I did none of my degrees in US, and my physics degree was 95% math and physics. Physics degree is quite sequential anyway. You can't do QM in your first year or QFT in your second year.

I've checked random people I know from oxford and none started after 3-year undergrad and those how did after 4 all did 4 year dphil (small sample size warning). 4+4 is reasonable.

Obvious disclaimer: At this point we are talking about outlier colleges/universities.

But to give some examples, I know colleges (both in US and abroad) where people did real analysis and abstract algebra in their first year (and why not - neither requires prerequisites other than maturity).

I know a college (in the US) where they did Jackson for E&M in the 3rd year (and some advanced students did in the 2nd year). In most US universities, people normally do Jackson in the first year of their PhD.

I think it's rare to do QM before 2nd year, but in principle, as long as you know calculus/diff eq, you can get going on it. The catch is that the interesting applications require other branches of physics (e.g. E&M). When I did QM, all those applications were part of QM II anyway.

But yes, again, these are outliers and I wouldn't want to say it's the norm in the whole country.

Maybe things have changed. We did QM in our first year at Imperial. I suppose we have to make allowances for Oxford. Got to fit the poetry in somewhere. =)