11 ms·

Quantum Leaps, Long Assumed to Be Instantaneous, Take Time

218 points by _Microft 7y ago

amatus 7y ago
Preprint: https://arxiv.org/abs/1803.00545 https://arxiv.org/abs/1803.00545
xwdv 7y ago
I feel like this could have profound implications on a macro level, but I’m not sure what.
joycian 7y ago
Uhm...forgive me for asking, but a continuous quantum jump is...what exactly? How is this in any way consistent with the rest of quantum mechanics? Edit: I don't mean to sound snide, I am genuinely confused about what this experiment means.
- Anon84 7y ago
  This is a common misconception. Quantum jump are jumps between two stable levels... there's nothing preventing "jumps" to unstable states, the particle just doesn't stay long in that specific state (although it can stay there long enough to be useful as in the case of two-photon absorption [0] and microscopy [1]). If I understand it correctly, what this seems to imply is that it's not so much a (discontinuous) jump but rather a continuous(-ish) transition from one state to another. [0] https://en.wikipedia.org/wiki/Two-photon_absorption https://en.wikipedia.org/wiki/Two-photon_absorption [1] https://en.wikipedia.org/wiki/Two-photon_excitation_microscopy https://en.wikipedia.org/wiki/Two-photon_excitation_microsco...
  - joycian 7y ago
    But in a quantum harmonic oscillator, the energy levels can only be certain values. As in the Hamiltonian is: H = omega*planckbar(N + 0.5) where N is the state counter (number operator). As a direct reply to your links: So did the fact that two photon excitation works then not make this entire paper not that interesting or novel?
    - pas 7y ago
      The interesting bit is the experiment here as far as I know, but that is completely consistent with QM (basically validates it). https://www.reddit.com/r/slatestarcodex/comments/bwlhh9/anyone_who_understands_quantum_physics_how/ https://www.reddit.com/r/slatestarcodex/comments/bwlhh9/anyo...
- trevyn 7y ago
  It’s a process of transition between two distinct states. Say a bit flips from 0 to 1; there is a short time period during which that bit is physically “in transition”, but it would be incorrect to say that the bit has a value of, say, 0.5 during the transition. Also remember that quantum mechanics is a way to make statistical predictions of outcomes of certain experiments; it does not claim to explain what is actually happening underneath.
  - joycian 7y ago
    With your second paragraph firmly in the back of my mind: In the sister comment thread, two photon excitation seems to indicate that this intermediate state (0.5 in your coin example) is not invalid. Can you help me understand better? Edit: Also, I think your coin "in transition" implicitly assumes that the system has more degrees of freedom than 1 bit (You can only flip a coin in 3 dimensions).
  - gaze 7y ago
    "it would be incorrect to say that the bit has a value of, say, 0.5 during the transition." In what sense? It has a <z>=0, meaning there's a statistically 50%/50% chance of measuring 1 or 0 but the system is in principle coherent. This means that half way through the jump, if you rotated it 90 degrees, you'd measure a _definite_ z value of -1 or 1, or you'd measure a bit value of 0 or 1, depending on whether you twisted it clockwise or counterclockwise.
    - wnoise 7y ago
      In the sense that it ignores that coherence. Any state on the disc of the Bloch sphere's equator has <z> = 0, and 50:50 chance of measuring 1 or 0. If you want to assign a real value of 0.5 to a bit, then the only one that makes sense is the center, completely decoherent mixture.
  - DiogenesKynikos 7y ago
    I strongly disagree with your second paragraph. Quantum theories do, we think, correspond to what is actually happening underneath. They might not be perfect correspondences, in that our theories are incomplete or approximate, in the same way that Newtonian gravity is an approximation of General Relativity in the weak-gravity regime. Bell's inequality places a strong constraint on what sort of physical theories can explain quantum phenomena. If you believe in locality (the universe has no global variables, and information propagates outwards through local interactions), then the wavefunction is a real thing, and the actual state of the universe.
- gaze 7y ago
  A continuous jump means that the system travels coherently through the superposition of |0>+|1> through the jump, and other such a|0>+b|1> states for a^2+b^2=1. It isn't in 0, and then suddenly 1.
molticrystal 7y ago
While not a perfect analogy, if I understand this properly, essentially if electrons jumping states were pitching in an unregulated game of baseball, the chances a pitcher will toss the ball increases as time goes on and previously we thought the ball just appeared over the plate instantaneously when that random time occurred. But instead, while you still don't know when exactly, you do know there will be a wind up for the pitch before the ball is thrown, and we can see this windup, and we can time things to hit the ball, or shoot the pitcher with a blowdart and keep the pitch from happening. So if there are systems in certain configurations to which this property is applicable to, and if we needed to keep things in that configuration until a time of our choosing, for instance if a state change occurs it would have cascading effects, we can do so.
- joycian 7y ago
  But what mechanism is keeping track of the time since the last pitch?
  - simonh 7y ago
    There doesn’t have to be one. The transitions are random and therefore not influenced by the recency of the last transition, so there’s no need for a ‘memory’. Having said that, the random chance of a transition occurring must be a probability over time. So if there is a fundamental probability, we can ask what is the unit of time over which that probability is expressed? I’m not sure that question makes sense, but maybe it’s the time it takes for the transition to occur, if that is fixed for a given transition?
