct consequence of our approach, we are able to provide a transport-based entanglement measure to certify the presence of quantum correlations, expressing the concurrence in terms of currents and correlations functions only.