For decades, scientists have been searching for direct evidence of dark matter, the invisible substance believed to account for roughly 85 percent of the mass in our universe.
Most searches have focused on particles with energies high enough to trigger detectable reactions. However, what if dark matter is far lighter than previously assumed, slipping quietly through detectors designed to catch much heavier prey?
A new experiment by researchers from the University of Zurich, the Hebrew University of Jerusalem, and Massachusetts Institute of Technology (MIT), named “QROCODILE” (Quantum Resolution-Optimized Cryogenic Observatory for Dark Matter Incident at Low Energy), is attempting to answer this question.
In their recent results, published in Physical Review Letters, researchers unveiled world-leading limits on light dark matter particles as small as 30 kilo-electronvolts (keV), a mass range once thought to be beyond the reach of conventional detectors.
This breakthrough brings scientists a step closer to their ultimate goal: directly detecting and confirming the existence of dark matter. A discovery could transform our understanding of the universe.
“For the first time, we’ve placed new constraints on the existence of especially light dark matter,” said co-author and professor of physics at Hebrew University. Dr. Yonit Hochberg said in a press release. “This is an important first step toward larger experiments that could ultimately achieve the long-sought direct detection.”
The QROCODILE experiment takes a unique approach to tracking down proof of dark matter. Instead of using massive underground tanks of liquid xenon or germanium crystals, researchers built a detector out of superconducting nanowire single-photon detectors (SNSPDs).
These are quantum sensors developed initially for ultra-sensitive photon counting. However, with QROCODILE, they serve as both the target and the sensor for dark matter.
Operating at an energy threshold of just 0.11 electronvolts (eV, equivalent to detecting photons with wavelengths of 11 micrometers, QROCODILE can pick up energy deposits far below the reach of most dark matter searches. This ultra-low threshold is crucial, since sub-MeV dark matter would deposit only the faintest traces of energy.
“The QROCODILE experiment uses a microwire-based superconducting nanowire single-photon detector as a target and sensor for dark matter scattering and absorption, and is sensitive to energy deposits as low as 0.11 eV,” the researchers write.
Physicists have long suspected that dark matter might exist at scales well below one mega-electronvolt (MeV). However, detecting it is no small feat. Particles lighter than an atomic nucleus don’t impart much energy when colliding, and traditional ionization-based detection methods can’t reach into this delicate regime.
That’s why QROCODILE’s design of thin superconducting layers just two nanometers deep is so significant. At these scales, the detector is inherently sensitive to the directionality of incoming particles.
Ultimately, this means QROCODILE could one day determine whether a candidate signal originates from the expected ‘dark matter wind,’ a theoretical concept that arises as Earth moves through the Milky Way’s halo, or whether it’s just background noise.
For its initial experiments, QROCODILE was cooled to 100 millikelvin inside a dilution cryostat and operated for more than 415 hours. During that time, the detector recorded 15 faint unexplained signals.
The research team stresses that these mysterious signals cannot be claimed as dark matter detections, as cosmic rays and environmental radiation remain possible culprits. Nevertheless, the ability to constrain dark matter models at these tiny masses is a significant milestone, providing crucial insights into the nature of dark matter and guiding future research in this field.
Importantly, the experiment has set new, world-leading limits on the strength of sub-MeV dark matter interactions with both electrons and nucleons. In fact, QROCODILE is the first superconducting sensor to probe both interaction types simultaneously, thanks to its ability to track how phonons (vibrations in the detector’s lattice) couple to quasiparticles.
What makes QROCODILE especially promising is its scalability. Researchers envision expanding from the current prototype to a 10-megapixel array of SNSPDs. With lower thresholds—down to 43 milli-electronvolts (meV)—and larger exposures, such an upgrade could push sensitivity orders of magnitude further. At this scale, the detector could, in principle, discriminate between background events and the cosmic signature of dark matter itself, offering a hopeful path towards a breakthrough in our understanding of the universe.
“QROCODILE is capable not only of excluding parameter space, but of discriminating between backgrounds and a modulating signal, thus allowing to establish a DM [dark matter] discovery,“ the researchers note.
QROCODILE’s early success highlights a shift in strategy in the hunt for direct evidence of dark matter. Instead of focusing only on massive WIMP (Weakly Interacting Massive Particle) candidates, physicists are diversifying their toolkit. From superconducting nanowires to diamond detectors and even quantum qubits, the new era of dark matter searches is betting big on quantum sensing.
This approach not only expands the search but also opens unexplored territory. By probing particles as light as 30 keV, QROCODILE has reached below the lower bounds of many previous experiments, ruling out models that had never been directly tested before.
The research collaboration is already preparing its Next Incremental Low-threshold Exposure (NILE QROCODILE) run, aiming for longer exposures, reduced background interference, and even lower detection thresholds. Each new step could bring science closer to discovering the hidden physics that explains the universe’s missing mass.
Ultimately, dark matter remains one of the deepest mysteries in physics. We can see its gravitational fingerprint shaping galaxies, bending light, and sculpting cosmic structures. Yet, no experiment has conclusively captured it.
QROCODILE’s first results don’t claim a discovery. However, they do prove that quantum sensors can extend the hunt into terrain once thought inaccessible. If dark matter is hiding in its lightest form, experiments like this may be the first to catch its shadow.
Tim McMillan is a retired law enforcement executive, investigative reporter and co-founder of The Debrief. His writing typically focuses on defense, national security, the Intelligence Community and topics related to psychology. You can follow Tim on Twitter: @LtTimMcMillan. Tim can be reached by email: tim@thedebrief.org or through encrypted email: LtTimMcMillan@protonmail.com
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