31 October 2022

New Hardware for Quantum Networking

Researchers at the Max-Planck-Institute of Quantum Optics and the Technical University of Munich have demonstrated that individual atoms in a thin crystalline slab can be resolved and individually controlled using light of a precisely adjusted color. This will enable the exchange of quantum information between them in order to create extended quantum networks. The work of the group led by Andreas Reiserer has been featured on the cover of Science Advances.

Model of different atoms controlled by light of a matching color. © A. Reiserer & C. Hohmann (MCQST) / Science Advances. 8, eabo4538 (2022)
The realization of global quantum networks, in which remote carriers of quantum information (called “qubits”) are connected by light in optical fibers, is among the most intensely pursued research goals in quantum technology. To implement such a network, one requires efficient interactions between the qubits and individual particles of light. These can be realized in a similar way as one would foster interactions between people: The idea is to confine them to a small region of space – the smaller, the better – and to force them to stay long – the longer, the better.

In the hardware used for quantum networks, this confinement is achieved by embedding the qubits into optical resonators. Previous experiments have used resonators with nanoscale dimensions to this end. While their small size strongly enhances the qubit-light interaction, the proximity of interfaces disturbs the qubits and spoils their properties, which has hindered quantum applications up to now.

This drawback is overcome in the work of Ulanowski, Merkel and Reiserer by integrating erbium atoms as qubits into a 0.02 millimeter-thin crystalline slab, which is sandwiched between two mirrors of at least 99.99% reflectivity. The mirrors trap the emitted light fields long enough to have strong interactions with the qubits. At the same time, the qubit-interface distance is large enough to avoid disturbance of the qubits. Capitalizing on these advances, the group can now resolve and control more than 100 qubits in the same resonator simply by tuning a laser to a matching frequency. The next step will be to connect these qubits with remote ones. This will demonstrate full quantum functionality and will establish the demonstrated experimental platform as a leading candidate for the secure connection of quantum computers in a future quantum internet.


Spectral multiplexing of telecom emitters with stable transition frequency
A. Ulanowski, B.Merkel, A. Reiserer.
Science Advances 8, Issue 43 (2022)
DOI: 10.1126/sciadv.abo4538


Prof. Dr. Andreas Reiserer
TUM Physics Department
James-Franck-Str. 1
85748 Garching

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