Quantum Teleportation over a Warm Cable ✛ ✎
Context
Superconducting quantum processors operate at millikelvin temperatures, but scaling to millions of qubits requires connecting many cryostats into a network. Neighboring works have already shown entanglement distribution between cryostats over cryogenic lines and even over channels warmer than 10 mK, but teleportation of states over a thermal channel remained an open problem. This work demonstrates for the first time quantum teleportation of microwave states between distant refrigerators with the channel temperature up to 4 K, bringing practical quantum networks closer.
Methods
The experiment used two dilution cryostats (Alice and Bob) connected by a 6.6-meter superconducting NbTi cable with losses of 1 dB/km. A heater placed at the cable's center allows raising the temperature to 4 K. In Alice, four Josephson parametric amplifiers generated two-mode squeezed states and performed an analog Bell measurement. The measurement result was sent to Bob over a classical cable, who used a directional coupler to displace his state. State tomography was performed with an FPGA receiver reconstructing density matrices in the Gaussian approximation.
Results
At a baseline channel temperature of 170 mK, the teleportation fidelity of coherent states reached 72.6±0.1%, exceeding the no-cloning threshold of 2/3 for states with up to 8.3 photons. When the channel center was heated to 4 K, entanglement was preserved (negativity remained positive), and the teleportation fidelity was 59.9±2.5%, above the classical limit of 1/2. The main error source was parasitic heating of the cryostats due to thermal coupling with the heater, not the channel noise itself. A model based on the Gaussian formalism accurately describes the experimental data.
Implications
This work shows that thermal fluctuations do not necessarily destroy quantum entanglement when transmitted over a low-loss channel. Unlike previous demonstrations where the channel remained cold, here teleportation is performed over a genuinely warm section of the network. This relaxes some of the stringent requirements on cryogenic infrastructure and makes distributed superconducting architectures more realistic.
Future development
The technology could evolve toward improving thermal isolation of nodes (thermal switches, multilayer insulation) and replacing passive microwave components with superconducting ones having lower losses. Also promising is combining continuous variables with qubit operations for hybrid protocols, such as teleporting Fock states or entanglement distillation.
Impact
The results will influence the design of distributed quantum computers, quantum networks, and hybrid systems connecting microwave and optical frequencies.
Next steps
Improve teleportation fidelity by reducing losses in passive elements and improving thermal decoupling between the heater and the cryostats.
Key open problems
For quantum networks, an open question remains how thermal noise and nonequilibrium processes limit entanglement distribution in large systems. This work directly links the problem of scaling superconducting processors to the physics of noisy channels.
The knowledge machine's view
This section is addressed to the author of the paper and their colleagues. Neighbouring works were found by meaning-based search across our archive, not by word overlap. We do not review: we show the field around the work.
What the work does
The authors teleported microwave coherent states between two cryostats over a 6.6 m superconducting cable heated to 4 K. They used two-mode squeezed states and achieved fidelities of 72.6% at 170 mK and 59.9% at 4 K, surpassing classical limits. They showed that the low loss in the NbTi cable suppresses thermal noise, preserving entanglement.
Where its strength is
This is the first demonstration of quantum teleportation over a channel at temperatures up to 4 K, relaxing some of the stringent requirements on cryogenic infrastructure. The experiment combines precise control of squeezed states with detailed characterization of loss and noise.
Where it could go next
- Nearby is a paper on a quantum bridge made of light, where microwave and optical photons are linked via transducers. It might be interesting to see how their approach to matching imperfect transducers could apply to teleportation between the microwave and optical domains.based on: Light in a Cryostat: How Imperfect Converters Build Quantum Bridges arXiv:2505.00542v1
- In the archive, there is an analysis of energy teleportation among five qubits. Perhaps their methods for handling multi-node protocols could help extend your scheme to a chain of several cryostats with warm sections between them.based on: Quantum Wallet: Energy Teleportation Between Five Qubits arXiv:2505.01863v1
- A neighboring paper on a quantum remote control that barely heats up discusses control with minimal heat dissipation. It might be useful to look at their techniques for reducing parasitic heating, which was the main source of errors in your experiment.based on: A Quantum Remote That Barely Generates Heat arXiv:2603.27231
Worth trying
- Try teleporting not only coherent states but also squeezed states at 4 K to test the preservation of nonclassical properties.
- Use a longer cable with the same loss per unit length to separate the effects of length from those of temperature.
- Assess the possibility of teleporting multimode states through a warm channel to increase throughput.
Nearby works in our archive
- A Kilometer-Long Bridge Between Cold Islandssimilarity 0.60
- A Quantum Remote That Barely Generates Heatsimilarity 0.58
- Liquid metal bridges quantum chipssimilarity 0.57
- Quantum Cold: How Wires Don't Get in the Way of Computingsimilarity 0.56
- Quantum Wallet: Energy Teleportation Between Five Qubitssimilarity 0.56
- Light in a Cryostat: How Imperfect Converters Build Quantum Bridgessimilarity 0.55
The archive is sparse around this work: the closest review is only 0.60, against a usual 0.64. It looks like few have drilled nearby.
The niobium-titanium cable has a critical temperature of about 10 K, so at 4 K it remains superconducting and introduces almost no losses, even though the environment is already 'hot' by quantum standards.
The idea of teleporting states over an unreliable channel resembles 'Star Trek', where information is transmitted through space, but here instead of dismantling matter, quantum information is transferred using entanglement.
Key numbers
- fidelity at 170 mK: 72.6%
- fidelity at 4 K: 59.9%
- cable length: 6.6 m
- channel temperature: up to 4 K
- cable losses: 1 dB/km