Commutation relations of P and H

In summary, the commutation relations of two observables can always be calculated. In the case of P (momentum) and H (Hamiltonian) in infinite square well, the commutator is [P,H] = -dV/dx, which in classical mechanics represents the force. This applies as long as D(AH)∩D(HA)≠ \emptyset and I(H)⊂D(A).
  • #1
orienst
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Can we always calculate the commutation relations of two observables? If so, what’s the commutator of P (momentum) and H (Hamiltonian) in infinite square well, considering that the momentum is not a conserved quantity?
 
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  • #2
For a quantum observable, call it A, it's not important that it doesn;t commute with the Hamiltonian. It only matters that

D(AH)∩D(HA)≠[itex] \emptyset[/itex]

and the domain of the product operator is the subset of D(H), such as

I(H)⊂D(A)
 
  • #3
Remember that [P,.] works like a derivative for x. So, generically, for H = P^2/2m + V(x) where V is any potential, [P,H] = -dV/dx. In classical mechanics, this is the force. For infinite square potential, it gives two delta spikes at the edges of the box.
 

FAQ: Commutation relations of P and H

What are commutation relations of P and H?

The commutation relations of P and H refer to the mathematical relationships between the momentum operator (P) and the Hamiltonian operator (H) in quantum mechanics. These relations dictate how the two operators interact with each other and how they affect the state of a quantum system.

How do the commutation relations of P and H affect quantum systems?

The commutation relations of P and H are fundamental to quantum mechanics and have a significant impact on the behavior of quantum systems. They determine the allowed energy levels and the dynamics of a system, such as the time evolution of a state.

What is the significance of the commutation relations of P and H?

The commutation relations of P and H are crucial for understanding and predicting the behavior of quantum systems. They are used to derive important principles and equations in quantum mechanics, such as the Heisenberg uncertainty principle and the Schrödinger equation.

Are there any exceptions to the commutation relations of P and H?

While the commutation relations of P and H hold in most cases, there are some exceptions, such as non-commuting operators. These exceptions can occur in systems with strong interactions or in situations involving particles with spin.

How are the commutation relations of P and H related to other operators in quantum mechanics?

The commutation relations of P and H are closely related to the commutation relations of other operators, such as the position operator (X) and the angular momentum operator (L). These relations allow for the calculation of the commutator between different operators, which is a fundamental concept in quantum mechanics.

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