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arXiv:2407.17330 · Optica Quantum

Quantum nonlocal modulation cancelation with distributed clocks

Stephen D. Chapman, Suparna Seshadri, Joseph M. Lukens, Nicholas A. Peters, Jason D. McKinney, Andrew M. Weiner, Hsuan‐Hao Lu

Published Dec 19, 2024• 8 citations
arXivHTMLPDF

Abstract

We demonstrate nonlocal modulation of entangled photons with truly distributed radio frequency (RF) clocks. Leveraging a custom radio-over-fiber (RFoF) system characterized via classical spectral interference, we validate its effectiveness for quantum networking by multiplexing the RFoF clock with one photon from a frequency-bin-entangled pair and distributing the coexisting quantum-classical signals over fiber. Phase modulation of the two photons reveals nonlocal correlations in excellent agreement with theory: in-phase modulation produces additional sidebands in the joint spectral intensity, while out-of-phase modulation is nonlocally canceled. Our simple, feedback-free design attains subpicosecond synchronization—namely, drift less than ∼0.5 ps in a 5.5 km fiber over 30 min (fractionally only ∼2×10 −8 of the total fiber delay)—and should facilitate frequency-encoded quantum networking protocols such as high-dimensional quantum key distribution and entanglement swapping, unlocking frequency-bin qubits for practical quantum communications in deployed metropolitan-scale networks.

