Quantum physics just got a lot weirder – and more exciting – because scientists are now spotting something called “magic” hidden inside particle collisions at the Large Hadron Collider (LHC). This isn’t fantasy magic, but a strange kind of quantum behavior that could reshape how we think about both the universe and future quantum computers.
At the LHC near Geneva, protons are smashed together about 90 million times every year, and in a fraction of those collisions, the debris includes a top quark and an anti–top quark, the heaviest elementary particles we know of. In the unimaginably short instant before they decay – roughly a trillionth of a trillionth of a second – these two particles rush away from each other but remain quantum mechanically entangled, which means the state of one is inseparable from the state of the other. If a measurement shows the top quark spinning one way, the anti–top quark is instantly locked into spinning the opposite way, no matter how far apart they’ve traveled.
Top quarks are unusual because, unlike other quarks that rapidly clump together into composite particles like protons and neutrons, they decay before they have time to combine with other quarks. That makes them a rare clean window into fundamental quantum behavior. The particles produced in their decay carry information about the original spins of the top and anti–top quarks, acting like a readable fingerprint of their entanglement, which experimentalists can reconstruct from the detector data.
In 2023, the ATLAS experiment at the LHC reported the first detailed measurement of how the spins of top and anti–top quarks are correlated, effectively mapping out their quantum linkage. That landmark result opened the door to a wave of new measurements that look at entanglement in different ways, using the LHC not just as a “particle smashing machine” but as a sophisticated probe of quantum information. Seventeen years after the collider first turned on, researchers are realizing they can repurpose it to study how quantum information flows and transforms in extreme conditions – a question right at the heart of quantum computing.
From this perspective, the two possible spin orientations of a quark can stand in for the 0 and 1 states of a qubit, the basic unit of quantum information. In other words, a high‑energy collision that produces top quarks can be treated a bit like a massively complex quantum processor acting on qubits created from the vacuum. As one physicist put it, the collider was not originally built to answer these kinds of questions – yet it turns out to be surprisingly good at them. And this is the part most people miss: a machine designed to find new particles is now doubling as a laboratory for some of the most abstract ideas in quantum information theory.
Quantum information meets colliders
This merging of quantum information theory with particle physics is so new that many researchers describe it as a genuinely emerging field rather than a mature area. One physicist involved in the CMS experiment, another major detector at the LHC, likened the current moment to a gold rush, with teams rushing to explore fresh ideas before the easiest discoveries are gone. There is a sense that a new conceptual toolkit has just been dropped into an old experiment, and no one yet knows how far it can go.
A particularly eye‑catching result arrived when the CMS collaboration measured something known in quantum information theory as “magic” in a pair of top quarks. In this context, magic is not a metaphor for mystery, but a technical label for certain highly entangled quantum states that are especially hard for ordinary, classical computers to simulate. These elusive states are critical for unleashing the full power of quantum computers.
To understand why, it helps to know that quantum computers can sometimes run specific algorithms exponentially faster than classical machines. They do this by exploiting entanglement to link many qubits together, creating a web of interdependent possibilities. A quantum computer can manipulate all these possibilities at once, rather than stepping through them one by one as a classical computer does. That makes entanglement sound like an automatic ticket to quantum advantage – but here’s where it gets controversial.
Why entanglement alone isn’t enough
For a long time, many people assumed that the more entangled a quantum system is, the better it must be for quantum computing. That intuition feels natural: if entanglement is the special ingredient, then more should always help. But researchers eventually showed that this simple picture is wrong, and in some cases very misleading.
In the 1990s, a major breakthrough came with the proof of the Gottesman–Knill theorem. This result demonstrated that certain quantum states called stabilizer states can be efficiently simulated on a classical computer, even when they are strongly entangled. In practice, that means if a quantum computer only ever produces stabilizer states, then, despite all the fancy quantum machinery, a classical computer could keep up just fine. No real speedup, no genuine quantum advantage.
This realization shifted the focus. Instead of treating “lots of entanglement” as the key metric, physicists began hunting for quantum states that differ as much as possible from stabilizer states. These outlier states, which resist efficient classical simulation, became known as magic states. Some practitioners still joke about the term and consider it a terrible name, but after being used for two decades, it has stuck – and that persistence alone shows how central the idea has become.
The role of contextuality
A big theoretical puzzle remained: what exactly makes magic states so special, beyond the fact that they are hard to simulate? In 2014, researchers connected the dots by identifying contextuality as the underlying feature that gives magic states their real computational power. Contextuality is a subtle property of quantum systems that has no analogue in classical physics.
