Josephson directional amplifier for quantum measurement of superconducting circuits

Understand

We have realized a microwave quantum-limited amplifier that is directional and can therefore function without the front circulator needed in many quantum measurements.

• The amplification takes place in only one direction between the input and output ports.
• Directionality is achieved by multi-pump parametric amplification combined with wave interference.
• We have verified the device noise performances by using it to readout a superconducting qubit and observed quantum jumps.