    - joycian 7y ago
      My question was about the probability governing the chance at a jump. Apparently, it is not constant and takes t as an input. (Otherwise how does it know that it is rising to 1)
      - simonh 7y ago
        Ok, I see, that makes sense. One thing I’d like to know is, does the frequency of transitions correlate to the time it takes for the transition to occur. I’m not sure. There must be some factor that causes one quantum transition to occur more or less frequently than another. That factor isn’t really hidden because we can measure the frequency of transitions, but as far as I know, we don’t understand it’s nature. That factor, whatever it is, may determine the time it takes for the transition to occur but it’s not necessarily like a memory, but more like a trajectory. Clearly something in the quantum state is changing, so it is a system of some sort.
wwarner 7y ago
Amazing. What is the energy of the system while it's in transition? I guess they're arguing superposition of 1 and 0, continuously sliding to a higher likelihood with time. I mean, eventually a photon is emitted, and that can't be continuous. I guess I'll have to read the preprint.
elliekelly 7y ago
Tangentially related request: I’m frequently very impressed with how many HN users seem to have a pretty solid grasp of physics (or maybe the right term is quantum mechanics?) and I’d love to be able to follow along but my science education more or else ended with high school. Could anyone recommend a good resource for someone with zero knowledge of this space to get very basic foundation?
- plokiju 7y ago
  I just finished "Now: The Physics of Time" by Robert Muller. I have mixed feelings about the book, especially the chapters devoted to the author's interpretation of philosophy. I did enjoy hearing a history/overview of modern physics from someone in the field though, and it was a very approachable book. He was very clear about the open questions in quantum mechanics instead of hand-waving them away, which I appreciated. I'm sure other books like Stephen Hawking's "A Brief history of Time" would be a good starting place too, but I can't speak to that one personally yet.
- blojayble 7y ago
  Quantum Mechanics: The Theoretical Minimum by Susskind Leonard could be a start.
- wwarner 7y ago
  I'll recommend Kip Thorne's Black Holes and Time Warps https://en.wikipedia.org/wiki/Black_Holes_and_Time_Warps https://en.wikipedia.org/wiki/Black_Holes_and_Time_Warps . It's about gravity, not quantum field theory, but it's still very sound, very intuitive and explains the principles of the LIGO gravity wave detector. Also contains a bit of speculation about the culture and psychology of scientific creativity which I thought was great. If you find a similar book on quantum phenomena, please post it!
- jcroll 7y ago
  Follow this blog: https://www.forbes.com/sites/startswithabang/#13cf5cce2c5e https://www.forbes.com/sites/startswithabang/#13cf5cce2c5e I spent a couple months going through its backdated articles and it was a great read
- 7y ago
pontifier 7y ago
I like the way they circumvented observation of the dark state. Very clever, and a very interesting result. There seems to be some sort of "hidden variable" there... can anyone explain it?
- woodandsteel 7y ago
  If I am understanding the article correctly, there is no hidden variable implied. Quantum physics claims changes are random, with nothing precise and determinate underneath that causes this. Think of the example of flipping a coin. It's random, but for each flip if you had exact data for the movement of the coin as it left your hand, you would presumably be able to predict if it would land heads or tails. Quantum physics claims that for events at the quantum level, there is nothing definite underneath that determines what will happen, it is just fundamental randomness. The hidden variable idea is that there is something definite underneath, we just haven't discovered it yet. What the experiment seems to have found is only that the probability of an event occurring changes smoothly over time from 0 to 1, not that there is some underlying exact cause for what the probability is at a given point in time.
  - pontifier 7y ago
    They detected a quiet period of slower transitions before the spontaneous drop to the middle state... this implies that "something" happens prior to the transition. They were able to detect this "something", and even prevent the state change. In my mind, that "something" represents a hidden state or something like it within the synthetic atom.
    - woodandsteel 7y ago
      The trouble is there are some strong arguments against that idea, so quantum physicists tend to assume that such "somethings" just don't exist. Yes, that is very counter-intuitive, but that is one reason quantum physics is so weird.
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Ono-Sendai 7y ago
well, obviously. This was always pretty clear to anyone who put some serious thought into it. Did anyone really think electrons just magically jump from state to state? There is a real physical process there that takes time.
- baq 7y ago
  I salute you if there’s anything clear to you in quantum physics...
  - Ono-Sendai 7y ago
    I have made some simulations of quantum 'jumps'. Although the veracity of the simulation could be debated, it's pretty clear what's happening when you see it in action. Some day i'll write it up in a blog post and put the videos on youtube.
- brummm 7y ago
  I mean, the paper just describes an experiment that confirmed the theory that's from the 90s. So it's definitely not a surprise, since this behaviour was expected...
