03-04-2025
Scientists Brought Schrodinger's Cat to Life—and Proved Something Incredible About Quantum Physics
Schrödinger's cat, the infamous thought experiment involving a cat that can be alive and dead at the same time, has been brought to life with qubits.
Schrödinger's cat experiments have been done with particles before, but all of them were cooled to near-absolute zero. It was like starting with a dead cat. This is the first time 'hot' particles were used.
In the future, the conditions under which this experiment was done could benefit applications in which it is not yet possible to put particles in a deep freeze.
Remember those hologram stickers that used to show two things at once, and all you had to do was turn the sticker slightly? There is a similar phenomenon in physics, and it even comes with a mascot.
In the famous thought experiment known as Schrödinger's cat—first proposed by physicist Erwin Schrödinger in 1929—a hypothetical cat is locked in a box with poison, or something else that could possibly kill it. Following Schrödinger's line of thinking, as long as the box remained closed, the cat is both dead and alive at the same time. When you open the box and observe the cat, however, it 'chooses' a state and loses that dual nature.
This thought experiment was meant to elucidate a part of quantum theory known as superposition. Quantum superposition describes the way that, on the smallest scales, matter that hasn't yet been measured can (like the cat) basically exists in two completely opposite states at the same time. It's why things like photons can be both particles and waves. The truth of a superposition state is much more complicated than the biological state of a cat, but it can most simply be described as a combination of all the states a particle can be in. For instance, a particle may be spinning or traveling in two directions at once. It can be either one, and also both, until we measure it.
Previous experiments that brought the concept of Schrödinger's cat to life (pun intended) involved cooling particles to near-absolute zero so they could reach the state with the lowest possible energy, known as the ground state. Those particles could then be manipulated into quantum states more easily. Until now, this type of experiment had never been done with particles not cooled to the ground state, as background noise from heat excitation could get in the way of measurements.
Led by physicist Gerhard Kirchmair from the University of Innsbruck in Austria, a team of researchers have now successfully achieved a Schrödinger's cat state with 'hot' particles.
'Schrödinger also assumed a living, i.e. 'hot' cat in his thought experiment,' Kirchmairsaid in a press release. 'We wanted to know whether these quantum effects can also be generated if we don't start from the 'cold' ground state.'
Excitingly, for Kirchmair's team, it seems the effects can, in fact, be generated in non-ground states. 'Standard quantum mechanical theory predicts no upper limit on and no loss of contrast [between states] due to the [heat] of a hot cat state,' the team wrote in their study, published today in the journal Science Advances.
To create a cat, particles known as a transmon qubits were exposed to microwaves in a microwave resonator. Think of a transmon qubit as merging a qubit (a quantum bit) and a superconductor—a basic unit of information able to conduct electricity without resistance because it is less sensitive to noise. Then, the team used two 'cat state protocols' that had previously been used at lower temperatures to generate quantum cats in order to try and create a superposition at 1.8 Kelvin (which is not very hot in the grand scheme of things, but is well above ground-state temperatures).
The effort was a success, and Kirchmair saw that the same protocols which succeed at cold temperatures also work with warmer temperatures. While the states of the particles were less clear due to noise—which was filtered and controlled as much as possible—they were still clear enough to identify. This proved that, so long as the conditions of cat protocols can be created, temperature should not interfere much.
'Hot Schrödinger cat states are in principle realizable,' the team said in the study. 'This is particularly relevant for systems where long [predictability] times have been achieved but ground-state cooling is not yet available.'
Long live physics cats.
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