Entangling atoms in a molecule

In summary: This is still true, but it's a bit more complicated than that. The idea is that you can use the state of the two ions to calculate the energy of a specific state of the electron. However, this calculation is not unique. There are actually a lot of possible ways to do it, and the accuracy of the calculation depends on the accuracy of the initial state of the ions. So, while the quantum spectroscopy method might allow for better bounds on the energy level, it's not always guaranteed to be more accurate than classical methods.
  • #1
BillKet
312
29
Hello! I came across several papers that use entangled states of 2 ions in a trap to perform measurements with a much higher accuracy than classical (non-entanglement) methods. Here is an example of such a paper where they achieve the best measurement to date of an isotope shift. I was wondering if something similar can be done (or has been done) in diatomic molecules. In that case we already have 2 ions close to each other, so I was wondering if there is a way to entangle the 2 constituents atoms such that you gain some further advantage over normal spectroscopy techniques. Thank you!
 
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  • #2
I've been out of the loop for a while, but I remember there were groups at NIST and Hannover that did spectroscopic measurements like that. Looks like there's a publication from Basel too in recent times. The technique you describe is called quantum logic spectroscopy. When I was in precision measurement, we would half-heartedly talk about pros and cons of using quantum logic. The biggest disadvantage is that you reduce your sample size to N=1. More molecules is more better for statistical reasons, especially in precision measurement. Quantum logic spectroscopy only pays off if your one entangled atom/molecule is more sensitive on its own than averaging down on a whole gas. There are cases where it pays off, like NIST's aluminum ion clock which is a more precise timekeeper than JILA's strontium lattice clock with its 1000 strontium atoms.

Also, please keep in mind that with molecules just preparing a single unentangled quantum state is cause for several bottles of champagne.
 
  • #3
Ah, sorry, realized you meant entangling the constituent atoms in a molecule, not entangling a molecule with an atom (that's what quantum logic spectroscopy is). The issue is that constituent atoms are already incredibly well entangled! Consider this, in quantum computing experiments where atomic ions are entangled, two ions are coupled by Coulomb forces acting over a distance on the order of a few microns. Compare that to a molecule where two "ions" are coupled over a few angstroms. The atomic states are so well mixed you'd be hard pressed to project them out. That's what molecular states are, after all.

With "halo dimers" it might be another story, but I haven't the faintest idea how you would project the molecular state onto an atomic state without first dissociating the dimer.
 
  • #4
Twigg said:
Ah, sorry, realized you meant entangling the constituent atoms in a molecule, not entangling a molecule with an atom (that's what quantum logic spectroscopy is). The issue is that constituent atoms are already incredibly well entangled! Consider this, in quantum computing experiments where atomic ions are entangled, two ions are coupled by Coulomb forces acting over a distance on the order of a few microns. Compare that to a molecule where two "ions" are coupled over a few angstroms. The atomic states are so well mixed you'd be hard pressed to project them out. That's what molecular states are, after all.

With "halo dimers" it might be another story, but I haven't the faintest idea how you would project the molecular state onto an atomic state without first dissociating the dimer.
Thank you for your reply! Yes, I was thinking about atoms in a molecule (maybe at high vibrational energy levels, where they are quite far apart relative to the ground state level), but I see your point. However the paper you sent me are really useful. I looked a bit over them and over some other similar experiments. It seems like this method is mainly useful when you can't measure that specific molecule directly for some reason (e.g. maybe it is hard to prepare it in a desired state) and it also offers an advantage as you can repeat the measurement on the same molecule without removing it from the trap. I was wondering if this can actually offer an advantage over molecules that are already measured with high accuracy using classical methods. For example they set bound on the electron electric dipole moment using classical Ramsey spectroscopy on ThO. Would this quantum spectroscopy methods in principle allow more accurate measurements of the energy levels and hence better bounds (or even a discovery!)? Or are we still to far from that and for now these methods are more of a proof of principle?
 
  • #5
BillKet said:
mainly useful when you can't measure that specific molecule directly for some reason (e.g. maybe it is hard to prepare it in a desired state)
This is also true but I didn't think to mention it! Especially for the aluminum ion clock. One day, there could even be a thorium-229 clock operating on this principle using the low-lying, super forbidden nuclear transition. Nuke clock! :oldbiggrin:

BillKet said:
For example they set bound on the electron electric dipole moment using classical Ramsey spectroscopy on ThO. Would this quantum spectroscopy methods in principle allow more accurate measurements of the energy levels and hence better bounds (or even a discovery!)?
Funnily enough, when I was talking about my conversation with other folks in precision measurement I was actually talking about my conversations with the HfF+ eEDM team. What I said there is exactly why no one has proposed a quantum logic eEDM search to the best of my knowledge. To justify using quantum logic, you'd need a molecule with such a high sensitivity to eEDM that it'd outperform a gas of 1000 HfF+ (I forget the final flux of useful molecules for ThO, but these experiments have comparable overall sensitivity). Recall that averaging over shot noise gives you an improvement of ##\sqrt{N}##, so to use quantum logic to compete with HfF+ you'd need a molecule that was ##\sqrt{1000} = 32## times more sensitive to eEDM.

Edit: sorry, I should've toned down the lingo, eEDM = electon electric dipole moment
 
  • #6
quantum computations have been performed using NMR to entangle the nuclear spins in molecules like caffeine.
 

Related to Entangling atoms in a molecule

1. What is entanglement in atoms and molecules?

Entanglement refers to a physical phenomenon where two or more particles become connected in such a way that the state of one particle is dependent on the state of the other, even when they are separated by a large distance. In atoms and molecules, entanglement occurs when the quantum states of the constituent particles are correlated and cannot be described independently.

2. How is entanglement achieved in atoms and molecules?

Entanglement in atoms and molecules can be achieved through various methods such as laser cooling and trapping, quantum control techniques, and quantum computing algorithms. These methods involve manipulating the quantum states of the particles to create entanglement between them.

3. What is the significance of entanglement in atoms and molecules?

Entanglement in atoms and molecules has significant implications in quantum information processing, quantum computing, and quantum communication. It allows for the creation of highly sensitive sensors and can also be used for secure communication through quantum cryptography.

4. Can entanglement be observed in macroscopic objects?

While entanglement is a quantum phenomenon, it has been observed in macroscopic objects such as crystals and superconducting circuits. However, the entanglement in these systems is typically short-lived due to decoherence from interactions with the environment.

5. What are the challenges in entangling atoms in a molecule?

One of the main challenges in entangling atoms in a molecule is controlling and manipulating the quantum states of the individual atoms. This requires precise control and measurement techniques, as well as minimizing interactions with the environment to prevent decoherence. Additionally, different molecules have different energy levels and bonding configurations, making it difficult to entangle them in a consistent manner.

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