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.

Comments (13)

  • milo Durfee commented on May 15 2012

    Could quantum entanglement be used as a way to communicate over large distances of space?

  • Robbie MacGregor commented on May 1 2012

    Not sure if I will get a response to my likely uneducated question…..but……

    At what point in the expansion and cooling of the universe would larger/”visible” objects begin to act in a quantum fashion? I guess another way of asking would be what is the maximum threshold for heat or iinteraction with other disturbances that would cause the quantum wave function to collapse into a defined state? And is it possible for the universe (or whatever verse we are in) to expand to the point where everything with mass would only exist in a quantum state?

    I probably asked this question poorly, but I hope someone has a vague idea of what I am getting at.

  • Kasi Phillips commented on Jan 29 2012

    Hello Aaron, your discovery was great, but It made me ask a few theoretical questions. Sense we’ve never seen a particle and it’s possible to be more than one place at the same time according to quantum mechanics.

    What if our souls or the self are the representation of being in all places at the same time meaning all organisms that are conscious of its self, and environment. Consciousness being the quantum particle or energy source.

    The human physical body vibrating at a high speed density and temperature compressed to house quantum energy (soul). The non vibrating portion of your experiment being the result of what we can’t see with our eyes yet still moving. Your experiment is a blueprint to understand in a way that we are everything, but only separated by our perceptions. Cool discovery…We are the physical manifestation of all atoms, I have children and see myself in them all the time.

  • Sofia Hurst commented on Sep 15 2011

    I’m in my last year of school and am planning to study a joint honors in physics and philosophy next year. As such, I’m writing a 4000 dissertation on how QM has influenced our perception of determinism and of objectivity. Your video was amazing and has greatly clarified the way I see QM, even though I am not at a level to understand the mathematics.. yet…

    So I was curious to know, how does everybody think that QM has changed our objectivity? We associate strong objectivity with the scientific method, and I was wondering that if we must re-assess objectivity in science, due to the interference of the observer etc,.. does that mean we must change the scientific method? Or does it lose credibility to a certain extent??

    Probably not going to get an answer as I’ve seemed to have missed the time when this thread was ‘active’ so to speak, but I thought I’d post on the off chance of some reply:)
    Thank you!

  • Rachel Kolbe Semhoun commented on Aug 25 2011

    To pick back up on Richard McMahon’s point, I too would like your input on quantum physics’ impact on time and space as we experience them. Should we continue to develop ourselves according only to linear time or should we be taking into greater account quantum physics?

  • Dustin Woods commented on Aug 23 2011

    Hey Aaron, Male Fasion Advice on Reddit would like to know, what were you wearing in your Ted Talk? Thanks! – http://www.reddit.com/r/malefashionadvice/comments/jrrkf/anybody_knows_what_aaron_oconnell_is_wearing_is/

  • Richard McMahon commented on Jun 16 2011

    Aaron: What are your thoughts about human consciousness? I can see it as almost an example of a quantum state in that we seem to exist in two places at the same time – our inner selves and our outer selves, which are at one time the same and different. On the other hand, it can be viewed as our greatest obstacle to the quantum world because we are never really alone on the “elevator.”

  • Pingback: Quantum Hoo-Ha | STEVE VOLK: THE GENERALIST

  • Des Greene commented on Jun 10 2011

    If the experiment was run for a very long time how would the paddle behave in terms of fatigue behaviour? Would it display normal fatigue life or perhaps half of same. Perhaps no fatigue at all?

  • Jennifer Dewalt commented on Jun 8 2011

    I think I can help answer your questions, Aaron Scott. You are spot on with your first question. By sufficiently isolating the device, Aaron and his colleagues were able to make it behave quantum mechanically. In the “everyday world,” things are constantly interacting with each other which keeps them solidly classical.

    Your second question requires a little background knowledge so bear with me.

    The short answer is that Aaron and his colleagues used a superconducting quantum circuit (qubit) to both control and measure his paddle. Working with John Martinis’ quantum computation group at UCSB, Aaron connected the vibrating paddle to a qubit which gave him the ability to transfer quantum states between the paddle and the qubit and also measure the system through the qubit.

    The qubit is a loop of wire. When electrical current runs around the loop it creates a magnetic field. This magnetic field, in turn, can be measured using a very sensitive magnetic field detector (called a SQUID). When the qubit is in the 0 state the current runs in one direction (e.g. clockwise) and when it is in the 1 state it runs the other way (e.g. counterclockwise), which produce different magnetic fields depending on which way the current is flowing.

    If the qubit is placed in an equal superposition of 0 and 1 then the current will be running in both directions at the same time. During this time the detector is turned off. To measure the system, the detector is turned on and the quantum state collapses to a classical one. The detector will read out either 0 or 1 so from a single measurement it is impossible to unambiguously determine the state of the system. Running this test many, many times will read out 0 half of the time and 1 the other half.

