2DMultiMems · Two-dimensionally multiplexed on-demand quantum memories

Two-dimensionally multiplexed on-demand quantum memories

Similar to the classical internet, a future quantum internet has the prospects to significantly impact our daily life. In such an internet, quantum computers will be connected over a network to perform complex computational tasks, e.g. an accurate simulation of drugs or materials. Connection of distant quantum computers will be performed optically through a network of fibers. However, these fibers have intrinsic losses, which limit the maximum distance over which a connection could be established. To connect these quantum processors over intercity distances, quantum repeaters will be dispersed between the quantum computers and entanglement will be distributed over the full network. A possible implementation of a quantum repeater is the combination of a source of photon pairs and a quantum memory. With this implementation, the source emits entangled pairs of photons of which one is sent to a distant detector and the other is stored in the quantum memory, thus, the quantum memory is entangled with the telecommunication photon. Entanglement is distributed in the network by using two of these quantum repeater nodes with a common detector with Bell-state measurement setup at the distance. A detection event heralds that one of the two memories has absorbed a photon, and since, there is no knowledge on where the photon came from, the quantum memories are in an entangled state. However, a fundamental limit is imposed on rate at which entanglement will be generated: the quantum repeaters have to wait for the travel time of the photons to the detector and the time necessary for the heralding signal to return before attempting another entanglement trial. Quantum repeaters based on multimode quantum memories overcome this limitation, as these can store entanglement in several degrees of freedom or modes without the limiting waiting time. With multiplexing, the entanglement rate increases linearly with the available number of modes. Quantum memories based on crystals doped with rare-earth-ions promise a particularly high degree of multiplexing, as these quantum memories have the unique prospect of combining time, frequency, and spatial multiplexing in one system. Until the start of this project, the record of available modes with on-demand storage and retrieval was limited to 30 as only temporal multiplexing was available. The scope of this Marie-Curie project was to explore a new type of quantum memory array that combines spatial and temporal multiplexing for increased number of modes. This project targeted three research objectives: First, we wanted to explore sequences of optical laser pulses as path to increase storage times of the quantum memories. Second, we wanted to store quantum information in the quantum memory array. Thirdly, we wanted to build a second quantum memory array and generate entanglement between these two systems.

Data: CORDIS, © European Union