Nobel Prize in Physics Winner: John Martinis on the State of Quantum

The interview opens by introducing John Martinis as a winner of the 2025 Nobel Prize in Physics, then turns to his background. The account describes growing up in San Pedro, California, with a father who was a fireman and a mother who stayed home to care for the family. Science and technology are described as a constant interest.

The early influence the conversation stresses most is practical. The father is described as having no high school education but as a very smart person who was always building projects in the garage. Growing up around that work is credited with giving an empirical, hands-on sense of how things work. High school physics then appealed because it joined that intuition to mathematics and concepts. The path continued to UC Berkeley, where a senior-year class with John Clarke, later the doctoral advisor, introduced work just beginning on quantum mechanics in electrical devices.

Graduate school was also at Berkeley, described as something "you're not supposed to do." The project that led to the prize began a couple of years into graduate study, and the exact start date is not remembered. In a side exchange, another participant recalls starting as a physics and math undergraduate at Berkeley, being put off math by the many proofs in an upper-division class, and finishing with a degree in astrophysics.

The research question came from Professor Anthony Leggett, whose Nobel Prize for superfluid helium-3 is placed, with stated uncertainty, "I think, in 2003." Helium-3 cooled far enough shows superfluid behavior, which is complicated because of the more complex helium-3 nucleus, and Leggett helped develop the theory. The interview notes that little helium-3 physics goes on today, but the question Leggett raised that led to this experiment grew into "a huge field."

And the question was, do macroscopic objects behave quantum mechanically?

In the interview, "macroscopic" could mean a small ball. In this experiment it meant an electrical circuit containing billions of electrons and atoms. The issue was whether the collective motion of such an object follows quantum mechanics. For a circuit, that means asking whether the currents and voltages of an electrical oscillator behave classically or show quantum behavior.

Schrödinger's cat frames the stakes. In the thought experiment, radioactive decay triggers a detector and a bottle of cyanide, and the question is whether, after some time, the cat is in a dead-and-alive state. The interview is unsure who first raised it ("Einstein brought it up, or Schroenner brought it up"). It credits Leggett with pointing out that the paradox depends on believing a macroscopic object could be in a quantum superposition, and that "there was no experimental evidence that this could happen." Leggett's call to test it struck a young graduate student as a great question. The original proposal was to look for tunneling, though the work "turned out to be more than that."

Before the experiment itself, the conversation spends some time on basics. At atomic scales, position, energy and motion must be described with probabilities, unlike the deterministic path of a thrown ball. Quantum mechanics was developed as a theory of small things such as electrons and atoms. One puzzle it solved is why atoms have size at all: classically, the electron and nucleus attract and would simply merge.