Scientists at the University of Chicago have made a breakthrough in quantum computing. They sent entangled states of qubits through a communication cable connecting one node of the quantum network to another.
Researchers at the University of Chicago’s Pritzker School of Molecular Engineering (PME) have sent entangled states of qubits for the first time through a communication cable connecting one node of a quantum network to another.
They also amplified the entangled state through the same cable. They first used a cable to entangle two qubits at each of the two nodes, and then entangle them with other qubits at the nodes.
The results, published in the journal Nature, will help make quantum computing more feasible and lay the foundation for future quantum communication networks.
“Developing methods to transfer entangled states will be essential for the scaling of quantum computing,” said Professor Andrew Cleland, who led the study.
Qubits, or quantum bits, are the basic units of quantum information. Using their quantum properties, such as superposition, and their ability to communicate with each other, scientists and engineers are creating the next generation of quantum computers. They will be able to solve previously unsolvable problems.
Cleland Lab uses superconducting qubits, tiny cryogenic circuits that can be controlled electrically.
To transmit entangled states through a communications cable – a one-meter-long superconducting cable – the researchers created an experimental setup with three superconducting qubits at each of two nodes. They connected one qubit at each node to the cable, and then sent quantum states in the form of microwave photons down the cable with minimal loss of information. The fragile nature of quantum states makes this process quite complex.
A former researcher at Cleland’s Laboratory and the first author of the article, Yupeng Zhong, developed a system in which the entire transmission process – from node to cable to node – takes only a few tens of nanoseconds (a nanosecond is one billionth of a second). This allowed them to send entangled quantum states with very little loss of information.
The system also allowed scientists to “amplify” the entanglement of the qubits. They used one qubit at each node and entangled them together, essentially sending a half-photon through a cable. The researchers then extended this entanglement to other qubits at each node. As a result, all six qubits in two nodes were entangled in a single globally entangled state.
In the future, quantum computers are likely to be built from modules in which families of entangled qubits compute. Ultimately, these computers will be built from many of these network modules. This process is similar to how supercomputers today perform parallel computations on many central processing units that are connected to each other. The ability to remotely entangle qubits in different modules or nodes is a significant step in implementing such modular approaches.
Such modules will have to send complex quantum states to each other, and the latest research is a big step towards that. The quantum communication network can also take advantage of this advance.
The scientists hope to then expand their system to three nodes to create three-way entanglement.
In this way, they hope to show that superconducting qubits will play a viable role in the future.