Multiplexed quantum state transfer in waveguides

In this article, we consider a realistic waveguide implementation of a quantum network that serves as a testbed to show how to maximize the storage and manipulation of quantum information in QED setups. We analyze two approaches using wavepacket engineering and quantum state transfer protocols. First, we propose and design a family of orthogonal photons in the time domain. These photons allow for a selective interaction with distinct targeted qubits. Yet, mode multiplexing employing resonant nodes is largely spoiled by cross-talk effects. This motivates the second approach, namely, frequency multiplexing. Here we explore the limits of frequency multiplexing through the waveguide, analyzing its capabilities to host and faithfully transmit photons of different frequencies within a given bandwidth. We perform detailed one- and two-photon simulations and provide theoretical bounds for the fidelity of coherent quantum state transfer protocols under realistic conditions. Our results show that state-of-the-art experiments can employ dozens of multiplexed photons with global fidelities fulfilling the requirements imposed by fault-tolerant quantum computing. This is with the caveat that the conditions for single-photon fidelity are met. Published by the American Physical Society 2024