Change text in annotation legend

[bakerwm]

How can I change the text in annotation legend?

For example. Change the "Exp1" to "Ex^p1" in the legend.

It sames that expression( ) function is not work for this purpose: expression("Ex"^"p1").

library(pheatmap)
# Generate some data
test = matrix(rnorm(200), 20, 10)
test[1:10, seq(1, 10, 2)] = test[1:10, seq(1, 10, 2)] + 3
test[11:20, seq(2, 10, 2)] = test[11:20, seq(2, 10, 2)] + 2
test[15:20, seq(2, 10, 2)] = test[15:20, seq(2, 10, 2)] + 4
colnames(test) = paste("Test", 1:10, sep = "")
rownames(test) = paste("Gene", 1:20, sep = "")

annotation <- data.frame(Var1 = factor(1:10 %% 2 == 0, labels = c("Exp1", "Exp2")))
rownames(annotation) <- colnames(test) # check out the row names of annotation

# change the color of annotation to what you want: (eg: "navy", "darkgreen")
Var1        <- c("navy", "darkgreen")
names(Var1) <- c("Exp1", "Exp2")
anno_colors <- list(Var1 = Var1)
pheatmap(test, annotation = annotation, annotation_colors = anno_colors)