The state I was thinking about is stable electron configuration. If an atom has two such configurations, and can switch between them, that's one bit worth of storage.
And what if a stray photon should strike your atom? Does that not have a chance of changing the state? I don’t know much about electron configurations.
I suppose a random photon won't have the right energy to switch the state. But even when this happens, we have error recovery algorithms: cells in regular hard disks die all the time.
A single atomic electron state will almost certainly switch to a problematic degree except for very exceptional materials in typical room temperature type conditions - free ozone, UV light, background radiation. most crystals will grow or change at room temperature in some way over time (normalizing to the lower energy state if they weren’t 100% already, or high energy perturbances like UV light damaging the matrix and then ‘falling down’ the energy ladder again). Diamonds ablate through oxidation as well.
Error correcting helps of course, but we already have to do a LOT of error correcting to make even the ‘low density’ spinning rust drives we have now work. At some point you have so much noise, your error correction overhead is too high to make it worthwhile - which is the current issue with high q-bit quantum computers for instance
We’re a long way from having the materials science to be able to do this. Same issues plague quantum computing. Maybe some day though?
MRI machines do something like this. Probably not at the atom scale accuracy. UV light can be ignored because the crystal would sit in a opaque case. A trivial error correction is writing a bit to many places, the idea similar to bloom filters.
If it's sitting in a truly opaque case, it definitely isn't a tape! Shutters aren't perfect, and they open every time the cassette is used. That sounds more like a hard drive? UV and other short wavelength light can come from inside the case or the crystal from background radiation or cosmic rays as well. Reed-solomon encoding, n-copies, they all have capacity tradeoffs and error rate detection/correction limits, and get away from the 'single bit' ideal quite a bit (for n-copies, at least by 2x, usually 3x even in the most ideal situation). It's also non-trivial to avoid something like a background radiation emission 'tunneling' through and causing non-trivial damage to a sector.
It's going to be statistical level analysis for awhile, at least at temps near room temperature or devices only practical in a specially shielded lab.
MRIs are heavily shielded and regularly calibrated, and are only doing bulk statistical analysis. AFM or MFM [https://en.wikipedia.org/wiki/Atomic_force_microscopy] is the closest we can currently get, and they suffer from a number of issues, including damage to what it's touching, repeatability/precision issues, thermal drift, etc. and that is just getting what is usually a one time read.
