Invention

Struggling with quantum logic: Q&A with Aaron O’Connell

Posted by: Ben Lillie

On stage at TED2011, Aaron O’Connell talked about building the largest object ever put into a quantum mechanical state, a vibrating piece of metal (called a mechanical resonator) — work he completed in the lab of professors John Martinis and Andrew Cleland, and working closely with Max Hofheinz and many others. Now he’s interested in starting a science company with the potential for dramatic impact on the world.

The TED Blog talked with him about his research, the nature of physics, and the differences between academia and the corporate world.

You made an object that’s an enormous breakthrough in physics, and then you have a huge challenge to try to explain to non-physicists why it’s a big deal. Where does that disconnect come from?

A lot of the impact of the experiment is that it forces you to change your perception of the world, and in such a way that you need to develop a new logic system. So, there’s two basic types of logic. There’s classical logic where things are either A or B, but they’re not A and B at the same time, and then there’s quantum logic which says that all the future possibilities are realizable today. That they actually exist in the present. You don’t have to wait for future contingency to realize the possibility now.

That’s a really tough concept.

How do you use your current classical logic system to get to the question of it possibly not being the only one you could use? And why is that important? Those things are really hard to wrap your head around.

Before Aristotle, when people thought about logic, they thought that all things in the future were true in the past. The argument goes like this: If you suppose there’s going to be a fight tomorrow, then necessarily in the past there was also going to be a fight on that day, so therefore it has to happen, because anything in the past that is true, has to be true.

And then Aristotle came along and said, “You guys are all nuts, man.” He said these events are neither true nor false. They’re not verifiable until the event actually happens. You have to actually wait until the event to see which one becomes the reality.

So, that was classical logic, but then quantum mechanics forced people to think differently. So you have these two possibilities, there could be a fight or there could not be a fight, and Aristotle said we have to wait. Quantum mechanics says you have to wait until the outcome, but you can influence it right now, because both of those possibilities are real things in the present. They’re not just an abstract concept, but they exist now.

This is something we have no intuition for. I know I studied wavefunctions for years and I still don’t know what these things are; there’s no visceral part to it.

Yeah, you make up some mental constructs, and then you go with them. But you don’t experience it too often. I mean, we do in the lab sometimes. I try to make the point that if you play with it every day, and it doesn’t behave quantum mechanically or probabilistically, then you think something’s wrong, it doesn’t sit right with you. If every time you make a measurement you always find your object in the excited state, then something’s wrong, because half the time it should be decaying, so it feels funny.

Do you ever find it bleeding over, and start wondering why your chair is where it’s supposed to be?

No, actually I don’t.

My outlook on the whole thing is that people have models of reality, and those models are descriptions, but they don’t get you any closer to the truth. I sort of believe that the truth is experiential, it’s “this is what is happening.” If I realize that actually there’s quantum mechanics happening around us all the time in some macroscopic, interconnected way, then that doesn’t change my perception of it, that doesn’t change my interaction with it, it just changes how I view my interaction.

And of course it might allow you to do some cool new stuff, like build new devices with that knowledge.

Yeah, what can you do with the mechanical resonator, or any large quantum object?

That’s hard to say right now, because it was a proof-of-principle experiment. So, practical applications are difficult to conceive of.

A lot of the things are tangentially related. Like, we made the world’s most sensitive motion detector, inadvertently, by doing this. It’s many orders of magnitude more sensitive than anything else that’s ever been built.

But what do you use that for? You could put chemicals on top of it, and the chemical reactions make it vibrate a little bit, and you could listen to the chemicals as they pop apart or join together. That was branded the quantum microphone.

It’s not practical, but one other interesting thing you could do is take a virus or bacteria, some very small living or questionably living thing, and put it on top of the resonator, it’s a big object. And then just re-do the experiment and put it in a superposition, bring it back together and then wake the bacteria. That would be interesting philosophically: whether quantum delocalization somehow affects the abilities for life processes to occur.

That’s amazing. That’s a philosophical question people have been posing for years, and you’re saying you can just directly test it.

Yeah, the definition of “living” is hazy. I’m not a biologist, I don’t know what people would agree upon. But you can look at the area of the vibrating resonator, and you can actually make it a lot bigger. I just chose that size because it happened to be the size I was working with. I’ve made them much larger and much smaller and they basically all work the same doing the classical tests. I only did the quantum tests with that one, but there’s no reason they wouldn’t all work the same.

You broke the previous limit on how big they could be. Is there a limit on how big you can make them?

I don’t see any limit — it just becomes technically more challenging as you try to make larger and larger objects. People are working on larger ones now for different reasons. Motion sensing is part of it, it’s intimately connected. For the gravitational wave experiments they have relatively large, kilogram-size objects that they would like to get into the quantum limit. So, they’re actively working toward putting those into quantum superposition states, but from a different angle.

Part of it is that it has to be disconnected from the rest of the world, or else it has the tendency to stay in one particular state, and not behave quantum mechanically. The larger the thing you have, the harder it is to do that.

One thing people ask me about is human teleportation. One aspect of our experiment is that an entangled quantum state was created between another object and the mechanical resonator, so when the macroscopic state was measured it broke the entanglement in a very similar way to a teleportation experiment.

It’s an interesting question, because you’d have to be very, very cold, so it probably wouldn’t work out for you.

You’d have to be within a Kelvin of absolute zero, right?

And in vacuum, yeah. And neither of those conditions is particularly good for humans. So it doesn’t particularly open a gateway to any sort of Star Trek-like teleportation.

What are you looking forward to seeing in macroscopic quantum objects?

In general: quantum computing. Half of this work was on quantum computation. The main part of this experiment was using one of their specially developed devices — a quantum bit, or q-bit — to read out the position of the mechanical resonator.

Another way to pitch the whole thing we did with the mechanical resonator is that it’s a quantum memory device. We had previously done experiments with electrical resonators, which are very similar, but they just store photons in them, one unit of energy. Those we developed specifically for memory devices for the q-bits. They’re quantum memory. You can drop your state in there and it’ll hang out for a while. It’s basically quantum RAM.

This mechanical resonator is another example of this quantum memory, except the way you store the memory is you store it in the vibration, and not the photon state. So I’d like to see that develop.

You’ve left academia for the corporate world. Are there any differences that stand out for you?

Yeah, every group of people has their cultural identity. Scientists and academics in particular focus on detail and the minutiae. When they talk to each other they usually don’t focus on the broad ideas; they don’t focus on social interconnectedness. They focus on the task that they’re doing.

Other fields tend to ask more the question: how can we work together? Or how does our work impact each other’s work? The scientific community does that as well, but those questions aren’t asked as frequently. It’s usually left to people to figure out how their work fits in with other people’s, as opposed to sitting down and having a dinner and discussing how we could work together to make things happen.

The one huge counter-example to what I just said is the experimental particle physics community, because they all work together in these gigantic groups to, you know, build CERN, and other things. But that’s rare.

And if you look at the author list from one of those experiments, there’s like a thousand authors on one of the papers, which is good because everyone contributed. But it’s still broken up individualistically; you have all these authors who’ve contributed, but they don’t really have a group identity. They don’t just put “The CERN Group” on it. So the focus is still on individual accomplishments as opposed to creating social groups that do work.

I personally see that as not beneficial for the scientific community to embrace this elevation of the individual. I think it would be more beneficial to the projects to have more of a group structure.