In simple terms, contextuality means that the outcome of a quantum measurement can depend on which other measurements are performed alongside it. The properties of the system are not fixed and waiting to be revealed; they are defined in part by the context in which they are probed. For stabilizer states, it is possible to interpret them in a way that avoids contextuality, treating the system as if it has a full set of definite properties at all times. But magic states refuse to be squeezed into that classical‑like picture.
Because of their inherent contextuality, magic states are extremely difficult for classical algorithms to mimic, and that is precisely what makes them such valuable “fuel” for quantum computation. In practice, many proposed quantum architectures need a steady supply of these magic states to achieve tasks that classical computers cannot manage in any reasonable time. So naturally, quantum information researchers have become increasingly interested in how to generate, preserve, and even amplify magic within physical systems.
Looking for magic in nature
Against this backdrop, some particle physicists started to wonder whether nature herself might already be producing magic states in high‑energy processes. After all, the LHC is a gigantic quantum system: when protons collide, they create strongly entangled quantum states of quarks, gluons, and other particles. If magic really is a generic resource in quantum mechanics, shouldn’t it show up there too? That line of thinking led brothers Martin and Chris White, both physicists working on high‑energy theory, to focus on top quarks as a promising testbed.
They proposed a concrete method for detecting magic in top–quark systems, outlining how one could translate measurable quantities in collider data into the language of quantum information. Interestingly, their paper was their first formal collaboration, which made the result personally meaningful to them as well as scientifically significant. For years they had wanted to work together, and this new intersection between quantum information and collider physics finally gave them the right project.
When Regina Demina, a physicist at the University of Rochester working with CMS, met the White brothers at a conference, their ideas struck a chord. She brought the proposal back to her team, helping launch the effort that would eventually lead to the CMS magic measurement. She even jokingly compared the twins themselves to an entangled pair spread across the globe: one based in the United Kingdom, the other in Australia, separated by distance but still deeply connected in their scientific lives.
How CMS measured magic
To uncover magic in top–quark pairs, the CMS collaboration dug into a vast dataset of proton–proton collisions, focusing on events where a top and an anti–top quark were produced and then decayed. By carefully reconstructing these events, they could determine how the spins of the two particles were correlated as they flew off in various directions from the collision point. Each event contributed a little bit of information about how the spins aligned or opposed each other along different axes.
From this information, the researchers built a mathematical object called a spin correlation matrix, which summarizes how the spin components of the top and anti–top quark relate in the x, y, and z directions. This matrix is essentially a compact description of the entanglement structure within the pair. Using tools from quantum information theory, one can translate this matrix into a measure of how much magic is present in the system.
When they performed this analysis, the CMS team found that the entangled top–quark pairs indeed exhibited a nonzero amount of magic. That result is remarkable: it shows that a concept once mostly discussed in the context of abstract qubits and small quantum devices has now been identified in the chaotic, high‑energy environment of a particle collider. In effect, a piece of quantum computing theory has jumped into the realm of experimental particle physics.
Surprise: a hint of toponium
The primary motivation for studying magic in this setting is not to discover new kinds of particles, but to deepen understanding of how to harness quantum resources for computing. However, the refined analysis techniques developed for these magic measurements turned out to be useful for more traditional particle‑physics questions as well. In particular, they helped reveal an unexpected signature in the data.
When scientists looked closely at the entanglement patterns, they noticed that in some cases the top and anti–top quark seemed to be even more tightly correlated than anticipated. This extra level of entanglement hinted that the two quarks were briefly binding together into a bound state before decaying. That bound state, known as toponium, had been predicted back in 1990 but was long considered too subtle for the LHC to detect clearly.
Toponium can be thought of as a fleeting “atom” composed of a top quark and an anti–top quark held together by the strong nuclear force. Because top quarks decay so quickly, the expectation was that this bound state would be extremely fragile and difficult to observe in practice. The fact that the LHC experiments are now seeing signs of it shows how far their analysis tools have come, and how much can be extracted from the data when viewed through a quantum‑information lens.
Both CMS and ATLAS have now reported measurements consistent with toponium, with CMS releasing its results in March and ATLAS following with complementary findings in July. One researcher described these observations as the first concrete “spin‑off” of the magic‑state program: by learning to measure entanglement and magic with high precision, the experiments also stumbled onto new evidence for a long‑anticipated bound state.
New questions about entanglement
Beyond specific discoveries like magic and toponium, many physicists are excited about the broader questions this line of work opens up. One key puzzle involves what happens to entanglement when particles decay. For instance, if a top quark and an anti–top quark are entangled, and then the top quark quickly decays into other particles, does that entanglement transfer to the decay products?
