Wrangling record qubit numbers
Two teams more than double previous quantum simulator totals. Andrew Masterson reports.
“Wiring” ions together using laser beams has allowed researchers to create a system comprising the one of the highest numbers of interacting atomic quantum bits ever achieved.
The system was designed by researchers from Harvard and the Massachusetts Institute of Technology. The team managed to confine and manipulate 51 quantum bits (better known as qubits) in the form of uncharged rubidium atoms.
At the same time, a second team of scientists from the University of Maryland and the US National Institute of Standards and Technology used an array of gold-coated electrodes to trap 53 ytterbium ions. By manipulating the initial states of the ions, they can be used to represent qubits.
Both studies are reported in the journal Nature, and represent a significant advance in the quest to develop a practical quantum computer.
“Each ion qubit is a stable atomic clock that can be perfectly replicated,” says University of Maryland team lead Christopher Monroe.
“They are effectively wired together with external laser beams. This means that the same device can be reprogrammed and reconfigured, from the outside, to adapt to any type of quantum simulation or future quantum computer application that comes up.”
The two teams did not create quantum computers as such, but more constrained systems called quantum simulators, in which qubits are used to mimic the interactions of complex quantum matter.
The researchers used each qubit to mimic a quantum magnet. These magnets interact with every other magnet in the system, creating an environment where things get very complicated very quickly. Previously constructed simulators have managed to corral only 20 qubits.
Creating systems involving more than 50 qubits creates a staggering number of possible states.
“With the 53 interacting quantum magnets in this experiment, there are over a quadrillion possible magnet configurations, and this number doubles with each additional magnet,” says Maryland team member Zhexuan Gong.
“Simulating this large-scale problem on a conventional computer is extremely challenging, if at all possible.”
Theoretically, both systems allow for the addition of extra qubits – they simply require more ions to be trapped within the lasers or the electrodes.
“We are continuing to refine our system, and we think that soon, we will be able to control 100 ion qubits, or more," says team member Jiehang Zhang.
“At that point, we can potentially explore difficult problems in quantum chemistry or materials design.”