John Martinis: The Nobel Physicist Behind Macroscopic Quantum Tunneling

**Brian Keating** (0:00)
Today, we're joined with one of my heroes.
It's not every day you get to talk to somebody who not only is such a great contributor to physics and has been inspiring not only the work that I do, but my whole collaboration is basically enabled by work that John and his collaborators did over the years. But he's also, once we say, a mensch, he's known for his teaching, for his group building. You're just kind of the physicist's physicist. So thank you for joining us.

**John Martinis** (0:25)
Well, that's very kind. Not everyone feels that way. I appreciate the kind words.

**Brian Keating** (0:31)
You're now the 26th Nobel Prize winner I've had on the podcast.
Every nine multiples of nine, I write a book featuring wisdom. I hope the third version will come out with you in the coming years. Well, I'll let you know about how that progresses. But I want to take us to that October morning last year. I was teaching quantum mechanics that day, advanced quantum mechanics with perturbation theory. I said, a guy I know just won the Nobel Prize. What was that like? What was the second thing that went through your mind when you got the phone call at whatever time it was?

**John Martinis** (1:01)
Well, I actually didn't get the phone call. The phone is way across the house. But my wife was up late reading and she heard the phone ringing. But she figured she'd get it in the next day. She looked at her email and there was a bunch of congratulations.
So she knew about it, but she knows that I need my sleep, especially the next day when you have to be on.
So she waited till about 6 o'clock. There were reporters who showed up soon after that. So it was actually better because my wife woke me up.
But she was very clever about it. She had me on the shoulder and said there was reporters coming over.
And I realized, oh, it's the beginning of October. So I opened my computer and saw that. Let me share something a tiny bit personal. There are things called Nobel Symposiums, where they look at a field and see if the field is noteworthy and look at people and the leaders in the field and the like. So you kind of understand a little bit that you might be on some kind of list. Okay. For me, that's the biggest honor because the Nobel Prize is just so crazy unlikely, right? Just being invited to that is really very special. And then for some years, you know, I'd wake up in beginning October, it's like, oh, okay. And it's just so wrong to be disappointed by this because of it. So after the years, you know, I just stopped kind of, I knew, well, it's beginning October, but I stopped really thinking about it. That's why my wife didn't know. We didn't talk about this at all, right? Because it's just, okay, you know, whatever happens. And it's actually better that way.

**Brian Keating** (2:53)
Yeah, there's a joke I sometimes will, you know, pull out on October 1st at 2 in the morning. I'll say, I'm working on my best, you know, Swedish accent to cause somebody. I don't like a heart attack. We are calling from the Swedish Royal Academy.

**John Martinis** (3:05)
I've heard people get pranks like that.

**Brian Keating** (3:07)
Well, yours isn't a prank. And the only thing that frustrated me is that I was talking about, you know, quantum tunneling. But I was talking about single electron tunneling and even nuclear tunneling. So you wanted for macroscopic tunneling. What was the impetus for? Obviously, you didn't set out to win another prize. Talk us through the history of why you thought macroscopic effects would manifest themselves, instead of just the already mysterious microscopic tunneling effects.

**John Martinis** (3:32)
Yeah. So this experiment in line of research was very much motivated by Anthony Leggett. You can just go back to the Schrödinger cat paradox where you do a microscopic atom decay that's connected up. So the atom decays, it kills the cat. Then before you open the box, is the cat in some dead and the live state?
I think for me, there are ways to answer this that are very sensible. But Leggett pointed out that there actually is no experimental evidence that macroscopic entities, especially a cat, can obey quantum mechanics. He said, if there's no evidence, we should be looking for evidence as a way to test quantum mechanics. He came up with the idea of these superconducting circuits, where you have a macroscopic number of electrons that are tunneling through the junction. For me, as a young student, you look at quantum mechanics, it's really wonderful. My personal hobby was electronics, like John Clark's group, because he was doing things on quantum noise and thinking about this. For me, it was the most natural experiment to want to do.