Photonics With Thin-film Lithium Niobate (by Harvard University)

LNoI Waveguide
Rare-Earth ion-doped thin-film Lithium Niobate
Optical photons have many attractive properties for realization of quantum technologies [1]: they
exist under ambient conditions, are generally impervious to environmental noise, and, to an extent,
can be generated, manipulated and detected easily. Since they can also travel long distances without
significant loss, individual photons are well-suited for quantum key distribution, which aims to secure
messages between distant parties using quantum uncertainty. Yet, these properties of photons also
introduce challenges to realize quantum technologies that require deterministic interactions between
individual photons, e.g. for photonic quantum information processing.
Thin film Lithium niobate (TFLN) has emerged as a promising quantum photonic platform. LN is
transparent to optical photons (band gap of ~4 eV), possesses a strong electro-optic (EO) effect,
allowing the phase of light to be rapidly varied using microwaves, and has a high second-order optical
nonlinearity that can be engineered through ferroelectric domain modulation (i.e. periodic poling) [2].
Importantly, 4” and 6” TFLN wafers have recently become commercially available, which have
stimulated interest in this exciting material platform.