  - woodandsteel 7y ago
    Theories are often mistaken, and this particular theory had not been previously confirmed. Were you really unaware that theories are often mistaken? Or perhaps you were making a joke.
- cjfd 7y ago
  Yes, that is a very good point. The 'quantum leap' thing comes from the origin of quantum mechanics when things were not well understood and a struggle for understanding was going on and crude concepts were introduced. The more correct theory for atomic decays has been known to be quantum electrodynamics for a long time now. Since an atom is a thing that extends over some space the Feynman diagrams that contribute to it have multiple vertices and the whole thing clearly should be extended over space and time. It is nice to have experimental confirmation of this but it really is quite the opposite of unexpected.
Xcelerate 7y ago
I guess I’m kind of confused on what the discovery is; we have a quantum system evolving unitarily from one state at t_0 to another state at t, and the probability of measuring the system in one of two discrete states changes continuously as well (despite the actual measurement outcome being discrete). I thought this has been known for a long time, implied by the time dependent Schrodinger equation, so I didn’t quite catch from the Quanta article what is new, mathematically. Can anyone clarify?
- pdonis 7y ago
  > I didn’t quite catch from the Quanta article what is new, mathematically Nothing is new. This experiment is simply confirming a prediction of standard QM. All the talk about "quantum jumps" and how something has supposedly changed about the way we understand them is just pop science reporters misunderstanding the actual science.
- asplake 7y ago
  I can’t myself, but Ars Technica’s take: https://arstechnica.com/science/2019/06/following-schrodingers-cat-to-its-death-and-giving-it-a-reprieve/ https://arstechnica.com/science/2019/06/following-schrodinge...
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rotrux 7y ago
Here's an interesting passage: > "The strategy reveals that quantum measurement is not about the physical perturbation induced by the probe but about what you know (and what you leave unknown) as a result. “Absence of an event can bring as much information as its presence,” said Devoret."
AnimalMuppet 7y ago
If a quantum system is going to transition between two states that have different energy, would we not expect it to take a time specified by the Heisenberg Uncertainty Principle? If the change in energy is delta E, would we not expect the transition to take delta T = h bar/delta E?
- pdonis 7y ago
  > would we not expect it to take a time specified by the Heisenberg Uncertainty Principle? There isn't actually an energy-time version of the uncertainty principle, at least not the simple one you're assuming here, although many pop science presentations talk as if there is. A good article discussing this is here: http://www.math.ucr.edu/home/baez/uncertainty.html http://www.math.ucr.edu/home/baez/uncertainty.html For a quantum system transitioning between states, the probability of transition in general will vary as a function of time; how it varies depends on the specific state of the system. There is no general rule that relates the expected transition time to the change in energy. (Note also that not all transitions are between energy eigenstates.)
- effie 7y ago
  No, the time to complete one transition is the inverse of Rabi frequency, which is actually determined by strength of external field and nature of the transition (its dipole moment matrix elements), see e.g. https://en.wikipedia.org/wiki/Rabi_frequency https://en.wikipedia.org/wiki/Rabi_frequency
trurl42 7y ago
As a quantum physicist: This might be an interesting experiment, but as far as the theory goes, this is exactly what is to be expected from standard quantum mechanics. Quantum leaps being instantaneous would be a (possibly common) misconception. The leap in a quantum leap is describing the notion of a discrete jump in measurement outcomes.
- neaanopri 7y ago
  Okay, so you're a quantum physicist and you can answer my question! My understanding of QM is that a quantum's system's state is suddenly and discontinuously changed by a measurement. My understanding of this article is a bit confused, and I think that there are two possible things we could be seeing: 1. Quantum collapses of superpositions actually do take time ("This Changes Everything") 2. This particular quantum system is not actually being measured, but is oscillating in superposition in some odd way. ("Just a Particular System") Which case is it?
  - trurl42 7y ago
    That would be 2. What's done in such an experiment is that we initialize a quantum state in a particular state (that this is possible is not actually obvious, but let's assume it's true) and then we make a lot of repeated measurements after different amounts of times. So we're not talking about a single system, but instead about statistics about a set of measurements with systems that have been set up in the same initial state. (Each system only being measured once after a certain time after it's being set up).
    - neaanopri 7y ago
      Gotcha, so the ideas of "Shut Up and Calculate" QM about wavefunction collapse for ideal systems aren't incomplete.
  - gaze 7y ago
    The system is being measured, collapses DO take time, but this is not news to people who study certain branches of quantum information. The experiment confirming it though is a breakthrough.
maxharris 7y ago
If you're a lay person like me and you want to make sense of this, read "Einstein’s Unfinished Revolution: The Search for What Lies Beyond the Quantum" by Lee Smolin. It was just published recently, and it anticipates this result! https://www.penguinrandomhouse.com/books/316818/einsteins-unfinished-revolution-by-lee-smolin/9781594206191/ https://www.penguinrandomhouse.com/books/316818/einsteins-un...
