Tardigrade is first multicellular organism to be quantum entangled

[CoolMint]

TL;DR Summary

Entanglement of a living organism

https://www.newscientist.com/articl...lticellular-organism-to-be-quantum-entangled/

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. Rainer Dumke and his colleagues at Nanyang Technological University, Singapore, placed one of these hibernating tardigrades on a superconducting qubit, an element …
Read more: https://www.newscientist.com/articl...ganism-to-be-quantum-entangled/#ixzz7FPSUT8uC

 

[Motore]

arXiv paper can be found here:
https://arxiv.org/pdf/2112.07978.pdf

 

[PeterDonis]

raises questions about what it means for living things to be entangled

Note that the tardigrade was not entangled while it was actually doing anything; it was basically "frozen" during the entanglement, and then un-entangled and "unfrozen". So this is not the same as putting a living thing that is actually engaging in any of the characteristic processes of life in an entangled state.

 

[Herzberg137]

Piggybacking off PeterDonis, I think it's really important to emphasize that the role of the tardigrade in these experiments is no different than that of a speck of dust (or any other dielectric placed inside the capacitor, for that matter). It wasn't entangled in any sense of the word, it merely shifted the resonance of some oscillator involved in the entanglement experiment.

 

[manyworldsBob]

"...it was basically "frozen" during the entanglement, and then un-entangled and "unfrozen". "

Hello, can anyone please tell me what proves that the tardigrade was in fact "quantum-entangled" while it was frozen?

I don't see how the state of the frozen tardigrade could not be described independently of the other components of the system. "Frozen" ("tun") and "Unfrozen" ("un-tun") seem to do just that.

From https://en.wikipedia.org/wiki/Quantum_entanglement :

Quantum entanglement is a physical phenomenon that occurs when a group of particles are generated, interact, or share spatial proximity in a way such that the quantum state of each particle of the group cannot be described independently of the state of the others, including when the particles are separated by a large distance.

https://arxiv.org/pdf/2112.07978.pdf

Thanks in advance for your explanation, and for your patience.

 

[StevieTNZ]

Hello, can anyone please tell me what proves that the tardigrade was in fact "quantum-entangled" while it was frozen?

I don't see how the state of the frozen tardigrade could not be described independently of the other components of the system. "Frozen" ("tun") and "Unfrozen" ("un-tun") seem to do just that.

From https://en.wikipedia.org/wiki/Quantum_entanglement :

Quantum entanglement is a physical phenomenon that occurs when a group of particles are generated, interact, or share spatial proximity in a way such that the quantum state of each particle of the group cannot be described independently of the state of the others, including when the particles are separated by a large distance.

https://arxiv.org/pdf/2112.07978.pdf

Thanks in advance for your explanation, and for your patience.

I'm not too sure I understand your statement "I don't see how the state of the frozen tardigrade could not be described independently of the other components of the system. "Frozen" ("tun") and "Unfrozen" ("un-tun") seem to do just that." and your justification for making it.

But in science, nothing can be proved because of statistical and systematic errors.

 

[CoolMint]

Hello, can anyone please tell me what proves that the tardigrade was in fact "quantum-entangled" while it was frozen?

I don't see how the state of the frozen tardigrade could not be described independently of the other components of the system. "Frozen" ("tun") and "Unfrozen" ("un-tun") seem to do just that.

From https://en.wikipedia.org/wiki/Quantum_entanglement :

Quantum entanglement is a physical phenomenon that occurs when a group of particles are generated, interact, or share spatial proximity in a way such that the quantum state of each particle of the group cannot be described independently of the state of the others, including when the particles are separated by a large distance.

https://arxiv.org/pdf/2112.07978.pdf

Thanks in advance for your explanation, and for your patience.

It shows that quantum entanglement would probably be ubiquitous under certain conditions. It seems temperature prevents everything to get entangled with everything else.

