A Municipal Quantum Network Link with Entangled Infrared-Photons Emitted from Strontium Ions

In analogy to the development of classical computing, the true potential of quantum devices at scale lies in their interconnection within a network. The “quantum internet” [1] is still a distant aspiration with the main limitation being the remote entanglement generation rate dropping off sharply with distance due to the fiber losses of the visible and UV photons involved. Still, there have been a number of successful demonstrations of remote entanglement with different platforms [2]–[5]. Ongoing efforts have focused on converting entangled photons emitted from atomic systems into fiber-compatible wavelengths, but this conversion process incurs efficiency loss, noise, and system complexity. In this conference paper, we present initial results from direct transmission of infrared ion-photons emitted from Strontium ions at 1,092 nm through a municipal dark fiber link. This wavelength falls into a low-loss window in fiber transmission that will allow for local area quantum networks without the frequency-conversion overhead. This comes at the cost of a smaller branching ratio, limiting the transmission rate. However, there is a distance range of a few kilometers where this is an advantageous choice, making this scheme highly promising for city-scale quantum networks. We stimulate trapped Strontium ions to emit single photons at 1,092 nm. After emission, the ion is left in one of two states, which form a metastable qubit (see diagram in figure 1).