>>13758730one photon at a time? I mean I guess that would be pretty standard. But can you engineer two different lasers perfectly the same so there's no offsets at all? And can you start both lasers at the exact same nanosecond so they can be perfectly in phase. I mean come on we're talking about the real world here.
That's why all of these experiments are generally splitting a single laser beam, directing the beam around, and then making it interfere with itself.
To give you confidence in my answer, I had the very same question and I asked my phsyics professors at a very top level university. This is what they told me
