Quantum entanglement plays a prominent role in both foundational physics and emerging quantum technologies. Light is especially promising as a platform for experimental realizations of highdimensional entanglement, for which the timefrequency degree of freedom provides a natural encoding. Here, we propose and demonstrate a technique to determine the full quantum state of a pair of photons entangled in the timefrequency domain. Our approach, based on spectral shearing interferometry, is entirely selfreferenced. To test our system, we measure a photonpair source with nonlocal spectral phase that results in entanglement between the photons, in which the time when either photon is detected is correlated with the frequency of the other photon. The results demonstrate an effective new tool for exploring the temporal and spectral characteristics of multipartite quantum systems exhibiting highdimensional entanglement.
 Award ID(s):
 1953045
 Publication Date:
 NSFPAR ID:
 10340539
 Journal Name:
 Science Advances
 Volume:
 7
 Issue:
 39
 ISSN:
 23752548
 Sponsoring Org:
 National Science Foundation
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