Entangled qubit states sent through a communication channel

Prof. Andrew Cleland’s lab sent entangled qubit states through a communication cable, laying the groundwork for future quantum communication networks. Credit: Cleland Lab

Researchers at University of Chicago have sent entangled qubit states through a communication cable linking one quantum network node to a second node for the very first time.

They have also amplified an entangled state via the same cable first by using the cable to entangle two qubits in each of two nodes, then entangling these qubits further with other qubits in the nodes.

They have used superconducting qubits, tiny cryogenic circuits that can be manipulated electrically. To send the entangled states through the communication cable—a one-meter-long superconducting cable—the researchers created an experimental set-up with three superconducting qubits in each of two nodes. They connected one qubit in each node to the cable and then sent quantum states, in the form of microwave photons, through the cable with minimal loss of information. The fragile nature of quantum states makes this process quite challenging.

The system also allowed them to “amplify” the entanglement of qubits. The researchers used one qubit in each node and entangled them together by essentially sending a half-photon through the cable. They then extended this entanglement to the other qubits in each node. When they were finished, all six qubits in two nodes were entangled in a single globally entangled state.

The team hopes to next extend their system to three nodes to build three-way entanglement.

The results have been published in Nature.