DOI
10.1364/opticaq.539083

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We demonstrate nonlocal modulation of entangled photons with truly distributed radio frequency (RF) clocks. Leveraging a custom radio-over-fiber (RFoF) system characterized via classical spectral interference, we validate its effectiveness for quantum networking by multiplexing the RFoF clock with one photon from a frequency-bin-entangled pair and distributing the coexisting quantum-classical signals over fiber. Phase modulation of the two photons reveals nonlocal correlations in excellent agreement with theory: in-phase modulation produces additional sidebands in the joint spectral intensity, while out-of-phase modulation is nonlocally canceled. Our simple, feedback-free design attains subpicosecond synchronization—namely, drift less than ∼0.5 ps in a 5.5 km fiber over 30 min (fractionally only ∼2×10 −8 of the total fiber delay)—and should facilitate frequency-encoded quantum networking protocols such as high-dimensional quantum key distribution and entanglement swapping, unlocking frequency-bin qubits for practical quantum communications in deployed metropolitan-scale networks.
We demonstrate a robust, high-visibility nonlocal Franson interferometry for fiber-based quantum networks by co-propagating a classical Radio-over-Fiber clock signal with energy-time entangled photon pairs in the same fiber. Utilizing cross-band allocation (O-band for classical, L-band for quantum signals), the spontaneous Raman scattering noise photons are effectively suppressed. At the same time, their environmental delay fluctuations remain highly correlated for common-mode noise cancellation, achieving a passive synchronization with picoseconds precision. Over 50 km of single-mode fiber, this co-propagation enables nonlocal quantum interference with a visibility of (88.35\pm3.62)%, without relying on external dedicated timing infrastructure. This work provides a practical, scalable synchronization solution for metropolitan-scale entanglement-based quantum networks.
Precise knowledge of position and timing information is critical to support elementary protocols such as entanglement swapping on quantum networks. While approaches have been devised to use quantum light for such metrology, they largely rely on time-of-flight (ToF) measurements with single-photon detectors and, therefore, are limited to picosecond-scale resolution owing to detector jitter. In this work, we demonstrate an approach to distributed sensing that leverages phase modulation to map changes in the spectral phase to coincidence probability, thereby overcoming the limits imposed by single-photon detection. By extracting information about the joint biphoton phase, we measure a generalized delay—the difference in signal–idler arrival, relative to local radio frequency (RF) phase modulation. For nonlocal ranging measurements, we achieve ( 2σ ) precision of ±0.04ps and for measurements of the relative RF phase, ( 2σ ) precision of ±0.7∘ . We complement this fine timing information with ToF data from single-photon time-tagging to demonstrate absolute measurement of time delay. By relying on off-the-shelf telecommunications equipment and standard quantum resources, this approach has the potential to reduce overhead in practical quantum networks.
As the main branch of microwave photonics, radio-over-fiber technology provides high bandwidth, low-loss, and long-distance propagation capability, facilitating wide applications ranging from telecommunication to wireless networks. With ultrashort pulses as the optical carrier, a large capacity is further endowed. However, the wide bandwidth of ultrashort pulses results in the severe vulnerability of high-frequency radio frequency (RF) signals to fiber dispersion. With a time-energy entangled biphoton source as the optical carrier combined with the single-photon detection technique, a quantum microwave photonics method in radio-over-fiber systems is proposed and demonstrated experimentally. The results show that it not only realizes unprecedented nonlocal RF signal modulation with strong resistance to the dispersion but also provides an alternative mechanism to distill the RF signal out from the dispersion effectively. Furthermore, the spurious-free dynamic ranges of the nonlocally modulated and distilled RF signals have been significantly improved. With the ultra-weak detection and the high-speed processing advantages endowed by the low-timing-jitter single-photon detection, the quantum microwave photonics method opens new possibilities in modern communication and networks.
Abstract Quantum networks enhance quantum communication schemes and link multiple users over large areas. Harnessing high dimensional quantum states - qu-d-its - allows for a denser transfer of information with increased robustness to noise compared to qubits. Frequency encoded qu-d-its can be manipulated at telecom wavelengths with off-the-shelf fibered devices. We use a low free spectral range silicon microresonator to propose, assess and optimize a reconfigurable entanglement-based quantum key distribution network with frequency-bin encoded Bell states of dimension d = 2 and d = 3, using a single fibered hardware. We achieve secure key rates of 1374 bit/s with qutrits ( d = 3), and estimate the communication range to 295 km with qubits ( d = 2) across 21 parallel two-user quantum channels. This multi-dimensional versatile demonstration is stable beyond 21 h and lays the groundwork for larger dimensionality implementations deployed on metropolitan fiber links.
Entangled photons have appeared to be a promising way both for fundamental tests of physical principles and for quantum information applications such as Quantum Key Distribution. In particular, using entangled photons could potentially allow the realization of key distribution protocols over distances greater than a few hundreds of kilometers and security certification without a priori trust in the devices employed. Recently we reported experiments in which entanglement is manipulated in the frequency domain using electro-optic phase modulators driven by radio-frequency signals. Such method allows observation of an accurate and stable high-visibility (better than 99%) two-photon Bessel interference patterns. However in long distance fibre implementation this scheme remains sensitive to chromatic dispersion effect. We report a simple non local dispersion cancellation method built entirely from off-the-shelf components. The figure 1 a) depicts a setup allowing a realization of a non local dispersion cancellation in frequency domain. Pairs of photon are created by parametric down conversion in a Periodically Poled Lithium Niobate (PPLN) waveguide symmetrically around the 1550 nm wavelength (pulsation ω0). A 3dB coupler separates photon pairs. One of the photons is launched in a fibre spool. The second is launched in equivalent fibre spool following by a commercial programmable optical filter based on solid-state Liquid Crystal on Silicon switching element (Waveshaper 4000S). This equipment allows introducing a negative dispersion necessary to cancel the positive dispersion effect experienced by the photons propagating in the fiber spools. Both photons are then modulated by independent electro-optic phase modulators (EOPM) at 25 GHz. The relative phases between the 25 GHz signals are independently controlled by two phase shifters PS1 and PS2. After modulation, the photons are sent through narrowband tunable filters (F1,2) centred on angular frequency ω0. The photons are detected by two Avalanche Photodiodes (D1, 2). The phase modulators perform Bessel-type interference between photons separately detected on D1 and D2 (see [3] for details). The figure 1 b) and 1c) shows respectively the theoretical evolution of the interference patterns versus the distance when the phase shift is varying between 0 and 2π without (b) and with (c) negative dispersion (the normalized amplitude of modulation is 2.74). The introduction of negative dispersion allows cancelling the dispersion effect on the observed interference patterns.