Eureka in a Cavity: Measuring Molecular Densities with Quantum Optics
Gerrit Groenhof
Recent years have seen a surge of claims that placing molecules between the mirrors of a Fabry-Pérot cavity can alter their chemical reactivity. Because such cavities confine photons at discrete wavelengths determined by the mirror separation, these effects are often attributed to the collective interaction of many molecules with a cavity mode. Knowing how many molecules participate is therefore a key step toward understanding cavity-modified chemistry. To address this, we fabricated a series of cavities containing BODIPY molecules. Combining nanofabrication, optical spectroscopy, theory, and computation, we find that approximately 10^7 molecules are collectively coupled to the cavity mode, while the field experienced by each individual molecule is on the order of 0.1 meV. This energy scale is two orders of magnitude smaller than the thermal energy at room temperature, suggesting that previously reported changes in reactivity are unlikely to originate from light-matter coupling alone. In this talk, I will present our approach and discuss its implications for cavity-modified chemistry. While our findings cast doubt on some of the more ambitious claims in the field, they do offer something more robust: a new, quantum-optical way to measure molecular densities—no buoyancy required ...
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Superconducting diodes in new quantum materials
Stefan Ilic
Superconductivity is a quantum state of matter in which electrical current flows without resistance. It typically emerges at low temperatures, when electrons form pairs and condense into a macroscopic quantum state. In simple materials this phenomenon is well understood, but the picture changes substantially when interactions that act on the electron spin, such as magnetism or spin–orbit coupling, are also present.
My research addresses superconductivity in these settings, both in engineered hybrid structures and in new quantum materials. The interplay between superconductivity and spin physics can produce new types of superconducting states and transport phenomena, a field broadly known as superconducting spintronics. In this talk I will mostly focus on superconducting diodes - systems that exhibit nonreciprocal transport of supercurrent. In these materials, dissipationless supercurrent flows in one direction while the reverse direction supports only a regular dissipative current. This asymmetry reflects broken symmetries in the underlying system. This effect has drawn considerable attention both as a route to the next-generation low-temperature devices and as a probe of unconventional superconductivity.
I will also connect these ideas to nanoscience, where control over matter at the nanoscale opens new possibilities for combining superconductivity with spin physics. A particularly compelling platform is 2D materials, where superconductivity, magnetism, and other ordered states can be combined by stacking different atomically thin layers.
