Josephson junction

Now, what Anthony Leggett said is it's actually very nice, is when you look at that paradox, you have this macroscopic system-based quantum mechanics, but is there any evidence at all that macroscopic systems can abate quantum mechanics? So it was a very fundamental question related to this kind of paradox and how quantum mechanics works.

And he said, well, with these Josephson junction system, with these electrical circuits, you could then get it into a parameter range where you could see that.

So the basic question was to demonstrate or not, you know, this phenomenon.

And I think that is a good fundamental physics question, whether you can do that.

And I think our experiment laid a lot of foundations on how to think about it.

And then the field was able to progress fairly rapidly over the years because of that good foundation.

And as I understand your experiment, it involved demonstrating this idea of quantum tunneling on an electrical circuit, or specifically Josephson Junction.

Now, two-part question, John.

Yes.

We are usually talking about a Josephson junction in these setups.

Which is what? A thin layer of insulating material sandwiched between two superconductors?

Exactly.

Yeah.

In quantum computing, the physical reality of the qubit is just a constant, exhausting battle against the environment.

A Josephson junction has discrete quantized energy levels, just like a natural atom.

We designate the lowest energy level as zero and the next level up as one.

So, so the t- t- transmon is in some sense the simpler cu- simplest qubit you can think of.

It's a Josephson junction, which is a nonlinear inductor and a capacitor.

So it's like an inductor-capacitor circuit, okay? So, uh, you know, and you know that in a regular LC circuit, you can have energy level states, and each, going up each energy level, you add a photon to it.

And very simply, you, you code the qubit zero state in the ground state, and the qubit one state in the one state.

For the nonlinear, uh, inductor-

Right

... uh, Josephson junction, I've, I've been thinking, uh, Josephson junction, uh, it requires, uh, like low temperature since it's, uh, superconducting.

Right.

and the calculation depends on the depth of the circuit or so and that's like on a micro millisecond time scale in the end

Yeah, I was trying to compare, though, what speed is like, let's say, with comparison to a superconducting Josephson Junction, you know, transmon-type setup.

Just trying to get a sense of that kind of speed and also maybe the, like, the gate speed, any kind of, like, comparison metric.

Absolutely.

You could look at a fluxonium, you could look at, I don't know, a Kerr cat or something else, and try to find if changing the underlying physics will help.

It doesn't seem that it's gonna be easy, whatever qubit you choose, because like the problem is that the Josephson junction is kind of too nonlinear, and all of our superconducting qubits involve Josephson junctions in one form or another.

Yeah.

So was there a noticeable trend with lower frequency qubits in the experiment in the paper that you brought up?