Cisco × Qunnect Brooklyn–Manhattan metro entanglement-swap

The first metro-scale entanglement-swap over deployed commercial telecom fibre. Two warm-rubidium photon-pair sources at Brooklyn end nodes sent their telecom-band photons through 17.6 km of New York City underground fibre to a Bell-state-measurement hub at 60 Hudson Street, with Cisco supplying the orchestration plane.

Operator: Qunnect (sources + end-node optics) · Cisco (orchestration / timing / control plane) · NYU and QTD Systems on the GothamQ testbed; BSM hub at QTD Systems' carrier-hotel building at 60 Hudson Street, Manhattan
Location: New York City — Brooklyn ↔ 60 Hudson Street, Manhattan
Year: Announced 18 February 2026
Technology: Entanglement-based; warm-rubidium four-wave-mixing sources (Qunnect Carina, 795 nm / 1324 nm bichromatic pairs); midpoint Bell-state-measurement; SNSPD detectors at the hub, room-temperature SPADs at the spokes
Scale: Three nodes (hub-and-spoke); 17.6 km of deployed New York City carrier fibre
Status: Vendor-run demonstration on the GothamQ testbed
Commercial model: Industrial demonstration — Qunnect hardware, Cisco software stack, deployed-fibre route through a commercial carrier hotel; not yet sold as a service

What it is

Two Qunnect Carina sources sit at two Brooklyn end nodes. Each is a room-temperature warm-rubidium vapour cell that produces polarization-entangled bichromatic photon pairs by four-wave mixing in a Rb diamond level scheme — one 795 nm photon (near-infrared, read locally) and one 1324 nm photon (telecom O-band, routed over fibre). The 1324 nm photons from both sources travel through 17.6 km of deployed New York City underground fibre to a hub at 60 Hudson Street, where they meet at a Bell-state analyser read out by superconducting-nanowire single-photon detectors (SNSPDs). A successful Bell-state measurement at the hub swaps the entanglement, leaving the two end-node 795 nm photons in a Bell pair.^{Cisco × Qunnect Brooklyn–Manhattan, 18 Feb 2026}

Cisco's contribution sits in the control plane: White Rabbit picosecond-level time alignment across all three sites, automated polarization-drift compensation on the fibre, calibration cycles, and event-correlation across the spokes and the hub.

The real headline: an untethered architecture, not just 17 km of fibre

For two photons to interfere at the midpoint BSA, they must be indistinguishable to sub-MHz frequency precision. The industry default is to derive both sources from a shared master laser distributed to every node over a phase-stabilised reference fibre — which works at lab scale, but tethers the network: extra fibres on every link, ~100 km reach limit on standard SMF, and any thermal or mechanical disturbance kills the BSM rate until the loop re-acquires. Topologically it confines you to a star or a hierarchy.

Qunnect's Carina sources lock to their own Rb hyperfine transition — the absolute frequency is given by physics, not by an engineered link, so the Brooklyn box and the Manhattan box are matched without any reference channel between them. The 17.6 km number is interesting; the untethered architecture is what scales. Drop a Carina at any new node and it interoperates with the existing fleet on day one. See the distribution page for the broader mode-matching context.

The hub-and-spoke topology is a deliberate scaling choice. Concentrating the SNSPDs (and the cryogenics they need) at one well-connected carrier-hotel building keeps each end node warm and cheap; adding a new spoke is a fibre pull plus a calibration cycle rather than a re-engineering of the optical clock distribution.

Verified claims

17.6 km of deployed New York City carrier fibre, Brooklyn to 60 Hudson Street and back to a second Brooklyn node — a three-node hub-and-spoke layout.^{Cisco × Qunnect Brooklyn–Manhattan, 18 Feb 2026}
5,400 swapped pairs per hour over the deployed-fibre link, with over 1.7 × 10⁶ pairs per hour measured locally on short fibre.^{Cisco × Qunnect Brooklyn–Manhattan, 18 Feb 2026}
Polarization fidelity above 99 % on the swapped end-to-end pairs.^{Cisco × Qunnect Brooklyn–Manhattan, 18 Feb 2026}
Independent warm-rubidium sources at the two end nodes — Qunnect Carina platform, room-temperature operation, no shared master laser between sites.^{Cisco × Qunnect Brooklyn–Manhattan, 18 Feb 2026}
SNSPDs at the hub; SPADs at the spokes — cryogenic detection concentrated at one site, room-temperature detection at every other site.^{Cisco × Qunnect Brooklyn–Manhattan, 18 Feb 2026}
Cisco-supplied control plane — White Rabbit timing, polarization-drift compensation, calibration and event correlation across the three sites.^{Cisco × Qunnect Brooklyn–Manhattan, 18 Feb 2026}

Things to note

Memoryless architecture. End nodes detect their 795 nm photon immediately. The stack does not include storage or cross-attempt synchronization. On-demand Bell-pair delivery — a user node requesting a fresh pair and acting on it milliseconds later — requires a quantum memory the stack does not include; that capability sits with the matter-qubit memory work (Pompili 2021, Knaut 2024).
Direct-fibre reach without a repeater. 17.6 km is within direct-fibre reach. The architecture has a single Bell-state measurement at a single hub, without nested swaps or entanglement purification. Pushing past roughly 80–100 km of telecom fibre still needs the memory and purification pieces that 1G / 2G repeater designs require.
Entanglement distribution, not state teleportation. The demonstration distributes entanglement; it does not consume that entanglement to teleport a qubit held on a quantum processor. Main et al. (Oxford Ba⁺, 2 m, 2025) and Knaut et al. (Boston SiV, 35 km, 2024) remain the references for entanglement-of-matter-qubits over deployed fibre.
Dedicated fibre strands. The reporting describes deployed-but-dedicated fibre strands rather than active co-propagation of live IP traffic alongside quantum signals. Co-existence with live classical traffic on the same fibre via WDM is the next integration step; it is not part of the demonstration.
Demonstration on commercial infrastructure. The demonstration runs on commercial-fibre infrastructure with vendor-supplied orchestration but is not yet sold as a service to outside customers. The GothamQ testbed previously logged a 99.84 % uptime single-link distribution run; commercial service offerings remain with the QKD networks (EPB, BT London, MadQCI).

What it is

Verified claims

Things to note

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