According to quantum field theory, the answer should be yes: the “daughter” particles created in the decay are expected to inherit entanglement from their parent. But this prediction has never been thoroughly tested in a system like the top quark at a collider. Experiments that carefully track correlations between decay products could finally probe this question in detail, giving concrete data on how entanglement flows and transforms during particle interactions and decays.
This, in turn, connects to the long‑standing mystery of the quantum‑to‑classical transition – the process by which a quantum system that can exist in many possible states at once ends up in a single definite outcome. In textbook examples, this happens when a measurement is made by some external apparatus. But at the LHC, there is an interesting twist: when a top quark decays, it seems to be “forced” to pick one of its possible spin states, and the resulting decay products fly off in directions that depend on that choice.
From a mathematical standpoint, this decay process is equivalent to a measurement being made on the quark’s spin, even though no human‑built detector has intervened yet. That perspective offers a fresh way to think about how quantum probabilities turn into concrete outcomes, using high‑energy collisions as a playground for questions that are usually associated with delicate tabletop experiments.
Time as an emergent concept?
Some researchers are also hoping to use these collider‑based quantum systems to explore ideas about the nature of time itself. One intriguing proposal, discussed in theoretical work by Don Page and William Wootters in the 1980s, suggests that time might not be a fundamental feature of the universe. Instead, the universe as a whole could be static and timeless, while observers inside it experience change due to entanglement between different parts of the system.
In the Page–Wootters picture, an observer can perceive time passing because the state of one subsystem – for example, something acting like a clock with a repeating pattern – becomes correlated with changes in another subsystem. The combined global state remains fixed, but from the perspective of the observer, it looks as though events evolve and clocks tick. This idea was given experimental support in 2013 when researchers demonstrated a version of the mechanism using entangled photons.
Inspired by these concepts, some LHC physicists dream of reproducing an analogous effect using elementary particles rather than photons. The goal would be to show that similar “timelike” correlations, arising purely from entanglement, can emerge in systems involving quarks and other fundamental constituents of matter. If successful, such experiments would push the boundaries of how and where deep questions about time and quantum reality can be tested.
A brewing controversy
Of course, not everyone is convinced that these top‑quark experiments are truly testing the foundations of quantum mechanics. Some theorists have raised concerns that the approach might be fundamentally circular. To infer entanglement and magic from collider data, experimentalists need to translate the angles and directions of the decay products into statements about the original spins of the top and anti–top quarks.
To make that translation, they rely on theoretical models that assume quantum mechanics is correct in the first place. Critics argue that if the analysis depends on quantum theory at every step, then the experiments cannot really be used to test whether quantum mechanics is valid – they can only confirm that the data are consistent with the theory they assumed. In that view, no matter how sophisticated the analysis is, it might not count as an independent test of the underlying framework.
Supporters of the program, however, see things differently. They argue that even if the experiments are not “theory‑free,” they can still provide stringent checks on the internal consistency of quantum field theory in regimes that were previously inaccessible. Moreover, by forcing theorists and experimentalists to translate between quantum‑information concepts and collider observables, these studies could uncover new ways of thinking about both fields. But here’s where it gets controversial: are these efforts genuine tests of quantum reality, or are they mainly clever reinterpretations of data we already trust?
Where does this all lead?
After nearly two decades of operation, the LHC has already delivered on many of its original promises, such as the discovery of the Higgs boson. Yet some physicists feel that simply repeating similar searches may not be enough going forward. There is a growing desire to extract new types of insight from the existing machine, rather than only hoping for spectacular surprises like brand‑new particles.
The emerging focus on entanglement, magic, and other quantum‑information ideas offers one such new direction. It invites researchers to “pull on the threads” of quantum structure embedded in collision data and see what unravels, even if the initial questions come from outside traditional particle‑physics agendas. Along the way, they may stumble across unexpected phenomena, just as the toponium hints emerged from an analysis originally motivated by quantum computing.
For now, there is plenty of skepticism alongside the enthusiasm. Some worry that these topics sound more exotic than they are, or that they risk overselling what the experiments can truly prove about deep questions like the nature of time or the quantum‑to‑classical transition. Others see this as a healthy sign that the field is exploring fresh territory, where disagreement and debate are inevitable parts of progress.
So what do you think: is using the world’s biggest particle collider to hunt for “magic” a brilliant new way to connect quantum computing and fundamental physics, or is it overhyping effects that mainly confirm what quantum theory already says? Do you see this cross‑disciplinary approach as the future of big science, or should colliders stay focused on more traditional particle hunts? Share whether you’re excited, skeptical, or somewhere in between – and why.
