Can we peek at Schrodinger's cat without disturbing it?

Can we peek at Schrodinger's cat without disturbing it?
Since the cat in the box (top left) is in a superposition that means it can be in numerous different states (e.g. dead and/or alive) and is marked with a quantum tag. The photo taken of the cat is entangled with the situation inside of the box. We can decide the fate of the cat by processing the photo in a certain way (bottom left), or we can keep it in superposition by restoring the quantum tag using a different process (bottom right). Credit: Associate Professor Holger F. Hofmann and Emma Buchet/Hiroshima University

Quantum physics is difficult and explaining it even more so. Associate Professor Holger F. Hofmann from Hiroshima University and Kartik Patekar from the Indian Institute of Technology Bombay have tried to solve one of the biggest puzzles in quantum physics: how to measure the quantum system without changing it?

Their new paper published this month has found that by reading the information observed from a away from the system itself researchers can determine its state, depending on the method of analysis. Although the analysis is completely removed from the quantum system, it is possible to restore the initial superposition of possible outcomes by a careful reading of the quantum data.

"Normally we would search for something by looking. But in this case looking changes the object, this is the problem with quantum mechanics. We can use complicated maths to describe it, but how can we be sure that the mathematics describes what is really there? When we measure something there is a trade-off and the other possibilities of what it could be are lost. You cannot find out about anything without an interaction, you pay a price in advance." explains Hofmann.

During Patekar's month-long stay at Hiroshima University when he was an , the two physicists tried to imagine ways of measuring the system without "paying the price" i.e. keeping the system's superposition or meaning that the system can exist in all states. In order to understand their results Hofmann describes their findings using the well-known physics story of Schrödinger's cat:

Schrödinger's cat is in a box and the scientists don't know whether it is dead or alive. A camera is set up looking into the box that takes a photo from a position outside of the box. The photo taken of the cat comes out blurry; we can see there is a cat but not whether it is dead or alive. The flash from the camera has also removed a "quantum tag" marking the superposition of the cat. This photo is now entangled with the fate of the cat—i.e. we can decide what happened to the cat by processing this photo in a certain way.

The photo could then be taken away from the box and processed on a computer or in a darkroom. Depending on what method is used to process the photo, we can find out either if the cat is alive or dead, or what the flash did to the cat, restoring the quantum tag. The choice of the reader determines what we know about the cat. We can find out if it's dead/alive or restore the quantum tag that was removed when the picture was taken, but not both.

This is only a step forward in our understanding of quantum mechanics. Today its full application remains confined to expert-level systems like quantum computers, although some of its aspects can also be used in , and for secure communication using quantum cryptography.

"This is a key part of my research. I really wanted to understand why this quantum weirdness is there. I focused on measurements because that's where the weirdness comes from!" says Hofmann.


Explore further

Generation of light in a photon-number quantum superposition

More information: Kartik Patekar et al, The role of system–meter entanglement in controlling the resolution and decoherence of quantum measurements, New Journal of Physics (2019). DOI: 10.1088/1367-2630/ab4451
Journal information: New Journal of Physics

Citation: Can we peek at Schrodinger's cat without disturbing it? (2019, October 2) retrieved 20 October 2019 from https://phys.org/news/2019-10-peek-schrodinger-cat-disturbing.html
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Oct 02, 2019
Nope. If you are extracting information from the system then you are interacting with it. The interaction of photons from the box with the film is an observation by any reasonably definition Game over.

We cannot assume any longer that only the cat is quantum and that the rest of the universe, including the observer is classical. Everything is quantum. The observer, the cat, the box, the apparatus, everything is quantum. The cat is massive entangled with the rest of the universe before it even goes into the box. You cannot think about it isolation.

Oct 02, 2019
Among other things, something that is never brought up. Everything is always in a state of "being observed"! Everything is always interacting with other things and they are interacting with it. Conventionally, that requires signals of sorts. Even if just gravitons, neutrinos. Too, note, it can be said that, since the moment when all began, there have been electromagnetic signals passing between all particles. A soup of sorts of real and virtual photons.
But consider another point. Everyone invokes the idea of an active event, like taking a picture, noting an occurrence. But what of passive signals, inherently emitted by the particle, then picked up. Seeing a footprint, it can be said, rather than taking a picture? If a system is set up, for example, to monitor the gravitational emissions from an object, would that disturb the object being emitted?