 

[Nugatory]

I don't see how the state of the frozen tardigrade could not be described independently of the other components of the system. "Frozen" ("tun") and "Unfrozen" ("un-tun") seem to do just that.

English is poorly suited to talking about quantum mechanics; the text you quoted from wikipedia is a good try at explaining entanglement using ordinary language but asks the word “independently” to do too much work here. We have to skip down to the section on “pure states” to see what’s really going on, explained using math instead of natural language.

But in this experiment the poor little tardigrade is “tun” during the entire time that it was entangled. The full paper (linked by @Motore above) explains how the entanglement was confirmed.

 

[CoolMint]

It's still a new and so far unknown phenomenon that a living organism can be put into a state of superposition and survive. It has some mind-bending consequences.

 

[manyworldsBob]

We have to skip down to the section on “pure states” to see what’s really going on, explained using math instead of natural language.

The full paper (linked by @Motore above) explains how the entanglement was confirmed.

Thank you for your reply.

I will look at the math again in the "pure states" section in the Wikipedia article again, and I do have the full article linked by @Motore above.

From that article, I am trying to fully understand this:

"In order to understand the entanglement with the tardigrade tun, we first expand the dressed states |gBT〉 and |eBT〉back into the larger qubit-tardigrade subspace using Eq. (4). Since the states of the oscillators involved in Eq. (4) are orthogonal, the tardigrade is effectively modeled by a qubit. The density matrix of this three-qubit system (qubitA - qubit B - tardigrade) can then be reconstructed from the tomographic data (see SI). Using tangles based on negativity as entanglement quantifiers [27–29], we observe that entanglement in various bipartitions of the tripartite system as well as genuine tripartite entanglement are monotonically increasing function of θ, the coupling strength between qubit B and tardigrade tun, see Fig. 3. In particular, for any finite interaction strength the tardigrade is entangled with both qubits."

A lot of moving parts in that paragraph, I think; at least for me.

 

[CoolMint]

The Tardigrade must have had no biological functions during the experiment and especially while in superposition. Yet, it returned to its definite classical state, resumed successfully its biological functions and lived on.

Should we conclude that physical matter is not fundamental but a phenomenon under certain conditions? And can be made to return to its quantum field state and come back?

 

[Nugatory]

Should we conclude that physical matter is not fundamental but a phenomenon under certain conditions? And can be made to return to its quantum field state and come back?

You are reading more into this experiment than is there. Basically they froze the little guy and then thawed him out again - remarkable but we already knew we could do that with tardigrades, which is why they were chosen for this experiment. While it was frozen they demonstrated that it behaves exactly like we'd expect any tiny bit of frozen protoplasm to behave - check posts #2 and #3 in this thread.

There's no such thing as going into a "quantum field state" and coming back: everything always behaves according to the laws of quantum mechanics. We usually don't notice when we're looking at objects comprised of a large number of particles (a tardigrade will be made of something like 10¹⁷ molecules) because all the microscopic quantum effects average out - it's analogous to the way that we think of the pressure in a flask of gas as a single number instead of calculating the impact of each individual gas molecule bouncing around inside. A good layman-friendly explanation would be David Lindley's book "Where does the weirdness go?", and also search this forum and google for some other experiments involving superposition of macroscopic objects.

 

[CoolMint]

You are reading more into this experiment than is there. Basically they froze the little guy and then thawed him out again - remarkable but we already knew we could do that with tardigrades, which is why they were chosen for this experiment. While it was frozen they demonstrated that it behaves exactly like we'd expect any tiny bit of frozen protoplasm to behave - check posts #2 and #3 in this thread.

There's no such thing as going into a "quantum field state" and coming back: everything always behaves according to the laws of quantum mechanics. We usually don't notice when we're looking at objects comprised of a large number of particles (a tardigrade will be made of something like 10¹⁷ molecules) because all the microscopic quantum effects average out - it's analogous to the way that we think of the pressure in a flask of gas as a single number instead of calculating the impact of each individual gas molecule bouncing around inside. A good layman-friendly explanation would be David Lindley's book "Where does the weirdness go?", and also search this forum and google for some other experiments involving superposition of macroscopic objects.

