Tardigrade is first multicellular organism to be quantum entangled

[PeterDonis]

Entanglement is referring to "subsystems" of a whole system.

It means no subsystem has a definite state on its own, only the whole system.

 

[vanhees71]

The subsystems of course have a definite state. Given the state $\hat{\rho}$ of the whole system, it's described by the reduced statistical operator obtained from the statistical operator describing the whole system by tracing over all other subsystems. For my spin example it's
$$\hat{\rho}_1= \sum_{\sigma_{13},\sigma_{13}',\sigma_{23}} |\sigma_{13} \rangle \langle \sigma_{13},\sigma_{23}|\hat{\rho} | \sigma_{13}',\sigma_{23} \rangle \langle \sigma_{13}'|$$
and analogously for $\hat{\rho}_2$. The sums are over the complete sets of orthornormal states (all $\sigma_{3}$'s running over $\pm \hbar/2$). I also used the more compact notation
$$|\sigma_{13},\sigma_{23} \rangle=|\sigma_{13} \rangle \otimes |\sigma_{23} \rangle.$$
If the whole system is in a pure state $\hat{\rho} = |\Psi \rangle \langle \Psi|$, the two subsystems are entangled if the subsystems are not in pure states, i.e., if the reduced density operators $\hat{\rho}_1$ and $\hat{\rho}_2$ are not projection operators.

 

[PeroK]

And there is Dr Mcdougall's work, also published.

There's also "21 Grams" the movie:

https://www.imdb.com/title/tt0315733/

 

[StevieTNZ]

https://phys.org/news/2021-12-peers-dispute-tardigrades-entangled-qubits.html

Scientists and journalists alike are disputing claims made by an international team of researchers that they had entangled a tardigrade with superconducting qubits. Their paper is published on the arXiv preprint server. Virtually all of those with an opinion pointed out that the work by the researchers in this new effort did not involve entanglement.

 

[manyworldsBob]

And this written on the blog "Nanoscale Views" on Saturday Dec 18, 2021, though I just stumbled on it now.

No, a tardigrade was not meaningfully entangled with a qubit​

https://nanoscale.blogspot.com/2021/12/no-tardigrade-was-not-meaningfully.html

By Douglas Natelson

 

[Nugatory]

True fact: A friend of mine once announced, after wandering around the internet in search of a better answer, that "My spirit animal is a tardigrade".

 

[manyworldsBob]

My new profile pic. (Photograph by Eye of Science / Science Source).

 

[MikeWhitfield]

https://phys.org/news/2021-12-peers-dispute-tardigrades-entangled-qubits.html

So is the true takeaway that this is more an experimental/modeling stunt than ground-breaking science? I cannot truly follow the math so it’s probably my deficiency speaking but I’m seeing nothing truly impressive. Seems more like “We modeled a tun-state water bear as a qubit and voila, it behaved like a qubit!” Is this a gross oversimplification?