Quantum Teleportation over thermal microwave network

Quantum communication networks promise revolutionary advances in computing and data transfer, but maintaining the delicate quantum states required for these networks presents a major hurdle. Researchers led by W. K. Yam, S. Gandorfer, and F. Fesquet, all at the Walther-Meißner-Institut, have now demonstrated a significant step towards practical quantum networks by achieving quantum teleportation over a thermal microwave channel at relatively high temperatures. This experiment successfully transfers quantum information between dilution refrigerators connected by a warm, noisy channel, exceeding key thresholds for quantum communication and proving the feasibility of distributed superconducting architectures. By distributing entangled microwave photons, the team achieves teleportation fidelities that pave the way for building larger, more robust quantum networks capable of operating in realistic environments and opening doors to applications across various frequency regimes.

Superconducting quantum circuits are essential for distributed quantum computing and hybrid quantum networks. However, their operation typically requires extremely low temperatures, presenting a significant challenge for developing large-scale microwave quantum networks. Researchers have now addressed this challenge by successfully teleporting microwave coherent states between two spatially-separated dilution refrigerators via a thermal microwave channel operating at 4 Kelvin. The team distributed two-mode squeezed states through the channel, leveraging the resulting quantum entanglement to achieve quantum teleportation of coherent states with fidelities exceeding 72% at 1 Kelvin and nearly 60% at 4 Kelvin. This achievement represents a major step forward in building practical quantum networks, as it relaxes the stringent cooling requirements typically associated with superconducting quantum systems. This new demonstration proves that quantum information can be reliably transferred even with a relatively “warm” connection, significantly simplifying the infrastructure needed for large-scale quantum communication.

Microwave Teleportation with Superconducting Qubits

Recent research focuses heavily on microwave photon quantum teleportation, a technique for transferring quantum states using microwave radiation. This area is gaining prominence as researchers explore new ways to build quantum networks and connect quantum computers. Superconducting qubits are central to this work, serving as the building blocks for encoding and measuring the quantum information being teleported. A key goal is to extend quantum teleportation beyond single laboratory setups, connecting different quantum systems over increasing distances to create networked quantum devices. Research explores both continuous variable (CV) and discrete variable (DV) teleportation approaches.

Improving the fidelity, or accuracy, of teleportation is a major focus, with researchers developing techniques to mitigate errors and enhance the quality of the transferred states. Several research groups are actively contributing to this field, demonstrating long-distance teleportation and achieving high-fidelity transfers. They are also exploring the integration of microwave-based quantum systems with existing optical quantum networks, paving the way for hybrid quantum communication systems.

Quantum Teleportation Between Dilution Refrigerators Demonstrated

Researchers have achieved a significant breakthrough in building large-scale quantum networks by successfully teleporting quantum information between two dilution refrigerators separated by six and a half meters. This was accomplished even with a relatively warm connection operating at up to 4 Kelvin, a temperature significantly higher than the ultra-cold conditions typically required for superconducting quantum computers. The team distributed entangled microwave signals through a specialized link and used this entanglement to teleport coherent quantum states, effectively transferring information without physically moving the quantum carrier. The experiment achieved teleportation fidelities exceeding 72% at the lowest channel temperature of 170 millikelvin, and remarkably maintained a fidelity of nearly 60% even when operating at 4 Kelvin.

This level of performance surpasses the thresholds required for practical quantum communication and demonstrates the feasibility of building networks where quantum nodes are not limited by the need for ultra-cold connections. The key to this success lies in the use of superconducting niobium-titanium cables, which exhibit exceptionally low microwave losses, preserving the delicate quantum correlations despite the warmer channel. This research represents a crucial step towards building distributed quantum computers, where multiple smaller processors are linked together to tackle complex problems beyond the reach of individual machines. By relaxing the stringent cooling requirements for network connections, this approach promises to significantly reduce the cost and complexity of building large-scale quantum systems.

Microwave Quantum Teleportation Between Refrigerators Demonstrated

This research demonstrates the successful teleportation of microwave quantum states between spatially separated dilution refrigerators, a crucial step towards building practical quantum networks. Researchers achieved this by distributing two-mode squeezed states over a thermal microwave channel and utilising the resulting entanglement to teleport coherent states, exceeding both the no-cloning and classical limits at low and moderate temperatures. The results prove the feasibility of distributed superconducting architectures and open possibilities for applications in various frequency regimes, including local area networks and hybrid quantum systems. The team successfully modelled the teleportation process, identifying parasitic heating of the cold nodes as a primary source of infidelity.

While acknowledging that insertion losses in current cryogenic devices constrain achievable fidelities, they highlight potential mitigation strategies, such as employing superconducting components or utilising dual-rail encoding. Future work could extend these techniques by combining Gaussian entanglement with non-Gaussian operations, or by investigating quantum networks in non-equilibrium scenarios to understand how quantum states thermalise in distributed systems. This work demonstrates that thermal fluctuations do not necessarily limit entanglement distribution, provided propagation losses remain low.