It seems, judging by the skeptical react above, that there are people here who don't think QT applies to cats and tardigrades. The cat would no doubt die, but it would still be a cat if they manage to put it into a superposition and then return it to its definite state. This is what the above experiment strongly suggests.
Weird. Very likely 99.999999% of the population consider matter to be fundamental and this experiment challenges this belief.

 

[Nugatory]

this experiment challenges this belief.

It does no such thing, and aside from using a bit of frozen protoplasm instead of a bit of metal is not fundamentally different from the substantial body of earlier work with macroscopic superpositions - for example https://physicsworld.com/a/quantum-effect-spotted-in-a-visible-object/ is more than ten years old now - lots of good discussion in contemporary threads here.

The experimental techniques are interesting and novel enough to make the experiment publishable even though there is no theoretical surprise.

 

[hutchphd]

It seems, judging by the skeptical react above, that there are people here who don't think QT applies to cats and tardigrades.

An alternative explanation might be that you are drawing unjustified conclusions because of misunderstanding the fundamentals of QT. Just a thought...

 

[CoolMint]

It does no such thing, and aside from using a bit of frozen protoplasm instead of a bit of metal is not fundamentally different from the substantial body of earlier work with macroscopic superpositions - for example https://physicsworld.com/a/quantum-effect-spotted-in-a-visible-object/ is more than ten years old now - lots of good discussion in contemporary threads here.

The experimental techniques are interesting and novel enough to make the experiment publishable even though there is no theoretical surprise.

It was a living thing that returned from a state of superposition. It's the very first of its kind.

 

[hutchphd]

It was a living thing that returned from a state of superposition. It's the very first of its kind.

Perhaps this is the first for which measurements were reported directly. Living things are notoriously squirmy unless frozen. Mostly they do not revive well.

 

[Nugatory]

It was a living thing that returned from a state of superposition. It's the very first of its kind.

I’m sorry, but you are completely misunderstanding what a superposition is. As well as the Lindley book that I suggested above, you might want to try Giancarlo Ghirardi’s book “Sneaking a look at god’s cards”. It is not a substitute for a proper (and necessarily fairly math-intensive) college-level intro to QM, but it does avoid many of the popular misunderstandings about how QM actually works.

 

[hutchphd]

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

 

[CoolMint]

I’m sorry, but you are completely misunderstanding what a superposition is. As well as the Lindley book that I suggested above, you might want to try Giancarlo Ghirardi’s book “Sneaking a look at god’s cards”. It is not a substitute for a proper (and necessarily fairly math-intensive) college-level intro to QM, but it does avoid many of the popular misunderstandings about how QM actually works.

So you are suggesting objects can stay entangled without being in a state of superposition? This is just plain wrong.
If you didn't mean this, what did you mean? If I have missed something, I'd like to know what.

 

[Nugatory]

So you are suggesting objects can stay entangled without being in superposition? This is just plain wrong.
If you didn't mean this, what did you mean?

Of course entanglement requires superposition, but that’s beside the point here. We can observe a coherent superposition between the tardigrade and the experimental apparatus as long as it’s frozen solid and otherwise isolated from random interactions with the environment; as we thaw it out the entanglement with the environment leads to decoherence.

The Lindley book is a good layman-friendly treatment, but if you want to dig into a serious treatment of these macroscopic quantum experiments you’ll need something more - and unfortunately the mathematical price of admission is fairly steep. The Wikipedia article https://en.wikipedia.org/wiki/Quantum_decoherence and its references might be a good starting point.

 

[ergospherical]

Fun concept, but question to the experts: is it anything more than a case of "a mate of mine at the bio faculty had some left over tardigrades, want to let it go for a spin on one of our superconducting transmon qubits?".

