Seminar Schedule

An amazing level of quantum control is routinely reached in modern experiments with atoms, but similar control over molecules has been an elusive goal. A method based on quantum logic spectroscopy [1] can address this challenge for a wide class of molecular ions [2,3]. We have now realized the basic elements of this proposal. In our demonstration, we trap a calcium ion together with a calcium hydride ion (CaH+) that is a convenient stand-in for more general molecular ions. We laser-cool the two-ion crystal to its motional ground state and then drive Raman-transitions in the molecular ion, where a transition in the molecule also deposits a single quantum of excitation in the motion of the ion pair (motional "sidebands"). We can efficiently detect this single quantum of excitation with the calcium ion, which projects the molecule into the final state of the sideband transition, a known, pure quantum state. The molecule can be coherently manipulated after the projection, and its resulting state read out by another quantum logic state detection. We demonstrate this by driving Rabi oscillations between different rotational states [4, 5] and by entangling the molecular ion with the logic ion [6]. All transitions in the molecule are either driven by a single, far off-resonant continuous-wave laser or by a far-off-resonant frequency comb. This makes the approach suitable for quantum control and precision measurement of a large class of molecular ions.

We address the challenge of bringing solid-state quantum emitters all to the same resonant frequency within one chip. The study of cooperative effects, and the possibility to scale up quantum photonic technologies depend on such ability. Here, we demonstrate optical frequency tuning of individual, lifetime-limited molecules by few hundred times their natural linewidth. The effect persists even after the pump laser is switched off, and is attributed to a local Stark shift associated with optically induced long-lived charge-separated states. The experimental observation is applied to independently tune five close-by molecules into resonance within twice their line-width.

The building of quantum networks is stimulating the development of multiple physical platforms and different types of encodings in a heterogeneous structure allowing full functionality. Central to this endeavour is the capability to distribute and interconnect optical entangled states relying on different discrete and continuous quantum variables. Here, we report an entanglement swapping protocol involving single-photon entanglement and hybrid entanglement between particle- and wave-like optical qubits and demonstrate the creation of hybrid entanglement heralded by a specific Bell-state measurement. This ability opens up the prospect of connecting heterogeneous nodes of a network, with the promise of increased integration and functionalities.

In this project, we explore the combination of sub-wavelength, two-dimensional atomic arrays, and Rydberg interactions as a powerful platform to realize strong, coherent interactions between individual photons with high fidelity. In particular, the spatial ordering of the atoms guarantees efficient atom-light interactions without the possibility of scattering light into unwanted directions, for example, allowing the array to act as a perfect mirror for individual photons. In turn, Rydberg interactions enable single photons to alter the optical response of the array within a potentially large blockade radius R_b, which can effectively punch a large "hole" for subsequent photons. We show that such a system enables a coherent photon-photon gate or switch, with an error scaling that is significantly better than the best-known scaling in a disordered ensemble.

This Seminar is a fast journey through the build-up of quantum thermodynamics, an emerging field at the crossroad between quantum information, quantum open systems and stochastic thermodynamics. Born at the time of industrial revolution to optimize the exploitation of thermal resources, the concepts of thermodynamics have been adapted to small systems where thermal fluctuations are predominant. Extending the framework to quantum fluctuations is a great challenge of quantum thermodynamics, that opens exciting research lines e.g. measurement fueled engines or thermodynamics of driven-dissipative systems. On a more applied side, it provides the tools to optimize the energetic consumption of future quantum computers.

Light-matter interaction at the nanometer scale lies at the heart of elementary optical processes such as absorption, emission or scattering. Over the past two decades, we have realized a series of experiments to investigate the interaction of single photons, single molecules and single nanoparticles. In this presentation, I discuss recent studies, where we reach unity efficiency in the coupling of single photons to single molecules and describe our efforts to exploit this for the realization of polaritonic states involving a controlled number of molecules and photons. Furthermore, I report on efforts to exploit the phononic degrees of freedom of molecules and their environment as a quantum resource.

The tremendous scientific opportunities presented by ultracold molecules have driven rapid progress in both the assembly of diatomic molecules from ultracold atoms and the direct cooling of diatomic and polyatomic molecules. Diatomic species have been magneto-optically trapped and sub-Doppler cooled and their collisions have been studied in several experimental systems, including magnetic traps and merged optical tweezers. The pioneering work that led advances in direct cooling began with Stark deceleration, buffer-gas cooling and loading of traps, buffer-gas beam sources, mechanical slowing, and a variety of electromagnetic trapping and cooling mechanisms. As the field of cold and ultracold molecules has grown, polyatomic molecules have attracted new focus as potential novel quantum resources that have distinct advantages (and challenges) compared to both atoms and diatomic molecules. For example, all polyatomic molecules have long-lived states arising from nuclear motion with angular momentum about the internuclear axis. These states exhibit linear, Debye-level Stark shifts at very low applied electric fields and offer distinct Stark-shifted level structures that are absent in laser-coolable diatomic molecules. These and other features in polyatomic molecules can be applied to quantum simulation, fundamental symmetry tests, searches for dark matter, and particle physics beyond the Standard Model, potentially at the 1 PeV scale. Generic classes of polyatomic molecules have been identified as amenable to laser cooling into the ultracold (~1 μK) regime. One class is that of metal oxide radicals (MOR), which includes linear, symmetric top, and asymmetric top species. In this talk I will discuss some of the past experiments that brought us to this point, and the challenges and scientific opportunities with the laser cooling of polyatomic molecules. Results on SrOH, YbOH, CaOH and CaOCH3 will be discussed, as well as preliminary work on more complex species.