Schrodinger’s Cat Lives

If quantum physics always sounded a little squirrelly to you, take heart. Yale researchers have announced that they can do what quantum physics claimed to be impossible: they can determine the state a quantum system will collapse to before it happens. This contradicts Schrodinger’s famous hypothetical cat that is superimposed as 50% alive and 50% dead at the same time. The research appears in Nature.

Schrodinger argued that until you open the box, the cat is half alive and half dead in the same way that a qubit can be in 50% of one state or another. When you observe it, you force the system to one state. Researchers at Yale, however, have found a way to use microwaves to indirectly monitor qubits to determine their state prior to the system making a jump. Unlike a normal observation which occurs too late, the Yale technique allows researchers to change the future state to their choice.

As you might expect, seeing the start of a quantum jump requires quite an experimental setup and FPGAs are employed, unsurprisingly. At the heart of it, though, is a simple LC oscillator. The oscillator emits at about 9 GHz and the frequency changes based on the state of the qubit.

It will be interesting to see if the physics community can reproduce this and if it causes any major changes to quantum theories. In particular, this could have a far-reaching impact on practical quantum computing, a topic we discussed last year. Now we just have to hack [Sean Boyce’s] quantum coffee maker.

31 thoughts on “Schrodinger’s Cat Lives

  1. “Schrodinger argued that until you open the box, the cat is half alive and half dead in the same way that a qubit can be in 50% of one state or another. When you observe it, you force the system to one state.” This is not at all what Schrodinger said at all.

    “It is typical of these cases that an indeterminacy originally restricted to the atomic domain becomes transformed into macroscopic indeterminacy, which can then be resolved by direct observation.” That is to say that you can’t say for sure what the state of the system is without a measurement of some kind. That’s a far cry from implying that observing the state of a system is what causes it to have that state in the first place.

    1. That statement may be a far cry from implying the observation is what causes the system to have a state. However that’s exactly what happens (until now), of course ‘observation’ means some interaction with the outside world which is why Schodinger’s cat would have to be in a completely closed system.

  2. It doesn’t really contradict Schrodinger. Math predicted that quantum state changes are gradual rather than instantaneous. That is, the probability distribution changes from entirely state A, to a superposition of states (which itself evolves over time), to entirely state B. Now we have experimental verification of that prediction.

    Those transition still start at unpredictable times, so the randomness hasn’t gone away.

    From the paper:

    “Our findings, which agree with theoretical predictions essentially without adjustable parameters, support the modern quantum trajectory theory…”

    1. I’ve been following this new experiment, and have also had a hard time reconciling news reports with the paper itself.

      So I went to stack exchange and had read this interesting post that aligns with what you’re saying:

      I feel the need to reflect carefully about this one before developing an opinion, but found the perspective expressed above useful.

      1. Thanks for that link. The author of that answer understands this stuff a lot better than I do, and therefore gave a much better description of what this paper does and doesn’t mean.

  3. Keep in mind, Schrödinger came up with the now-famous thought experiment to point out how silly the Copenhagen understanding of Quantum Mechanics was. He wasn’t suggesting you could actually have a superposition of a dead/living cat. Quite the opposite, he was arguing that such a superposition was so obviously impossible, the underlying theory must be flawed.

    1. Schrödinger’s premise was flawed in the first place, because the box in which the cat is placed is conceptually impossible.

      It isolates the cat perfectly from the environment, which is the same as saying “the cat does not exist in this universe”, because no such cat can be observed or measured by anything or anyone. However, that violates the conservation of energy, so either the whole setup is non-physical, or the cat is destroyed as it is placed in the box and the energy is spread around.

      Either way, you can’t even say that there is a cat in the box, let alone whether it’s dead or alive.

      1. I disagree with most of your second paragraph: perfect isolation between two systems doesn’t violate conservation of energy, it just describes the condition where there is no exchange of energy, information, etc. between the two systems. While this does mean that the state (or existence) of the cat cannot be measured from the isolated system (i.e. outside the box) it doesn’t mean that the cat “doesn’t exist”, and it certainly doesn’t mean that the cat has to be destroyed and its energy distributed to the rest of the universe.

        When the cat is placed in the box and the box is closed there is no change in the total energy of the universe (or any subsystem including the box), one part of the system (the inside of the box) is simply isolated from the rest (outside the box).

