Parametric amplification and entanglement generation in a left-handed Josephson transmission line: Experiment (Part 2)

Left-handed (or negative-index) Josephson transmission lines are a new modality for realizing low-noise traveling-wave parametric amplifiers (TWPA). In contrast to conventional right-handed devices, four-wave mixing in a left-handed TWPA is natively phase-matched, leading to high gains over GHz bandwidths without requiring any complicated dispersion or nonlinear engineering [1]. In addition, owing to its inverted dispersion relation, left-handed TWPA supports unique operating regimes, such as (i) reversed dispersion regime that can be leveraged for achieving flat broadband gain, and (ii) counter-propagating amplification where it operates as a narrow-band high-gain amplifier. We will discuss the first experimental realization of a left-handed Josephson transmission line and the observation of two distinct parametric amplification processes. These processes enable the generation of broadband two-mode vacuum squeezed states and spatially separated entangled photon pairs, respectively. Our device shows two-mode squeezing of 6-dB below vacuum between two modes separated of approximately 10 GHz and traveling in opposite directions. This novel Josephson transmission line architecture opens new perspectives for quantum radar and illumination protocols, and more generally for quantum sensing and computing applications.

[1] C. Kow, V. Podolskiy, A. Kamal, Phys. Rev. Applied 24 024026 (2025)