If a superconducting Quantum Interference Device which consists of a 3 mm ring can measure 1/5,000 of a fluxon, calculate the magnetic field that can be detected (1 fluxon, φ0 = h/2e = 2.0678 × 10−15Tm2, is the smallest unit of flux).
ΔB = ϕ/A = (1/5, 000)ϕ0/π(3 × 10−3)2
Substituting φ0 = 2.0678 × 10−15 Tm2, we get
ΔB = 2.93 × 10−14T
