Of water bears and quantum weirdness.

If you’re looking to the animal kingdom for tough customers, you need look no further than tardigrades. These eight-legged critters are capable of surviving searing temperatures of 150 degrees Celsius (302 degrees Fahrenheit or 423.15 Kelvin) and freezing conditions of absolute zero. Even the vacuum of space is a walk in the park for them.

Wherever they are found—the lofty Himalayas, scorching volcanic mud, crushing depths of the Mariana Trench, chilling in Antarctica, or just hanging out in your backyard pond—tardigrades owe their incredible resilience to their ability to survive without water. Under extreme stress, they activate their “cryptobiosis” mode, drying themselves up and coating their cells with special proteins and sugars. They can be revived by water, which combined with their chubbiness has earned them the cute nickname “water bears”. Check out this video of a water bear in its mossy habitat.

Now pair this fascinating creature with one of the most mind-boggling scientific fields—quantum mechanics—and you’d end up with some of the toughest, and maybe some the weirdest experiments ever.

Schrödinger’s tardigrade???

Quantum water bears.

In a paper on ArXiv, yet to be peer-reviewed, a team of quantum physicists claims to have done something near to impossible: quantum entangle a water bear with a pair of quantum bits, or qubits.

In the mind-bending, classical-physics-defying realm of quantum mechanics, entanglement means that two things or systems are linked, or dependent on each other, and will therefore mirror each other no matter where they are. Or according to Einstein: spooky interaction at a distance.

But what does it mean to “quantum entangle a water bear”? In simpler terms, it means that whatever happens to the qubits, happens to the water bear, or vice versa. Previously, only small inanimate objects have been entangled. So if true, this would be the first-ever quantum entanglement involving animals.

However, this experiment has also precipitated fierce debate over its claims. Many detractors echo the view that the water bear did not achieve true quantum entanglement—only classical interactions existed between the water bear and the qubits.

So what was the experiment?

Water bears claimed to affect qubits.

To entangle a biological system with a quantum system, the researchers needed an organism that is so robust that it can survive the ultra-cold temperatures requisite for a quantum computer. Naturally, a tardigrade springs to mind.

At temperatures of just slightly above absolute zero and pressures 166,666,666 times lower than the atmosphere’s, three lucky water bears entered cryptobiosis. In this state, the tardigrades can be regarded as a purely dielectric element, capable of conducting electric current without resistance. Then, the team entangled the tardigrades with two superconducting transmon qubits and carried out three experiments, each with a different tardigrade.

In the experiments, a tardigrade was placed on top of the capacitive parts of one of the two already coupled transmon qubits. And since the researchers treated the tardigrade like a conductor of electric current, they claimed it shifted down the resonance frequency of the qubit it was coupled with—the evidence of entanglement.

Hold your horses, or in this context, water bears.

Other quantum scientists were sceptical of this inference too. Some said that just because the tardigrade modified the qubit’s frequency doesn’t mean that quantum entanglement had taken place. To truly prove that, the quantum properties of the tardigrade would have to be measured—an experimental step that needs to be taken to fill the gap.

Some also suggested the fluctuation in qubit frequency was caused by the temperature change of the quantum system.

Either way, a rigorous peer review is still needed to solidify these claims. We’ll have to wait and see if this experiment filled with quantum weirdness could be a step in the right direction to show how quantum physics might be involved in the processes of life.

But one thing’s for sure. The hardiness of tardigrades isn’t at all inflated: one of them pulled through the whole ordeal and made it out alive!

By Mitchell Lim

Mitchell Lim is DUG's Scientific Content Architect. With a PhD in Chemical Engineering, Mitch is an expert in the fields of catalysis and ultrasonics. Full-time science geek, part-time fitness junkie, Mitch strives to deliver effective and engaging science communication, as he believes that easily digestible scientific perspectives have the potential to impact and benefit society at large.

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