Use different repositories for frontend and backend?

I'd like to ask a question.

Lets say we have a web app that uses Rails api on the backend and Ember on the front end. The folder structure I guess would look like this:

my-app
- backend (rails api)
- frontend (ember)

In this case how do we create a repository and push the app on github/bitbucket?
a. all in one repo
b. use different repo for the backend/rails and different for the frontend? if thats the case how do we deploy on production/staging both repositories?