The United Nations proclaimed 2025 the International Year of Quantum Science and Technology to raise awareness of the importance and impact of quantum science and its applications. By vastly improving computing power, the interdisciplinary, cutting-edge field of quantum information science has the potential to revolutionize everything from artificial intelligence to supply chain logistics to drug discovery.
Hartmut Häffner in his lab (Photo by Sarah Wittmer)
Hartmut Häffner is a professor of physics at UC Berkeley. He studies trapped ions and electrons to determine how to create the best qubit — the information storage and retrieval unit used in quantum computers. Unlike a classical computer’s binary bits, qubits can simultaneously exist in multiple states while being instantly linked to other qubits through a phenomenon called quantum entanglement. These features allow quantum computers to conduct faster, more complex calculations on multiple possibilities at the same time.
UC Berkeley writer Alexander Rony spoke with Professor Häffner to learn about the state of quantum information science on campus.
Hartmut Häffner: We have two pillars. On the one hand, we're driving the technology forward to build quantum computers, and on the other, we're using the emerging abilities to address new science questions.
In the field of quantum information science, we are addressing fundamental challenges to building quantum computers. We anticipate the problems where the industry will be stuck in 10-20 years and find ways around the challenges.
For this, we build pieces of mini quantum computers and control the qubits (in our case, trapped ions and electrons). We also probe fundamental laws in physics using entanglement to control the quantum state of ions or atoms.
At the moment, we are testing that individual atoms that never came close to each other can be made indistinguishable from each other and are fundamentally the same. That's a strange concept. You can do experiments to prove that specific atoms have exactly the same properties; we demonstrated that all calcium ions are exactly the same.
Häffner is now studying electrons trapped by electric fields generated by electrodes.
Häffner uses 3D-printing scaffolding traps that optimize geometry and apply radio-frequency voltages to the trap electrodes.
Häffner in the lab (Photo by Sarah Wittmer)
The fact that ions and atoms have the same properties makes them very good qubits. The questions are how to actually control them in the best way, whether we can control them well enough, and how that stacks up against other approaches to building quantum computers. We're investigating this technology to explore the accuracy and speed with which we can execute quantum operations and to develop technologies that allow us to build quantum computers with thousands or even millions of high-quality qubits.
Recently, we used a new technology — a special 3D printing method called two-photon direct laser writing — to build much better ion traps. Now that we have the ability to confine many ions efficiently, we need to control them. Ions, atoms, and many other qubit types are controlled with laser light, and the control of laser light is not nearly as well-developed as it is for electronic circuits. We are developing the technology to allow optical control of qubits.
In another space, we are exploring trapped electrons for quantum computing. Three challenges of quantum computing are scale, accuracy, and speed. Ions are very good with respect to scaling and accuracy, but they are heavy, and that makes things slow. Electrons are fast because they are light. Other approaches trap electrons differently in a solid state material — quantum dots, for instance — but the nearby materials disturb the electrons, causing information loss.
That is a very new, very speculative approach, but in 20 years or so, speed will become an important factor. Being able to use electrons trapped in a vacuum instead of ions might be the key to overcoming the speed problem.
We have a course plan that emphasizes the practical aspects of quantum computing. The first two courses are traditional lecture courses. We're coming up with a third project-based course now. For instance, students will design a circuit and run microwave simulations to plan a superconducting qubit. Pursuing this novel type of course is possible because of a grant from the Berkeley Frontier Fund.
We want to encourage teamwork across multiple disciplines. You can think about three poles: one is computer science and math, one is physics, and one is engineering. They form a triangle, and quantum information would go in the center. One challenge of quantum information science education is that students have very different backgrounds. A computer scientist needs to work with a physicist or chemist, and they have different languages. We want to pair students so they're working together on up to four projects to learn this essential skill.
Let’s say they are learning the design of a device together. In this case, the electrical engineer has an advantage. They can teach the computer scientist about it, and together they accomplish something. Then, there is a project on how to compile a quantum circuit or design a quantum algorithm so that it's free of decoherence [editor’s note: the deterioration of quantum properties, an issue of concern for qubits]. That's where the computer scientist has more of a background, and they can help the electrical engineer. That's the idea of this course.
Maybe. A couple of years ago, the industry took quantum research seriously and started investing, and now we are seeing the first payoffs of those investments. But it's still a long road.
I'm excited about the advent of quantum error correction. We are now at an inflection point where quantum error correction circuits actually make things better. Whether quantum computers could be built to overcome errors was the big science question, and it seems that at least at a small scale, devices can have very, very low error rates. Now, it's “only” a question of scaling.
Quantum has definitely changed our understanding of how we see parts of science; that is very clear. Computer scientists are very interested in what's computable, and quantum information changed that. There are now things that can be computed by nature that were thought not computable before, so it expands the applicability of their field. It's a fundamental shift.
Quantum information has also influenced high-energy physics and our understanding of the universe. Physicists push the boundaries of our experiments to see whether the laws break down. We found out Isaac Newton's laws of motion are wrong by investigating things that move at the speed of light and smashing particles together. What quantum information does is push the frontier of complexity. It enables improved precision measurements like gravitational wave detection [editor’s note: ripples in space-time caused by extremely powerful forces].
That's the interesting part for me as a scientist. I'm using quantum computing as a guidestar. This direction brings us into a new territory, and there will be things to discover that will totally change our understanding and have unforeseen applications that are likely much more transformative than quantum computing.
For my research with trapped ions, one of the speed limitations comes from the readout of the qubits of the ions. Harry Levine has some ideas on how to speed it up for atoms that apply to ions as well, and he wants to build a neutral atom quantum computer. I'm very interested in a neutral atom approach, so I started collaborating with Dan Stamper-Kurn, but now, with Harry, we have more critical mass to push on quantum computing with neutral atoms..
Then there is Aziza Suleymanzade. She's interested in hybrid technologies [editor’s note: a combination of different quantum platforms, such as atomic and solid-state systems] and quantum networking. Scaling is a challenge, and networking is a way of scaling. There are ideas to connect a trapped ion and a neutral atom quantum computer, and she is very good in thinking how to connect the qubits that are optically controlled with qubits that are electrically controlled.
Chiara Salemi uses quantum technologies to search particles that are thought to make up the majority of the mass of the universe. Victoria Xu does gravitational detection, but she uses quantum concepts, namely, the squeezing of light to make the detector more sensitive. We were at one point toying around with whether we can use our ions as detectors for dark matter as well as for gravitational waves, so maybe something will come out of working with them.
These young people have mastered all these different technologies. I've been in this field for 25 years. What drives the research forward is this fresh perspective, like looking at things from a different angle and suddenly seeing something you haven't seen before that could be the game changer.
I talked to Harry and Aziza three weeks ago, and it was invigorating to be around all their plans and ideas. The new generation is going to push things forward.
