From 16555851b6514a736c5c9d8e73de7da7fc9b6288 Mon Sep 17 00:00:00 2001 From: Prefetch Date: Thu, 20 Oct 2022 18:25:31 +0200 Subject: Migrate from 'jekyll-katex' to 'kramdown-math-sskatex' --- source/know/concept/heisenberg-picture/index.md | 26 ++++++++++++------------- 1 file changed, 13 insertions(+), 13 deletions(-) (limited to 'source/know/concept/heisenberg-picture') diff --git a/source/know/concept/heisenberg-picture/index.md b/source/know/concept/heisenberg-picture/index.md index 59ed2da..359ecfe 100644 --- a/source/know/concept/heisenberg-picture/index.md +++ b/source/know/concept/heisenberg-picture/index.md @@ -13,9 +13,9 @@ mechanics, and is equivalent to the traditionally-taught Schrödinger equation. In the Schrödinger picture, the operators (observables) are fixed (as long as they do not depend on time), while the state -$\Ket{\psi_S(t)}$ changes according to the Schrödinger equation, -which can be written using the generator of translations $\hat{U}(t)$ like so, -for a time-independent $\hat{H}_S$: +$$\Ket{\psi_S(t)}$$ changes according to the Schrödinger equation, +which can be written using the generator of translations $$\hat{U}(t)$$ like so, +for a time-independent $$\hat{H}_S$$: $$\begin{aligned} \Ket{\psi_S(t)} = \hat{U}(t) \Ket{\psi_S(0)} @@ -26,12 +26,12 @@ $$\begin{aligned} \end{aligned}$$ In contrast, the Heisenberg picture reverses the roles: -the states $\Ket{\psi_H}$ are invariant, +the states $$\Ket{\psi_H}$$ are invariant, and instead the operators vary with time. An advantage of this is that the basis states remain the same. -Given a Schrödinger-picture state $\Ket{\psi_S(t)}$, and operator -$\hat{L}_S(t)$ which may or may not depend on time, they can be +Given a Schrödinger-picture state $$\Ket{\psi_S(t)}$$, and operator +$$\hat{L}_S(t)$$ which may or may not depend on time, they can be converted to the Heisenberg picture by the following change of basis: $$\begin{aligned} @@ -42,7 +42,7 @@ $$\begin{aligned} } \end{aligned}$$ -Since $\hat{U}(t)$ is unitary, the expectation value of a given operator is unchanged: +Since $$\hat{U}(t)$$ is unitary, the expectation value of a given operator is unchanged: $$\begin{aligned} \expval{\hat{L}_H} @@ -55,7 +55,7 @@ $$\begin{aligned} \end{aligned}$$ The Schrödinger and Heisenberg pictures therefore respectively -correspond to active and passive transformations by $\hat{U}(t)$ +correspond to active and passive transformations by $$\hat{U}(t)$$ in [Hilbert space](/know/concept/hilbert-space/). The two formulations are thus entirely equivalent, and can be derived from one another, @@ -63,15 +63,15 @@ as will be shown shortly. In the Heisenberg picture, the states are constant, so the time-dependent Schrödinger equation is not directly useful. -Instead, we will use it derive a new equation for $\hat{L}_H(t)$. -The key is that the generator $\hat{U}(t)$ is defined from the Schrödinger equation: +Instead, we will use it derive a new equation for $$\hat{L}_H(t)$$. +The key is that the generator $$\hat{U}(t)$$ is defined from the Schrödinger equation: $$\begin{aligned} \dv{}{t}\hat{U}(t) = - \frac{i}{\hbar} \hat{H}_S(t) \: \hat{U}(t) \end{aligned}$$ -Where $\hat{H}_S(t)$ may depend on time. We differentiate the definition of -$\hat{L}_H(t)$ and insert the other side of the Schrödinger equation +Where $$\hat{H}_S(t)$$ may depend on time. We differentiate the definition of +$$\hat{L}_H(t)$$ and insert the other side of the Schrödinger equation when necessary: $$\begin{aligned} @@ -99,7 +99,7 @@ $$\begin{aligned} \end{aligned}$$ This equation is closer to classical mechanics than the Schrödinger picture: -inserting the position $\hat{X}$ and momentum $\hat{P} = - i \hbar \: \idv{}{\hat{X}}$ +inserting the position $$\hat{X}$$ and momentum $$\hat{P} = - i \hbar \: \idv{}{\hat{X}}$$ gives the following Newton-style equations: $$\begin{aligned} -- cgit v1.2.3