- outlace 7y ago
  I just it but don’t recall where he predicted this. Do you remember what he said?
coldcode 7y ago
In physics if you wait long enough, everything you know will have changed: often it happens on many scales at once.
songeater 7y ago
Does this imply anything about the Many Worlds Interpretation [1]? I am not a physicist (IANAP?), but if states change continuously vs discretely... should that not discount MWI? [1]: https://en.wikipedia.org/wiki/Many-worlds_interpretation https://en.wikipedia.org/wiki/Many-worlds_interpretation
- gaze 7y ago
  It does not. The could be a continuum of universes... or something.
bladedtoys 7y ago
>..to be instantaneous... By which frame of reference? I never understood the language around "instantaneous". Isn't simultaneity relative? So that where one frame of reference says two events are simultaneous, there or others that say they are not?
- effie 7y ago
  The old quantum theory was developed in non-relativistic setting, so this was not a concern. But you are right, relativity complicates lots of things in quantum theory, including the idea of "instantaneous" quantum jumps. In relativity, if some event is to be universally instantaneous, then it has to happen at a single point of space. Which is possible with point particles, but then you get the problem how those point particles can find each other to interact at a single point so often as measured cross sections indicate... perhaps they are not exactly points, but waves, but then we can't have instantaneous events, the event has to happen to the wave in big region of space where simultaneity is relative.
- Dylan16807 7y ago
  Simultaneity is only relative when events A and B are far enough apart that it would have been impossible for light to get from one to the other between the two events. When there is a single location, it's objective whether something has zero or nonzero duration. And while observers disagree on their personal measurements of duration, they will always agree about what a clock sitting at the location will measure.
sova 7y ago
"Natura Facit Saltus or No" was something Schrodinger wrote in 1952! (does nature jump or no?) Of course it's a continuous process, how else would water flow? As they mention in the article, here's the link to Schrodinger's paper "ARE THERE QUANTUM LEAPS?" https://academic.oup.com/bjps/article-abstract/III/11/233/1456020 https://academic.oup.com/bjps/article-abstract/III/11/233/14...
kgwgk 7y ago
“Another text saying that the founding fathers of quantum mechanics were not only wrong but idiots, as some current geniuses revealed. In reality, it's the other way around, of course. [...] I don't think it makes sense for me to discuss the paper and Ball's summary more deeply. One would have to correct every sentence that is wrong or at least misleading – which is basically every sentence both in Ball's text as well as the text in Nature.“ https://motls.blogspot.com/2019/06/experimenters-and-especially.html https://motls.blogspot.com/2019/06/experimenters-and-especia...
- deepspace 7y ago
  Any statement by Motl regarding the work of other physicists should be taken with a heap of salt. https://rationalwiki.org/wiki/Lubo%C5%A1_Motl https://rationalwiki.org/wiki/Lubo%C5%A1_Motl
drenvuk 7y ago
My undereducated guess is that there is nothing random about it. We just don't understand the underlying workings of the system enough yet.
- Simon_says 7y ago
  Your view was the consensus view among physicists until Bell's Inequality was verified to be violated. Now it's the minority view.
lisper 7y ago
This headline is deeply misleading. It is true that energy states are quantized. It does NOT follow that the transition between them is "instantaneous". The transition has always been known to be gradual, but the "gradualness" is not a smooth transition in the energy of the system, it's a smooth transition between being in one energy state to being in a superposition of two energy states to being entirely in the second energy state. That process plays out over (typically a very short but nonetheless non-zero) time. This has been known since the very beginning of QM. What's news here is that this transition, which has always been predicted by theory, has been experimentally observed for the first time.
- soulofmischief 7y ago
  Thank you. I was extremely confused by the proposition because yes, it's known that energy states are quantized but I've never heard of any popular literature before suggesting the transition itself was quantized. Intuitively it doesn't even make sense that it could be quantized. Was this a popular scientific opinion?
  - lisper 7y ago
    I can't figure out what the antecedent of "this" is. But like I said, the fact that quantum jumps are not instantaneous is not and has never been controversial AFAIK.
    - lisper 7y ago
      UPDATE: It turns out that in the VERY early days of QM, some researchers (notably Niels Bohr) thought that quantum jumps were instantaneous. But it has been known and universally accepted that they are not for decades now.
- posix_compliant 7y ago
  I have questions: you describe the change of states of particle as "a smooth transition between being in one energy state to being in a superposition of two energy states to being entirely in the second energy state." At the terminus of this transition, is the particle no longer in a superposition? IE there is now a 100% chance it's in the second state and 0% chance that it's in the original state? If so, does that imply that the function of the particle's state (with respect to time) is discontinuous? Since there's a point at which it goes from being a superposition to exactly 0%.
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nixarian 7y ago
oh boy

