challenge: What is the condition for the Heisenberg uncertainty relation in the context of spin squeezing?
  
  A. (ΔJx)^2(ΔJy)^2 = 4|⟨Jz⟩|^2
  B. (ΔJx)^2(ΔJy)^2 ≤ 1/4|⟨Jz⟩|^2
  C. (ΔJx)^2(ΔJy)^2 ≥ 1/4|⟨Jz⟩|^2
  D. (ΔJx)^2(ΔJy)^2 = 1/4|⟨Jz⟩|^2
  Answer: 