IYQ 2025: Caltech’s Role in 100 Years of Quantum Mechanics

This year marks a century since the establishment of quantum mechanics as a formal discipline. Considered a scientific revolution that has reshaped our understanding of the physical world, from early debates about wave-particle duality to the latest breakthroughs in quantum computing and entanglement, quantum mechanics has consistently pushed the boundaries of science. Significantly, Caltech played an essential role in expanding quantum theories, leading innovations, and expanding the possibilities of what science can be achieved.

Recognizing the importance of this field, the United Nations has declared 2025 the International Year of Quantum Science and Technology (IYQ) to commemorate a century of quantum mechanics and its global impact. At Caltech, this legacy is evident in the institute’s ongoing leadership in quantum research, building on a tradition established by some of the most influential physicists of the past century. To understand the cultural and intellectual impact of Caltech’s quantum legacy, even today’s students at the Institute reflect on its deeper purpose.

“Quantum mechanics is the backbone of modernity, the efforts of those early theorists and experimentalists having paved the way for the information age and its innumerable splendors. What I believe Caltech manages to stress like few other institutes, however, is the incalculable value of fundamental science in and of itself. While their work may have led to it, Bohr, Heisenberg, Planck, and their cadre weren’t motivated by transistors and MRI machines, but rather the demystification of the universe for its own sake. Will quantum gravity prompt another technological revolution? It’s impossible to say, but we shall work tirelessly to understand it anyway.” — Damian Wilson, PMA undergrad and high energy physics researcher at INQNET

As researchers celebrate this milestone, Caltech continues to lead cutting-edge projects that build upon the foundation laid by quantum pioneers. For example, at Caltech’s Institute for Quantum Information and Matter (IQIM), scientists are developing next-generation quantum technologies, furthering Richard Phillips Feynman’s (B.S., Caltech, 1939) vision of quantum simulations and expanding on John Francis Clauser’s (B.S., Caltech, 1964) groundbreaking work on entanglement. Both Feynman and Clauser won the Nobel Prize in Physics; Feynman received the award in 1965, while Clauser was awarded in 2022.

Unquestionably, Caltech has been the catalyst of scientific discovery for decades, especially in quantum mechanics. This is due to physicists like Feynman, whose pioneering theories created prominent advances in quantum computing and gravitational wave detection. While Caltech has significantly shaped the field, at the heart of this legacy are not just theories and equations but the brilliant minds dedicated to unraveling the mysteries of the quantum world.

As we see it today, quantum mechanics owes much to Feynman. His path integral formulation introduced a novel way to understand quantum mechanics, demonstrating how particles behave by considering all possible paths. This approach remains a cornerstone of quantum field theory and continues to influence modern physics. This integration of theory and experimentation continues today, as noted by one of Caltech’s leading theoretical physicists.

“One of the most important challenges is to unify quantum mechanics and general relativity. Caltech physicists have made important contributions in the past, including Feynman’s discovery of a concept known as the Faddeev-Popov ghosts in the quantization of gravity, and Schwarz’s discovery that string theory contains Einstein’s gravity in low energy. More recently, the close connection between quantum error-correcting codes and the holography of quantum gravity was discovered, in which Caltech physicists played a key role. With the world-leading programs in quantum information, high energy theory, and gravitational physics, Caltech is an excellent place to develop such connections.” — Prof. Hirosi Ooguri, Fred Kavli Professor of Theoretical Physics and Mathematics and Founding Director of Caltech’s Walter Burke Institute.

Beyond his theoretical contributions, Feynman played a crucial role in envisioning new technological applications. He was among the first to propose the concept of quantum computing, which has steadily gained momentum. During the 1980s, he suggested that quantum systems could be used to model complex physical processes that classical computers struggle to simulate. His vision laid the foundation for a technological revolution that Caltech researchers continue to explore today. While Feynman advanced quantum theory, Clauser, would take these ideas from theory to experiment—pushing quantum mechanics into uncharted territory. While Feynman’s work has been significantly monumental, Clauser’s achievement further pushed Caltech to the frontier of quantum research, advancing quantum networks while improving secure quantum communication and exploring the landscape of new quantum states, thus catapulting the field into unknown territory.

Extrapolating from the theoretical groundwork already laid, Clauser took Caltech’s quantum legacy from theory to experiment. In the 1970s, he and his colleagues conducted the first major experimental tests of Bell’s inequalities, demonstrating that entangled particles exhibit correlations that classical physics cannot explain. His findings provided the first definitive evidence of the non-local nature of quantum mechanics—one of the field’s most counterintuitive yet fundamental aspects.

Yet, Clauser’s path was not without resistance. Even Feynman, a towering figure in quantum physics, dismissed further experimental tests as unnecessary. Reflecting on this, Clauser later remarked, “Feynman similarly told me that further testing the predictions was pure folly. If I had taken Feynman’s advice to abandon my pursuit, I never would have won the Nobel Prize.”

Unapologetically, Clauser’s research not only confirmed Bell’s theorem but also reshaped our understanding of quantum entanglement. His groundbreaking experiments challenged long-held assumptions about locality and determinism, paving the way for advancements in quantum networks, secure quantum communication, and the exploration of new quantum states.

Ultimately, Clauser’s pioneering work earned him the 2022 Nobel Prize in Physics. And while he has made many contributions to quantum mechanics, his research on entanglement remains his most defining achievement. His legacy, like Feynman’s, continues to shape Caltech’s role at the forefront of quantum science. Today, his experiments continue to influence a new generation of quantum research at Caltech, where scientists are building on these foundational discoveries to drive new innovations.