218 points by _Microft 7y ago

amatus 7y ago

Preprint: https://arxiv.org/abs/1803.00545 https://arxiv.org/abs/1803.00545

xwdv 7y ago

I feel like this could have profound implications on a macro level, but I’m not sure what.

joycian 7y ago

Uhm...forgive me for asking, but a continuous quantum jump is...what exactly? How is this in any way consistent with the rest of quantum mechanics? Edit: I don't mean to sound snide, I am genuinely confused about what this experiment means.

Anon84 7y ago
This is a common misconception. Quantum jump are jumps between two stable levels... there's nothing preventing "jumps" to unstable states, the particle just doesn't stay long in that specific state (although it can stay there long enough to be useful as in the case of two-photon absorption [0] and microscopy [1]). If I understand it correctly, what this seems to imply is that it's not so much a (discontinuous) jump but rather a continuous(-ish) transition from one state to another. [0] https://en.wikipedia.org/wiki/Two-photon_absorption https://en.wikipedia.org/wiki/Two-photon_absorption [1] https://en.wikipedia.org/wiki/Two-photon_excitation_microscopy https://en.wikipedia.org/wiki/Two-photon_excitation_microsco...
- joycian 7y ago
  But in a quantum harmonic oscillator, the energy levels can only be certain values. As in the Hamiltonian is: H = omega*planckbar(N + 0.5) where N is the state counter (number operator). As a direct reply to your links: So did the fact that two photon excitation works then not make this entire paper not that interesting or novel?
  - pas 7y ago
    The interesting bit is the experiment here as far as I know, but that is completely consistent with QM (basically validates it). https://www.reddit.com/r/slatestarcodex/comments/bwlhh9/anyone_who_understands_quantum_physics_how/ https://www.reddit.com/r/slatestarcodex/comments/bwlhh9/anyo...
trevyn 7y ago
It’s a process of transition between two distinct states. Say a bit flips from 0 to 1; there is a short time period during which that bit is physically “in transition”, but it would be incorrect to say that the bit has a value of, say, 0.5 during the transition. Also remember that quantum mechanics is a way to make statistical predictions of outcomes of certain experiments; it does not claim to explain what is actually happening underneath.
- joycian 7y ago
  With your second paragraph firmly in the back of my mind: In the sister comment thread, two photon excitation seems to indicate that this intermediate state (0.5 in your coin example) is not invalid. Can you help me understand better? Edit: Also, I think your coin "in transition" implicitly assumes that the system has more degrees of freedom than 1 bit (You can only flip a coin in 3 dimensions).
- gaze 7y ago
  "it would be incorrect to say that the bit has a value of, say, 0.5 during the transition." In what sense? It has a <z>=0, meaning there's a statistically 50%/50% chance of measuring 1 or 0 but the system is in principle coherent. This means that half way through the jump, if you rotated it 90 degrees, you'd measure a _definite_ z value of -1 or 1, or you'd measure a bit value of 0 or 1, depending on whether you twisted it clockwise or counterclockwise.
  - wnoise 7y ago
    In the sense that it ignores that coherence. Any state on the disc of the Bloch sphere's equator has <z> = 0, and 50:50 chance of measuring 1 or 0. If you want to assign a real value of 0.5 to a bit, then the only one that makes sense is the center, completely decoherent mixture.
- DiogenesKynikos 7y ago
  I strongly disagree with your second paragraph. Quantum theories do, we think, correspond to what is actually happening underneath. They might not be perfect correspondences, in that our theories are incomplete or approximate, in the same way that Newtonian gravity is an approximation of General Relativity in the weak-gravity regime. Bell's inequality places a strong constraint on what sort of physical theories can explain quantum phenomena. If you believe in locality (the universe has no global variables, and information propagates outwards through local interactions), then the wavefunction is a real thing, and the actual state of the universe.
gaze 7y ago
A continuous jump means that the system travels coherently through the superposition of |0>+|1> through the jump, and other such a|0>+b|1> states for a^2+b^2=1. It isn't in 0, and then suddenly 1.

molticrystal 7y ago

While not a perfect analogy, if I understand this properly, essentially if electrons jumping states were pitching in an unregulated game of baseball, the chances a pitcher will toss the ball increases as time goes on and previously we thought the ball just appeared over the plate instantaneously when that random time occurred. But instead, while you still don't know when exactly, you do know there will be a wind up for the pitch before the ball is thrown, and we can see this windup, and we can time things to hit the ball, or shoot the pitcher with a blowdart and keep the pitch from happening. So if there are systems in certain configurations to which this property is applicable to, and if we needed to keep things in that configuration until a time of our choosing, for instance if a state change occurs it would have cascading effects, we can do so.

