how to add an autocomplete for my new "Person or Group" site column, to get immediate results when start typing username

I have a publishing site collection, and i add a new site column named "Assigned To" of type "Person or Group", as follow:-

i added the new site column to the page layout using SP designer. and it worked well. but the problem i am facing is that i am unable to autocomplete the users/Groups , i can only search for them . but if i start typing a username i will not get immediate results, as follow:-

so can anyone advice how to add autocomplete feature for my new site column ?

Thanks.