Lesson_learnt_from_the_rise_and_fall_of Quantum Radar
TL;DR
Quantum radar—once promoted as capable of detecting stealth aircraft—is physically impossible for military applications. Despite 15 years of research, 300+ publications, and peak annual funding of $2 billion across quantum technologies, the fundamental physics of microwave photons limits detection ranges to single-digit meters rather than kilometers. The technology requires car-sized cryogenic systems, offers no advantages over conventional radar, and has been abandoned by major defense contractors. This case reveals critical lessons about research evaluation, publication bias, and technological hype in emerging quantum fields.
The Revolutionary Promise
In the mid-2000s, quantum radar captivated defense researchers with an elegant concept: exploit quantum entanglement—the mysterious correlation between pairs of photons—to detect targets that conventional radar could not, including stealth aircraft specifically designed to evade detection.
The theoretical foundation appeared sound. Quantum illumination involves transmitting quantum-entangled photons toward a target while keeping their entangled partners at the transmitter. When reflected photons return, they theoretically maintain quantum correlations with their stored twins, providing a detection advantage in noisy environments.
By 2011, Marco Lanzagorta's book Quantum Radar promised the technology would enable "detecting, identifying, and resolving stealth targets" with "quadratic increases in resolution" compared to conventional systems. Defense agencies and private investors took notice, and research funding began flowing rapidly.
The Physics That Couldn't Be Overcome
Fundamental physics imposed constraints that no amount of engineering could circumvent. At X-band frequencies (around 10 GHz)—standard for many radar applications—a single photon carries merely 6×10⁻²⁴ joules of energy. For quantum illumination to work, systems must transmit an average of one photon per mode or less, translating to transmitted power around one femtowatt (10⁻¹⁵ watts).
The radar equation reveals the devastating consequence: while conventional radar with just one milliwatt of transmitted power can detect a 1-square-meter target at tens of kilometers, quantum radar operating at quantum-limited power achieves detection ranges measured in single-digit meters, even with one-second integration times.
"The fact that a long-range microwave quantum radar is physically impossible is easily explained by the need for transmitting an average photon per mode or less," write Galati, Pavan, and Daum in their 2025 review in Academia Quantum. "In realistic applications, it will correspond, for the available radar bandwidths, to unacceptable durations of the illumination time."
A 2018 MIT Lincoln Laboratory assessment, commissioned by the Defense Science Board, reached similar conclusions across multiple radar frequency bands, finding no practical path to operational systems.
The Hype Cycle and Publication Cascade
Despite mounting evidence, publications exploded from 2017 to 2020. IEEE Xplore catalogs 132 quantum radar articles starting from 2013, peaking at over 30 papers annually in 2020-2021.
The publications exhibited classic hype cycle characteristics:
- Theoretical focus: Many papers emphasized quantum physics while ignoring system-level requirements like range, size, weight, power (SWaP), and operational feasibility
- Unrealistic assumptions: Some evaluated performance using two-way propagation attenuations of only -20 dB—orders of magnitude less than the -100 to -150 dB experienced by practical radar systems
- Laboratory-only demonstrations: One published "quantum radar demonstrator" consisted of two horn antennas taped to a desk at less than one meter separation—with no radar target
Critical voices emerged but faced resistance. Fred Daum, a Raytheon distinguished engineer, presented a 2021 IEEE Distinguished Lecture titled "Quantum Radar: Good Idea or Snake Oil?" French researchers Sorelli, Treps, Grosshans, and Boust provided detailed 2022 technical analysis showing why quantum entanglement cannot provide advantages for target detection in practical scenarios.
As documented in the 2025 review, "enduring" groups of connected researchers worked to continue publishing optimistic results and prevent contrasting publications from appearing—a clear example of publication bias.
The Infrastructure Reality
Beyond fundamental physics, quantum radar confronts insurmountable practical challenges. Systems require Josephson Parametric Amplifiers operating at cryogenic temperatures in the micro-Kelvin range—requiring dilution refrigerators cooled with liquid helium, including the hard-to-obtain Helium-3 isotope.
A 2021 analysis revealed the scale: "When the helium tanks and other equipment required by a dilution refrigerator are considered, the total space needed is about the size of a large car. The power consumption is rather large, too: approximately 15 kilowatts."
For military applications, this translates to deployment impossibility. Mobile radar systems must fit on vehicles or aircraft and operate with constrained power budgets. A car-sized cryogenic plant consuming 15 kilowatts—more than many small homes—fails every practical test.
