change var

This commit is contained in:
Zheyuan Wu
2025-07-10 14:55:56 -05:00
parent d64d10ef6d
commit da283e28cc
5 changed files with 24 additions and 14 deletions

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@@ -49,12 +49,26 @@ A state $|\psi\rangle$ is entangled if it cannot be expressed as a product state
Example: the Bell state $|\psi^+\rangle=\frac{1}{\sqrt{2}}(|00\rangle+|11\rangle)$ is entangled.
Assume it can be written as $|\psi\rangle=|\psi_1\rangle\otimes|\psi_2\rangle$ where $|\psi_1\rangle=a|0\rangle+b|1\rangle$ and $|\psi_2\rangle=c|0\rangle+d|1\rangle$. Then:
$$|\psi\rangle=a|00\rangle+b|01\rangle+c|10\rangle+d|11\rangle$$
$$
|\psi\rangle=a|00\rangle+b|01\rangle+c|10\rangle+d|11\rangle
$$
Setting this equal to $|\psi^+\rangle=\frac{1}{\sqrt{2}}(|00\rangle+|11\rangle)$ gives:
$$ac|00\rangle+ad|01\rangle+bc|10\rangle+bd|11\rangle=\frac{1}{\sqrt{2}}(|00\rangle+|11\rangle)$$
$$
ac|00\rangle+ad|01\rangle+bc|10\rangle+bd|11\rangle=\frac{1}{\sqrt{2}}(|00\rangle+|11\rangle)
$$
This requires:
$$ac=bd=\frac{1}{2}$$
$$ad=bc=0$$
$$
ac=bd=\frac{1}{2}
$$
$$
ad=bc=0
$$
This is a contradiction, so $|\psi^+\rangle$ is entangled.

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@@ -21,4 +21,6 @@ export default {
},
Math401_P1: "Math 401, Paper 1: Concentration of measure effects in quantum information (Patrick Hayden)",
Math401_P1_1: "Math 401, Paper 1, Side note 1: Quantum information theory and Measure concentration",
Math401_P1_2: "Math 401, Paper 1, Side note 2: Page's lemma",
Math401_P1_3: "Math 401, Paper 1, Side note 3: Levy's concentration theorem",
}