UMass Amherst Research Reveals New Technology for Weak Quantum Computers

Inside Short

• Researchers at the University of Massachusetts Amherst and the University of California Santa Barbara have demonstrated laser and ion-trap devices that could significantly reduce quantum computing resources.
• The study shows that the large, complex optical systems used to control confined qubits can be replaced by integrated photonic chips while maintaining high fidelity performance.
• The work marks the first step towards scalable and portable quantum systems, with future efforts aimed at integrating all the components onto a single chip.
• Image: UMass Amherst

NOTE – Scientists from the Riccio College of Engineering at the University of Massachusetts Amherst and the University of California Santa Barbara have demonstrated the key features of the laser and ion trap needed to significantly reduce the size of quantum computers, an achievement that coincides with the reduction of integrated microprocessors in the 1970s that allowed computers from 900 to 900. to today’s ultrathin smartphones.

The latest technology for quantum computing is too large and complex to scale, and too light to be portable. The largest and most sensitive parts of this quantum system are the optics, which include multiple lasers and temperature-controlled vacuum chambers with ultrastable optical cavities. These cavities stabilize the lasers to be very precise in order to manipulate the trapped ions for quantum computing and optical clocks.

In a new paper, researchers demonstrate the stable laser particles needed for an integrated quantum computing-on-a-chip system that has the potential to shrink quantum computing devices from the size of a room to chip-scale the size of a deck of cards. This is the first important step towards the scalability of quantum computing and the possibility of making optical clocks (based on the same ion technology) portable.

Robert Niffenegger, assistant professor of electrical and computer engineering says: “If you want scalability or portability with quantum technology, you need lasers to be all there. “We could have millions of qubits on one chip in a way that would be impossible if you needed rooms full of lasers and optics. If you are determined to reach that scale, you should look at how much traditional computers have increased through integration. That is the vision we are following.”

In quantum computers, trapped ions act as “qubits,” which perform the same functions as traditional computer units for storing and processing data, but they do so according to the laws of quantum physics, not binary 0’s and 1s. Optical clocks keep time by reading the oscillations of visible light and verifying those frequencies through the atomic changes of trapped ions, which results in unprecedented accuracy for applications such as mapping the earth’s gravity to centimeter accuracy and powering deep space systems and GPS devices.

Working with colleagues at the University of California Santa Barbara led by Professor Daniel Blumenthal, the team showed, for the first time, that these large precise lasers can be replaced by small photonic chips. They show that this new photonic technology can be used to manipulate trapped ions to create a qubit and a clock.

They tested how their design performs important quantum operations, including tuning the qubit’s quantum state. Their results show the system already achieves the high-level qubit preparation and scale required for quantum computing, while further improvements will enable quantum sensing applications. Their full findings are published in Nature Communication.

“We’re not quite up to speed with modern clockwork, but we’ve come a long way in the beginning and we’ve made even more progress since then,” Niffenegger adds.

In the long run, he says the design is an important first step toward creating supercomputers capable of solving problems too complex for today’s supercomputers, such as deciphering the encryption that protects the world’s most sensitive data. Many experts estimate that such applications would require millions of qubits.

“To build something that really works, something that goes beyond what a traditional computer can do, you’re going to need an integrated quantum system on a chip,” Niffenegger says. “You can’t have football fields full of lasers and optics. It won’t work. Integration is the only way that works.”

In the short term, Niffenegger sees this new technology as an opportunity to push the optical watch movement forward. By shrinking lasers and cavities into photonic chips, optical clocks can become more compact, enabling them to go places they’ve never been before, like space.

“This is the only way to get an accurate clock in space,” Niffenegger says. “It could allow new experiments in fundamental physics.”

For example, he thinks that he is testing the basics of nature by having a watch that goes around the sun to see if there is a difference in different places. He adds: “Now that our system is smaller and more resistant to vibration, it will be the best clock you can put in space.”

A major technical challenge was to maintain the stability of the laser without the many isolation devices used in conventional optical cavities. “We don’t have the luxury of using this chip,” says Niffenegger. “And that’s by design. If we were to say that this is a portable, integrated solution, it must be dynamic. “It’s still controlled by temperature, but it’s not coming out.” Instead, they devised a method to compensate for active drift by combining measurements and experiments.

“It felt like tickling a bull.” He adds: “The clock is running away, and you try to catch it with a very precise atomic clock, not just catch it, but lock it while it’s running.”

The next goal is full integration, combining an ion trap chip, laser chip, optical cavity chip, and other photonics on a single chip. “Now that we’ve shown that precise quantum processing is possible with integrated photonics,” Niffenegger says, the next step is to integrate everything into an integrated quantum-on-a-chip system.

This work was funded by a CAREER Award to Niffenegger from the US National Science Foundation.