The Money Trail
According to The Quantum Insider, private investment in all quantum technologies reached $2.391 billion in 2022, the peak year, before declining 48% to $1.238 billion in 2023. Public funding reached roughly twice private investment levels, suggesting total annual spending approaching $4-5 billion at peak.
While quantum radar represented only a fraction of this total, hundreds of millions of dollars were directed toward research that fundamental physics showed could not succeed in its stated military objectives. DARPA, which funded early quantum radar explorations beginning in 2003, has not published recent assessments, but the technology's absence from operational programs speaks volumes.
International Claims and Geopolitical Dimensions
Chinese media reported quantum radar developments purportedly capable of detecting stealth aircraft in publications between 2016 and 2021. However, technical analysis revealed these claims suffered from the same fundamental limitations. No publicly documented demonstrations showed detection of actual stealth targets at operationally relevant ranges.
French physicist Fabrice Boust of ONERA stated bluntly: "I am convinced that when they [China] announced their quantum radar it was not working. But they knew they would get a reaction."
Technology Readiness Level (TRL) assessments consistently rated quantum radar at TRL 1-2 (basic principles observed) with a time horizon listed as "None"—the only technology among quantum applications to receive this assessment. By contrast, quantum key distribution reached TRL 7-8, and quantum sensing for gravimetry achieved TRL 5-6, all with clear deployment timelines.
International Scientific Consensus
Skepticism spans multiple countries and institutions:
- France: Fabrice Boust (ONERA), Giacomo Sorelli (now Fraunhofer IOSB)
- United States: Fred Daum (Raytheon), MIT Lincoln Laboratory
- Austria: Johannes Fink (IST Austria)
- Canada: Christopher Wilson (University of Waterloo)
Significantly, even researchers who successfully demonstrated quantum illumination in laboratories acknowledge the vast gap to practical systems. Fink's 2020 press release stated: "But to show an advantage in practical situations we will also need the help of experienced electrical engineers and there still remains a lot of work to be done in order to make our result applicable to real-world detection tasks."
Matthew Brandsema's 2020 work proved particularly devastating, demonstrating that "quantum and classical scattering in the far-field regime" are essentially equivalent—meaning at distances relevant for radar applications, quantum effects produce results identical to classical physics.
The Collapse
By 2025, interest had largely evaporated:
- Publications fell from 32 papers in 2020 to single digits annually by 2024
- The 2024 IEEE Radar Conference included only one quantum radar paper
- The 2025 European Radar Conference relegated quantum radar to a subsection under "Ultra-Wideband, Noise, and Polarimetric Radar"
- Major defense contractors quietly moved away from development
Critical Lessons for Science Policy
The quantum radar saga offers multiple lessons:
1. First-Principles Analysis: Simple order-of-magnitude calculations using the radar equation could have revealed fundamental limitations before extensive research programs began. Single-photon energy at microwave frequencies immediately constrains quantum-limited systems to impractical detection ranges.
2. Publication Bias and Echo Chambers: The literature exhibited clear publication bias, with optimistic theoretical papers far outnumbering critical system-level analyses. Peer review failed to adequately filter submissions ignoring practical constraints. Connected research groups created echo chambers that amplified positive results while marginalizing criticism.
3. Solution Looking for a Problem: Unlike successful quantum technologies emerging to solve existing problems (atomic clocks improving GPS accuracy), quantum radar represented a solution seeking application. When military applications proved impossible, proponents suggested medical imaging—itself impractical given car-sized cryogenic requirements.
4. Honest Assessment Obligations: As physicist Scott Aaronson noted, "it is not enough not to say anything false" for scientists. Researchers have ethical obligations to clearly communicate limitations alongside possibilities. The quantum radar community often failed this test, with promotional language about defeating stealth technology persisting even after fundamental limitations were well-established.
Contrast with Genuine Quantum Successes
Quantum radar's failure stands in stark contrast to genuine successes:
- Quantum sensing: Revolutionized metrology, with quantum-based definitions underpinning all SI base units
- Atomic clocks: Achieve unprecedented accuracy, enabling advanced GPS and fundamental physics research
- Quantum cryptography: Companies like Leonardo building quantum-secure metropolitan networks
- Quantum computing: While far from practical general-purpose machines, has proven advantages for specific algorithms with clear (if challenging) paths toward error correction
These technologies succeeded because they addressed fundamental physical advantages, often operating at room temperature or with manageable infrastructure requirements. Quantum radar faced fundamental physical constraints that no amount of engineering could overcome.
