Research

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. 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. Moreover, the second nonlinear crystal, by amplifying the quantum state generated by the first nonlinear crystal, can greatly improve the reconstruction of this quantum state. 

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. Moreover, even strong-field effects like high harmonic generation and above-threshold ionization, can be driven by bright squeezed vacuum. 

One of the current tendencies in photonics is miniaturization and integration of nonlinear optical devices. In this project, we generate entangled photons via spontaneous parametric down-conversion and spontaneous four-wave mixing from ultrathin strongly nonlinear layers and metasurfaces. These novel sources are not constrained by the phase matching condition and can be made of strongly nonlinear materials. Their efficiency can be further increased by nanostructure resonances. These sources can be also multifunctional, enabling several processes on the same platform, and easily tunable. One example is a liquid crystal, where entangled photons generation is efficient and tunable through external electric field.

We generate photon pairs through four-wave mixing in hollow-core photonic-crystal fibres filled with noble gas (xenon or argon). By changing the gas pressure, we can tune the wavelengths of both photons within an extremely broad range, covering more than two octaves and reaching the ultraviolet range on one side and the infrared range on the other side. The current goal is a broadband source of entangled photons, and its application to sensing. 

Our target is a new quantum effect, third-order parametric down-conversion: direct decay of a high-frequency photon into a photon triplet. It can take place in any third-order nonlinear material but we think that the best candidates are (i) submicron fibre tapers immersed into high-pressure gas for tuning the phasematching, (ii) ultrathin strongly nonlinear layers, and (iii) resonant metasurfaces with high third-order susceptibility. The latter two do not need any special measures to satisfy the phase matching, due to their extremely small thickness.