Jeffrey H Shapiro, Clark Embleton, J Gabriel Richardson
High-rate, high-fidelity entanglement distribution is essential for the creation of a quantum internet, and spontaneous parametric downconverters (SPDCs) are, at present, the preferred sources of entangled signal-idler photon pairs for transmission to Alice and Bob's quantum nodes. SPDCs using phase-matched spectral islands are especially attractive in this regard because they provide wavelength-division-multiplexed signal-idler pairs with single-mode temporal behavior. This paper compares the entanglement distribution rates of islands-based zero-added-loss multiplexing (ZALM), which uses idler detections for heralding, and an islands-based Sagnac SPDC source, which operates without heralding. For 90% heralding efficiency with Alice and Bob's receivers allocating a single quantum memory per pump pulse, ZALM's per-pump-pulse entanglement distribution rate with 10 or more islands significantly exceeds that of unheralded operation. However, the reverse is true when both systems employ NI spectral islands and allocate NM = NI quantum memories to each pump pulse. Moreover, these behaviors must be weighed against the two systems' differing equipment requirements, e.g., ZALM requires two perfectly matched Sagnac sources, and it suffers in comparison with unheralded operation if it cannot realize high heralding efficiency.