Josephson Junction
Quantum phase locking in a superconducting tunnel junction
Voltage (mV)0.000
Current (I/I_c)0.000
Phase φ (rad)0.000
Frequency (GHz)0.000
Shapiro Step—
IV Characteristic
Phase trajectory (φ vs dφ/dt)
Bias Current I/I_c 0.50
Damping (βc) 1.0
Microwave Amplitude A 0.00
Microwave Frequency f 0.50
The Josephson junction — two superconductors separated by a thin insulating barrier — is one of physics' most elegant quantum devices. A DC bias below the critical current I_c produces zero voltage as Cooper pairs tunnel coherently. Above I_c, the phase difference φ between the two superconductors evolves in time, generating AC oscillations: the DC Josephson effect becomes AC. Under microwave irradiation, the junction phase-locks to rational multiples of the drive, producing Shapiro steps — flat plateaus in the IV curve where voltage quantizes to nℏω/2e.