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  • Featured in Physics
  • Open Access

Teleportation and Entanglement Swapping of Continuous Quantum Variables of Microwave Radiation

Baleegh Abdo*, William Shanks, Oblesh Jinka, J. R. Rozen, and Jason Orcutt

  • *Contact author: babdo@us.ibm.com
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Phys. Rev. X 15, 031075 – Published 25 September, 2025

DOI: https://doi.org/10.1103/9cpm-kr4h

Abstract

Quantum communication is needed to build powerful quantum computers and establish reliable quantum networks. At its basis lies the ability to generate and distribute entanglement to separate quantum systems, which can be used to run remote quantum operations on them or teleport quantum states from one system to another with the help of classical channels. To this end, it is useful to harness the resource of continuous-variable (CV) entanglement, since it can be efficiently and unconditionally produced by squeezing light in a nonlinear medium and can be easily manipulated, distributed, and measured using standard components. While various aspects of CV-based quantum communication have been successfully demonstrated in the optical domain, some key capabilities, such as entanglement swapping, have been lacking in the microwave domain. Here, we demonstrate three key elements of CV-based microwave quantum communication: (i) a Josephson mixer operating as a nondegenerate two-mode entangler with maximum measured logarithmic negativity EN=1.5, (ii) a quantum teleportation apparatus, capable of teleporting vacuum and coherent states with a maximum fidelity of 73%, which exceeds the 50% classical limit and is mainly limited by intermediate losses in the setup, and (iii) an entanglement-swapping system which generates entanglement between two remote noninteracting modes via entanglement-swapping operations applied to input vacuum and coherent states with maximum measured logarithmic negativity EN=0.53. Such hardware-efficient CV entanglement building blocks that are based on nondegenerate Josephson mixers could enable wide-ranging applications in modular quantum computation, quantum cryptography, and quantum communication.

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synopsis

Building Blocks for Microwave Quantum Communication

Published 25 September, 2025

A certain superconducting device can entangle separate microwave signals, enabling reliable quantum teleportation and entanglement swapping.

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Popular Summary

Quantum communication relies on the ability to generate and distribute entanglement, a key resource for building quantum networks and modular quantum computers. Entanglement enables powerful tools such as quantum teleportation, which lets two parties transmit an unknown quantum state without physically sending it if they share both a classical communication channel and entangled correlations. In this work, we present a method for creating and using continuous-variable (CV) entanglement in the microwave domain, an important step toward practical quantum communication systems.

We use a nondegenerate Josephson mixer, a superconducting device that generates entanglement between two distinct frequency modes traveling along separate transmission lines. This setup provides a fast and unconditional source of CV entanglement. We then integrate this source into two teleportation systems. The first teleports vacuum and coherent states with fidelities exceeding the classical limit achievable without entanglement. The second demonstrates entanglement swapping, where one-half of an entangled pair is teleported, a critical capability for quantum repeaters that extend communication distances.

Our approach shows that hardware-efficient CV entanglement sources based on Josephson mixers can support essential building blocks of microwave-domain quantum communication. Looking ahead, these techniques could be used for long-distance quantum links, secure quantum cryptography, and scalable modular quantum computing.

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Phys. Rev. X 15, 031075– Published 25 September, 2025
  • Received 9 January 2025
  • Revised 7 July 2025
  • Accepted 5 August 2025
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