Conference Agenda

Macroscopic quantum electrodynamics is the quantum theory of light in dispersive and absorbing dielectric materials. It combines the quantum properties of the electromagnetic field, represented by the equal-time commutation relation between field operators, with the quantum statistical properties of the light-matter interaction by means of the fluctuation-dissipation theorem. However, it is currently limited to linearly responding media. Several attempts have been made over the years to effectively incorporate nonlinear material responses, but a consistent picture of nonlinear macroscopic quantum electrodynamics that includes nonlinear extensions to the fluctuation-dissipation theorem are still missing.

Here, we will present a microscopic construction by setting set up a path-integral description of a nonlinear oscillator model from which we derive nonlinear susceptibilities and show that they obey certain nonlinear fluctuation-dissipation relations, which paves the way to a consistent nonlinear macroscopic quantum electrodynamics.

We present a fully analytical and fully quantized theoretical quantum optical framework for describing third‑harmonic generation (THG) in epsilon‑near‑zero (ENZ) materials. The model provides precise expression for THG efficiency as a function of wavelength and angle of incidence to compare with experiments. The theoretical predictions show excellent agreement with measured THG from ultra‑thin and thick indium tin oxide (ITO) slabs by reproducing very close trends, angular dependence, and efficiency magnitude.

This framework is based on macroscopic quantum electrodynamics and Green’s tensor quantization to describe the nonlinear light–matter interactions in dispersive and lossy ENZ media. The approach overcomes the limitations of semiclassical models and is applicable to the quantum regime of light, including single‑ and few‑photon fields.

Beyond THG, the model can be extended to other third‑order nonlinear processes such as Kerr nonlinearities, cross‑phase modulation, and four‑wave mixing. These results highlight the potential of ENZ materials as platforms for quantum nonlinear optics and future quantum photonic technologies.

Quantum shot noise (QSN) and quantum back action (QBA) set the Standard Quantum Limit (SQL) for interferometric displacement measurements. We target broadband sub-SQL sensitivity using a cryogenic nanogram-scale SiN membrane in a fiber-based membrane-at-the-edge cavity.

Our approach employs bright squeezed light with a frequency-dependent angle to simultaneously suppress QSN off-resonance and QBA at resonance. We have implemented a filter cavity providing the required phase rotation and demonstrate 2 dB of detected bright squeezing.

In parallel, we developed a fully fiber-integrated high-finesse cavity with coated fiber facets, compatible with cryogenic operation and homodyne readout. These results mark key progress toward broadband quantum-enhanced sensing beyond the SQL.

We study squeezing of optical coherence in two-slit interference. We

characterize the coherence of light at the slits via Hermitian operators, formulate

coherence uncertainty relations, and establish a corresponding squeezing condition.

We analyze light states that exhibit coherence squeezing and visualize it

through a Poincaré-sphere-like representation. Finally, we show how coherence

squeezing manifests itself in reduced interferometric intensity fluctuations.