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arXiv:2604.09846 · Journal of Optical Communications and Networking

Polarization Tracking and Active Compensation Using Classical Headers in Quantum Wrapper Networking

Gamze Gül, James van Howe, Gregory S. Kanter, Shannon G. Tan, Liam E. Beaudoin, Mehmet Berkay On, Roberto Proietti, S. J. Ben Yoo, Prem Kumar

quant-phSubmitted Apr 10, 2026• Announced Apr 14, 2026• 1 citation

v1 · Apr 10, 2026 v2 · Aug 5, 2026

Abstract

Quantum wrapper networking (QWN) is an emerging quantum networking protocol that wraps qubits in classical header bits to enable switching/routing, monitoring, and control without detecting the quantum signal. In this work, we encode header bits with two nonorthogonal polarization references to track and actively compensate for the changing birefringence of a 48 km deployed fiber link. Our method is analytical and deterministic, using motorized waveplates and a variable phase retarder to accurately and stably compensate the channel. We verify successful compensation by measuring the polarization stability of single photon qubits and the visibility of entangled photon pairs under both slow birefringence drift due to environmental fluctuations and large sudden changes designed to emulate those that occur during packet switching and rerouting over different fiber paths. For large, sudden changes, our compensator recovers the Stokes vector of single photons to within 10 degrees of the target state on the Poincaré sphere and restores two-photon interference visibilities to better than 79% on a deployed fiber link. Additionally, experiments monitoring long-term compensation over 44 hours show that visibilities remain above 84.5% with compensation active and degrade to below the quantum threshold of 70.7% within 4 hours of the compensator being turned off. These results add a polarization-control layer to QWN and illustrate that information-carrying headers can enable deterministic physical-layer compensation in the quantum channel over long-distance deployed fiber links.

DOI: 10.1364/JOCN.599980
Comments: 13 pages, 15 figures

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Quantum wrapper networking (QWN) is an emerging quantum networking protocol that wraps qubits in classical header bits to enable switching/routing, monitoring, and control without detecting the quantum signal. In this work, we encode header bits with two nonorthogonal polarization references to track and actively compensate for the changing birefringence of a 48 km deployed fiber link. Our method is analytical and deterministic, using motorized waveplates and a variable phase retarder to accurately and stably compensate the channel. We verify successful compensation by measuring the polarization stability of single photon qubits and the visibility of entangled photon pairs under both slow birefringence drift due to environmental fluctuations and large sudden changes designed to emulate those that occur during packet switching and rerouting over different fiber paths. For large, sudden changes, our compensator recovers the Stokes vector of single photons to within 10 degrees of the target state on the Poincaré sphere and restores two-photon interference visibilities to better than 79% on a deployed fiber link. Additionally, experiments monitoring long-term compensation over 44 hours show that visibilities remain above 84.5% with compensation active and degrade to below the quantum threshold of 70.7% within 4 hours of the compensator being turned off. These results add a polarization-control layer to QWN and illustrate that information-carrying headers can enable deterministic physical-layer compensation in the quantum channel over long-distance deployed fiber links.

The fundamental properties of quantum mechanics, such as the no-cloning theorem, make management and control of quantum networks challenging. Quantum wrapper networking (QWN) offers a solution to this problem by wrapping quantum payloads with classical bits (as headers and/or tails) that can be used to assist with networking, performance monitoring, and probing the properties of the fiber interconnection. Since the classical header and quantum payload travel in the same fiber, one should carefully design the system to mitigate potentially deleterious effects such as noise and cross-talk. In this paper, we identify and characterize the noise induced by the classical headers by in-fiber scattering processes. We study the noise by using a tunable continuous-wave laser to emulate O-band (∼1310 nm) classical headers, which are time- and wavelength-multiplexed with O-band quantum signals. The noise is characterized as a function of the headers’ power, classical-quantum wavelength detuning, and optical fiber length. We demonstrate that the dominant noise contribution originates from spontaneous Raman scattering for wavelength detunings that are larger than 3 nm. We also observe that some noise photons can bleed into the quantum payload due to Rayleigh scattering of backward Raman scattered photons. We further investigate system level impacts of the noise created by classical headers that are produced by employing a small form-factor pluggable transceiver. We demonstrate that the associated noise level has negligible impact on quantum payloads for a 47.8 km deployed fiber link, the longest length used in QWN experiments to date, achieving a coincidences-to-accidentals ratio of 56 and a two-photon interference visibility of 88.8%.

