Gaetano Frascella, Sascha Agne
A nonlinear interferometer is a device where two nonlinear effects can enhance or suppress each other. For example, if parametric down-conversion occurs in each of the two successive nonlinear crystals, the nonlinear interference affects the mode structure of the output light. Moreover, the output light is very sensitive to the phase introduced between the crystals. This allows one to perform phase measurements with the accuracy exceeding classical limits.
Paula Cutipa, Gaetano Frascella, Denis Kopylov (with Lomonosov Moscow State University)
One of the important features of bright squeezed vacuum is extremely enhanced intensity fluctuations. This makes it very efficient for all multiphoton effects, including harmonic generation. We are using it as a pump in the generation of optical harmonics and supercontinuum. We see that it is by orders of magnitude more efficient than coherent light. In addition, similar to two-photon light, bright squeezed vacuum enables simultaneously high time and frequency resolution in multi-photon spectroscopy.
Tomás Santiago-Cruz, Denis Kopylov (with Lomonosov Moscow State University)
One of the current tendencies in photonics is miniaturization and integration of nonlinear optical devices. In this project, we will generate entangled photons via spontaneous parametric down-conversion (SPDC) from ultrathin strongly nonlinear layers and metasurfaces. These novel SPDC sources will benefit from high quadratic nonlinearity of various materials where phase matching is absent, as well as from nanostructure resonances. The resulting sources will have not only small footprint, but also unprecedentedly high spatial and temporal entanglement, leading to subwavelength and subcycle photon correlations.
Santiago López Huidobro (with the group of Nicolas Joly, Division Russell)
We aim at observing a new quantum effect, third-order parametric down-conversion: direct decay of a high-frequency photon into photon triplets. This effect can take place in any material with cubic nonlinearity but we think that the best choice is photonic-crystal fibres. In particular, we are going to use gas-filled hollow-core fibres, all-solid dual-bandgap fibres we developed recently, and tapered submicron fibers in a gas cell.
High-gain parametric down-conversion produces bright squeezed vacuum in a large number of spatial modes. Most of these modes carry orbital angular momentum (OAM), an optical phase twist. Moreover, due to the photon-number correlations, each mode with a certain OAM value contains exactly the same photon number as the mode with the opposite OAM value, and these photon numbers are huge, up to hundreds billions. This poses an interesting problem: to filter out these OAM modes, populated with equal photon numbers, and use them for the interaction with matter or for high-precision measurements.
Radiation of parametric down-conversion manifests an interesting type of coherence, with the spatial coherence coupled to the temporal one. In particular, under certain conditions the coherence function will have a funny `O'-shape in space and time. We are going to test it in a complex Young-Michelson experiment.
If a source of radiation, classical or quantum, is multimode in frequency, how can one filter out a single mode without introducing losses or admixing other modes? So far, no efficient solution has been implemented. We are going to do it using a dispersive element and the projective operation of a planar waveguide.
Fiber source of entangled photons with giant tunable frequency separation (with N. Joly, 2020-2022).
Multi-photon nonclassical states of light based on high-gain parametric down-conversion
Generation of photon triplets via three-photon parametric down-conversion
Homodyne detection of macroscopic quantum states of light
FP7 project Bright Squeezed Vacuum and its Applications "BRISQ2", 2013-2016, was coordinated by our group.