        Of course I agree that this is somewhat irrelevant in an actual experiment, since it’s impossible to build a box that perfectly isolates the inside from the outside. Schrödinger proposed this as a thought experiment however, and for that purpose a perfectly-isolating box is not a problem.

        1. >”perfect isolation between two systems doesn’t violate conservation of energy, it just describes the condition where there is no exchange of energy, information, etc. between the two systems.”

          True, but that implies a situation where you have a “God’s eye view” of both systems. In reality, you’re either in one, or the other, and if the other is not accessible to you in any way then for all practical purposes it does not exist for you.

          So, in order to put a cat in the Shrödinger’s box, you have to find a way to destroy energy from YOUR universe, and as far as we know nothing can do that. Even if you throw matter into a black hole, the information/energy is not lost because you observe a corresponding increase in the mass of the black hole.

          The Shrödinger’s box however would not get any heavier because that would imply we feel the gravity of the cat, which means we can observe the cat from the outside, and, at least in theory, determine by the gravity waves whether its heart is still beating.

          1. That also gives a clue about what happens with the box, or any system it describes: when an object is placed in such a quantum “box” in regards to some of its property, we are isolating that property from interacting with our reality – we aren’t looking – but in order to truly not know what the property or state is we have to remove that information from the state.

            In other words, if we put an entire cat in such a state, we would have a huge burst of radiation as all the mass-energy of the cat would escape the box just as the lid is closing. The information that a cat was here must be preserved.

            Likewise, if we open the Shrödinger’s box and find a cat there, the information about a cat cannot appear from nothing – that would be creating energy out of nothing. The information of the cat must rush back into the box to reconstitute it, and the important notion is that the information comes from the surrounding reality: it’s not that anything happens to the cat inside the box – the universe around decides whether it turns out dead or alive. By looking into the box, we create the cat.

            Out of the EPR triad of local, causal, real, where one must be excluded, this is the only sensible version of quantum mechanics. Things happen here, happen for a cause, but are not real independently by themselves – there is not actually any concrete cat that you can put into the box, it’s just that the local reality “knows” of a cat and behaves as if there is a cat right there.

          2. And as for two initially isolated realities coming together: you can’t observe a state where something pops out of nowhere. Since the universe demands causality, when the two systems combine their information, it assumes a state (a history if you will) that appears internally consistent.

            Suddenly, what you know of the universe changes to include the other system and it seems that it was always there. That’s because when the information content of the local universe changes, you change with it. After all, you the observer are not independently real either.

            If part of your reality (the cat) actually leaves your system and becomes isolated, the entire existence of the cat must be forgotten by the local universe and erased from its causal history because its information is no longer here – it cannot be accounted for – which is another reason why the Shrödinger’s box doesn’t work like its supposed to.

  4. Whelp, that proves it for me. If David said it could be done, then by God there must be a way. Entire nations should dedicate their economies to doing everything he says exactly how he says to.

  5. “For a tiny object such as an electron, molecule, or an artificial atom containing quantum information (known as a qubit), a quantum jump is the sudden transition from one of its discrete energy states to another. In developing quantum computers, researchers crucially must deal with the jumps of the qubits, which are the manifestations of errors in calculations.
    The enigmatic quantum jumps were theorized by Bohr a century ago, but not observed until the 1980s, in atoms.”

    Isn’t quantum jumping how discrete spectrum (observed >100ya) works??

  6. Well,
    the cat example of quantum theory…. isn’t that just how archeology works?

    That is, well the system is “self observant” i.e. the cat observes it’s own death or not, whilst the explosive observes it’s fate or not….
    Thus by looking in the box, we’re just looking into the result of the past, that is, if the cat’s alive, then we can be sure the explosive never went off,
    yet if the cat’s dead, we know to check if the cat died from an explosion (fragments) or lack of air (sealed “super-imposed” container).

  7. Seriously, i don’t understand anything about this, but as long as it’s only a thought experiment and no cats are harmed just go ahead, i’m fine with that…

  8. Al, Did read the nature Article?

    Reading the abstract one can read this:

    “Our findings, which agree with theoretical predictions…”

    So this experement from the saying of experementers themself doesn’t contratic any theoritical basis.

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