Adapting the architecture and protocols of classical networks to quantum networking is challenging due to the quantum mechanical properties. In this paper, we utilize a Quantum Wrapper Networking architecture that enables transparent and interoperable transportation of quantum wrapper (QW) datagrams, consisting of quantum payloads and classical headers, over optical fiber networks. We experimentally demonstrate end-to-end transportation of QW datagrams in a three-node packet-switched optical network testbed. The header and payload of a QW datagram are multiplexed in time and wavelength, i.e., the 1561.41 nm header precedes the L-band payload. A QW switch/router performs packet switching by reading the headers, generating new headers, and routing the datagrams to their destinations without disturbing quantum information in the payload. We use 20 km fiber links from the source to two distinct destinations in the testbed. Our experiments show$>

22 coincidence-to-accidental ratio (CAR) for both destinations at two different wavelength channels and clear visibility,

>$79%. We further investigate impairments such as chromatic dispersion and wavelength-dependent polarization rotations in the fiber. We observe that the classical headers' bit-error rate (BER) and the quantum payloads' CAR are correlated under the wavelength-independent channel attenuation. Thus, QW network control and management can utilize a type of performance monitoring. We also discuss the QW datagram design constraints and future fast packet switching implementations.

Polarization qubits offer a direct route to fiber-based quantum communication, yet the fiber that carries them also scrambles their reference frame through uncontrolled birefringence. Active compensation commonly relies on monitoring and feedback, raising a natural question: can the link itself suppress coherent polarization drift before it reaches the receiver? We show that it can within a regime of sufficiently correlated unitary drift. Our central idea is to embed a fixed cyclic sequence of Pauli rotations along the fiber, turning propagation distance into a spatial toggling frame. Rather than estimating and inverting the unknown transformation, the sequence repeatedly reverses its leading action. We establish exact refocusing for constant generators compatible with a two-segment echo, show that a four-frame Pauli cell cancels the leading contribution of any traceless quasi-static generator, and bound the residual error for smoothly varying birefringence. We then connect these guarantees to operational BB84 quantities, including measured QBERs, the resulting secret fraction, and insertion loss. In simulations of a 50 km fiber with spatially correlated birefringence, a representative design reduces the mean QBER from 6.11% to 0.224% at a device spacing of 1.25 km. With an assumed per-device transmission of t = 0.997, this raises the asymptotic key rate per launched pulse by a factor of approximately 2.5. For this parameter set, the best design in the tested scan is not the densest one: error suppression and optical loss create a finite operating window. These results provide a loss-aware design principle for passive polarization stabilization and suggest a low-overhead complement to active tracking in polarization-encoded QKD networks.

In polarization-encoded satellite-to-ground quantum communication, the on-board transmitter and a receiver at the optical ground station encode and decode linearly polarized quantum bits for execution of quantum key distribution (QKD) protocol. Dynamic polarization tracking and compensation is a key technique in realizing such a space based QKD system. In this work, we report the design and development of motorized waveplate based active polarization compensation system. Integrated testing and validation with Decoy-state enabled BB84 QKD testbed over ~5m free space channel and quantum link polarization extinction ratio (PER) ≥ 100:1 has been carried out successfully. Satellite motion was emulated as a continuous 1°/s polarization basis rotation at the Quantum Tx output. When active polarization compensation system was enabled, sazimuth (Az.) deviation was measured with ±1.5° accuracy. During this experiment, overall signal QBER was consistently maintained at <3.5% with secure key generation rate of ~1350kbps, proving the suitability of this scheme for realistic satellite-to-ground QKD scenarios.

Entanglement distribution through optical fibers is essential for quantum communication networks; however, fiber transmission can alter photon polarization and modify the observed correlations of polarization-entangled states, necessitating polarization compensation to recover the desired entangled state in the measurement basis. Here, we experimentally evaluate two passive polarization compensation techniques: a free-space Quarter-Half-Quarter (QHQ) waveplate configuration and an in-fiber three-paddle Fiber Polarization Controller (FPC). The polarization transformation along each downconverted-photon path is independently compensated through a systematic path-by-path optimization procedure. Using both techniques, we recover high-quality polarization correlations and entanglement, with visibilities exceeding

93\%

in three mutually unbiased bases and fidelities above

94.5\%

. The results demonstrate comparable restoration using free-space waveplate-based and fiber-based control, establishing a systematic framework for laboratory and short-reach quantum communication links.