Is decoherence the quantum/classical boundary?

Dec 23, 2019
I think they are the same thing. Somewhere around 50,000 bonded atoms will automatically be decohered. Anything smaller requires a decoherence event in its path to be classical.

Can any volume of free particles, coherent light, and 30 micrometer objects (for interaction with particles without causing decoherence) be an environment for quantum weirdness events just waiting for us to do something with?

The most obvious "something" is upgrading quantum computers and harnessing photosynthesis. It's a long shot ..but, maybe even alchemy. Strong, unhindered, wireless power is another candidate. If we find a way to control coherent quantum waves, possibly with the electromagnetic force, we could make hoverboards.
Nov 11, 2019
They're older, but there have been a pile of papers on quantum coherence (and decoherence) discussing just this thing:

Much more recently, there have been discussions on whether or not specific exploration of quantum entanglement opens various doors to decoherence. Take a read here if you haven't yet:

If I were to venture a guess, I'd say that understanding decoherence is the boundary, but implicit understanding of entanglement is a prerequisite to even scoping out the breadth of unraveling decoherence.