Use a keyboard shortcut to switch between two most recent tabs.
By default, the hotkey is Alt+Q (⌥Q on Mac) but can be configured by accessing the following URL: chrome://extensions/shortcuts
Please, take note that it's not possible to use existing Chrome hotkeys on this page.
If you still want to set e.g. Ctrl+Tab as a hotkey, you have to change the Chrome settings file.
On Windows: Press Win+R and execute "notepad %LOCALAPPDATA%\Google\Chrome\User Data\Default\Preferences".
On Ubuntu: gedit ~/.config/google-chrome/Default/Preferences
Then change all occurrences of Alt+Q to Ctrl+Tab
Important: if you're using Google account sync, disable settings synchronization. Otherwise, Chrome will be overriding the changed hotkey on each restart.
If the above way doesn't work for you, follow the instructions on this Gist: https://gist.github.com/ilyachase/49c7a6d1aa543d16568520560cfaf226
