Hi,
just create an item as follow:
From URL: ^/about-us$
To URL: http://{siteurl}/index.php?option=com_content&view=article&id=46&Itemid=55
Note that there's a little problem with you wish: "to look like this in the browser bar:".
With the 301 redirect, when the user call the shot URL he get redirected to the final destination. SO, the user can notice the change. If you need to hide the destination URL, you should use the 200 internal redirect, available in the Enterprise version.
Let me know if you need more help.
Regards,
Luigi