 

[CoolMint]

Of course entanglement requires superposition, but that’s beside the point here. We can observe a coherent superposition between the tardigrade and the experimental apparatus as long as it’s frozen solid and otherwise isolated from random interactions with the environment; as we thaw it out the entanglement with the environment leads to decoherence.

The Lindley book is a good layman-friendly treatment, but if you want to dig into a serious treatment of these macroscopic quantum experiments you’ll need something more - and unfortunately the mathematical price of admission is fairly steep. The Wikipedia article https://en.wikipedia.org/wiki/Quantum_decoherence and its references might be a good starting point.

So you appear to agree that the tardigrade, a living organism no less, was put into a state of superposition and then returned to its definite state(a state where it is alive).
It's weird that it seems I am the only one who is shocked by this experiment.

 

[PeterDonis]

a living organism no less, was put into a state of superposition

No, a state of entanglement. (Although as I read the experiment, the entanglement was only determined indirectly.) "Superposition" is basis dependent. Entanglement is not.

 

[PeterDonis]

a living organism

The tardigrade was not engaging in any life processes while it was entangled. Its metabolism was completely shut down. That's what the "tun" state it was in means.

 

[PeterDonis]

Of course entanglement requires superposition

No, it doesn't. Superposition is basis dependent. Entanglement is not. I can always find a basis of the joint Hilbert space of the system in which the entangled state is a basis state, not a superposition. But the state will still be entangled.

 

[PeterDonis]

So you are suggesting objects can stay entangled without being in a state of superposition? This is just plain wrong.

No, it isn't. See my posts #24 and #26.

 

[StarMan]

The Tardigrade must have had no biological functions during the experiment and especially while in superposition. Yet, it returned to its definite classical state, resumed successfully its biological functions and lived on.

Should we conclude that physical matter is not fundamental but a phenomenon under certain conditions? And can be made to return to its quantum field state and come back?

Or should we simply conclude that the whole Tardigrade was not in fact entangled but only some tiny part on its exterior surface, which allowed them to claim the entire organism was entangled.

 

[StevieTNZ]

Or should we simply conclude that the whole Tardigrade was not in fact entangled but only some tiny part on its exterior surface, which allowed them to claim the entire organism was entangled.

That wouldn't make sense, nor support their claim.

 

[StarMan]

That wouldn't make sense, nor support their claim.

Exactly. I don't think their claim can be supported since there is zero likelihood they entangled an entire Tardigrade, frozen or not. How do you verifiably entangle the vast quantity of disparate molecules, especially those internally, with a single qubit? They have overstated their claim if they can't validate all parts of the Tardigrade were in fact entangled.

 

[mitchell porter]

It has been argued that there was no entanglement at all (see tweet #10).

Exactly what part of the tardigrade or property of the tardigrade was entangled with the qubit? The paper itself says "the charges inside the tardigrade are represented as effective harmonic oscillators that couple to the electric field of the qubit via the dipole mechanism".

 

[manyworldsBob]

It has been argued that there was no entanglement at all (see tweet #10).

I expressed my skepticism of "proof of entanglement" by the authors of the article first in post # 5 (and also in #10).

However, I am open to being shown the error of my ways; which has not happened yet as far as I'm concerned.

But I am enjoying the conversation very much. Thank you.

 

[mitchell porter]

I read more of the paper now. They took this organism and froze it until it's basically a crystal, and it's presumably numerous individual dipoles in this crystal (proteins? water molecules?) that get entangled with the qubits. Then afterwards they thawed the organism, and one time out of three, it came back to life. (The paper seems to be vague about how complete the revival was; there's a remark about how "mechanically remov[ing]" tardigrades from the filter paper is "irreversibly damag[ing]"; perhaps the revival consisted of the organism wiggling a bit while still stuck in its new webbing?)

