Inline multiphoton quantum state tomography

Abstract

Latest advances in integrated single-photon detectors offer possibilities for gaining information inside quantum photonic circuits. We introduce a concept and provide experimental evidence for the inline tomographic mea-surement of multiphoton quantum states, while keeping the transmitted ones undisturbed. We establish that by recording photon correlations from optimally positioned detectors on top of coupled waveguides with de-tuned propagation constants, one can perform robust reconstruction of multiphoton density matrices describing the amplitude, phase, coherence and quantum entanglement. We report proof-of-principle experiments. Our method opens a pathway towards practical and fast inline state tomography for diverse applications in quantum photonics. Show more