Eloquent Many to Many - how to find records that are only related to certain other records?

Question

ORM

Simplified View: Model and Properties

Route
id

City 
id
name

RouteCityPivot
id
city_id
route_id

One Route has only 2 City (many to many relationship via pivot table).
Given the names of two cities - such as Berlin and Munich - how can you find the Route containing these two cities?

$route = Route::whereHas('cities', function ($q) use ($from, $to){
            q->whereIn('name', [$from, $to]);
        })->get();

This code will find all Routes that contain at least one of the cities, and you need to find exactly the one where this pair exists.