Material Challenges in Scalable Quantum Radar Systems

By Abdul Ahad NazakatReviewed by Louis CastelMar 24 2026

Classical radar detects targets by transmitting electromagnetic waves and measuring the reflected energy. Quantum radar takes a different approach: it exploits quantum entanglement between pairs of photons so that detection performance can exceed what is achievable with any classical system using the same transmitted power, even in highly noisy environments. This principle, quantum illumination (QI), was first theorised by Lloyd in 2008.¹

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Despite over a decade of theoretical development and recent proof-of-concept demonstrations, quantum radar remains a laboratory technology. The limiting factor is not the underlying physics but the materials: every subsystem, photon source, detector and signal processor, requires performance levels that current materials cannot reliably deliver outside tightly controlled cryogenic conditions.

How Quantum Illumination Works

In a quantum illumination protocol, an entangled pair of photons is generated: the signal photon is transmitted toward a target, while the idler photon is stored at the receiver. After the signal returns, or fails to, both are measured jointly. Because they share correlated quantum states, this joint measurement extracts a detection signal with lower error probability than an equivalent classical system, even when entanglement has been partially destroyed by loss and noise in the channel.²

Two frequency domains are under active investigation. Optical QI operates at photon energies well-suited to efficient generation and single-photon detection, but atmospheric absorption limits its practical range. Microwave QI operates at frequencies compatible with conventional radar bands and benefits from lower propagation loss, but requires superconducting circuits cooled to millikelvin temperatures to generate and preserve entanglement. The landmark experimental confirmation came from Assouly et al. (2023), who implemented a superconducting Josephson ring modulator circuit at ENS Lyon and demonstrated a microwave quantum radar providing more than 20% better detection performance than any classical equivalent under comparable conditions (a proof-of-principle carried out inside a dilution refrigerator).³ That millikelvin operating requirement remains a central material and engineering constraint.

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Photon Source Materials

Entangled photon pairs at optical frequencies are most commonly generated via spontaneous parametric down-conversion (SPDC) in nonlinear crystals. Bulk lithium niobate (LiNbO₃) has long been the standard material: its large second-order nonlinear coefficient and wide transparency window make it effective, but it suffers from photorefractive damage under high optical intensities and requires careful phase-matching engineering.²

Thin-film lithium niobate on insulator (TFLN) has emerged as a more capable successor. By confining light to submicron waveguide geometries, TFLN achieves substantially stronger nonlinear interactions than bulk devices at the same power level. A 2024 demonstration on a TFLN device generated time-bin entangled photon pairs with on-chip brightness of 242 MHz/mW and two-photon interference visibility exceeding 90%.⁴ A 2025 review confirmed TFLN as one of the leading integrated platforms for scalable entanglement generation.⁵

Gallium arsenide (GaAs) and aluminium gallium arsenide (AlGaAs) offer even larger nonlinear coefficients and support III-V photonic integration, but their broader refractive index dispersion complicates phase matching. Silicon photonics platforms have the advantage of CMOS-compatible fabrication but rely on weaker third-order nonlinearity for photon pair generation.

For microwave QI, entangled states are generated by Josephson parametric amplifiers (JPAs) and related circuits. These produce high-quality entanglement but at signal levels so faint that amplification for room-temperature use degrades the quantum correlations on which the advantage depends. This amplification problem is among the most consequential unsolved challenges in the field.⁶

Detector Materials and Cryogenic Constraints

Quantum radar imposes stringent requirements on detectors: single-photon sensitivity, low dark count rates and fast timing resolution. Superconducting nanowire single-photon detectors (SNSPDs) are currently the leading technology for optical and near-infrared wavelengths. Devices based on niobium nitride (NbN) nanowires operating at 1–4 K achieve system detection efficiencies above 90% with timing jitter below 50 ps. Niobium titanium nitride (NbTiN) is increasingly favoured for its polycrystalline structure, which improves fabrication yield and allows waveguide integration; NbTiN SNSPDs have demonstrated dark count rates in the mHz range, providing a significant signal-to-noise advantage for weak-signal applications.²

More recent work is exploring materials that could relax the cryogenic requirement. A 2025 study reported SNSPDs based on NbReN ultrathin films achieving 95% internal detection efficiency at 1,548 nm with timing jitter of 28 ps at 3.5 K - performance comparable to NbN at a modestly elevated operating temperature.⁷ For microwave quantum radar, transition-edge sensors (TES) and microwave kinetic inductance detectors (MKIDs) offer single-photon sensitivity but require sub-100 mK cooling, imposing serious constraints on system portability and power consumption.

