Does anyone know how to create a similar animation to the login animation used in the Google Plus Android app?
Is there something similar in the Android SDK that I can use? Or should I just build it from scratch? I’m interested especially in the fact that the UI behind the modal animation is dimmed and disabled.
Thank you.

Are you taking about that progress dialog spinning thingy that says “signing in”? That’s not a custom animation at all, it’s a common widget.
Here’s the code:
A ProgressDialog done this way, automatically takes care of dimming/blurring the background. You should really read about dialogs: http://developer.android.com/guide/topics/ui/dialogs.html