Oct 02, 2019
If you could read the cat state then you could also intercept and read any secure quantum message from Alice to Bob.

Oct 02, 2019
So this is like discombobulating someones atoms in a transporter and then reassembling them elsewhere and pretending you havent killed that person to begin with and then created a totally new person out of the ashes of the first one?

IOW are you sure you got everything back in the right place?

Hey julian remember my analogy called 'Collapse of the Waveform Jesus'? That was pretty funny eh? But that was perhaps before jesus knew ye.

Oct 02, 2019
Here was the thread
https://medicalxp...ity.html

-but I see my analogy got deleted when the original otto got discombobulated. Too bad. It was the answer to literally everything in the entire universe.

"They know not what they have done." - otto

Oct 02, 2019
The Schrodinger's cat "thought experiment" is meaningless since the cat was alive while it was placed into the box. Whatever happens to it afterward as a result of being in the box, it is dead as a result of asphyxiation while being in a closed-lid box with no air holes. Thus, the experiment is useless as well as senseless animal cruelty. The RSPCA would not approve of it.

Oct 02, 2019
Is anyone else in agreement with me - I'm honestly getting absolutely fed up hearing about shrodingers cat thought experiment - about as astute as applying the second law of thermodynamics to negentropic life systems - or given the said logic at the time in the Middle Ages the logical debate was of how many angels could fit on the head of a pin ! Please Wake me up when you hear anything different x:)

Oct 02, 2019
Trust me; Angels are much too large to fit on the head of a pin. Not even one. Humans are often silly/foolish who spend their time and brain cells thinking up impossible scenarios full of faerie dust and unicorns. This is why the Middle Ages was a time of transcendental periods interspersed with the search for Truth. And they didn't even need Cannabis.

Oct 02, 2019
Scientists ask - "Can we peek at Schrodinger's cat without disturbing it?"
Philosophers respond - "Can we peek at Schrodinger's cat without being disturbed by it?

Oct 02, 2019
Isn't this just another 'reconstruction' method via inference from the recorded information? For example the Large Hadron Collider at Cern uses a barrage of detectors to acquire information on the 'products' flying out of the collisions and collate/analyse that info via supercomputer/simulations etc and so INFER the original energy/collisional attitude etc etc STATES which would result in the particular ejecta-pattern(s) observed via the detectors?

Oct 02, 2019
This reads like someone's come up with a new formalism for so-called "weak measurements." I'll have to see if I can get to the paper.

Oct 02, 2019
Joy, the paper is open access. So I don't have to rely on the less-than-high-school description in this article. I'll have something to say after I've read the paper. This "quantum tag" might or might not be better described there. I'm also going to check out the journal, but so far they seem to be on the up-and-up.

Oct 02, 2019
This is essentially the Quantum Eraser double slit experiment with entangled photons.
- Dead/Alive == First photon behaves like a particle / wave depending on if you look at the second.
- Flash is the process of creating the entangled pairs.
- Photo is the unknown (blurry) state of the second photon.
- Cat is the other photon.

Oct 02, 2019
Oh forgot, "quantum tag" is just there to confuse the ignorant.

Oct 02, 2019
Oh forgot, "quantum tag" is just there to confuse the ignorant.


Must have f***ed you up big style!

Oct 02, 2019
Hmmm, well, no, it's not a new formalism for weak measurements, as far as I can tell so far. It's associated with the same ideas, but it's broader in scope than that. The quantum logic is a bit difficult so it's taking me a little while to make a synopsis, but I promise not to directly use Schroedinger's Cat, though I may comment on the use of it in this article. I hope they didn't use it in the paper. I'm still reading and ruminating.

Oct 02, 2019
And that should have been, Delayed-Choice Quantum Eraser. https://en.wikipe...m_eraser

Oct 02, 2019
. ........I'm still reading and ruminating.


I've given up, and retreated to music. Just went through the soundtrack to A Clockwork Orange. As one does. A full Beethoven symphony is on the cards! Probably the 9th.

Oct 02, 2019
Beethoven never really did it for me. My favorites are the Strausses and Old Bach. My wife likes Rimsky-Korsakov, but then again she also likes musicals. :P On the other hand, I also like John Cage, so you might very well think the same of me. One modern composer you might want to check out is Morton Subotnick; you will find some very interesting stuff there, though it may not be to your taste. If you like chamber music, you might check out the Turtle Island String Quartet. And I regularly listen to The Rite of Strings, which is a trio of violin, cello, and guitar featuring some musicians you might have heard of.

