We design and grow rare earth doped crystals in which we aim at controlling optical and spin non-classical states. These materials, produced in the form of bulk and nanostructured single crystals, show extremely long-lived quantum states at low temperature. This unique property in the solid state enables us to address a broad range of applications, from quantum information processing and communication, to spectral analysis and medical imaging.
We belong to the Material for Photonics and Opto-Electronics team of the Institut de Recherche de Chimie Paris. The Institute is a joint unit between Chimie ParisTech graduate school and the Centre National de la Recherche Scientifique.
To meet the high demands of quantum technologies, systems with multiple quantum degrees of freedom that can be addressed by light and coupled to other quantum systems in hybrid architectures are strongly needed. We aim at building such devices from solid-state nanostructures that exploit the uniquely narrow optical transitions of rare earth ions. We expect these devices to have a strong impact on quantum communication, quantum sensing and quantum opto-electronics.
A key point of nanoscale quantum systems is to preserve long-lived quantum states despite the larger environmental noise present at surfaces and interfaces, or originating in additional defects.
We develop rare earth doped nanocrystals and thin films with high crystalline quality and purity by bottom-up approaches based on soft chemistry and other techniques. The combination of structural characterization and optical spectroscopy allows us to synthesize nanostructures with low perturbations to the optical quantum states. High performance materials can be used to build hybrid devices, where ions like europium or erbium can provide a quantum interface between light and other quantum systems.
Quantum memories are devices capable of faithfully storing photonic quantum states into matter. Their applications include long distance quantum cryptography and more generally quantum networks. Rare-earth ions are promising candidates for solid-state quantum memories, because of the long-lived superposition states of their optical and spin transitions.
We investigate crystals with multiple degrees of freedom, in which quantum states can be transferred between optical, electron and nuclear spins. In this way, quantum interfaces can be achieved between propagating quantum bits (optical and microwave photons), and long-lived quantum bits (nuclear spins). We aim at increasing quantum states lifetimes by material design and control techniques based on external electromagnetic fields. We also study schemes for improved quantum memories in terms of storage times, efficiency or bandwidth.
High temperature crystal growth techniques are used to produce state of the art samples doped with rare earth ions like europium (optical memories) or neodymium (optical and microwave memories). Optical coherent and high resolution spectroscopy, spectral hole burning, as well as optically detected magnetic resonance allow us to determine all relevant parameters and investigate memory schemes.
Single crystals for quantum memories
Nanostructures for hybrid quantum systems
Long-lived quantum states translate into narrow linewidths. Thus, rare earth doped crystals can exhibit extremely narrow optical linewidths, in the range of a few kHz or even a few 100 Hz in some cases. This enables highly selective spectral filtering that has applications in acousto-optic medical imaging, laser frequency stabilization for metrology or wireless and radar signal analysis.
We develop crystals in which a strong optical absorption line can be tailored to create narrow transmission windows. These features, called spectral holes, can then be used as a frequency reference or a filter. As an example, for deep tissue imaging in the infrared, we grow thulium doped crystals that can filter light that interacted with ultrasound waves. In this way, the optical signal provides images that carry additional information compared to ultrasound only diagnostic. We also investigate transparent ceramics as an alternative to single crystals. These materials can be produced in large volumes and complex shapes that can benefit to spectral analysis applications, while showing linewidths nearly as narrow as the best single crystals.