December 9, 2022

When memory qubits and photons get entangled

When memory qubits and photons get entangled Fig. 1: Experimental setup. Credit: npj Quantum Information ISSN 2056-6387 (online)

Scientists at the University of Bonn have been able for the first time to demonstrate quantum entanglement between a stationary qubit, i.e. a two-state quantum system, and a photon with direct coupling to an optical fiber.

In their experimental setup, the scientists implemented a special interface between light and matter. To this end, they used an optical resonator consisting of two opposing mirrors realized on the end facets of two optical fibers. For the concave mirrors, they ablated part of the optical fiber with a laser pulse and subsequently had the optical fiber ends coated with a reflective coating. The fiber diameter of 150 micrometers was roughly on the order of a hair (approx. 60 micrometers).

The small resonator volume increases the light-matter interaction, which enables high bandwidths for the distribution of quantum information in a network. Another advantage is that the fiber resonator leads to so-called intrinsic coupling of photons to optical fibers. This greatly simplifies their distribution in a network.

The team observed that even at a distance of one and a half meters, the single ion and the photon shared a common entangled quantum state.

The results of the study may be relevant for so-called distributed quantum computing or provably secure communication. (

The study has been published in the journal npj Quantum Information.

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