Integration, Scalability and Emerging Solutions

Moving from discrete laboratory components to a deployable device requires integrating photon sources, detectors and signal processing on a common chip. Photonic integrated circuits (PICs) on TFLN or silicon nitride (Si₃N₄) platforms are the leading candidates. Each material presents trade-offs: TFLN provides superior nonlinearity and modulation speed; Si₃N₄ offers lower propagation loss and CMOS compatibility. Fabrication defects, waveguide losses and fiber-to-chip coupling inefficiencies all erode the quantum correlations that determine system performance.⁵

Microwave-to-optical transduction, converting quantum states between frequency domains, would allow microwave QI systems to use optical detectors and bypass some cryogenic constraints. A 2024 study on TFLN-based photonic circuits for quantum transducer applications at MDPI demonstrated a passive PIC incorporating ring resonators and Mach–Zehnder interferometers capable of supporting microwave-optical entanglement generation, validating the integration architecture at the component level even as system-level conversion efficiency remains a challenge.⁸ Institutional programs include work at the University of Calgary (Barzanjeh group), the University of Waterloo, and defence research programs in the US, EU and China, all targeting short-range quantum sensing as a near-term stepping stone.⁶

The Materials Path Forward

The barriers to field-deployable quantum radar are well-defined: TFLN and GaAs photon sources must achieve lower fabrication variance and optical loss; SNSPDs need to operate reliably above 4 K without sacrificing efficiency or dark count performance; microwave-to-optical transducers must reach conversion efficiencies usable in a practical system; and the entire stack must fit within a realistic size, weight and power envelope. Progress on each front is real but incremental. Near-term applications, short-range quantum sensing, secure communications and quantum-enhanced biomedical imaging, are likely to justify continued materials investment and provide the engineering base on which longer-range radar capability can eventually be built.

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References & Further Reading

1. Lloyd, S. (2008). Enhanced sensitivity of photodetection via quantum illumination. Science, 321(5895), 1463–1465. https://doi.org/10.1126/science.1160627
2. Torromé, R. G., & Barzanjeh, S. (2024). Advances in quantum radar and quantum LiDAR. Progress in Quantum Electronics, 93–94, 100497. https://doi.org/10.1016/j.pquantelec.2023.100497
3. Assouly, R., Dassonneville, R., Peronnin, T., Bienfait, A., & Huard, B. (2023). Quantum advantage in microwave quantum radar. Nature Physics, 19, 1418–1422. https://doi.org/10.1038/s41567-023-02113-4
4. Finco, G., et al. (2024). Time-bin entangled Bell state generation and tomography on thin-film lithium niobate. npj Quantum Information, 10, 135. https://doi.org/10.1038/s41534-024-00925-7
5. Labbé, F., et al. (2025). Thin-film lithium niobate quantum photonics: review and perspectives. Advanced Photonics, 7(4), 044002. https://doi.org/10.1117/1.AP.7.4.044002
6. Karakoc, M. C., Ersoy, O., Salmanoghli Khiavi, A., & Sahin, A. B. (2025). Quantum Radar: An Engineering Perspective. arXiv preprint arXiv:2510.10699. https://arxiv.org/abs/2510.10699
7. Avitabile, F., et al. (2025). Superconducting nanowire single photon detectors based on NbRe nitride ultrathin films. Applied Physics Letters, 127, 172601. https://doi.org/10.1063/5.0282478
8. César-Cuello, J., et al. (2024). Towards a Lithium Niobate Photonic Integrated Circuit for Quantum Sensing Applications. Photonics, 11(3), 239. https://doi.org/10.3390/photonics11030239

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