Degenerate states of 2 particles in a 1D harmonic oscillator potential

captainjack2000
Messages
96
Reaction score
0

Homework Statement


"Two non-interacting particles are placed in a one-dimensional harmonic oscillator potential. What are the degeneracies of the two lowest energy states of the system if the particles are
a)identical spinless bosons
b)identical spin-1/2 fermions?

Homework Equations





The Attempt at a Solution


I think degeneracy is equal to n^2
for b) two fermions can be in the same spatial state if they are in different spin states. one would be in spin up and spin down so this would affect the degeracy. Apart from that..I'm not sure
 
Physics news on Phys.org


exactly so there is no degeneracy for fermions (at least for the wavefunction of the entire state)

and for bosons there is no such pauli exclusion principle.

i would like someone to confirm however, if we are asked for the degeneracy are we meant to write a number i.e. 2 for the boson case or are we expected to write a spiel about pauli exclusion etc.

also isn't degeneracy given by something like g_n =\sum_{l=0}^n l(l+1) - can someone tell me whether this is true or not?
 


I am not sure about your equation

Why is there no degeneracy for fermions - is that just because there are only two particles? What would the degeneracy be if there were three particles? What do you mean at least for the wavefunction of the entire state?
 


didn't read your question properly. my above argument is tru for the ground state only. but in the first excited state it's possible to have two fermions with different wavefunctions and still have the same degenaracy. i.e. if you use the symmetric spatial wavefrunction then you need to put it in a spin singlet state - can you figure out the other possibility?
 


actually it looks like the degeneracy relation is g_n=\sum_{l=0}^{n-1} (2l+1)=n^2
 


The number of degeneracies is just the number of configurations you can have to get a specific energy. How many different ways can you arrange 2 fermions/bosons to get them to have the lowest total energy?

@Latentcorpse: It looks like your formula is for the degeneracies of the hydrogen atom (or a hydrogenic atom), I don't think that applies to this problem...? (Correct me if I'm wrong)
 
Thread 'Need help understanding this figure on energy levels'
This figure is from "Introduction to Quantum Mechanics" by Griffiths (3rd edition). It is available to download. It is from page 142. I am hoping the usual people on this site will give me a hand understanding what is going on in the figure. After the equation (4.50) it says "It is customary to introduce the principal quantum number, ##n##, which simply orders the allowed energies, starting with 1 for the ground state. (see the figure)" I still don't understand the figure :( Here is...
Thread 'Understanding how to "tack on" the time wiggle factor'
The last problem I posted on QM made it into advanced homework help, that is why I am putting it here. I am sorry for any hassle imposed on the moderators by myself. Part (a) is quite easy. We get $$\sigma_1 = 2\lambda, \mathbf{v}_1 = \begin{pmatrix} 0 \\ 0 \\ 1 \end{pmatrix} \sigma_2 = \lambda, \mathbf{v}_2 = \begin{pmatrix} 1/\sqrt{2} \\ 1/\sqrt{2} \\ 0 \end{pmatrix} \sigma_3 = -\lambda, \mathbf{v}_3 = \begin{pmatrix} 1/\sqrt{2} \\ -1/\sqrt{2} \\ 0 \end{pmatrix} $$ There are two ways...
Back
Top