Building on Clauser’s discoveries, Caltech researchers have continued exploring how quantum entanglement can be applied to computing and secure communication. His findings have fueled research into quantum cryptography, quantum networks, and the development of quantum computers that leverage entanglement to outperform classical systems. As Clauser’s work showed, “Our experiments demonstrated that there exist quantum mechanical entities [qubits] that violate the fundamental premises of Local Realism, whereupon Local Realism must be discarded as a fundamentally incorrect universal description of nature.”

Clauser’s work not only revolutionized our understanding of entanglement but also cemented its role in the future of quantum science. As quantum mechanics transitioned from theoretical exploration to practical applications, Caltech emerged as a leader in experimental research. At IQIM, physicists, computer science, and engineers collaborate to push the boundaries of quantum science and explore new possibilities.

Caltech has been a crucible for quantum physics, producing and attracting many of the field’s most influential minds. Feynman, longtime professor of theoretical physics, revolutionized quantum electrodynamics and later laid the conceptual groundwork for quantum computing. Clauser, a Caltech alumnus, conducted pioneering experimental tests of Bell’s inequalities, advancing the understanding of quantum entanglement. Murray Gell-Mann, former professor of theoretical physics, reshaped particle physics with his quark model and contributions to quantum chromodynamics. Kip Thorne, Feynman Professor of Theoretical Physics, bridged quantum theory and general relativity through his work on black holes and gravitational waves. John Preskill, professor of theoretical physics and director of Caltech’s Institute for Quantum Information and Matter, is a leading figure in quantum information science. Frederick Reines, Caltech Ph.D. alumnus, co-discovered the neutrino, while Jeff Kimble, professor emeritus, pioneered advances in quantum optics and cavity quantum electrodynamics. Visiting scholars such as Alexander Polyakov and Jeff Goldstone have also left their mark, further cementing Caltech’s role as a nucleus of quantum innovation. Looking ahead, Caltech researchers remain energized by the profound mysteries that lie at the frontier of quantum science.

“We are getting to understand quantum mechanics better, including measurement, locality, non-locality, and soon will get to answer the questions we have the right way, so we’ll get insights on whatever is shaking with quantum gravity. Expect rapid theoretical and experimental progress!” — Prof. Maria Spiropulu, Shang-Yi Ch’en Professor of Physics

Among the surfeit of Caltech’s significant contributions is cavity quantum electrodynamics (cavity QED), a field of quantum physics that explores confined light-matter interactions.

Under the leadership of physicists like Jeff Kimble, who was a professor at Caltech, researchers have studied the precise interactions between atoms and photons under controlled conditions. These experiments paved the way for advancements in quantum communication and computing.

Moreover, Caltech physicists have made important progress in quantum error correction, identified as a principal challenge in building reliable quantum computers. Alexei Kitaev, who also worked as a professor at Caltech, was a key figure in the field who introduced topological quantum computing concepts that are now being investigated to create more stable and scalable quantum systems.

Although Caltech is widely recognized for its work in quantum computing and information science, it has also extended quantum principles into astrophysics. One notable example of this interdisciplinary approach is the Laser Interferometer Gravitational-Wave Observatory (LIGO), one of Caltech’s most ambitious projects, which detects spacetime distortions from cosmic collisions using laser interferometry. This groundbreaking project was co-founded by Thorne, Feynman Professor of Theoretical Physics at Caltech, alongside Rainer Weiss of MIT and Ronald Drever, professor of physics at Caltech. Thorne, together with Weiss and fellow Caltech professor Barry Barish, was awarded the 2017 Nobel Prize in Physics for contributions leading to LIGO’s historic detection of gravitational waves—an achievement rooted in astrophysics, but enabled by advances in quantum optics. In bridging the quantum and cosmic realms, LIGO exemplifies Caltech’s enduring legacy of transforming quantum principles into groundbreaking technological and scientific achievements.

Initially developed in partnership with the Massachusetts Institute of Technology (MIT), LIGO made history in 2015 when it caught gravitational waves for the first time. This validated a key prediction of Einstein’s theory of general relativity and marked a significant milestone in astrophysics.

Though quantum technology, particularly in quantum optics, played a crucial role in LIGO’s success, Caltech researchers continue to pioneer squeezed light techniques, enhancing the sensitivity of LIGO’s interferometers, thus allowing them to detect faint gravitational signals from crashing black holes and neutron stars, which are the expelled remnants of supernovae.

Caltech remains at the forefront of quantum science, shaping the next-generation quantum technologies. This is why researchers are developing quantum networks that leverage entanglement-based encryption, a breakthrough that could revolutionize secure communication.

Concurrently, experimental physicists continue discovering new ways to manage quantum states for practical applications. Whether advancing photonic quantum computing or refining superconducting qubits, Caltech researchers are at the forefront of pushing quantum technology into new frontiers.

As scientists build upon the work of pioneers like Feynman and Clauser, they grapple with fundamental questions: What is the true nature of reality? How can quantum mechanics be harnessed for technological breakthroughs? Moreover, ultimately, how will quantum science transform our understanding of the universe?

From its foundational theories to the advanced experiments that have shaped modern quantum mechanics, the work of visionaries like Feynman, Clauser, and their successors underscores Caltech’s lasting influence on quantum science and technology. As the world celebrates a century of quantum mechanics, Caltech stands as a driving force, shaping the quantum frontier for generations to come.