AUTHOR=Hwang Kyumin , Seong Jiheon , Park Kyungdeuk , Kim Jinwook , Pramanik Tanumoy , Bae Joonwoo , Shin Heedeuk TITLE=Entanglement witness measurement of time-bin two-qubit states using fiber-based Franson interferometers JOURNAL=Frontiers in Physics VOLUME=11 YEAR=2023 URL=https://www.frontiersin.org/journals/physics/articles/10.3389/fphy.2023.1254044 DOI=10.3389/fphy.2023.1254044 ISSN=2296-424X ABSTRACT=

Entanglement, that is, quantum correlations that do not have a classical counterpart, is a precondition to establishing communication protocols beyond the existing classical protocols, such as quantum key distribution, that achieves a higher level of security without computational assumptions. In this work, we present a proof of demonstration of detecting various entangled states, prepared by time-bin encoding with photons that are natural resources for long-distance quantum communication. We generate a maximally entangled state in time-bin qubits and verify the state in two ways. We first consider measurements that realize entanglement witnesses for the verification of entanglement. We then perform a quantum state tomography for the full characterization. Experimental resources are also discussed.