How to write both superscript and subscript text using geom_text in R?

I'd like to write a model equation in the graph.

nitrogen<- c(10,15,20,25)
yield<- c(50,70,85,30)
dataA<- data.frame(nitrogen,yield)

ggplot(data=dataA, aes(x=nitrogen, y=yield))+
  geom_point (col="Black", size=4) +
  stat_smooth(method='lm', linetype=1, se=FALSE, formula=y~poly(x,2, raw=TRUE), size=0.5, color="Blue") +
  windows(width=5.5, height=5)

Now I'd like to write below equation inside the graph. I know there are many questions about this, but I cannot find a solution, and still struggling. So I ask again. Sorry for duplicated question.

Could you please let me know how to write both superscript and subscript text?

Always many thanks!!

library(ggplot2)

nitrogen<- c(10,15,20,25)
yield<- c(50,70,85,30)
dataA<- data.frame(nitrogen,yield)
coef = coef(lm(yield ~ poly(nitrogen,2, raw=TRUE)))

ggplot(data=dataA, aes(x=nitrogen, y=yield))+
  geom_point (col="Black", size=4) +
  stat_smooth(method='lm', linetype=1, se=FALSE, formula=y~poly(x,2, raw=TRUE), size=0.5, color="Blue") +
  windows(width=5.5, height=5) + 
  annotate("text", x=15, y=16, label = bquote(~ Y[i][j]==.(coef[1])+.(coef[2])*x+.(coef[3])*x^2))

Edit This version gives more control on formula display:

ggplot(data=dataA, aes(x=nitrogen, y=yield))+
  geom_point (col="Black", size=4) +
  stat_smooth(method='lm', linetype=1, se=FALSE, formula=y~poly(x,2, raw=TRUE), size=0.5, color="Blue") +
  windows(width=5.5, height=5) + 
  annotate("text", x=15, y=16, label = bquote(
    ~ paste(Y[i][j],"=", .(sprintf("%.2f", coef[[1]])), .(sprintf("%+.2f",coef[[2]])),x, .(sprintf("%+.4f",coef[[3]])),x^2)))