Is the Evidence for Quantum Entanglement in Bacteria Strong Enough?

[jedishrfu]

In a recent Scientific American article, researchers have claimed to have quantum entangled some bacteria:

https://www.scientificamerican.com/...cterium-could-be-a-quantum-biology-milestone/

So a new paper from a group at the University of Oxford is now raising some eyebrows for its claims of the successful entanglement of bacteria with photons—particles of light. Led by the quantum physicist Chiara Marletto and published in October in the Journal of Physics Communications, the study is an analysis of an experiment published last year, conducted by David Coles from the University of Sheffield and his colleagues. In that experiment Coles and company sequestered several hundred photosynthetic green sulfur bacteria between two mirrors, progressively shrinking the gap between the mirrors down to a few hundred nanometers—less than the width of a human hair. By bouncing white light between the mirrors, the researchers hoped to cause the photosynthetic molecules within the bacteria to couple—or interact—with the cavity, essentially meaning the bacteria would continuously absorb, emit and reabsorb the bouncing photons. The experiment was successful; up to six bacteria did appear to couple in this manner.

Marletto and her colleagues argue the bacteria did more than just couple with the cavity, though. In their analysis they demonstrate the energy signature produced in the experiment could be consistent with the bacteria’s photosynthetic systems becoming entangled with the light inside the cavity. In essence, it appears certain photons were simultaneously hitting and missing photosynthetic molecules within the bacteria—a hallmark of entanglement. “Our models show that this phenomenon being recorded is a signature of entanglement between light and certain degrees of freedom inside the bacteria,” she says.

According to study co-author Tristan Farrow, also of Oxford, this is the first time such an effect has been glimpsed in a living organism. “It certainly is key to demonstrating that we are some way toward the idea of a ‘Schrödinger’s bacterium,’ if you will,” he says. And it hints at another potential instance of naturally emerging quantum biology: Green sulfur bacteria reside in the deep ocean where the scarcity of life-giving light might even spur quantum-mechanical evolutionary adaptations to boost photosynthesis.

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[Demystifier]

They didn't entangle light with a whole bacteria. They entangled light with certain degrees of bacteria, those degrees which are responsible for the photosynthesis. Those degrees are microscopic, so this experiment does not put us much closer to a realization of the Schrödinger cat.

 

[PeterDonis]

"progressively shrinking the gap between the mirrors down to a few hundred nanometers—less than the width of a human hair."

First of all, a few hundred nanometers is not just "less" than the width of a human hair; it's several orders of magnitude less. This kind of lack of attention to detail in favor of sensationalism is a big reason why I no longer read Scientific American.

Second, a few hundred nanometers is about the size of a single bacterium (if the bacterium is on the small side), so I'm not clear how they managed to fit several hundred bacteria between the mirrors.

Third, with the gap between the mirrors of the same order as the size of a bacterium, I'm not sure how they would know that whatever they were seeing was not just a garden-variety interaction between the bacteria and the mirrors.

 

[PeterDonis]

Reading the Marietto et al paper, I find this striking admission (in the paragraph before equation 6):

"It is worth pointing out that the same results (namely the observation of the vacuum Rabi splitting) can equally well be explained by a completely classical analysis"

So how do they justify their claim that the results demonstrate quantum entanglement?

"There is no contradiction with the entanglement witness in our model, because the witness already assumes that both systems are quantum and checks whether the subsystems are entangled."

And then later on they refer to "The witness of non-classicality provided by the Rabi splitting". Either I'm missing something or they have simply ignored the fact that the classical analysis gives the same results.