Curator's Take
This article reports the first fully fiber‑integrated quantum buffer that works across the entire telecom C‑band, delivering sub‑0.5 dB input/output loss, >18 µs storage and a 12.5 THz bandwidth—all at room temperature. By using an actively switched dual‑Sagnac cavity with cross‑phase modulation, the device can store over 200 temporal modes and faithfully preserve time‑bin, frequency‑bin and polarization qubits as well as entanglement, addressing the long‑standing trade‑off between low loss, broadband operation and universality. The result removes a major bottleneck for synchronising asynchronous photons in quantum‑network hardware and paves the way for near‑term deployment of high‑rate quantum repeaters on existing fiber infrastructure.
— Mark Eatherly
Summary
The realization of a scalable quantum internet relies on the ability to temporally align asynchronous photonic signals through on-demand buffering. While matter-based quantum memories achieve long storage times, their extremely narrow bandwidths and cryogenic requirements pose significant barriers to integration with existing telecommunications infrastructure. Conversely, current all-optical memories operate at room temperature but are hampered by high input/output losses and a lack of universality across different photonic degrees of freedom. Here, we demonstrate a universal, fully fiber-integrated quantum buffer operating over the full telecom C-band that overcomes these fundamental trade-offs. By implementing an actively switched dual-Sagnac cavity driven by cross-phase modulation, we achieve an ultra-low input/output loss of 0.46 dB and a storage time exceeding 18 $μ$s. The device exhibits an operational bandwidth exceeding 12.5 THz ($\sim$100 nm), covering the full telecom C-band. We show the simultaneous buffering of over 200 temporal modes with the ability to address them either collectively or one by one. We demonstrate high-fidelity storage for all three degrees of freedom compatible with optical fiber propagation, namely time-bin, frequency-bin, and polarization qubits, along with faithful preservation of entanglement, confirming the platform's true universality. These results provide a robust, room-temperature solution for the high-rate synchronization of multidimensional quantum states, clearing a major hurdle for the deployment of global photonic quantum networks.