    So there are two possible explanations for what is going on here. One option is that the qubit is behaving classically and it is actually in the 0 state half the time and 1 state the other half as opposed to a superposition of the two. The other option is that the qubit is in a superposition of 0 and 1.

    Einstein, Podolsky, and Rosen pointed out that there is a fundamental difference between these two options but it took 30 years for someone to develop a definitive experimental test to prove that this phenomenon is quantum mechanical (Bell’s inequality). As Aaron links to above, the Martinis group showed that their qubits are definitely quantum mechanical.

    So back to how the paddle was measured. First, Aaron put the qubit in a superposition of 0 and 1 and sent that quantum state to the paddle. He then disconnected the qubit from the paddle and measured the qubit to ensure all of the state was transferred. Meanwhile, the superposed state was causing the paddle to both vibrate and not vibrate at the same time. Finally, Aaron reconnected the system, transferred the state back into the qubit and read out the state using the magnetic field detector. By repeating the experiment many, many times, it was clear that the qubit was injecting the superposed state into the paddle and that the paddle was receiving the state, maintaining it and then sending it back to the qubit.

    I know that was a bit lengthy but hopefully it helps to answer your question!

  • Aaron Scott commented on Jun 6 2011

    Aaron, I am far below the requisite level to discuss this intelligently with you, but a couple of thoughts and questions….

    I noticed in your talk that you spoke of pretty much getting everything else “out of the elevator”–i.e., secluding the material–in order to get it to act in a quantum way. That, to me, explained why the quantum world behaves so seemingly different from the classic world. There, in those incredibly small places, they are “alone” on the elevator, and so act alone. But at the classic level, we are no longer alone, so we “conform” to classic rules. Am I reading you correctly on that?

    The one thing I don’t “get” (and may never get) is how you can measure that something both is and is not vibrating. Is there perhaps someway you could explain how that can be done? It would seem that if you use a single device, you’d get only one reading: Either vibrating or not vibrating. If you use two identical measuring devices, you’d expect the same reading from both. I know I’m missing something important–help!

  • Jacob Stevens commented on Jun 2 2011

    When the UCSB guys checked the paddle over and over, it alternated between vibrating and not vibrating each time (I believe in a random manner, no apparent pattern). That is truly remarkable, and it fits the model of quantum mechanics even though the model is so tantalizingly, exasperatingly difficult to contemplate.

    But it sure seems to be quite a reach to me to deduce that this demonstrates the object being in two simultaneous quantum states. I know that’s the first thing most of us would think about when something like this is done. But it’s still exhibiting the same phenomenon of wavefunction collapse when a measurement/observation occurs, just on a larger scale.

    We would still expect an object to have a quantum super-position, and this gives fantastic empirical weight to the idea that each measurement/observation forces the object to “choose” a state. If entanglement is a real thing, then it would figure to behave like this, but I’m not so sure this actually showed what Aaron has been saying it showed. Wave-particle duality, yes. Two simultaneous states, cannot be conclusively inferred.

    As Niels Bohr said, if Quantum Mechanics doesn’t profoundly shock you, you haven’t understood it. This is still profoundly shocking, but still eludes understanding.

    • Aaron O'Connell commented on Jun 4 2011

      Thanks for the comment, Jacob. Quantum mechanics is neat stuff. What we did specifically was to take a qubit (quantum bit), a device we developed for quantum computing, and connect it to the “paddle”. We did this in order to carefully control the “paddle” in a quantum way.

      In 2009 in the Nature paper by Ansmann et al.:

      http://www.nature.com/nature/journal/v461/n7263/full/nature08363.html

      we conclusively showed that our qubits are indeed quantum objects. Although the thrust of that paper was showing that we can create entangled qubits, it also showed that we can put out qubits into simultaneous quantum states (a superposition of |0> and |1> unit of energy). By connecting the energy of the qubit to the vibration of the “paddle”, we were able to both impart energy to the “paddle” and not impart energy to the “paddle” at the same time. Technically, we transferred the superposed electrical excitation of the qubit to a superposed vibrational excitation of the “paddle”. The “paddle” was then both vibrating and not vibrating (in excess of the quantum limit) at the same time, or in other words, was in a superposed phonon state.

      To check if it was indeed in this quantum state we did not measure it directly. Instead, we used a trick and transferred the superposed quantum vibrational state back to the qubit. We did this in a way that has been proven to preserve quantum coherence. We then read out the sate of the qubit, which was a direct indication of the state that the “paddle” had been in.

      Since we used a qubit to both prepare and measure the “paddle” (thanks to Michael R. Geller and Andrew N. Cleland for the idea) we were able to carefully create arbitrary single phonon states in the “paddle” in a known and controllable way. In addition to the superposed phonon state, we created a few different states that I did not talk about. We specifically chose to make the vibrating and not vibrating (in excess of the quantum limit) state because it is really fun to think about.

      It is impossible to understand quantum mechanics using classical logic. Quantum logic is the only way to understand quantum mechanics, and understanding quantum logic can be a powerful thing.