In this project, we will demonstrate an integrated quantum memory for single photons with unprecedented functionality. This will be realised in fs-laser written waveguides fabricated in rare earth doped crystals [1]. Rare earth ions feature unique coherence properties both for electronic and spin transitions, making them ideal for high performance photonic quantum memories [2]. However so far, the efficiency for on-demand storage protocols with single photon level light has been limited to around 40% often with the aid of resonators [3,4]. Our chosen protocol instead has the potential of enabling ultra-high efficiencies, > 80%, without the use of optical cavities [5]. Rare earth doped crystals also possess massive multiplexing capabilities, being able to store qubits in various degrees of freedom, e.g. temporal, spectral, polarisation… [6]

In addition to these, our integrated design will allow us to enhance this capability by adding spatial multimodality, as different memories will be fabricated and independently operated on the same chip. This ability will be a crucial step towards the development of efficient local quantum photonic processors.

We will also fabricate integrated Bragg reflector to enhance even further the interaction of the light with the rare earth ions, and this will open the way to functionalities that wouldn’t be possible in bulk realisation, like a non-destructive detector for single photons [7].