Physicists have coaxed clusters of thousands of atoms into a delicate quantum limbo, creating a record breaking version of Schrödinger’s famous cat that is both “here” and “there” at once. By pushing superposition into ever larger and hotter systems, they are turning a once abstract thought experiment into a concrete laboratory tool. The result is a striking step toward a future in which quantum weirdness shapes technologies and even brushes against the scale of living matter.
At the heart of this advance is a simple but unsettling idea: objects do not have to choose a single reality until something forces the issue. By engineering nanoparticles that behave like tiny cats, alive and dead in parallel, researchers are testing how far quantum mechanics can stretch before everyday intuition finally reasserts itself.
From paradox to laboratory benchmark
Long before anyone could juggle thousands of atoms in a vacuum chamber, Erwin Schrödinger imagined a sealed box in which a cat was both alive and dead, a metaphor for a quantum system that exists in multiple states at once. The paradox was meant to expose how strange it is to apply quantum rules to everyday objects, yet over time Schrödinger’s Cat has become a standard way to explain superposition and to probe the boundary between quantum and classical worlds. The thought experiment has left a deep imprint on how physicists frame reality, casting a shadow over classical interpretations that assume objects always occupy definite states, as detailed in modern explanations of Schrödinger’s Cat.
Turning that metaphor into hardware has taken decades of incremental progress. Early experiments managed “cat states” with just a handful of particles, such as carefully prepared photons or small groups of atoms, and even then the states were fragile and short lived. Creating this situation experimentally is very difficult, especially for systems made up of many particles, because any interaction with the environment tends to destroy the delicate quantum correlations, a challenge that was already clear in pioneering work on the creation of a six atom cat state.
Supersizing the cat: thousands of atoms at once
The latest experiments have blown past those early few particle demonstrations by putting entire metal nanoparticles into superposition. A team based at the University of Vienna prepared individual clusters of around 7,000 atoms of sodium metal, each roughly 8 nanometres wide, and then arranged for each cluster to travel along two paths at once. In the final interference pattern, the nanoparticles behaved like waves spread across different locations, a direct signature that the entire 7,000 atom object was in a superposition of positions.
What makes this feat so striking is not just the number of atoms but the distance between the alternative realities. The two paths were separated by 133 nanometres, more than 20 times the width of the nanoparticles themselves, which one analysis likened to a ping pong ball being in two places around 80 centimetres apart simultaneously, a comparison highlighted in coverage of the world’s biggest Schrödinger’s. In other words, this is not a tiny quantum blur but a macroscopically distinct separation on the scale of the object itself, a point underscored in reports describing the largest ever superposition.
Measuring how “macroscopic” a quantum cat really is
Physicists have long debated what it means for a quantum state to be truly macroscopic, and recent work has tried to quantify that intuition. One influential analysis argues that there are two main properties that clearly must be “large” for a quantum state to count as macroscopic: the number of microscopic constituents involved and the degree to which the alternative branches differ in some observable quantity. This perspective, laid out in a theoretical study that uses simple models to illustrate how many particles and how distinct the branches must be, is captured in a technical discussion that begins with the word However.
By that yardstick, the Vienna nanoparticles are not just a curiosity but a genuine step into the macroscopic regime. From the interference data, the team extracted a “macroscopicity” value of μ = 15.5, which surpasses the previous record by an order of magnitude, as detailed in their analysis of μ = 15.5 and the earlier benchmark of 33. An accompanying summary notes that the experiment tests the validity of quantum theory at this scale and further limits alternative extensions of quantum mechanics, emphasizing that μ = 15.5 is about one order of magnitude beyond what had been achieved before.
Keeping big cats alive: decoherence, heat and control
Scaling up cat states is not just a matter of adding more atoms, it is a fight against the environment. Larger objects constantly interact with stray gas molecules, thermal radiation and electromagnetic noise, which rapidly destroy quantum superpositions in a process known as decoherence. In practice, quantum effects are extremely fragile, and as one overview of the nanoparticle work stresses, larger objects are especially vulnerable to this kind of environmental monitoring. Theoretical treatments describe decoherence as the way a system in a superposition of states, such as being in many places at once, is driven into a single classical outcome when it becomes entangled with its surroundings, a phenomenon explored in work on quantum decoherence.
To keep their cats alive long enough to study, researchers rely on extreme isolation and clever control techniques. Some groups have focused on “hot Schrödinger cat states,” using two special protocols to create superpositions that persist even when the underlying system is not cooled to near absolute zero, an approach highlighted in work led by Ian Yang. Others have developed long lived cat states in atomic ensembles that achieve Heisenberg limited sensitivity, paving a new way for atomic magnetometry, quantum computations and the exploration of new physics beyond the Standard Model, as described in reports on a long lived Schrödinger. Even the ability to assemble and manipulate nanoparticles one by one with an electron beam, as demonstrated when They at Berkeley Lab used this tool to build nanostructures, feeds into the precise engineering needed for these quantum feats.
Where quantum meets life and everyday reality
As the cats grow larger, the experiments begin to brush against objects that feel less like abstract particles and more like the stuff of daily life. The latest evidence for this shift comes from metallic particles the size of some viruses, which have just broken the record for the most macroscopically distinct quantum superposition, moving the edge of the quantum world closer to our reality and to the original vision of Schrödinger. One recent experiment explicitly frames its achievement as pushing the boundaries of quantum mechanics to the limit, describing the world’s largest Schrödinger’s cat and noting that the team have pushed the boundaries of quantum mechanics by putting an object in two places around 80 centimetres apart, a claim echoed in reports that the Researchers have indeed reached that separation.
The next frontier, hinted at in several analyses, is biological material. One overview of the nanoparticle work notes that this discovery opens the door for future experiments where scientists could feasibly observe biological materials, such as a virus, in a quantum superposition, bringing the phenomenon tantalizingly close to the real world, a prospect highlighted in coverage of how physicists push thousands into cat states. The idea of putting a living object like a bacterium or a virus into a superposition has been discussed as a natural extension of current methods, with one essay noting that such methods might soon be capable of placing a bacterium or virus so that it could be observed in either of two possible locations, as described in a reflection on how Such techniques could evolve. At the same time, biologists remind us that a virus is not really alive, even though it is made from biological material and shares some functions with human organs and tissues, a nuance emphasized in a conversation that notes for example how ambiguous life can be at that scale.
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