Only Observables can be in Superposition?

In summary, only observables can be in superposition and classical objects cannot be superposed due to their lack of phase. In the Many Worlds Interpretation, it is possible for a cat to be in a superposition of dead and alive, but it is not clear if this is referring to a true quantum superposition or a mixed state.
  • #1
Varon
548
1
Hi, is it true that only Observables can be in Superposition? Meaning superposition of dead and live cats is invalid by some unknown mathematical reasoning? Jambaugh stated thus in the other forum that only observables can be in superposition. What's the mathematical or quantum logical proof?

"Note my qualification about the temperature is not me merely being pedantic. There is a critical thermodynamic aspect of the measurement process. Note also temperature is a critical aspect of the "cat" when we speak of "alive" vs "dead". These are not properly quantum observables any more than is temperature and so it is not proper to speak of them being in superposition. This aspect is part of what makes the "cat" necessary as a "macroscopic system" for the purpose of the thought experiment. Recall also that the original purpose was to distance the meanings of classical states of reality and the quantum "state vectors" (which in CI do not represent states but rather classes of systems)."
 
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  • #2
Varon said:
Hi, is it true that only Observables can be in Superposition? Meaning superposition of dead and live cats is invalid by some unknown mathematical reasoning? Jambaugh stated thus in the other forum that only observables can be in superposition. What's the mathematical or quantum logical proof?

"Note my qualification about the temperature is not me merely being pedantic. There is a critical thermodynamic aspect of the measurement process. Note also temperature is a critical aspect of the "cat" when we speak of "alive" vs "dead". These are not properly quantum observables any more than is temperature and so it is not proper to speak of them being in superposition. This aspect is part of what makes the "cat" necessary as a "macroscopic system" for the purpose of the thought experiment. Recall also that the original purpose was to distance the meanings of classical states of reality and the quantum "state vectors" (which in CI do not represent states but rather classes of systems)."

Yes, that seems correct. Remember a superposition is *coherent* ... it necessarily involves a well-defined phase relation between the components. You can add states together without the phase relationship to create mixed states ... that is actually what happens to superpositions when they decohere .. they become mixed states. You can mixed states from two pure quantum eigenstates with a 50-50 weighting, so that as for superpositions, half of the measurements on an ensemble of such systems give either value for the observable. However, mixed states do not exhibit quantum phenomena like coherence, interference, or entanglement.

Since classical objects do not have phase, they cannot be superposed. Thus a mixed state is a more appropriate designation for logic constructions like the (dead + alive) cat.
 
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  • #3
SpectraCat said:
Yes, that seems correct. Remember a superposition is *coherent* ... it necessarily involves a well-defined phase relation between the components. You can add states together without the phase relationship to create mixed states ... that is actually what happens to superpositions when they decohere .. they become mixed states. Since classical objects do not have phase, they cannot be superposed. Thus a mixed state is a more appropriate designation for logic constructions like the (dead + alive) cat.

Uhm... how come in Many Worlds Interpretation, cat can be in superposition of dead and alive. I thought MWI just follow the same mathematics as QM. ?
 
  • #4
Varon said:
Uhm... how come in Many Worlds Interpretation, cat can be in superposition of dead and alive. I thought MWI just follow the same mathematics as QM. ?

I don't know much about MWI ... my guess is that it can't be in such a superposition in MWI either ... I doubt you will find that statement in texts by experts, but I could be wrong. Or perhaps they are using "superposition" loosely to include mixed states as well ... I don't know enough about MWI to say for sure. Do measurements on mixed states cause the same kind of branching as measurements on quantum superpositions in MWI?
 

1. What does it mean for an observable to be in superposition?

In quantum mechanics, superposition refers to a state in which a physical system exists in multiple states simultaneously. In the case of observables, this means that the system can have multiple possible values for that observable at the same time.

2. Why can only observables be in superposition in quantum mechanics?

This is because observables, such as position, momentum, or energy, are the properties that can be measured and observed in a physical system. In quantum mechanics, the state of a system is described by a wave function that can be in a superposition of different states. When an observable is measured, the wave function collapses, and the system is observed to have a definite value for that observable.

3. Can macroscopic objects be in superposition?

No, macroscopic objects are too large and complex to exhibit quantum behavior. Superposition is a principle that only applies to the microscopic world of atoms and subatomic particles. As objects become larger and more complex, they are subject to classical mechanics rather than quantum mechanics.

4. How is superposition used in quantum computing?

In quantum computing, superposition is utilized to perform multiple calculations simultaneously. By encoding information in the form of quantum bits, or qubits, a quantum computer can process a vast number of possibilities at once, allowing for faster and more efficient computations.

5. Does superposition violate the laws of physics?

No, superposition is a fundamental principle of quantum mechanics. It does not violate any laws of physics, but it does challenge our understanding of how the physical world works. Superposition is a key aspect of the quantum world that allows for many of the strange and counter-intuitive phenomena observed in quantum systems.

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