When subatomic particles chat

Recent work by researchers at the Yale Quantum Institute provides a key contribution to the development of quantum computers, which promise computational power orders of magnitude beyond anything available today.

Just as the fundamental unit of computing is a bit—a single piece of information, denoted by a zero or a one and stored electromagnetically—quantum computers are founded on the operation of quantum bits, or “qubits.” Information is typically stored at the subatomic level, using particles like electrons or photons. One example: the spin of an electron, which can be up or down.

Qubits are exceedingly sensitive. “They are very susceptible to noise or perturbations in the environment, and they easily ‘forget’ their state,” says Kevin Chou ’18PhD, one of the project’s lead researchers. (Chou now works at Quantum Circuits.) Robert Schoelkopf, director of the Quantum Institute, was the principal investigator on the work, which was published in Nature.

To get around this problem, Chou and his collaborators separated qubits from each other using a modular design. Each was maintained in a tightly controlled environment at a fraction of a degree above absolute zero. But this introduced a problem of its own: “If you take a qubit, put it in a tightly sealed box, and throw away the key, then you may have a perfect qubit. But it’s also perfectly useless.”

Here is where the real novelty came in. The team used a distinct feature of quantum mechanics known as entanglement, in which two particles are tied together due to quantum interaction—or in “a quantumy way,” as Chou put it. They were able to open a line of communication and conduct an operation between two qubits. Since it wasn’t a physical interaction, quantum scientists call it “teleportation,” though only information was sent. 

Computing takes communication among multiple bits. This operation between two separate qubits—first proposed 20 years ago—is a major step toward quantum computing.