joycian 7y ago
But what mechanism is keeping track of the time since the last pitch?
- simonh 7y ago
  There doesn’t have to be one. The transitions are random and therefore not influenced by the recency of the last transition, so there’s no need for a ‘memory’. Having said that, the random chance of a transition occurring must be a probability over time. So if there is a fundamental probability, we can ask what is the unit of time over which that probability is expressed? I’m not sure that question makes sense, but maybe it’s the time it takes for the transition to occur, if that is fixed for a given transition?
  - joycian 7y ago
    My question was about the probability governing the chance at a jump. Apparently, it is not constant and takes t as an input. (Otherwise how does it know that it is rising to 1)
    - simonh 7y ago
      Ok, I see, that makes sense. One thing I’d like to know is, does the frequency of transitions correlate to the time it takes for the transition to occur. I’m not sure. There must be some factor that causes one quantum transition to occur more or less frequently than another. That factor isn’t really hidden because we can measure the frequency of transitions, but as far as I know, we don’t understand it’s nature. That factor, whatever it is, may determine the time it takes for the transition to occur but it’s not necessarily like a memory, but more like a trajectory. Clearly something in the quantum state is changing, so it is a system of some sort.

wwarner 7y ago

Amazing. What is the energy of the system while it's in transition? I guess they're arguing superposition of 1 and 0, continuously sliding to a higher likelihood with time. I mean, eventually a photon is emitted, and that can't be continuous. I guess I'll have to read the preprint.

elliekelly 7y ago

Tangentially related request: I’m frequently very impressed with how many HN users seem to have a pretty solid grasp of physics (or maybe the right term is quantum mechanics?) and I’d love to be able to follow along but my science education more or else ended with high school. Could anyone recommend a good resource for someone with zero knowledge of this space to get very basic foundation?

plokiju 7y ago
I just finished "Now: The Physics of Time" by Robert Muller. I have mixed feelings about the book, especially the chapters devoted to the author's interpretation of philosophy. I did enjoy hearing a history/overview of modern physics from someone in the field though, and it was a very approachable book. He was very clear about the open questions in quantum mechanics instead of hand-waving them away, which I appreciated. I'm sure other books like Stephen Hawking's "A Brief history of Time" would be a good starting place too, but I can't speak to that one personally yet.
blojayble 7y ago
Quantum Mechanics: The Theoretical Minimum by Susskind Leonard could be a start.
wwarner 7y ago
I'll recommend Kip Thorne's Black Holes and Time Warps https://en.wikipedia.org/wiki/Black_Holes_and_Time_Warps https://en.wikipedia.org/wiki/Black_Holes_and_Time_Warps . It's about gravity, not quantum field theory, but it's still very sound, very intuitive and explains the principles of the LIGO gravity wave detector. Also contains a bit of speculation about the culture and psychology of scientific creativity which I thought was great. If you find a similar book on quantum phenomena, please post it!
jcroll 7y ago
Follow this blog: https://www.forbes.com/sites/startswithabang/#13cf5cce2c5e https://www.forbes.com/sites/startswithabang/#13cf5cce2c5e I spent a couple months going through its backdated articles and it was a great read
7y ago

pontifier 7y ago

I like the way they circumvented observation of the dark state. Very clever, and a very interesting result. There seems to be some sort of "hidden variable" there... can anyone explain it?

woodandsteel 7y ago
If I am understanding the article correctly, there is no hidden variable implied. Quantum physics claims changes are random, with nothing precise and determinate underneath that causes this. Think of the example of flipping a coin. It's random, but for each flip if you had exact data for the movement of the coin as it left your hand, you would presumably be able to predict if it would land heads or tails. Quantum physics claims that for events at the quantum level, there is nothing definite underneath that determines what will happen, it is just fundamental randomness. The hidden variable idea is that there is something definite underneath, we just haven't discovered it yet. What the experiment seems to have found is only that the probability of an event occurring changes smoothly over time from 0 to 1, not that there is some underlying exact cause for what the probability is at a given point in time.
- pontifier 7y ago
  They detected a quiet period of slower transitions before the spontaneous drop to the middle state... this implies that "something" happens prior to the transition. They were able to detect this "something", and even prevent the state change. In my mind, that "something" represents a hidden state or something like it within the synthetic atom.
  - woodandsteel 7y ago
    The trouble is there are some strong arguments against that idea, so quantum physicists tend to assume that such "somethings" just don't exist. Yes, that is very counter-intuitive, but that is one reason quantum physics is so weird.

