[pittsburghjoe (OP)]

H2O atoms are not bonded to other H2O atoms. We still get fringes when doing the double slit underwater ..suggesting water is not large enough to be considered a spacetime object and cause decoherence.
I guess the same can be said about oxygen.

[Kryptid]

H2O atoms are not bonded to other H2O atoms.

To some extent, they are: https://en.wikipedia.org/wiki/Hydrogen_bond

[pittsburghjoe (OP)]

"on average about one in every 5.5 × 10⁸ molecules gives up a proton to another water molecule"

[pittsburghjoe (OP)]

Isn't it curious that water has at least three states (liquid, solid, gas) ..I'd say gas represents superposition.

[Bored chemist]

Isn't it curious that water has at least three states (liquid, solid, gas)

No.
It's not curious.
In principle (almost) everything has at least two; solid and gas.
Those materials whose molecules are held together strongly enough also have a liquid state.
Helium has a 4th state.
There's a 5th state- plasma- that isn't so well defined for molecules- but exists for all elements.

.I'd say gas represents superposition.

I doubt anyone else says so.

"on average about one in every 5.5 × 10^8 molecules gives up a proton to another water molecule"

True, but proton transfer isn't the question here.
Hydrogen bonding occurs between pretty nearly all the molecules of water in the condensed phases.

[pittsburghjoe (OP)]

They aren't going to bond together enough to be considered a spacetime object. I wonder if the double slit has been performed with ice.

[Bored chemist]

What does this

spacetime object.

mean?
And also what do you mean by this

I wonder if the double slit has been performed with ice.

[pittsburghjoe (OP)]

An object that isn't going to go into superposition ..too large to be used in the double slit experiment.
I want to know if laser light still shows fringes when traveling through ice.

[Bored chemist]

None of that makes much sense.
Water molecules, even if stuck together in bunches are smaller than, for example, buckyballs, which have been shown to act in a wavelike manner when going through slits.

I have put a diffraction grating in some water in the freezer.
I can't imagine that it won't work when the water freezes, but it's a trivial experiment so why not just do it?

[pittsburghjoe (OP)]

yes, smaller than buckballs ..so they are not spacetime objects they are only part of the quantum field. Light doesn't collapse until it hits something considered a spacetime object. Do water molecules keep their quantum state when frozen?

[Bored chemist]

Do water molecules keep their quantum state

What do you think "quantum state" means?

[pittsburghjoe (OP)]

I want a quantum computer made with water. If the spin can be stored ..it would be 10x more valuable than the current light ones.

[pittsburghjoe (OP)]

What's not to love about a steampunk quantum computer?

[pittsburghjoe (OP)]

We are mostly water, maybe our brains are quantum after all.

[evan_au]

suggesting water is not large enough to be considered a spacetime object and cause decoherence.

Another way of looking at "decoherence" is "becoming entangled with the rest of the universe".

Every time a water molecule collides with another water molecule, or donates a proton (or attracts an extra proton), its quantum state becomes entangled with the other water molecule/ion.

Because of hydrogen bonding, water interacts very strongly with all surrounding molecules, and so decoherence occurs frequently. Perhaps in a rarified gas the decoherence time will be a bit longer.

If the spin can be stored

I expect that angular momentum of the water molecule will be quantised.
A water molecule has multiple vibration modes, and every time a water molecule bumps into another water molecule, these quantised vibration and angular momentum states change in complex ways.

I want a quantum computer made with water.

For a quantum computer, you want to maximise the decoherence time, and allow controlled quantum interactions with other quantum objects.
- Light has a very long decoherence time (almost a microsecond, in optical fiber, at room temperature), but it is very hard to get a specific photon to interact with another specific photon in a controlled way.
- Water has too many vibrational states for these interactions to be easily controlled (you would need to bombard it with infra-red or microwaves of just the right wavelength and phase).
- What you want is something with fewer quantum states than a water molecule, but stronger interactions than a photon. Preferably something with 2 states (1 or 0) that can become entangled in a controlled way (allowing states defined by 2 complex numbers)
- But to get a coherence time of 1 microsecond, most materials have to be cooled within a whisker of absolute zero.

[pittsburghjoe (OP)]

We shouldn't ever get fringes underwater if everything is decohering.

[pittsburghjoe (OP)]

If light sees water as a solid body of touching molecules ..it should be acting like a photon, not waves.

[pittsburghjoe (OP)]

I think it means water is quantum no matter the quantity.

[pittsburghjoe (OP)]

oh, I got an answer here "There is no absorption and re-emission process when light travels in a transparent medium. Medium does absorb some portion of the light, but no re-emission happens, or re-emission is so small that it can be neglected."

https://physics.stackexchange.com/questions/490324/why-the-randomness-in-glass-water-air-does-not-destroy-coherence-of-light-over-f

[evan_au]

We shouldn't ever get fringes underwater if everything is decohering.

What are you measuring the interference patterns of?
- Interference patterns of light: Light can pass through pure water quite well, without being scattered. In this case, you will get fringes in water just as you do in glass, air or a vacuum. However, the spacing of the firnges will vary because light travels at a different speed through different media.
- Interfering patterns of water molecules: Water molecules can't pass through solid or liquid water very well at all, as the water molecule will bump into all the other water molecules, and you won't get fringes in the double-slit experiment (the hydrogen bonds don't help, either!). If you want to create interference patterns of water molecules, you will need to do it in a vacuum. (...and the hydrogen bonds won't help, either!)