Undergrad Annihilation vs. Creation Operators: What's the Difference?

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Coherent states are defined as eigenstates of the annihilation operator, while there are no eigenstates of the creation operator. This distinction highlights an asymmetry in quantum mechanics, where the basis of states includes a lowest element but lacks a highest one. The essential difference between the two operators lies in their roles in quantum state representation, with annihilation operators corresponding to physical existence. The discussion emphasizes that this is not merely a convention but a fundamental aspect of quantum theory. Understanding this difference is crucial for grasping the nature of quantum states and their behaviors.
gerald V
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Cohererent states are defined as eigenstates of the annihilation operator. Never the creation operator is referred to.

Is this just a convention or is more behind? What is the essential difference between eigenstates of the annihilation- versus the creation operator?

Thank you very much in advance!
 
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There are no eigenstates of the creation operator. The asymmetry between creation and annihilation operators stems from the fact that the ordered basis ##\{|0\rangle, |1\rangle, |2\rangle,\ldots\}## has the first element but not last element.
 
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gerald V said:
What is the essential difference between eigenstates of the annihilation- versus the creation operator?

Existence!
 
Got it. Thank you very much.
 
Time reversal invariant Hamiltonians must satisfy ##[H,\Theta]=0## where ##\Theta## is time reversal operator. However, in some texts (for example see Many-body Quantum Theory in Condensed Matter Physics an introduction, HENRIK BRUUS and KARSTEN FLENSBERG, Corrected version: 14 January 2016, section 7.1.4) the time reversal invariant condition is introduced as ##H=H^*##. How these two conditions are identical?

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