Oct 02, 2019
Can you change the past? No.

Oct 02, 2019
--MrKP
Sure about that?
There might be a Nobel waiting for you if you can explain the Delayed-Choice Quantum Eraser.

Oct 02, 2019
Beethoven never really did it for me. My favorites are the Strausses and Old Bach. My wife likes Rimsky-Korsakov, but then again she also likes musicals. :P On the other hand, I also like John Cage, so you might very well think the same of me. One modern composer you might want to check out is Morton Subotnick; you will find some very interesting stuff there, though it may not be to your taste. If you like chamber music, you might check out the Turtle Island String Quartet. And I regularly listen to The Rite of Strings, which is a trio of violin, cello, and guitar featuring some musicians you might have heard of.


I'm not the best when it comes to classical. However, some of it has left a....whatsit... on me. Delibes, Flower Duet. Love the 9th. Holst, The Planets, Mars particularly. Vivaldi, The Four Seasons. Usual stuff. Probably Mozart, but my Dad would know better than me!

Oct 02, 2019
Ahhh, but you see, you never see "now." Your measuring devices, if they are entangled with the measurement (and they always must be or how can they measure anything?) will tell you what they saw only after you have read them and by reading them you are entangling the reader with the measuring device. And, more importantly, decohering the measuring device from the original entanglement with the measured system.

Now, since they are entangled and superposed, how precisely do you intend to establish what "happened" in the "past?" Because, you see, there is no measurement until the superposition is decohered and gives a single answer- and your device is doubly entangled with superposed states.

Perhaps you now begin to see why I said I have to read and ruminate a while.

Oct 02, 2019
Delibes: Lakmé - Duo des fleurs (Flower Duet), Sabine Devieilhe & Marianne Crebassa

Just rehearsing. Sigh.............

https://www.youtu...L5AxmK_A

Oct 02, 2019
Fur mich -- Gustav Mahler, Richard Wagner, Holst, und Claude Debussy

@MrKP
If it were possible to change the past, you and everyone else who lives now would never have existed. This is due to the past being "set in stone", so to speak. The past is gone and can never be changed. If it were possible to change it, how far back would you go to make changes? AND if you did that, the person who is doing the changes (YOU) could no longer BE in the present.

Oct 02, 2019
This is a fundamental flaw of Schrodinger's Cat. People use it as a way to describe the strangeness of quantum mechanics when in fact Schrodinger created it to do the opposite.

The point is that it's preposterous that the cat is two states at once, but rather it's one of the two and we just don't know until we look. It's not "both" or some kind of meaningless garbage.

I get it, Pauli exclusion principle and all that, but this isn't to say that elections aren't in definite points of space with definite vectors, because they very much are. That's the whole point of this thought experiment. Probability/uncertainty only exists in models and isn't in any way descriptive of a determinate Universe.

Quantum mechanics only predicts/models behavior: it does not describe it with terms like superposition and entanglement..

Don't confuse a model with reality.

Oct 02, 2019
Take, for instance, in 1619, the first slaves from the African continent were bought from the Arabs and then taken to America. So, for 400 years, Blacks whose ancestors had been slaves have lived in America. They are still complaining about the slavery that their ancestors had undergone, and that's understandable. However, those who are alive NOW would never have been born and existed AT ALL if their ancestors hadn't been brought to America. This is because many Black-Americans also have some White ancestors.
So, it their Black ancestors had never copulated with their White ancestors, there could not have been any descendants born in America.
So, be careful what you wish for......

Oct 02, 2019
-contd-
And, of course, if in 1619 the African slaves that the Arabs owned hadn't been sold to the Whites and brought to America, those slaves would have remained IN AFRICA...as slaves. And that would have changed the whole future of not only America/US, but also the whole world and its history. There are those who just don't seem to understand this principle of the past begetting the future, and if something didn't happen in the past, the whole future is changed.

Oct 02, 2019
Schroedinger's Cat is a thought experiment that assumes the cat is a quantum object. Most of the defects when trying to use it pedagogically with an advanced audience arise from this defect.

But the proof is decades old that in fact, while a cat cannot have a superposed quantum state, quantum particles in fact can. And do.

Much of the best evidence is from quantum optics, but there were earlier hints. Superposition explains both Pauli exclusion and laser coherence.

