Scientists from the Riccio School of Engineering at the University of Massachusetts Amherst and the University of California Santa Barbara have identified the essential laser and ion trapping components needed to significantly reduce the size of quantum computers. This achievement mirrors the miniaturization of microprocessors in the 1970s, 80s, and 90s, which led to the transition from room-sized computers to today’s ultra-thin smartphones.
Current cutting-edge technology for quantum computing is too bulky and complex for scalability, and too sensitive and cumbersome for portability. The largest and most sensitive components of these quantum systems are the optics, which include multiple lasers and vacuum chambers isolated from vibrations and controlled temperature, housing ultra-stable optical cavities. These cavities stabilize lasers with extreme precision to control trapped ions for quantum computing and optical clocks.
In a new article, researchers demonstrate the crucial stabilized laser components needed for an integrated on-chip quantum computing system, capable of reducing parts of quantum material from the size of a room to that of a deck of cards. This is a critical first step towards the scalability of quantum computing and an opportunity to make optical clocks (based on the same trapped ion technology) portable.
“If you want scalability or portability with quantum technology, you also need all the laser systems on a chip,” explains Robert Niffenegger, assistant professor in electrical and computer engineering. “We could have millions of qubits on a single chip, which is impossible if you need rooms filled with lasers and optics. If you are serious about achieving this scale, you need to look at how traditional computers evolved through integration. That’s the vision we are following.”
In quantum computers, these trapped ion systems serve as “qubits.” They perform a function similar to traditional computer bits by storing and processing data, but do so according to quantum physics rules, not in binary (0 and 1). Optical clocks measure time by counting visible light oscillations and verifying this frequency with atomic transitions of trapped ions, providing unprecedented precision for applications such as mapping the Earth’s gravitational field with centimeter precision, or improving distant space navigation and GPS systems.
In collaboration with researchers from the University of California Santa Barbara, led by Professor Daniel Blumenthal, the team has shown for the first time that these large precision lasers can be replaced by small photonic chips. They demonstrate that this new photonic technology can be used to control trapped ions to perform qubit and clock operations.
They tested how their design performs crucial quantum operations, including preparing the quantum state of a qubit. Their results show that the system already achieves the high fidelity required for quantum computing state preparation and measurement, while further improvements will enable applications in quantum sensing.
“We have not yet matched the performance of state-of-the-art clocks, but we have come a long way since the first attempt and have made even more progress since then,” adds Niffenegger.
In the long term, he asserts that this design is a crucial first step towards creating large-scale functional quantum computers, capable of solving problems too complex for current supercomputers, such as decrypting encryption securing a significant portion of global sensitive data. Many experts believe that such applications could require millions of qubits.
“To build something truly useful beyond what a traditional supercomputer can do, you will need an on-chip quantum system,” declares Niffenegger. “You cannot have football fields filled with lasers and optics. It simply will not work. Integration is the only viable path.”
In the short term, Niffenegger sees this new technology as an opportunity to advance the portability of optical clocks. By miniaturizing the laser and cavity on photonic chips, optical clocks could become much more compact and robust, allowing them to go to places they have never explored before, like outer space.
“This is really the only way to put a precise optical clock in space,” affirms Niffenegger. “This could enable new tests of fundamental physics.”
For example, he envisions testing the fundamental constants of nature by having an optical clock orbit elliptically around the sun to see if there is variation at different distances. “Currently, because our system is smaller and more vibration-resistant, it would be the best optical clock we could put in space,” he adds.
A major technical challenge has been maintaining laser stability without the bulky isolation systems used in conventional optical cavities. “We do not have that luxury when using this chip,” explains Niffenegger. “And that’s deliberate. If we want to say it’s an integrated and portable solution, it must be robust. It’s still temperature-controlled, but not vacuum-sealed.” Instead, they developed a method to actively compensate for drift by interleaving calibrations with experiences.
“It really felt like taming a bull,” he adds. “The clock gets away, and you try to catch it with a very, very precise atomic clock, and then not only catch it but lock it in place as it drifts away.”
The next goal is full integration, combining the ion trap chip, the laser chip, the optical cavity chip, and other photonic elements on a single chip. “Now that we have shown that precise quantum operations are possible with integrated photonics,” says Niffenegger, “the next step is to bring it all together into a single unified on-chip quantum system.”
Article: Chip scale coil stabilized Brillouin laser driving a room temperature trapped ion qubit – Journal: Nature Communications – Method: Experimental study – DOI: Link to the study
Source: UMASS
