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Superconducting quantum circuits are one of the most promising platforms for realizing large-scale quantum computing devices, where in the near future a coherent integration of 100-1000 qubits is feasible. However, the required temperatures of only a few mK currently restrict quantum operations to superconducting qubits that are located within the same dilution refrigerator. This imposes a serious constraint on the realization of even larger quantum processors or the implementation of local- and wide-area quantum networks based on superconducting technology.

The targeted breakthrough of this project is to overcome this limitation, demonstrating for the first time the operation of a quantum local area network (QuLAN), where superconducting qubits housed in spatially separated refrigerators are connected via a cryogenic transmission line.

First steps twoards this technology have been already demostrated by the group at ETH, in the longest-to-date link (5m) between separate cryostats. The group not only showed that the linked could be cooled sufficiently down, but they also confirmed that it acts as a viable quantum link between separate chips, as explained in this paper and in this talk of the Virtual March Meeting 2020

Building on this technology, SuperQuLAN will develop new state transfer protocols and distributed quantum algorithms between superconducting qubits that are tens of meters apart. In parallel, we will develop and demonstrate new electro-optical quantum transducer designs for fast microwave-to-optics conversion and many other essential components and protocols for efficiently integrating multiple superconducting quantum computing units into a single coherent network.

The outcomes of this project will enable the non-incremental step from intra- to inter-fridge quantum communication and will facilitate the implementation of first quantum computing clusters. In the long run, this technology provides the basis for the realization of metropolitan-area scale quantum networks using superconducting circuits.

The project will be carried out by an interdisciplinary team of experts in the fields of superconducting circuits, nanophotonics and quantum information theory, and in close collaboration with industry partners. The complementary expertise of this consortium will ensure the scientific and economic success of this project.