One of the scientific phenomena that did a great job at keeping scientists and researchers up at night is the well-known, dead-and-alive paradox, the Schrödinger’s cat. An astounding problem that many thought was just proof of loopholes in quantum physics has actually turned out to be solvable, and a groundbreaking study deeply shocked the scientific world. A macroscopic object has all the characteristics of a particle set in a superposition, mirroring the effect observed in Schrödinger’s experiment. The study has become the first proof of superposition on macro-objects, showing that scientific research methods are constantly evolving.
But what exactly is the Schrödinger’s cat experiment?
Schrödinger’s cat is a thought experiment proposed by physicist Erwin Schrödinger in 1935. It illustrates the concept of superposition in quantum mechanics, one of the key principles to quantum physics as a whole. In the experiment, a cat is placed in a sealed box with a radioactive atom, a Geiger counter, a hammer, and a vial of poison. If the atom decays, the Geiger counter triggers the hammer to break the vial, killing the cat. Quantum mechanics suggests that until the box is opened, the cat is simultaneously alive and dead, as we do not have the possibility to know the contents of the box before taking a look inside. The animal is both alive and dead, the atom decayed and not. All at the same time.
In physics, that is what we call a superposition – a state in which a particle can exist in multiple states or conditions simultaneously. The discovery of superposition has led many people to believe the experiment could only exist in theory, as it is impossible for any animal or physical object to enter two separate states – existing and not – in the same second. Many have successfully replicated the study with various objects of many masses and states, but nobody could prove it on a macro-object.
At first glance, the existence of something in two or more states at the same time sounds abstract. Maybe that is the reason as to why the experiment has gotten a reputation of just a theorem showing loopholes without any practical meaning. And yet, we judged Schrödinger’s cat’s possibilities too soon. One of the bigger experiments with the aim to prove the existence of a bigger object in superposition was described in the paper “Schrödinger cat states of a 16-microgram mechanical oscillator” authored by physicists from the Quantum Centre in Switzerland.
In 2023, the scientists have successfully created an animal just like the one described in the thought experiment. It is not a cat, a kitten, nor a lion, though. It is a macroscopic object weighing about 16.2 micrograms, which might seem like a minuscule number, but, in case of atomic particles, it is the heaviest “cat” to ever be created. It weighs several billion times more than an atom. M. Bild, Yiwen Chu, and the other researchers achieved this with the use of an oscillator placed into simultaneous oscillation in two opposing phases. An oscillator is a system that undergoes repetitive motion around an equilibrium point. In the case of cat states, a high-overtone bulk acoustic-wave resonator was used as the oscillator. It can generate high-frequency vibrations and allows creation and control of phonon states. The HBAR was then connected to a transmon superconducting qubit, which is a tiny quantum bit, and manipulated to produce a superposition of the phonon.
This achievement mirrors the concept of the original Schrödinger’s cat, challenging traditional boundaries between quantum and classic physics. Something many thought of as unprovable turned out to be both provable and measurable. Through this research, physicists now aim to produce an object of an even bigger scale than the physicists from Zurich managed to do, even if their so-called cat states only lasted milliseconds. This experiment shows us that physics as a science is rapidly expanding and evolving in the methods used, which seems to promise even more spectacular and useful studies on many undiscovered yet topics.
