Near-Ideal Quantum Efficiency with a Floquet Mode Traveling Wave Parametric Amplfier.

Broadband quantum-limited amplifiers would advance applications in quantum information processing, metrology, and astronomy. However, conventional traveling-wave parametric amplifiers (TWPAs) support broadband amplification at the cost of increased added noise. In this work, we develop and apply a multi-mode, quantum input-output theory to quantitatively identify the sidebands as a primary noise mechanism in all conventional TWPAs. We then propose an adiabatic Floquet mode scheme that effectively eliminates the sideband-induced noise and subsequently overcomes the trade-off between quantum efficiency (QE) and bandwidth. We then show that a Floquet mode Josephson traveling-wave parametric amplifier implementation can simultaneously achieve $>20\,$dB gain and a QE of $\eta/\eta_{\mathrm{ideal}}> 99.9\%$ of the quantum limit over more than an octave of bandwidth. Crucially, Floquet mode TWPAs also strongly suppress the nonlinear forward-backward wave coupling and are therefore genuinely directional. Floquet mode TWPAs can thus be directly integrated on-chip without isolators, making near-perfect measurement efficiency possible. The proposed Floquet scheme is also widely applicable to other platforms such as kinetic inductance traveling-wave amplifiers and optical parametric amplifiers.