Bosons/fermions trapped in a 1 dimensional trap

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SUMMARY

The discussion focuses on the Hamiltonian for a system of bosons and fermions trapped in a one-dimensional potential, specifically a harmonic oscillator defined by the equation V(x) = mw²x²/2. The participant successfully formulates the Hamiltonians in both first quantization, H = ∑(p_i²/2m + 1/2 mw²x_i²), and second quantization, H = ∫dx ψ†(x)[-ħ²/2m ∇² + 1/2 mw²x²]ψ(x). The key distinction between bosons and fermions is highlighted, where bosons can occupy the ground state collectively while fermions adhere to the Pauli exclusion principle, filling states according to energy levels.

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  • Understanding of quantum mechanics concepts, particularly Hamiltonians.
  • Familiarity with first and second quantization techniques.
  • Knowledge of bosons and fermions, including their statistical behaviors.
  • Basic grasp of harmonic oscillator potentials in quantum systems.
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  • Study the derivation of the Hamiltonian for many-body systems in quantum mechanics.
  • Explore the implications of the Pauli exclusion principle on fermionic systems.
  • Learn about the properties of ground states in quantum systems, focusing on bosonic and fermionic behaviors.
  • Investigate the role of field operators in second quantization, particularly in many-body physics.
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Students and researchers in quantum mechanics, particularly those studying many-body systems, quantum statistics, and the behavior of bosons and fermions in potential traps.

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Homework Statement


A system of bosons or fermions trapped in a potential.
I'm being asked to write the Hamiltonian in 1st and 2nd quantization and "describe the ground state" of the system.

My main question is: what does it mean to describe the ground state? What should I look for? Should I look for the lowest energy?

Homework Equations


1 dimensional MOT-trap: ##V(x)=mw^2x^2/2##

The Attempt at a Solution


My attempt for writing the hamiltonian:
1st quantization ##H=\sum_{i=1}^{N}\frac{p_i^2}{2m}+\frac{1}{2}mw^2x_i^2##
2nd quantization: ##H=\int dx \psi^{\dagger}(x)\left[-\frac{\hbar^2}{2m}\nabla^2+\frac{1}{2}mw^2x_i^2\right]\psi(x)##
Where ##\psi(x)## isthe field operator.

Do you think this is enough? Are the hamiltonians equal for both bosons or fermions? Am I missing all the important stuff?

As for describing the ground state I don't know, my attempt has been writing down the many-body wavefunction (I don't know why, just to put something) for each case and explain that bosons can all be at the ground state and fermions have the exclusion principle.
##\Psi^{(S)}=N_S\sum_p \phi_1(x_1) \phi_2(x_2)... \phi_N(x_N)##
##\Psi^{(A)}=N_A\sum_p sgn(p)\phi_1(x_1) \phi_2(x_2)... \phi_N(x_N)##

Any advice/guidance?
Thanks
 
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zinDo said:
My main question is: what does it mean to describe the ground state? What should I look for? Should I look for the lowest energy?
Yes, that is the ground state by definition.
zinDo said:
and explain that bosons can all be at the ground state and fermions have the exclusion principle.
That's the important difference between the two. Which states will be filled in the different cases?
 

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