In a breakthrough for quantum computing, University of Chicago researchers
have sent entangled qubit states through a communication cable linking one
quantum network node to a second node.
The researchers, based in the Pritzker School of Molecular Engineering (PME)
at the University of Chicago, 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.
The results, published February 24, 2021 in Nature, could help make quantum
computing more feasible and could lay the groundwork for future quantum
communication networks.
"Developing methods that allow us to transfer entangled states will be
essential to scaling quantum computing," said Prof. Andrew Cleland, who led
the research.
Sending entangled photons through a network
Qubits, or quantum bits, are the basic units of quantum information. By
exploiting their quantum properties, like superposition, and their ability
to be entangled together, scientists and engineers are creating
next-generation quantum computers that will be able solve previously
unsolvable problems.
Cleland Lab uses 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.
Cleland's former postdoctoral fellow, paper first author Youpeng Zhong, was
able to develop a system in which the whole transfer process—node to cable
to node—takes only a few tens of nanoseconds (a nanosecond is one billionth
of a second). That allowed them to send entangled quantum states with very
little information loss.
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.
Creating a scaled, networked quantum computer
In the future, quantum computers will likely be built out of modules where
families of entangled qubits conduct a computation. These computers could
ultimately be built from many such networked modules, similar to how
supercomputers today conduct parallel computing on many central processing
units connected to one another. The ability to remotely entangle qubits in
different modules, or nodes, is a significant advance to enabling such
modular approaches.
"These modules will need to send complex quantum states to each other, and
this is a big step toward that," Cleland said. A quantum communication
network could also potentially take advantage of this advance.
Cleland and his group hope to next extend their system to three nodes to
build three-way entanglement.
"We want to show that superconducting qubits have a viable role going
forward," he said.
Reference:
Youpeng Zhong et al. Deterministic multi-qubit entanglement in a quantum
network, Nature (2021).
DOI: 10.1038/s41586-021-03288-7
Tags:
Physics