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A tardigrade has been quantum entangled with a superconducting qubit – and lived to tell the tale. It is the first time a multicellular organism has been placed in this strange quantum state and raises questions about what it means for living things to be entangled.

Tardigrades are microscopic animals that can survive extreme temperatures and pressures in a hibernating state called a tun. and his colleagues at Nanyang Technological University, Singapore, placed one of these hibernating tardigrades on a superconducting qubit, an element of a quantum computer.

They then lowered the pressure and temperature to almost a perfect vacuum and near absolute zero, reducing any outside influence, or excitations, on the qubit and tardigrade.

“Because all the excitations are frozen out, you can actually describe [the system] in terms of physics, there’s no need to describe it in terms of biology,” says Dumke.

When researchers measured the natural frequency at which the tardigrade and qubit combination vibrates, the result only made sense if the two objects were in a state of quantum entanglement, meaning that their quantum properties were linked.

After they had finished making measurements, the researchers slowly depressurised and warmed up the tardigrade, bringing it out of its tun state and back to life.

The temperature involved, just 0.01°C above absolute zero, is the lowest a tardigrade has ever survived. The fact that the creatures can tolerate such extreme conditions suggests their hardiness is a result of completely shutting off their metabolic processes.

“There was still some discussion that perhaps there is a little bit of metabolism that actually goes on [in the tun tardigrade],” says team member at the University of Gdańsk, Poland. “But this experiment shows – because it’s so cold, and for such a long time – that it’s really ametabolic. There is no chemistry going on in this piece of stuff.”

“The fact you can maintain a quantum state, which has quantum coherence in it and involves the degrees of freedom of a biological system as large as a tardigrade, is very exciting,” says at the University of Oxford, who entangled a bacterium with light in 2018.

While the tardigrade was certainly living before and after the entanglement, one point of contention is whether it was alive during the entanglement, and exactly how it was entangled.

“You never know in this kind of experiment what exactly is the part of [the tardigrade] that takes part in the entanglement,’ says Paterek.

The tardigrade was actually the third to undergo the entanglement experiment, as the first two didn’t survive the process as a result of being warmed up too quickly. Despite these technical hurdles, Dumke and his team hope to entangle other forms of life in future.

While technically challenging and not involving live organisms, researchers have entangled photons at room temperature, as well as 3-millimetre-wide diamonds.

But the tardigrade entanglement is an important first step to going further. “It is really in the best tradition of theoretical experimental physics, where you’re being playful, but at the same time, you’re trying to understand and answer deep questions,” says Marletto. “That’s inherently risky, but very rewarding if it works out well. We need more of this stuff.”

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