- #1
Adel Makram
- 635
- 15
Homework Statement
I would like to know how to derive the quantum commutation relations in matrix form,
$$i \hbar \partial_t x(t)= [x(t),E]$$
$$i \hbar \partial_t P(t)= [P(t),E]$$
Where X(t), P(t) and E are the position, momentum and the energy of the particle, respectively.
2. Homework Equations
The solution of harmonic oscillator as expressed in Fourier expansion;
$$X(t)=\sum X_{mn} e^{i \omega (m-n)t} $$
$$P(t)=\sum P_{mn} e^{i \omega (m-n)t} $$
differentiate X(t) relative to t would give P(t) assuming the mass of the particle=1.
$$\partial_t X(t)=\sum X_{mn} i\omega(m-n) e^{i \omega (m-n)t} $$
$$\partial_t X(t)=\sum X_{mn} i \frac{E_m - E_n}{\hbar} e^{i \omega (m-n)t} $$
But how to arrive to the commutation formula from here?
The Attempt at a Solution
I tried retrospectively from the commutation relation to prove the equivalence with the original equation;
$$i \hbar \partial_t x(t)= [x(t),E]$$
So I started from;
$$=[X(t) E - E X(t)]$$
$$=X_{mn} E_m \delta_{mn} - E_m \delta_{mn} X_{mn}$$
where $$E=E_{mn}=E_m \delta_{mn}$$
But this did not give me;
$$\partial_t X(t)=\sum X_{mn} i \frac{E_m - E_n}{\hbar} e^{i \omega (m-n)t} $$
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