Loss Asymmetries in Quantum Traveling-Wave Parametric Amplifiers

Traveling-wave parametric amplifiers (TWPAs) are widely used in quantum information science for amplification and measurement at the quantum limit, but their development is held back by a lack of understanding of their susceptibility to internal loss. The authors use both lumped-element and distributed-loss models to describe the output of a lossy TWPA, and identify a surprising, strong dependence on the symmetry of loss between signal and idler modes. This insight will have immediate impact on the design of TWPAs as both quantum-limited amplifiers and sources of squeezed radiation.