Molecules are ubiquitous in natural phenomena and man-made products, but their use in quantum optical applications has been hampered by incoherent internal vibrations and other phononic interactions with their environment. We have now succeeded in turning an organic molecule into a coherent two-level quantum system by placing it in an optical microcavity. This allows several unprecedented observations such as 99% extinction of a laser beam by a single molecule, saturation with less than 0.5 photon, and nonclassical generation of few-photon super-bunched light. Furthermore, we demonstrate efficient interaction of the molecule-microcavity system with single photons generated by a second molecule in a distant laboratory. Our achievements pave the way for linear and nonlinear quantum photonic circuits based on organic platforms.

Electronic dynamics in liquids are of fundamental importance, but time-resolved experiments have so far remained limited to the femtosecond time scale. We report the extension of attosecond spectroscopy to the liquid phase. We measured time delays of 50 to 70 attoseconds between the photoemission from liquid water and that from gaseous water at photon energies of 21.7 to 31.0 electron volts. These photoemission delays can be decomposed into a photoionization delay sensitive to the local environment and a delay originating from electron transport. In our experiments, the latter contribution is shown to be negligible. By referencing liquid water to gaseous water, we isolated the effect of solvation on the attosecond photoionization dynamics of water molecules. Our methods define an approach to separating bound and unbound electron dynamics from the structural response of the solvent.

In a recent comment, 1 Ruth Signorell raises a number of issues that she considers to question the validity of our approach to determine mean free paths for electron scattering in liquid water 2 and our comparison with the results on amorphous ice by Michaud, Wen, and Sanche. 3 Here, we show that these critiques are unjustified, being either unfounded or based on misconceptions by the author of the comment. We nevertheless welcome the opportunity to further clarify certain aspects of our work that we did not discuss in detail in our letter. 2 Our reply is structured as the comment, i.e., the four main points of the comment are discussed individually.(1) Signorell incorrectly claims that the effective attenuation length (EAL) as defined in our work is different from the definition used in the analysis of the measurements of Suzuki et al. 4 , which we take as input for our simulations.Both our work and the analysis of Suzuki et. al. are based on the same standard definition of the EAL, i.e., the electron signal S(z) detected outside the liquid decays exponentially with the distance from the point of ionization to the surface z,and the EAL r EAL is the width parameter of 0 r EAL ionization depth 0 N photoelectron signal Ne z/rEAL Figure 1: Exponential decay of the photoelectron signal with ionization depth. The area under the exponential function is equal to the area in the box given by N × r EAL , which is used by Suzuki et al. 4 to determine r EAL experimentally. 1 arXiv:2003.05820v1 [physics.chem-ph]

We report on cryogenic coupling of organic molecules to ring microresonators obtained by looping subwavelength waveguides (nanoguides). We discuss fabrication and characterization of the chipbased nanophotonic elements which yield a resonator finesse in the order of 20 when covered by molecular crystals. Our observed extinction dips from single molecules reach 22%, consistent with an expected enhancement factor of up to 11 for the molecular emission into the nanoguide. Future efforts will aim at efficient coupling of a handful of molecules via their interaction with a ring microresonator mode, setting the ground for the realization of quantum optical cooperative effects. Coupling to nanoguide ring-resonatorsIt is known that the density of modes for the electromagnetic field is modified in the presence of boundaries, e.g. the mirrors of a Fabry-Perot cavity. This modification in turn affects the radiation properties of an emitter