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Ono-Sendai 7y ago

well, obviously. This was always pretty clear to anyone who put some serious thought into it. Did anyone really think electrons just magically jump from state to state? There is a real physical process there that takes time.

baq 7y ago
I salute you if there’s anything clear to you in quantum physics...
- Ono-Sendai 7y ago
  I have made some simulations of quantum 'jumps'. Although the veracity of the simulation could be debated, it's pretty clear what's happening when you see it in action. Some day i'll write it up in a blog post and put the videos on youtube.
brummm 7y ago
I mean, the paper just describes an experiment that confirmed the theory that's from the 90s. So it's definitely not a surprise, since this behaviour was expected...
- woodandsteel 7y ago
  Theories are often mistaken, and this particular theory had not been previously confirmed. Were you really unaware that theories are often mistaken? Or perhaps you were making a joke.
cjfd 7y ago
Yes, that is a very good point. The 'quantum leap' thing comes from the origin of quantum mechanics when things were not well understood and a struggle for understanding was going on and crude concepts were introduced. The more correct theory for atomic decays has been known to be quantum electrodynamics for a long time now. Since an atom is a thing that extends over some space the Feynman diagrams that contribute to it have multiple vertices and the whole thing clearly should be extended over space and time. It is nice to have experimental confirmation of this but it really is quite the opposite of unexpected.

Xcelerate 7y ago

I guess I’m kind of confused on what the discovery is; we have a quantum system evolving unitarily from one state at t_0 to another state at t, and the probability of measuring the system in one of two discrete states changes continuously as well (despite the actual measurement outcome being discrete). I thought this has been known for a long time, implied by the time dependent Schrodinger equation, so I didn’t quite catch from the Quanta article what is new, mathematically. Can anyone clarify?

pdonis 7y ago
> I didn’t quite catch from the Quanta article what is new, mathematically Nothing is new. This experiment is simply confirming a prediction of standard QM. All the talk about "quantum jumps" and how something has supposedly changed about the way we understand them is just pop science reporters misunderstanding the actual science.
asplake 7y ago
I can’t myself, but Ars Technica’s take: https://arstechnica.com/science/2019/06/following-schrodingers-cat-to-its-death-and-giving-it-a-reprieve/ https://arstechnica.com/science/2019/06/following-schrodinge...

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rotrux 7y ago

Here's an interesting passage: > "The strategy reveals that quantum measurement is not about the physical perturbation induced by the probe but about what you know (and what you leave unknown) as a result. “Absence of an event can bring as much information as its presence,” said Devoret."

AnimalMuppet 7y ago

If a quantum system is going to transition between two states that have different energy, would we not expect it to take a time specified by the Heisenberg Uncertainty Principle? If the change in energy is delta E, would we not expect the transition to take delta T = h bar/delta E?

pdonis 7y ago
> would we not expect it to take a time specified by the Heisenberg Uncertainty Principle? There isn't actually an energy-time version of the uncertainty principle, at least not the simple one you're assuming here, although many pop science presentations talk as if there is. A good article discussing this is here: http://www.math.ucr.edu/home/baez/uncertainty.html http://www.math.ucr.edu/home/baez/uncertainty.html For a quantum system transitioning between states, the probability of transition in general will vary as a function of time; how it varies depends on the specific state of the system. There is no general rule that relates the expected transition time to the change in energy. (Note also that not all transitions are between energy eigenstates.)
effie 7y ago
No, the time to complete one transition is the inverse of Rabi frequency, which is actually determined by strength of external field and nature of the transition (its dipole moment matrix elements), see e.g. https://en.wikipedia.org/wiki/Rabi_frequency https://en.wikipedia.org/wiki/Rabi_frequency

trurl42 7y ago

As a quantum physicist: This might be an interesting experiment, but as far as the theory goes, this is exactly what is to be expected from standard quantum mechanics. Quantum leaps being instantaneous would be a (possibly common) misconception. The leap in a quantum leap is describing the notion of a discrete jump in measurement outcomes.

neaanopri 7y ago
Okay, so you're a quantum physicist and you can answer my question! My understanding of QM is that a quantum's system's state is suddenly and discontinuously changed by a measurement. My understanding of this article is a bit confused, and I think that there are two possible things we could be seeing: 1. Quantum collapses of superpositions actually do take time ("This Changes Everything") 2. This particular quantum system is not actually being measured, but is oscillating in superposition in some odd way. ("Just a Particular System") Which case is it?
- trurl42 7y ago
  That would be 2. What's done in such an experiment is that we initialize a quantum state in a particular state (that this is possible is not actually obvious, but let's assume it's true) and then we make a lot of repeated measurements after different amounts of times. So we're not talking about a single system, but instead about statistics about a set of measurements with systems that have been set up in the same initial state. (Each system only being measured once after a certain time after it's being set up).
  - neaanopri 7y ago
    Gotcha, so the ideas of "Shut Up and Calculate" QM about wavefunction collapse for ideal systems aren't incomplete.
- gaze 7y ago
  The system is being measured, collapses DO take time, but this is not news to people who study certain branches of quantum information. The experiment confirming it though is a breakthrough.

maxharris 7y ago

If you're a lay person like me and you want to make sense of this, read "Einstein’s Unfinished Revolution: The Search for What Lies Beyond the Quantum" by Lee Smolin. It was just published recently, and it anticipates this result! https://www.penguinrandomhouse.com/books/316818/einsteins-unfinished-revolution-by-lee-smolin/9781594206191/ https://www.penguinrandomhouse.com/books/316818/einsteins-un...

