QUINTESSEnCE · Quantum interfaces with single molecules

Isolating and addressing individual quantum systems has allowed for breakthrough results in quantum mechanics. Today, increasing the complexity of the system while maintaining control at the single-quantum level is vital for the next generation of quantum devices and research. QUINTESSEnCE will take up this challenge by developing interfaces between single photons, spins and phonons, all within one simple physical system, i.e. a single molecule.Fundamental systems like molecules have the inherent advantage, in comparison to artificial structures, of being nominally identical. A molecule can have the coherence properties of an atom even when embedded in a solid, without losing the access and customization opportunities typical instead of the solid state. Molecules differ from atoms in being more complex systems, with rich energy diagrams structured over multiple scales. We propose to leverage this complexity to coherently connect optical frequency photons with microwave spin excitations and gigahertz phonons. Unprecedented control over the molecules’ degrees of freedom will be achieved by integrating them in nanostructured devices. We will develop a ground-breaking lab-in-a-molecule platform, benefiting from the tunability and scalability of molecules, so as to aim at the following main objectives:• Complex states of light: integrating multiple molecular sources of indistinguishable photons on chip• Single-molecule cavity optomechanics: accessing the regime of single-photon strong coupling in an unconventional cavity optomechanical system• Optical addressing of single molecular spins: providing a crucial knob to read out and control the spin state of a single moleculeQUINTESSEnCE will therefore allow us to entering unexplored quantum territories and to develop quantum-technology tools unavailable today. Notably, the outcome of this project will impact a broad scientific community, touching quantum optics, optomechanics and molecular quantum technologies.