The Bundesliga leaders took a 3-1 win over the Gunners at the Emirates Stadium earlier this evening.
The 29-year-old told Sky Sports News: "At the moment we are at a very good level. We have a great squad. We improved again compared to last year and are moving in the right direction.
"Tonight, we met a very big step into the quarter-finals but of course we still have a home game to play and we have to stay focus on our own game. We have to try and improve again.
"It wasn't just that we scored two goals but that we expected a very big start from Arsenal here with the fans behind them. I remember it from my time in England. I think we did very well. Of course, if you score two goals then you are in a great position."