Obtain an expression for the expectation value in terms of energy

In summary, the ground state wave function for a particle in a one-dimensional harmonic oscillator potential can be expressed as u(subscript 0) (x)= N(subscript 0) exp((-alpha^2)(x^2)/2) where alpha=sqrt (m *omega/h-bar) and N(subscript 0) is a normalization constant. For the ground state, the quantum mechanical expectation values for position and momentum are both zero. For the uncertainties delta x and delta p, the expectation value for energy can be obtained by the expression ((delta p)^2 - <p>^2)^2)/2m. If ΔxΔp = c, the value of c can be deduced by minimizing the ground state
  • #1
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Homework Statement


The ground state wave function for a particle of mass m moving with energy E in a one-dimensional harmonic oscillator potential with classical frequency omega is:

u(subscript 0) (x)= N(subscript 0) exp((-alpha^2)(x^2)/2) and alpha=sqrt (m *omega/h-bar)

where N(subscript 0) is some normalisation constant

a) for the ground state, show explicitly that the quantum mechanical expectation values <x> and <p> are both zero
b) if the uncertainties delta x and delta p are given by:

(delta x)^2=<x^2>-<x>^2
(delta p)^2=<p^2>-<p>^2

obtain an expression for the expectation value of E in terms of the uncertainties
c)If ΔxΔp = c for c a constant, deduce a value for c by minimising the ground state energy. What significance
does the value of c have in light of the uncertainty principle ?

The Attempt at a Solution



I haven't tried part a yet, but for part b:

<E>=<p^2>/2m
=((delta p)^2 - <p>^2)^2)/2m

I don't know if the above is correct and I have no idea how to get it in terms of delta x. Please help
 
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  • #2
The expectation value (average over an ensemble) for the Hamiltonian is

[tex] \langle H\rangle =\frac{1}{2m} \langle p^2\rangle + C \langle x^2\rangle [/tex]

, wherer C=C(m,ω)>0.
 

1. What is an expectation value?

An expectation value is a mathematical concept that represents the average value that is expected to be obtained from a given set of data or observations.

2. How is an expectation value calculated?

An expectation value is calculated by multiplying each possible outcome by its probability and then summing all of these products together. This is also known as taking the weighted average.

3. How is an expression for the expectation value obtained in terms of energy?

An expression for the expectation value in terms of energy is obtained by using the Hamiltonian operator, which is a mathematical representation of the total energy of a system. The expectation value can be calculated by taking the integral of the wave function multiplied by the Hamiltonian operator.

4. What is the significance of obtaining an expression for the expectation value in terms of energy?

The expression for the expectation value in terms of energy is significant because it allows us to determine the average energy of a system, which is a crucial factor in understanding the behavior and properties of physical systems.

5. Can the expectation value in terms of energy be used to make predictions about a system?

Yes, the expectation value in terms of energy can be used to make predictions about a system. It provides valuable information about the average energy of a system and can be used to calculate other important quantities such as the uncertainty of the energy or the probability of obtaining a certain energy value.

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