Pauli exclusion happens only to fermions, that is, matter particles. What it means is that particles of matter, that is particles with half-integer spins, cannot simultaneously occupy the same state. They are prevented from doing so by their probabilities of occupying those states, which for identical particles reduce to zero. Pauli exclusion is supported by many experiments; in fact, those experiments are reproduced every year in physics laboratories by students in universities.
[contd]

Oct 02, 2019
If it were possible to change the past, you .... could no longer BE in the present.

What is the past,
but remnants of time,
etched with memories of
what once were, promises of
what became.
To alter it, is
to unleash chaos, on
a future already seen.

Oct 02, 2019
[contd]
Meanwhile, coherence (in the sense of lasers) only happens to bosons; that is, energy particles with unit spins. What it means is that bosons, unlike fermions, are *more likely* to occupy identical states, rather than less like fermions/matter. They are encouraged by the laws of spin and statistics by their probabilities of occupying those states, which for identical bosons reduce to a probability of 1, or 100%. Coherence of lasers is supported by at least as many experiments as Pauli exclusion, and again, by many experiments reproduced every year in physics laboratories by students in universities.

None of this is cutting edge. It's been being done for decades. Now it's standard practice.

If you want to see the quantum optics that shows this, start with the Delayed Choice Quantum Eraser. Come back and talk about it, @DeadOrAlive, if you still have trouble understanding superposition.

Oct 03, 2019
Oh, and as further observational evidence of superposition, let me offer Bell tests. Once you understand what really has to be happening, you either have to admit to the reality of superposition, or to the reality of non-local effects, that is, superluminal communication between events. So you can either postulate that reality is not local, and admit these superluminal entanglements, or that reality is not real, and admit that these superpositions are real states of real particles, in which case they cannot have both a well-defined position and a well-defined vector at the same time.

The horns of the dilemma.

Oct 03, 2019
Okay, who looked and altered Da Schneibo's quantum state, and now he's someone whose post is actually worth reading.

Oct 03, 2019
Wondering what the impact on spooky action from a distance will be if this is true.

Oct 03, 2019
@antigoracle.
Okay, who looked and altered Da Schneibo's quantum state, and now he's someone whose post is actually worth reading.
You and DS must somehow have become 'quantum entangled', mate! I say that because I have been noticing both his and your posts over the last few days, and (for the most part) both have been, as you put it, "worth reading". I also note that you may have found your forte in amusing wordplay based on double meanings of words (eg, your 'naysaying' some poster's suggestion that Planet Nine is Pluto; simply by your posting of only one German word that is phonetically similar: "Nein"...lol). I especially also noticed an uptick in your polite/reasonable science/logic based comments/observations, @antigoracle. Kudos to both of you. Both of you keep this up, and both of you may soon leave your past indiscretions behind you, forgiven and forgotten. Cheers. :)

Oct 03, 2019
Not bad thread, the parts I can see is mostly discussing the topic (thanks, DS!) for once.

Nope. If you are extracting information from the system then you are interacting with it. The interaction of photons from the box with the film is an observation by any reasonably definition ... The observer, the cat, the box, the apparatus, everything is quantum. The cat is massive entangled with the rest of the universe before it even goes into the box. You cannot think about it isolation.


Your opinion is noted and rejected - by the paper that you did not read. "The choice of
readout in the meter determines the trade-off between irreversible decoherence and measurement information by steering the system into a corresponding set of conditional output states."

It is a delayed choice experiment in the sense of choosing between leaving the original system superpositioned or observing it.

Oct 03, 2019
This is a fundamental flaw of Schrodinger's Cat. People use it as a way to describe the strangeness of quantum mechanics when in fact Schrodinger created it to do the opposite.

The point is that it's preposterous that the cat is two states at once, but rather it's one of the two and we just don't know until we look. It's not "both" or some kind of meaningless garbage.

I get it, Pauli exclusion principle and all that, but this isn't to say that elections aren't in definite points of space with definite vectors, because they very much are. That's the whole point of this thought experiment.


Like the preceding EPR paradox suggestion by Einstein et al who did not like pre-relativistic quantum physics, the Cat was constructed precisely to demonstrate counterintuitive "strangeness" [ https://en.wikipe...%27s_cat ].

And like EPR it fails on Bell tests, showing that there is superposition of states, and no definite positions then but definite laws. QM 101.

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