Caltech Mourns the Passing of Jeff Kimble (1949-2024)

Harry Jeffrey Kimble, the William L. Valentine Professor of Physics, Emeritus, passed away on September 2, 2024, at the age of 75. A giant in the field of physics, Kimble—who was also known as H.J. Kimble and Jeff Kimble—performed groundbreaking experiments in quantum optics and quantum information science. His achievements include some of the earliest demonstrations of quantum squeezing and quantum teleportation, among many other trailblazing experiments.

Kimble is perhaps best known for his pioneering work in a field known as cavity quantum electrodynamics, or cavity QED, which is the study of single atoms trapped in cavities in which they strongly interact with single photons of light. Kimble's cavity QED experiments formed the basis of many quantum technologies being developed today. His research also led to experiments that laid the foundations for research into quantum networks—essentially a quantum internet—in which ensembles of atoms are entangled.

"Jeff had a very deep influence on me as a scientist and as a person," says John Preskill, Caltech's Richard P. Feynman Professor of Theoretical Physics. "I was a particle physicist originally but became interested in quantum computers around 1994 and 1995 when they were first starting to get attention. If not for Jeff, I wouldn't have made the pivot that I did from particle physics to quantum information science. He was a very inspiring and daring scientist whom I am grateful for."

Oskar Painter, Caltech's John G Braun Professor of Applied Physics and Physics, says Kimble "was an explorer at heart, who deeply loved the challenge of a solo back-packing trip to Patagonia almost as much as he loved uncovering the mysteries of the quantum world. He was the most intense and inspirational person I have ever worked with, and he had a tremendous impact on numerous generations of students like myself who dreamed of one day taming quantum systems and applying them to new ways of communicating and processing information."

Kimble's work on quantum squeezing—a method for dealing with quantum noise that limits precision measurements—included not only conceiving and demonstrating a squeeze technique that has since been widely adopted, but also coming up with a theoretical idea about how to further improve the method. This research has been crucial to improving the current sensitivity of LIGO (Laser Interferometer Gravitational-wave Observatory), which regularly detects ripples in space-time known as gravitational waves.

"The LIGO team spent nearly 20 years perfecting Kimble's techniques at LIGO's audio frequencies, making them robust, and then implemented them into LIGO," says Kip Thorne, a co-founder of LIGO and the Richard P. Feynman Professor of Theoretical Physics, Emeritus. "Today they are a major contributor to LIGO's remarkable sensitivity and ability to see several black hole collisions a week by comparison with one every six weeks in 2015 and 2016."

Kimble also helped establish the Institute for Quantum Information and Matter (IQIM) at Caltech, together with Preskill, who is currently the Allen V. C. Davis and Lenabelle Davis Leadership Chair of IQIM. The center's roots go back to the late 1990s, when Kimble and Preskill received a grant from the Defense Advanced Research Projects Agency (DARPA) to study quantum computing's potential applications in cryptography. Later, in 2000, they were awarded funding from the National Science Foundation (NSF) for their growing group, which, at that time, was called the Institute for Quantum Information (IQI).

By 2011, advances in quantum computing hardware gave Kimble, Preskill, and other colleagues the impetus to apply for more NSF funding to broaden IQI's scope to include experimental work. They received that funding and changed the center's name to the Institute for Quantum Information and Matter, of which Kimble became the inaugural director.

"IQIM would not have happened without Jeff," Preskill says. "Over the years, we did several research proposals together and those interactions were very exciting and helped to steer us scientifically."

"Jeff's impact on Caltech went well beyond his own research," says Fiona Harrison, the Harold A. Rosen Professor of Physics and the Kent and Joyce Kresa Leadership Chair of the Division of Physics, Mathematics and Astronomy. "He set unwaveringly high standards, his scientific interests were very broad, and Jeff never did anything half-heartedly. As a result, his advice was highly sought on issues ranging from who to hire onto the faculty to what new strategic directions Caltech physics should pursue. His presence as an admired colleague and friend influenced generations of Caltech scientists, including myself."

Kimble was born in Floydada, Texas, in 1949. He obtained his bachelor's degree from Abilene Christian University in Texas in 1971, and his PhD from the University of Rochester in New York in 1978. From 1979 to 1989, he served as a professor of physics at University of Texas at Austin. Kimble became a professor of physics at Caltech in 1989, the William L. Valentine Professor in 1997, and professor emeritus in 2021.

In an IQIM blog post, one of Kimble's former postdocs, Jun Ye, now a professor of physics at the University of Colorado Boulder, recalled shaking hands with Kimble when they first met. "His grip was more than just firm; it actually squeezed the bones of my hand. So naturally, I took the handshake as a sign that he really wanted me to join his group. When an offer of a Caltech fellowship arrived three months later, I accepted it without hesitation. In 1997, I had no way of knowing that Jeff's way of doing science would leave a profound mark on my career and that his deep friendship would continue to enrich my life and that of my family for many years … He is a daring pioneer, an original thinker, a groundbreaking technologist, and a relentless seeker of ultimate truth and knowledge."

Kimble summed up his own attitude toward science in an animated video produced by PHD Comics that explains entanglement. "If you want to be on the cusp of the future, you have to be willing to fail," he said at the end of the movie. "We've come up some climb, and it didn't work; you better go down, try another way. You better believe it's scary. But it's an exhilarating intellectual adventure."

Kimble received many awards for his pioneering research, including the Leonard Mandel Quantum Optics Award (2024), the Herbert Walther Award (2013), the Julius Edgar Lilienfeld Prize (2004), the Albert A. Michelson Medal of the Franklin Institute (1990), the Einstein Prize for Laser Science (1989), and Optica's Max Born Award (1996). He was a member of the U.S. National Academy of Sciences and a fellow of Optica, the American Association for the Advancement of Science (AAAS), and the APS, as well as a National Security Science and Engineering Faculty Fellow.

Family was also very important to Kimble. "What also stood out to me about Jeff was his devotion to his family," Painter says. "He really drew strength from them and prioritized them in a way I have rarely seen in someone so driven by their work."

Kimble is survived by his wife Midge Kimble, their children Katie Grooms and Megan Kimble, and their grandchildren Ellie, Bryn, and Madeline. He is also survived by two brothers, Jim Kimble and John Kimble.

A full obituary will be posted at a later date.