Randomly controlling and reading out a single qubit of a network allows to infer the complete quantum state.
The research team led by Prof. Jianming Cai, Dr. Ralf Betzholz (HUST) and Dr. Christian Arenz (Princeton University) proposes a new principle for quantum tomography designed for realistic settings where measurement and/or control access to all system components is not attain-able. They prove that if the system is driven by a single, random field, then measurements of a single observable are almost always sufficient for complete quantum-state tomography.
They experimentally demonstrate the utility of this principle by reconstructing (strongly correlated) electron-nuclear spin states in an NV-center system in diamond with high fidelity, by accessing the electron spin only. Furthermore, in settings where the underlying system model is not (or only partially) known, they outline how this principle can be leveraged for performing full quantum process tomography and for designing quantum controls.
The principle they introduce here could dramatically simplify the task of measuring many-body correlations and will offer the quantum science and engineering communities a much-needed solution to the practical challenges of characterizing and controlling quantum devices with limited access.
Complete quantum-state tomography with a local random field, Pengcheng Yang, Min Yu, Ralf Betzholz, Christian Arenz, and Jianming Cai, Phys. Rev. Lett. 124, 010405 (2020).
Link: https://doi.org/10.1103/PhysRevLett.124.010405