outlace 7y ago
I just it but don’t recall where he predicted this. Do you remember what he said?

coldcode 7y ago

In physics if you wait long enough, everything you know will have changed: often it happens on many scales at once.

songeater 7y ago

Does this imply anything about the Many Worlds Interpretation [1]? I am not a physicist (IANAP?), but if states change continuously vs discretely... should that not discount MWI? [1]: https://en.wikipedia.org/wiki/Many-worlds_interpretation https://en.wikipedia.org/wiki/Many-worlds_interpretation

gaze 7y ago
It does not. The could be a continuum of universes... or something.

bladedtoys 7y ago

>..to be instantaneous... By which frame of reference? I never understood the language around "instantaneous". Isn't simultaneity relative? So that where one frame of reference says two events are simultaneous, there or others that say they are not?

effie 7y ago
The old quantum theory was developed in non-relativistic setting, so this was not a concern. But you are right, relativity complicates lots of things in quantum theory, including the idea of "instantaneous" quantum jumps. In relativity, if some event is to be universally instantaneous, then it has to happen at a single point of space. Which is possible with point particles, but then you get the problem how those point particles can find each other to interact at a single point so often as measured cross sections indicate... perhaps they are not exactly points, but waves, but then we can't have instantaneous events, the event has to happen to the wave in big region of space where simultaneity is relative.
Dylan16807 7y ago
Simultaneity is only relative when events A and B are far enough apart that it would have been impossible for light to get from one to the other between the two events. When there is a single location, it's objective whether something has zero or nonzero duration. And while observers disagree on their personal measurements of duration, they will always agree about what a clock sitting at the location will measure.

sova 7y ago

"Natura Facit Saltus or No" was something Schrodinger wrote in 1952! (does nature jump or no?) Of course it's a continuous process, how else would water flow? As they mention in the article, here's the link to Schrodinger's paper "ARE THERE QUANTUM LEAPS?" https://academic.oup.com/bjps/article-abstract/III/11/233/1456020 https://academic.oup.com/bjps/article-abstract/III/11/233/14...

kgwgk 7y ago

“Another text saying that the founding fathers of quantum mechanics were not only wrong but idiots, as some current geniuses revealed. In reality, it's the other way around, of course. [...] I don't think it makes sense for me to discuss the paper and Ball's summary more deeply. One would have to correct every sentence that is wrong or at least misleading – which is basically every sentence both in Ball's text as well as the text in Nature.“ https://motls.blogspot.com/2019/06/experimenters-and-especially.html https://motls.blogspot.com/2019/06/experimenters-and-especia...

deepspace 7y ago
Any statement by Motl regarding the work of other physicists should be taken with a heap of salt. https://rationalwiki.org/wiki/Lubo%C5%A1_Motl https://rationalwiki.org/wiki/Lubo%C5%A1_Motl

drenvuk 7y ago

My undereducated guess is that there is nothing random about it. We just don't understand the underlying workings of the system enough yet.

Simon_says 7y ago
Your view was the consensus view among physicists until Bell's Inequality was verified to be violated. Now it's the minority view.

lisper 7y ago

This headline is deeply misleading. It is true that energy states are quantized. It does NOT follow that the transition between them is "instantaneous". The transition has always been known to be gradual, but the "gradualness" is not a smooth transition in the energy of the system, it's a smooth transition between being in one energy state to being in a superposition of two energy states to being entirely in the second energy state. That process plays out over (typically a very short but nonetheless non-zero) time. This has been known since the very beginning of QM. What's news here is that this transition, which has always been predicted by theory, has been experimentally observed for the first time.

soulofmischief 7y ago
Thank you. I was extremely confused by the proposition because yes, it's known that energy states are quantized but I've never heard of any popular literature before suggesting the transition itself was quantized. Intuitively it doesn't even make sense that it could be quantized. Was this a popular scientific opinion?
- lisper 7y ago
  I can't figure out what the antecedent of "this" is. But like I said, the fact that quantum jumps are not instantaneous is not and has never been controversial AFAIK.
  - lisper 7y ago
    UPDATE: It turns out that in the VERY early days of QM, some researchers (notably Niels Bohr) thought that quantum jumps were instantaneous. But it has been known and universally accepted that they are not for decades now.
posix_compliant 7y ago
I have questions: you describe the change of states of particle as "a smooth transition between being in one energy state to being in a superposition of two energy states to being entirely in the second energy state." At the terminus of this transition, is the particle no longer in a superposition? IE there is now a 100% chance it's in the second state and 0% chance that it's in the original state? If so, does that imply that the function of the particle's state (with respect to time) is discontinuous? Since there's a point at which it goes from being a superposition to exactly 0%.

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nixarian 7y ago

oh boy