For decades, physicists have been chasing shadows. They know that something invisible and elusive—something we call dark matter—makes up about 27% of the universe. And yet, no telescope can see it, no camera can capture it, no ordinary detector can measure it. Dark matter does not emit, reflect, or absorb light. It passes through stars, planets, and even our own bodies without leaving a trace.
But while it hides in the dark, its fingerprints are everywhere. Galaxies spin too fast for the amount of visible matter they contain, and only the invisible pull of dark matter can explain why they hold together instead of flying apart. On a cosmic scale, dark matter shapes the large-scale structure of the universe, guiding the formation of galaxies like an unseen architect. Without it, the universe as we know it would not exist.
Physicists around the world have built highly sensitive detectors, buried deep underground to shield them from cosmic noise, all in the hope of catching even the faintest interaction between dark matter and regular matter. Yet the silence persists.
Now, a new experiment—strangely named QROCODILE—may bring us closer to finally hearing the whispers of this cosmic mystery.
Introducing QROCODILE
QROCODILE, short for Quantum Resolution-Optimized Cryogenic Observatory for Dark matter Incident at Low Energy, is a joint research effort by scientists at the University of Zurich, the Hebrew University of Jerusalem, and the Massachusetts Institute of Technology (MIT).
At first glance, it might sound like just another entry in the long line of dark matter experiments. But QROCODILE introduces something radically new: a detector so sensitive that it can pick up energy signals thousands of times smaller than those most other detectors can detect.
In a recent study published in Physical Review Letters, the QROCODILE team demonstrated that their technology not only works but has the potential to probe uncharted territory in the search for dark matter.
From Quantum Optics to Cosmic Shadows
The heart of the QROCODILE experiment lies in a device called a superconducting nanowire single-photon detector (SNSPD). Normally, SNSPDs are used in quantum optics to catch single particles of light. But physicists realized they could be repurposed for something far more ambitious: detecting particles of dark matter.
These detectors are made of extremely thin wires of tungsten silicide (WSi), cooled to just 0.1 degrees above absolute zero. At this temperature, the wires become superconductors. In this exotic state, electrons pair up into what physicists call Cooper pairs. Breaking one of these pairs requires an almost impossibly tiny amount of energy—much smaller than what traditional detectors need to record an event.
If a dark matter particle collides with the nanowire and deposits even the tiniest sliver of energy, it can break a Cooper pair. This creates a small disturbance, a tiny resistive “hot spot” in the superconducting wire. That disturbance produces an electrical pulse—a signal that can be measured.
In other words, QROCODILE can listen to the universe’s faintest whispers, energy deposits as low as 0.1 electronvolts (eV). That’s thousands of times more sensitive than conventional detectors, opening the door to exploring a regime of light dark matter that has been nearly invisible until now.
Why This Is Revolutionary
Traditional dark matter detectors rely on processes like ionization or scintillation, which require relatively large energy deposits to register a signal. That makes them blind to very light dark matter particles—those with masses in the range of tens of kilo-electronvolts (keV).
QROCODILE breaks through this limitation. By reaching thresholds as low as 0.11 eV, the team has shown that their technology can probe dark matter particles much lighter than what other direct detection experiments can currently access.
This could be a game-changer. If dark matter is lighter than expected, then many of the world’s largest detectors—massive tanks filled with liquid xenon or argon—might never find it. But QROCODILE, with its quantum-level sensitivity, might.
The First Promising Results
Though QROCODILE is still in its proof-of-principle stage, the results from the first test run were nothing short of impressive.
The experiment achieved one of the lowest-ever energy thresholds for a dark matter detector, 0.11 eV. It also set new constraints on the possible interactions between dark matter and electrons down to masses of just 30 keV—a frontier unexplored until now.
Even more intriguing, the detector showed sensitivity not only to electrons but also to nuclei, thanks to how vibrations in the nanowire material (called phonons) can couple with incoming particles. This dual sensitivity broadens the possibilities for catching different kinds of dark matter interactions.
Perhaps the most exciting feature of all, however, is directional sensitivity. The QROCODILE detector responds differently depending on the incoming direction of the particle. This matters because if dark matter truly exists, its signal should align with Earth’s motion through the Milky Way, while background noise from cosmic rays or natural radioactivity would not. Directional detection could provide the kind of unambiguous evidence that physicists have been chasing for decades.
The Road Ahead
Of course, QROCODILE’s work has just begun. The prototype has proven itself, but to truly hunt for dark matter, the team must scale up.
They plan to build larger-area sensors and fine-tune the material composition to further enhance performance. They will also need to lower background noise and carefully calibrate their detectors at these incredibly low energies, using controlled sources such as the isotope iron-55.
The next big leap will be moving underground. Cosmic rays, even rare ones, can produce false signals. To minimize this interference, QROCODILE will soon be installed at the Gran Sasso Laboratory in Italy, the world’s largest underground physics laboratory. Shielded beneath mountains of rock, the experiment will enjoy protection from cosmic noise, making it a more pristine environment to search for the faint footprints of dark matter.
The Bigger Picture
QROCODILE represents more than just another experiment. It is part of a larger scientific movement: the relentless drive to uncover the unseen. Physicists know that without dark matter, galaxies would not hold together, cosmic structures would look very different, and the universe itself might not exist as it does.
But dark matter’s true nature remains hidden. Is it a new kind of particle? Is it something even stranger that challenges our understanding of physics itself? Each experiment, whether it finds dark matter or rules out certain possibilities, brings us closer to an answer.
QROCODILE’s innovation lies in its quantum-level sensitivity, pushing boundaries that seemed unreachable just a few years ago. By venturing into lighter mass ranges and introducing directional detection, it may help us finally corner dark matter—or at the very least, narrow the possibilities with unprecedented precision.
A Future Written in Shadows and Light
The story of dark matter is one of humanity’s greatest scientific quests. It is a reminder that most of the universe lies beyond our senses, and yet, we dare to seek it.
QROCODILE is still small compared to the giant detectors buried under mountains and oceans. But sometimes, it is not size that matters, but sensitivity. Like a finely tuned instrument, QROCODILE may pick up the cosmic notes that others miss.
If it succeeds, it won’t just detect dark matter—it will open a new chapter in our understanding of the cosmos, revealing secrets hidden since the dawn of time.
Until then, we wait, listening for the faintest pulses in superconducting wires cooled to near absolute zero, hoping that somewhere in that silence lies the answer to one of the greatest mysteries of existence.
More information: Laura Baudis et al, First Sub-MeV Dark Matter Search with the QROCODILE Experiment Using Superconducting Nanowire Single-Photon Detectors, Physical Review Letters (2025). DOI: 10.1103/4hb6-f6jl.
