Send them a thank you note? Hah!
Who has time for that these days?
When I interview people for open positions for the company I work for, I never tell them either way if they got the job or not. That can be an implied verbal agreement.
There are way too many legal land-mines to imply anything because of gender, racial, ethnic, age or disability issues that pond scum lawyers will sue you in a heartbeat over.
Every applicant is given a full interview and thanked for coming in and told they will be considered with all the other applicants.
The ones I like and are qualified, I call back for a second interview.
You would be shocked on how many don't come back because never wanted the job in the first place.
Maybe they couldn't wait for the "Human Resources" jerks to screen them for a job which was only understood by the supervisor of the department with the employment need.
One could starve to death waiting for that process!