Parallels to Cold Fusion
The authors of the 2025 review draw explicit comparisons to cold fusion—the discredited 1989 claim that nuclear fusion could occur in tabletop electrochemical cells. Despite scientific consensus rejecting cold fusion by the late 1990s, Google quietly invested $10 million in a research program in 2015, confirming that "no experiment showed evidence of nuclear reactions."
Both followed similar patterns: initial excitement from theoretical possibilities, rapid investment growth, peak hype coinciding with maximum publications, followed by disillusionment as physical reality intruded—a lifecycle of approximately 20 years despite obvious theoretical problems evident early.
Recommendations for Future Research Evaluation
The quantum radar experience suggests several reforms:
Mandatory System-Level Analysis: Applied technology proposals should require early system-level analysis using established engineering principles, not just theoretical physics.
Diverse Peer Review: Review panels should include specialists from relevant engineering disciplines, not only theorists in the emerging field.
Staged Funding with Go/No-Go Criteria: Programs should include clear milestones with objective criteria. Quantum radar could have been terminated much earlier with requirements like "demonstrate detection beyond 100 meters."
Transparency About Limitations: Publications should prominently discuss fundamental limitations, not bury them in technical appendices while highlighting optimistic possibilities in abstracts.
Protection for Critical Voices: Research ecosystems must protect scientists who raise legitimate concerns. Some quantum radar critics faced professional pushback—precisely the opposite of healthy scientific discourse.
Conclusion: The Value of Negative Results
Karl Popper's philosophy emphasized that scientific progress depends on testing hypotheses and accepting negative results. By this standard, the quantum radar saga represents a successful scientific outcome: a hypothesis was tested and found wanting. The physics community now understands quantum radar's limitations clearly.
However, this success came at substantial cost in funding, researcher time, and opportunity cost for alternative approaches. The 15-year timeline and hundreds of publications exceeded what rigorous early evaluation would have required.
As quantum technologies continue developing—quantum computing, communications, and sensing all vying for investment—the quantum radar cautionary tale deserves careful study. Some quantum technologies will succeed spectacularly. Others will fail, confronting fundamental limitations no amount of engineering can overcome.
The challenge for researchers, funders, and policymakers is distinguishing between these categories as early as possible—applying rigorous physical analysis, honest assessment of limitations, and willingness to accept negative results.
Quantum radar has been eliminated. The lessons from its elimination should guide future quantum technology development, helping separate genuine revolution from quantum hype.
Key Technical References
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Galati, G., Pavan, G., & Daum, F. (2025). Lesson learnt from the rise and fall of quantum radar research. Academia Quantum, 2. https://doi.org/10.20935/AcadQuant7586
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Sorelli, G., Treps, N., Grosshans, F., & Boust, F. (2022). Detecting a target with quantum entanglement. IEEE Aerospace and Electronic Systems Magazine, 37(5), 68-90.
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Daum, F. (2020). Quantum radar cost and practical issues. IEEE Aerospace and Electronic Systems Magazine, 35(11), 8-20.
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Hardy, N., Dixon, B., Shapiro, J., & Hamilton, S. (2018). Quantum illumination radar feasibility. Defense Science Board Report. https://apps.dtic.mil/sti/pdfs/AD1132052.pdf
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Brandsema, M., Lanzagorta, M., & Narayanan, R. (2020). Equivalence of classical and quantum electromagnetic scattering in the far-field regime. IEEE Aerospace and Electronic Systems Magazine, 35(4), 58-73.
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Cho, A. (2020). The short, strange life of quantum radar. Science, 369(6511), 1556-1557.
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Krelina, M. (2021). Quantum technology for military applications. EPJ Quantum Technology, 8, 24.
Technology Readiness Assessment
| Technology | TRL | Time Horizon |
|---|---|---|
| Quantum Computing | 4-5 | 2030 |
| QKD (Satellite) | 7-8 | 2025 |
| Quantum Communication Network | 1-3 | 2030-2035 |
| Quantum Clocks | 4-6 | 2030 |
| Quantum Magnetic/Gravity Sensing | 5-6 | 2025 |
| Quantum Radar | 1-2 | None |
Source: Krelina (2021), EPJ Quantum Technology
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