Quantum information science is the field of research that studies the information present in a quantum system. It opens the way to the knowledge of unexplored fundamental physical mechanisms and to the development of novel technologies that will profoundly transform the way we communicate and process our data. Indeed, a number of new technological applications can be envisaged thanks to exquisitely quantum phenomena. While classical information encoding relies on bits, which can be either 0s or 1s, the quantum bits (or qubits) are associated to the state of quantum objects, e.g., single atoms, single spins, or single photons. Because of the quantum superposition principle, the qubits can then be 0s, 1s, or coherent superposition of both, thus giving access to an exceptionally richer alphabet. Quantum information science also exploits quantum entanglement, i.e., strong correlation between quantum objects, as a resource for fast and secure quantum communication protocols.
In view of realizing networks for quantum communication, quantum memories are fundamental devices as they act as interfaces between the photons, used as information carriers (or flying qubits), and stationary qubits, exploited for information storage and processing. While atomic gases enabled the first remarkable quantum storage experiments, solid-state systems, and specifically rare earth ion doped crystals, also offer interesting perspectives thanks to the absence of atomic motion and the high density, and the fact that they unleash prospects of integration, which facilitates scalability and employability in real-life quantum technology demonstrations. As a matter of fact, the implementation of quantum information protocols on a small chip has the potential to replicate the revolution of modern electronic miniaturization and intense research efforts are indeed devoted to developing miniaturized photonic integrated circuits for quantum information processing. Yet, on chip memories for single photons, key components of future quantum communication technology, are currently missing. This Fellowship addresses this pressing challenge by developing waveguide quantum memories based on ultrafast laser micromachining of rare earth ion doped crystals. We will engineer the necessary tool kit for the integrated quantum memories to fulfil simultaneously all the requirements for their employability in real-life quantum networks, as on-demand read-out, high efficiency, long storage time, and multimodality. Moreover, we will demonstrate how the integrated design gives access to functionalities that are not possible with bulk devices, like the non-destructive detection of single photons. This vision represents a technological breakthrough toward the realization of complex memory-enhanced quantum photonics circuitry on chip.
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