Worked Out Example of Consecutive Observations in QM

In summary, the conversation discusses how measurement or observation affects the wave function in quantum mechanics. Different approaches and models are mentioned, but there is a lack of clear explanation and a need for further development in this area. The idea of an observation operator is mentioned, but it is not commonly used in quantum mechanics, possibly due to the focus on single observations. A suggestion is made to refer to other sources for a more comprehensive understanding.
  • #1
boderam
24
0
I know that in QM, one observation like position will alter the wavefunction so that momentum changes. But how do we see this mathematically when we include time dependence, whether in matrix mechanics or wave mechanics? Is it as simple as writing PQx where x is the state, Q position matrix, P momentum matrix? How do we include the time dependence in the matrices, i.e. so the P measurement is done t seconds after Q? Thanks.
 
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  • #2
There are several methods. They differ by the way "observation" is described. Some of them are consistent, other not so. Notice that Qx has very little to do with "observation of the position". You need to have a model of a measurement first. Then you need to find out whether your model is compatible with what is being observed in reality.

An approximate effect of the action of a position detector put at the point x=a and activated at the moment t=t0, and only at that moment, will be changing the Schrodinger wave function at t=t0 by multiplying it by a Gaussian function of x centered at x=a, and of the width corresponding to the resolution of the detector. After that you can continue your Schrodinger evolution. But that is only an approximation, not a very realistic one, if only because no real detector is activated just for an instant of time of zero width.
 
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  • #3
arkajad said:
There are several methods. They differ by the way "observation" is described. Some of them are consistent, other not so. Notice that Qx has very little to do with "observation of the position". You need to have a model of a measurement first. Then you need to find out whether your model is compatible with what is being observed in reality.

An approximate effect of the action of a position detector put at the point x=a and activated at the moment t=t0, and only at that moment, will be changing the Schrodinger wave function at t=t0 by multiplying it by a Gaussian function of x centered at x=a, and of the width corresponding to the resolution of the detector. After that you can continue your Schrodinger evolution. But that is only an approximation, not a very realistic one, if only because no real detector is activated just for an instant of time of zero width.

This all is very vague, I find a lot of explanation lacking. I am looking for some sort of formulation where we can have an observation operator of some sort, so when we look at it together with the wave function we have the evolution of the wave function by being changed by the observation. It seems to me that this sort of idea would be well developed yet I haven't seen it very much. Perhaps it is that most of QM is applied to single observations and has no need for such a theory as I am describing? Could you point me to a reference on what you were describing?
 
  • #4
It would be unfair for me to suggest checking my own papers. Just gave you a vague alas neutral reply, hoping that someone else will give you a more objective answer.
 

Related to Worked Out Example of Consecutive Observations in QM

1. What is a worked out example of consecutive observations in quantum mechanics?

A worked out example of consecutive observations in quantum mechanics refers to a scenario where an object or system is observed multiple times in a row, with each observation affecting the outcome of the next one. This is a fundamental concept in quantum mechanics, as it demonstrates the probabilistic nature of quantum systems and the role of observation in determining their behavior.

2. How does consecutive observation in quantum mechanics differ from classical mechanics?

In classical mechanics, the state of a system can be precisely determined through measurements and its behavior can be predicted with certainty. However, in quantum mechanics, the act of observation itself can change the state of the system and introduce uncertainty into its behavior. This is known as the observer effect and is a key distinction between the two theories.

3. Can consecutive observations in quantum mechanics be predicted or controlled?

No, consecutive observations in quantum mechanics cannot be predicted or controlled with certainty. The probabilistic nature of quantum systems means that the outcome of each observation is unpredictable and can only be described in terms of probabilities. This is a fundamental principle in quantum mechanics and is known as the uncertainty principle.

4. What are some real-life applications of consecutive observations in quantum mechanics?

Consecutive observations in quantum mechanics have many practical applications, such as in quantum computing, quantum cryptography, and quantum teleportation. These technologies rely on the probabilistic nature of quantum systems and the ability to manipulate them through observation to perform complex calculations and secure communication.

5. How does the concept of consecutive observations relate to the measurement problem in quantum mechanics?

The measurement problem in quantum mechanics refers to the paradox of how a quantum system can exist in multiple states simultaneously until it is observed, at which point it collapses into a single state. Consecutive observations demonstrate this paradox, as each observation changes the state of the system in an unpredictable way. This highlights the fundamental difference between our intuitive understanding of reality and the probabilistic nature of quantum mechanics.

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