Heralded Entanglement of On-Demand Spin-Wave Solid-State Quantum Memories for Multiplexed Quantum Network Links

The ability to distribute heralded entanglement between distant matter nodes is a primitive for the implementation of large-scale quantum networks. Some of the most crucial requirements for future applications include high heralding rates at telecom wavelengths, multiplexed operation, and on-demand retrieval of stored excitations for synchronization of separate quantum links. Despite tremendous progress in various physical systems, the demonstration of telecom-heralded entanglement between quantum nodes featuring both multiplexed operation and on-demand retrieval remains elusive. In this work, we combine narrow band parametric photon-pair sources and solid-state quantum memories based on rare-earth doped crystals to demonstrate telecom-heralded entanglement between spatially separated spin-wave quantum memories with fully adjustable recall time and temporal multiplexing of 15 modes. In a first experiment, the storage in the spin state is conditioned on the entanglement heralding. We take advantage of the control over readout pulse phase to achieve feedforward conditional phase shifts on the stored photons depending on which heralding detector clicked. We exploit this effect to double the entanglement heralding rate for a given quantum state up to <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mrow><a:mn>510</a:mn><a:mtext> </a:mtext><a:mtext> </a:mtext><a:mtext>counts</a:mtext><a:mo>/</a:mo><a:mi mathvariant="normal">s</a:mi></a:mrow></a:math>, with an associated detection rate of <d:math xmlns:d="http://www.w3.org/1998/Math/MathML" display="inline"><d:mrow><d:mn>0.32</d:mn><d:mtext> </d:mtext><d:mtext> </d:mtext><d:mtext>counts</d:mtext><d:mo>/</d:mo><d:mi mathvariant="normal">s</d:mi></d:mrow></d:math> and measured positive concurrence by up to 6 standard deviations. In a second experiment, we simulate the communication time of a long-distance link by implementing an unconditional storage scheme with a dead time of <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:mrow><g:mn>100</g:mn><g:mtext> </g:mtext><g:mtext> </g:mtext><g:mi mathvariant="normal">μ</g:mi><g:mi mathvariant="normal">s</g:mi></g:mrow></g:math>. We take advantage of temporal multiplexing to increase the entanglement rates by a factor of 15 with respect to single mode storage, reaching a value of <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"><k:mrow><k:mn>22</k:mn><k:mtext> </k:mtext><k:mtext> </k:mtext><k:mtext>counts</k:mtext><k:mo>/</k:mo><k:mi mathvariant="normal">s</k:mi></k:mrow></k:math> per heralding detector. These results establish our architecture as a prime candidate for the implementation of scalable high-rate quantum network links.