Project start: 1.10.2025.

Various applications of the quantum theory, like quantum cryptography over long distances and interconnection of quantum computers, require the distribution of quantum resources, such as quantum entanglement. Associated fiber losses dictate the need for quantum repeaters, and for quantum memories as the crucial constituents of the former. Different protocols for quantum memories have been proposed, but existing realizations have failed to combine all of the following desired properties in a single system: high efficiency, long coherence time, readout on demand and compatibility with the telecom C-band. In QOMPFOQM, we will work on the optimization of a particular optomechanical system, the membrane-in-the-middle (MIM) cavity, to be used as a wavelength-versatile memory for single photons (SPs). Exploiting optomechanically induced transparency to store the SPs in a vibrational mode of an ultracoherent membrane resonator, the platform can be used in conjunction with a suitable SP source to fulfil all of the above requirements. We will test the MIM system with optical pulses, showcasing record storage times and efficiencies among optomechanical memories. In parallel, we will work towards a source of heralded SPs to be stored, based on resonantly-enhanced spontaneous parametric down conversion in an optical parametric oscillator (OPO). Following QOMPFOQM, we plan to operate the MIM together with the OPO. The expected correlations between two generated SPs measured after one's storage will testify to the MIM setup's utility as a quantum memory. Looking further ahead, the platform can be used to store polarization qubits generated by on-demand SPs from semiconductor quantum dots, propelling the state of the art of quantum networks towards practical applications.