How to declare observables or computed properties in Ember using ES6?

Trying to use ES6 for all of my Ember work. I have the following ES6 syntax issue:

How do I convert standard ES5 object literal computed property to ES6 syntax?

ES5:

 export default Ember.Controller.extend({
     foo: function() {
         return "bar";
     }.property()
    });

ES6:

export default Ember.Controller.extend({
  foo() {
    return "bar"
}.property()
});

What I have so far does not seem to work because .property is not referenced correctly. How is this achieved?