 

[vanhees71]

I have no clue, what the value of this experiment might be with regard to quantum theory and living beings. As has been stressed repeatedly the entanglement cannot be stable if the tardigrade is in its "living state", because then it is strongly coupled to the environment, which is not controllable in all details and any possible initial entanglement between it and the superconducting qbits will be very rapidly gone through decoherence. What they did after all is to entangle a piece of matter cooled down to temperatures in the mK range, which can of course be entangled for some time with the qbit.

It's of course amazing that there are liveforms which can "survive" such low temperatures in some "inactive state" and then come to "active live" again, but what has all this to do with the fact that one can entangle macroscopic systems. This is nothing new, and it's even possible at room temperature (for vibrational states of two diamonds this has been achieved some years ago). PhysicsWorld has another example called the "breakthrough achievement of the year":

https://physicsworld.com/a/quantum-...-physics-world-2021-breakthrough-of-the-year/

https://arxiv.org/abs/2009.12902

 

[vanhees71]

No, it doesn't. Superposition is basis dependent. Entanglement is not. I can always find a basis of the joint Hilbert space of the system in which the entangled state is a basis state, not a superposition. But the state will still be entangled.

Entanglement is referring to "subsystems" of a whole system. The most simple example are two qbits, e.g., realized by the spins of two spin-1/2 particles (or polarization states of two photons). The Hilbert space of the whole system ("two spins") is described by the product of the two "single-spin" Hilbert spaces
$$\mathcal{H}=\mathcal{H}_1 \otimes \mathcal{H}_2.$$
Now the total system is by definition in an entangled pure state $\hat{\rho}=|\Psi \rangle \langle \Psi|$ if the corresponding reduced states of the single systems
$$\hat{\rho}_1 = \mathrm{Tr}_2 \hat{\rho}, \quad \hat{\rho}_2 = \mathrm{Tr}_1 \hat{\rho}$$
are not pure states. This is a completely basis-independent definition of entanglement.

It is clear that product states are not entangled. Indeed, if
$$|\Psi \rangle=|\psi_1 \rangle \otimes |\psi_2 \rangle$$
Then
$$\hat{\rho}_1 = |\psi_1 \rangle \langle \psi_1|, \quad \hat{\rho}_2=|\psi_2 \rangle \langle |\psi_2 \rangle,$$
i.e., in this case the two subsystems are both prepared in a pure state.

However, if you have a state like the singlet (total spin 0),
$$|\Psi \rangle=\frac{1}{\sqrt{2}} (|\hbar/2 \rangle \otimes |-\hbar/2 \rangle - |-\hbar/2 \rangle \otimes |\hbar/2 \rangle),$$
then it's easy to show that
$$\hat{\rho}_1=\frac{1}{2} \hat{1}_1, \quad \hat{\rho}_2=\frac{1}{2} \hat{1}_2.$$
So in this case the spins of the two subsystems are no pure state but even "maximum-entropy states", i.e., the single spins are completely indetermined although the whole system is in a pure state with total spin 0. So the two spins are in an entangled state, and because it's even leading to the minimal possible knowledge about each of the subsystems, it's called a "maximally entangled state" or a "Bell state".

So a priori entanglement has nothing to do with superposition (which is always basis dependent) but with being described by a product state or not.

You can of course also use another basis of the whole system. In our case we can use the four Bell states defined by
$$|\Psi^{(\pm)} \rangle = \frac{1}{\sqrt{2}} (|\hbar/2 \rangle \otimes |-\hbar/2 \rangle \pm |-\hbar/2 \rangle \otimes |\hbar/2 \rangle),$$
$$|\Phi^{(\pm)} \rangle = \frac{1}{\sqrt{2}} (|\hbar/2 \rangle \otimes |\hbar/2 \rangle \pm |-\hbar/2 \rangle \otimes |-\hbar/2 \rangle).$$
In this basis our singlet-Bell state is not a superposition of these basis states but simply $|\Psi^{(-)} \rangle$.