Abstract
Quantum logic gates are fundamental building blocks of quantum computers. Their integration into quantum networks requires strong qubit coupling to network channels, as can be realized with neutral atoms and optical photons in cavity quantum electrodynamics. Here we demonstrate that the long-range interaction mediated by a flying photon performs a gate between two stationary atoms inside an optical cavity from which the photon is reflected. This single step executes the gate in $2\,\mathrm{\mu s}$. We show an entangling operation between the two atoms by generating a Bell state with 76(2)% fidelity. The gate also operates as a CNOT. We demonstrate 74.1(1.6)% overlap between the observed and the ideal gate output, limited by the state preparation fidelity of 80.2(0.8)%. As the atoms are efficiently connected to a photonic channel, our gate paves the way towards quantum networking with multiqubit nodes and the distribution of entanglement in repeater-based long-distance quantum networks.
Highlights
Quantum logic gates are basic building blocks of quantum information processing protocols [1,2]
An ideal platform for this is provided by neutral atoms in an optical cavity
The implementation of a quantum gate inside such a multiqubit node, as demonstrated here, has been a long-standing goal as it adds the capacity for local quantum information processing to the network nodes
Summary
Once an atom is in j↑i, it strongly reduces the intracavity pump light via a normal-mode splitting and will hamper the preparation of a second atom. To herald a successful preparation of both atoms, we employ a global π pulse, perform a state detection in fluorescence, and postselect on those cases in which no fluorescence photons are detected. This results in an effective preparation of the state j↓↓i. J↓↑ih↓↑jÞ can be prepared by resonantly pumping a first atom to the strongly coupled state j↑i, followed by a π pulse to j↓i and another resonant pumping sequence for the second atom. If a low transmission is observed in both statedetection intervals, the antiparallel state preparation has been successful
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