Martina Esposito - CNR SPIN Institute Napoli

Vacuum squeezing generation in a flux tunable Josephson Traveling Wave Parametric Amplifier

In addition to their traditional use as quantum-noise-limited microwave amplifiers [1], Josephson Traveling Wave Parametric Amplifiers (JTWPA) have recently emerged also as sources of non-classical microwave radiation in the form of vacuum squeezing and broadband entanglement [2-4], key resources for different areas in quantum technology. 

We will present an experimental study of vacuum squeezing generation in a prototypical JTWPA based on superconducting nonlinear asymmetric inductive elements (SNAILs) unit cells with alternated flux polarity. Such a device was first introduced in the literature as a four-wave mixing (4WM) amplifier [5] and 4WM squeezer [2]. Subsequent investigations have shown that typical Josephson junctions’ fabrication imperfections can activate residual three wave mixing (3WM), allowing second harmonic generation [6]. We will present experimental results that demonstrate for the first time that residual 3WM can also be used for squeezing generation. By investigating competition between 4WM and 3WM nonlinearities, we prove that vacuum squeezing generation via residual 3WM is possible provided that competing 4WM nonlinear processes are mitigated via an appropriate choice of the flux operating point.

Our results [7] provide valuable insights on the impact of competing nonlinearities on JTWPA squeezers, potentially extending the range of applications in the framework of microwave photonics.

[1] M. Esposito et al. Appl. Phys. Lett., 119, 12, 120501, (2021).

[2] M. Esposito et al. PRL 128, 15, 153603 (2022).

[3] M. Perelshtein et al. Physical Review Applied 18, 024063 (2022)

[4] J. Y. Qiu et al. Nature Physics 19, 706 (2023).

[5] A. Ranadive et al. Nature Communications 13, 1737 (2022)

[6] A. Y. Levochkina et al. Superconductor Science and Technology 37, 115021 (2024)

[7] I. Chatterjee et al. arXiv:2605.05830 (2026)