Multipartite continuous-variable entanglement generation using Josephson metamaterials

The generation of quantum resources, most notably quantum entanglement, is an essential task for the new emerging industry employing quantum technologies. While entanglement in discrete variables represents the standard approach for quantum computing, continuous variable entanglement between microwave photons is a cornerstone for more robust quantum computing, sensing and communication schemes. 

We have developed a low-loss Josephson metamaterial comprising superconducting, non-linear, asymmetric inductive elements to generate frequency-entangled photons from vacuum fluctuations at a rate of 2 Giga entangled bits per second spanning over 4 GHz bandwidth [1]. The device is operated as a travelling wave parametric amplifier under Kerr-relieving biasing conditions that allow us to generate microwave entanglement over previously inaccessible bandwidth. Furthermore, for the first time to our knowledge, we realize a single-mode squeezing in such devices: more than 3 dB below the zero-point level at half of the modulation frequency. 

As we demonstrated, the broadband features of the TWPA allow operation over a few gigahertz bandwidth, and in combination with multiple pumps, pave the way toward the generation of "frequency-based" multimode entanglement. We propose a method for high-quality generation and control of entanglement between microwaves in multiple frequency ranges. Using the developed scheme, we generate on-demand tunable entangled 3-partite and 4-partite states in a lumped-element Josephson parametric amplifier [2]. 

Multimode schemes can be employed for various quantum applications, such as CV computing with cluster states, secure and robust communications, distributed quantum-limited sensing, and search for dark matter [2]. We envision that generated quantum resources offer enhanced prospects for quantum data processing using parametric microwave cavities.

[1] M. Perelshtein, et al., Phys. Rev. Applied 18, 024063 (2022)

[2] K. Petrovnin, M. Perelshtein, et al., Adv. Quantum Tech. 202200031 (2022)