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Quantum 2.0 Conference and Exhibition

Zero-Added-Loss Multiplexing with Phase-Matched Spectral Islands

Clark Embleton, Michael G. Raymer, Brian J. Smith, Franco N. C. Wong, Jeffrey H. Shapiro

Published Jan 1, 2025• 0 citations
Publisher

Abstract

Zero-added-loss multiplexing (ZALM) was proposed [Phys. Rev. Appl. 19, 054209 (2023)] for high-rate, high-purity entanglement distribution in quantum networks. We show that ZALM enables quasi-deterministic, polarization-entangled photon-pair production with phase-matched spectral islands.
DOI
10.1364/quantum.2025.qw2b.5

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Boosting the communication rate of quantum networks is a central challenge in quantum information science. Recently, an efficient entanglement distribution scheme employing quasi-deterministic Bell-pair sources based on time-frequency multiplexing, referred to as zero-added-loss multiplexing~(ZALM), has been proposed. Its implementation, however, requires high-fidelity entanglement swapping across densely multiplexed time-frequency modes, which has remained an experimental challenge. Here we demonstrate entanglement swapping across 16 parallel frequency modes with a high average fidelity of 93.9±\pm±\SI{1.4}{\%}. Notably, polarization-entangled photon pairs in each frequency mode are spectrally single-mode using only off-the-shelf 50-GHz dense wavelength-division multiplexing~(DWDM) filters, eliminating the need for additional narrowband filtering. Furthermore, in order to fully exploit the temporal degree of freedom, the pump pulse is operated with a repetition frequency of \SI{3.0}{GHz}. By combining the frequency and time multiplexing, the total swapping rate reaches 5.38$\pm$0.17\,\si{pairs\,s^{-1}}, which corresponds to the ZALM Bell-pair rate of \SI{8.2e2}{pairs\,s^{-1}}. Our results establish the key experimental capabilities required for ZALM and demonstrate a scalable route toward practical high-rate quantum repeaters and long-haul quantum networks.
Photonic entanglement distribution is key for the emerging quantum internet. Here, the authors propose a spectral-multiplexing scheme that delivers favorable entanglement rates by combining domain-engineered crystals with zero-added-loss multiplexing. Their scheme uses a down-conversion crystal that can produce photon pairs in distinct, spectrally factorable ``islands'', and by combining same- and cross-island heralding, they dramatically reduce the number of required spectral channels.
The recently proposed zero-added-loss multiplexing (ZALM) source of entangled photons enables higher efficiency in entanglement distribution than spontaneous parametric down-conversion sources and can be carried out using both space-to-ground and ground-to-ground links. We demonstrate the flexibility of ZALM architectures to be adapted to alternative entanglement distribution protocols. Focusing on the counterintuitive result that entanglement can be generated between distant parties without using any entanglement as a resource, we analyze two protocols for entanglement distribution to memories via separable states. Modeling them in a ZALM setup, we consider the effects of noise both in the communication channels and in the memories. We thereby identify the optimal protocol to use with respect to the highest entanglement generated, given the noise conditions of the network. Published by the American Physical Society 2024
We propose a scheme for optical entanglement distribution in quantum networks based on a quasideterministic entangled photon-pair source. By combining heralded photonic Bell-pair generation with spectral mode conversion to interface with quantum memories, the scheme eliminates switching losses due to multiplexing in the source. We analyze this ``zero-added-loss multiplexing'' (ZALM) Bell-pair source for the particularly challenging problem of long-baseline entanglement distribution via satellites and ground-based memories, where it unlocks additional advantages: (i) the substantially higher channel efficiency $\ensuremath{\eta}$ of downlinks versus uplinks with realistic adaptive optics, and (ii) photon loss occurring before interaction with the quantum memory---i.e., Alice and Bob receiving rather than transmitting---improve entanglement generation rate scaling by $\mathcal{O}(\sqrt{\ensuremath{\eta}})$. Based on numerical analyses, we estimate our protocol to achieve >10ebit/s>10\phantom{\rule{0.2em}{0ex}}\text{ebit/s}>10ebit/s at memory multiplexing of 102{10}^{2}102 spin qubits for ground distance >102km>{10}^{2}\phantom{\rule{0.2em}{0ex}}\text{km}>102km, with the spin-spin Bell-state fidelity exceeding 99%. Our architecture presents a blueprint for realizing global-scale quantum networks in the near term.