I want to know the answer to the following question:
What country was afforded access to design of improved nuclear weapon through espionage?
All the background I'm provided with is that "The Fuchs–von Neumann work was passed on, by Fuchs, to the Soviet Union as part of his nuclear espionage, but it was not used in the Soviets' own, independent development of the Teller–Ulam design.". Is that enough to answer the question?
Answer: yes