QM: Problem with an assignment using bra and ket notation

In summary, the problem involves calculating the action of two operators, \widehat{A} and \widehat{B}, on the normalized energy levels labeled |n>. The step up and step down operators, \widehat{a}+ and \widehat{a}-, are also involved, and the equations \widehat{a}+|n> = √(n+1)|n+1> and \widehat{a}-|n> = √(n)|n-1> are used. The calculation for \widehat{A}|n> is found to be \alpha (√(n+1)|n+1> + √(n)|n-1>),
  • #1
Vilashjorthen
1
0

Homework Statement


This problem is about the 1-dimensional harmonic oscillator.
The normalized energy levels are labeled |n>, n=0,1,2...
Two operators are given by

[itex]\widehat{A}[/itex] = [itex]\alpha[/itex] ([itex]\widehat{a}[/itex]++[itex]\widehat{a}[/itex]-)
[itex]\widehat{B}[/itex] = i[itex]\beta (\widehat{a}[/itex]+2+[itex]\widehat{a}[/itex]-2)

where [itex]\alpha[/itex] and [itex]\beta[/itex] are real numbers and [itex]\widehat{a}[/itex]+ and [itex]\widehat{a}[/itex]+ are the step up and step down operators

Calculate [itex]\widehat{A}[/itex]|n> and [itex]\widehat{B}[/itex]|n>

Homework Equations


[itex]\widehat{a}[/itex]+|n> = √(n+1)|n+1>
[itex]\widehat{a}[/itex]-|n> = √(n)|n-1>


The Attempt at a Solution


I have inserted the above equations and got an answer for [itex]\widehat{A}[/itex]|n> (although I am not sure if it is sufficient):
[itex]\widehat{A}[/itex]|n>=[itex]\alpha[/itex] (√(n+1)|n+1> + √(n)|n-1>)
But with [itex]\widehat{B}[/itex]|n> I am stuck at
[itex]\widehat{B}[/itex]|n>= i[itex]\beta (\widehat{a}[/itex]+√(n+1)|n+1> - [itex]\widehat{a}[/itex]-√(n)|n-1>)

Any help will be much appreciated. Thank you in advance.

P.S.: This is my first post, so please let me know if I have posted something "the wrong way".
 
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  • #2
hey, welcome to physicsforums :)
Your work looks good so far. What is it you are stuck with? In the last line, you have operators acting on something that is a number times a vector. What is the general rule for this?
 

1. What is bra and ket notation in quantum mechanics?

Bra and ket notation is a mathematical notation used in quantum mechanics to represent quantum states. It consists of a left-pointing arrow, called a ket, and a right-pointing arrow, called a bra. The ket represents a quantum state and the bra represents its dual state.

2. How do you use bra and ket notation in quantum mechanics?

To use bra and ket notation, you first need to identify the quantum state you want to represent. Then, you write the state as a ket, with the arrow pointing to the right. To represent the dual state, you write the ket as a bra, with the arrow pointing to the left. To perform operations, you can combine kets and bras using mathematical operations such as inner products and tensor products.

3. What kind of problems can arise when using bra and ket notation?

One common problem that can arise when using bra and ket notation is confusion with the notation itself. The arrows can be easily mixed up, leading to incorrect representations of quantum states. Additionally, bra and ket notation can be complex and difficult to understand, making it challenging for beginners to use correctly.

4. How can you overcome issues with bra and ket notation?

To overcome issues with bra and ket notation, it is important to have a clear understanding of the notation and practice using it correctly. It can also be helpful to work with a visual representation of the notation, such as a diagram, to help prevent confusion with the arrows. Additionally, seeking guidance from a more experienced individual or using online resources can also aid in understanding and using bra and ket notation correctly.

5. Are there alternative notations for representing quantum states?

Yes, there are alternative notations for representing quantum states, such as Dirac notation and matrix notation. These notations can be easier to understand and use, but they may not be as concise as bra and ket notation. It is important to familiarize yourself with different notations and choose the one that works best for you and the problem at hand.

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