Creating New Paradigms for Quantum Technology
Engineers in the UMass Amherst Trapped Ions and Photonics lab are trapping ion qubits on a chip fabricated and packaged entirely on campus. Why? The lab, run by Robert Niffenegger, assistant professor of electrical and computer engineering, is working to develop new integrated technologies to help make scalable quantum computing a reality.
While classical computers rely on “bits”—binary digits that represent either a zero or one—to store information, quantum computers use “qubits” (quantum bits). Qubits can exploit quantum superposition to explore two possibilities of a computation at the same time and then use quantum entanglement with other qubits to layer logical operations onto these superpositions. So
one qubit being in two places at once can grow to many qubits being in many places at once. Theoretically, a sufficiently powerful quantum computer could program these multi-dimensional quantum interference patterns for computing, with revolutionary applications in drug discovery, scientific simulation, cryptography, and machine learning.
However, to fully realize this promise, quantum computers will need many tens of thousands of qubits that can retain their information and interact easily with each other. State-of-the-art quantum computers are only just approaching hundreds of qubits, even when built upon conventional computer technology like those used to fabricate CPUs with millions of transistors at foundries like Intel. Niffenegger saw this firsthand while working at Intel to develop 7nm process technology prior to coming to UMass.
“Combining integrated technologies with atomic systems is the only way that both the quality and the quantity of qubits needed for practical quantum computing can be achieved,” says Niffenegger.
Therefore, the Trapped Ions and Photonics lab is taking a different approach, one that can be achieved in a compact, room-temperature vacuum chamber, yet still
utilize the powerful integrated technologies classical computers are built with.
Niffenegger’s lab is using “trapped” ions, which are positively charged atoms that have had an electron removed. Atoms are natural qubits as their atomic states can be used to store information. Once ionized, they can be controlled with electric fields, making it possible to trap them on the surface of a computer chip. Chris Caron, who earned his BS and MS at UMass Amherst and is now a PhD student working in the lab, helped to fabricate these ion trap chips entirely within UMass cleanrooms. The chips are approximately a centimeter square in size and patterned with metal electrodes, which can confine the ions and push them to the center of the chip.
“Building an ion trap apparatus from scratch, including fabrication of the ion trap chip, is not an easy task and one that few other laboratories in the world have achieved,” says Niffenegger. “We were able to do it on our first try.”
The lab uses lasers to remove electrons from strontium atoms before trapping them, and another set of lasers to cool the strontium ions and prepare their quantum state. The qubit state can then be detected by capturing scattered light from these lasers with a sensitive camera.
“Trapped ions have the lowest error rates of any qubits but face the most challenges to scaling up their control. Aligning thousands of lasers to thousands of qubits is a daunting task if approached manually, but manageable using integrated photonics,” says Niffenegger. “We are testing chips which will attempt to address individual qubits tightly packed in chains, which could provide a path to scale up quantum computers.”
Thus far, the group has already succeeded in developing a new chip fabrication process, new techniques for designing circuit boards in ultra-high vacuum chambers, and several novel approaches to the layout and design of the lasers needed for trapping ions.
“I hope that our research breaks conventions and creates new paradigms for quantum technology— pushing the field toward things that we consider now as impossible, like building a portable quantum computer,” says Niffenegger.
