What is/are the origin(s) of the phrase "Quantum of Solace" from, and what does it mean?

The phrase was used as the title of a short story in the Ian Fleming book "For Your Eyes Only". "Solace" means, generally, comforting or alleviation of distress, and "quantum" in science is the minimum amount involved in some activity. In the short story, Fleming has the governor of the Bahamas tell James Bond a story about a couple that had separated, where the wife had openly taken another lover and, in response, the husband behaved very badly toward her, in a way that he would not have behaved previously, finally abandoning her in Bermuda. The governor tells Bond that the lesson from the story is that "when the quantum of solace drops to zero, humanity and consideration of one human for another is gone".

Actually, it made a surprisingly appropriate title for the movie, considering Bond was seeking vengeance after the death of Vesper Lynd. His quantum of solace had also dropped to zero, shown by the number of dead bodies left in his wake in the movie.

https://en.wikipedia.org/wiki/For_Your_Eyes_Only_(short_story_collection)#.22Quantum_of_Solace.22