Simple, cost-effective trapped ion qubit technology developed

Physics professor Mark Saffman, affiliate professor Mikhail Kats and their groups have developed a simplified but ingenious method for trapping atoms of different species to make quantum bits or qubits, they published in Science Advances.

Capturing two types of neutral atoms next to each other, the method creates interleaved grids of cesium and rubidium atoms that can be used as qubits in quantum computing and quantum sensing. The setup is much simpler and cost-effective than previous efforts and is already being used in early-stage quantum devices.

“Other groups have trapped two types of neutral atoms, but their setups are pretty sophisticated, use multiple lasers, and are expensive,” Kats says. “We have demonstrated that you can do this kind of trapping with a single laser and single micro-fabricated mask.”

As quantum computing emerges, there is no clear consensus on which material should be used to make the qubits which are the building blocks of quantum computers. Researchers are looking into qubits made of superconductors, diamond, trapped ions, and other specialized materials. But one relatively scalable qubit candidate is neutral atoms — those, like rubidium and cesium, that have a net zero electrical charge — that can be isolated, or “trapped,” using lasers.

All qubits are sensitive to their environment and need to stay as isolated from the outside world as possible so they maintain their quantum state: external influences can cause them to “decohere” and lose information. However, when the time is right, otherwise well-isolated qubits need to be able to interact with each other and with external inputs.

Trapping two types of neutral atoms next to each other is a promising approach to these seemingly contradictory requirements for components of quantum computers and quantum sensors. To isolate two types of atoms in the same space, the team fabricated a specialized optical mask using ultrathin layers of gold and the semiconductor germanium.

Sending a specific frequency range of laser light through this semitransparent mask divides it into a pattern of bright, dark, and intermediate areas, which interact to form the traps. The researchers filter and demagnify the light pattern before it enters a vacuum cell filled with cesium and rubidium atoms. Rubidium is attracted to the areas with high electromagnetic field, called bright traps. Conversely, the cesium migrates into the dark traps. The result is two sets of neutral atoms in distinct patterns in close proximity to each other.

These interleaved patterns of atoms can then be used for computing; one set of undisturbed atoms is for computation while the other set communicates commands and information with users. The atoms can also be used for sensing, with one set of atoms interacting with and collecting data from the environment while the other set records and processes the signals.