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# Math 401, Paper 1: Concentration of measure effects in quantum information (Patrick Hayden)
[PDF](https://www.ams.org/books/psapm/068/2762144)
## Quantum codes
### Preliminaries
#### Daniel Gottesman's mathematics of quantum error correction
##### Quantum channels
Encoding channel and decoding channel
#### Quantum capacity for a quantum channel
#### Lloyd-Shor-Devetak theorem
### Surprise in high-dimensional quantum systems
#### Levy's lemma
### Random states and random subspaces
#### ebits and qbits
### Superdense coding of quantum states
### Consequences for mixed state entanglement measures
#### Quantum mutual information
### Multipartite entanglement

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#### Definition of measure-preserving map
Let $P$ be a probability measure on a $\sigma$-algebra $\mathscr{F}$ of subsets of $\Omega$. A measurable transformation $T:\Omega\to\Omega$ is said to be measure-preserving if for all random variables $\psi:\Omega\to\mathbb{R}$, we have $\mathbb{E}(\psi\circ T)=\mathbb{E}(\psi)$, that is:
Let $P$ be a probability measure on a $\sigma$-algebra $\mathscr{F}$ of subsets of $\Omega$. (that is, $P:\mathscr{F}\to$ anything) A measurable transformation $T:\Omega\to\Omega$ is said to be measure-preserving if for all random variables $\psi:\Omega\to\mathbb{R}$, we have $\mathbb{E}(\psi\circ T)=\mathbb{E}(\psi)$, that is:
$$
\int_\Omega (\psi\circ T)(\omega)dP(\omega)=\int_\Omega \psi(\omega)dP(\omega)
$$
#### Definition of ergodic map
Example:
A measurable transformation $T:\Omega\to\Omega$ is said to be ergodic if for all random variables $\psi:\Omega\to\mathbb{R}$, we have $\mathbb{E}(\psi\circ T)=\mathbb{E}(\psi)$, that is:
$$
\int_\Omega (\psi\circ T)(\omega)dP(\omega)=\int_\Omega \psi(\omega)dP(\omega)
$$
The doubling map $T:\Omega\to\Omega$ is defined as $T(x)=2x\mod 1$, is a Lebesgue measure preserving map on $\Omega=[0,1]$.
#### Definition of isometry
@@ -35,3 +31,31 @@ The composition operator $\psi\mapsto U\psi=\psi\circ T$, where $T$ is a measure
The composition operator $\psi\mapsto U\psi=\psi\circ T$, where $T$ is a measure preserving map defined on $\mathscr{H}=L^2(\Omega,\mathscr{F},P)$ is unitary of $\mathscr{H}$ if $U$ is an isometry and $T$ is invertible with measurable inverse.
## Section 2: Continuous time (classical) dynamical systems
### Spring-mass system
![Spring-mass system](https://notenextra.com/Math401/Spring-mass_system.png)
The pure state of the system is given by the position and velocity of the mass. $(x,v)$ is a point in $\mathbb{R}^2$. $\mathbb{R}^2$ is the state space of the system. (or phase space)
The motion of the system in its state space is a closed curve.
$$
\Phi_t(x,v)=\left(\cos(\omega t)x-\frac{1}{\omega}\sin(\omega t)v, \cos(\omega t)v-\omega\sin(\omega t)x\right)
$$
Such system with closed curve is called **integrable system**. Where the doubling map produces orbits having distinct dynamical properties (**chaotic system**).
> Note, some section is intentionally ignored here. They are about in the setting of operators on Hilbert spaces, the evolution of (classical, non-dissipative e.g. linear spring-mass system) system, is implemented by a one-parameter group of unitary operators.
>
> The detailed construction is omitted here.
#### Definition of Hermitian operator
A linear operator $A$ on a Hilbert space $\mathscr{H}$ is said to be Hermitian if $\forall \psi,\phi\in$ **domain of $A$**, we have $\langle A\psi,\phi\rangle=\langle\psi,A\phi\rangle$.
It is skew-Hermitian if $\langle A\psi,\phi\rangle=-\langle\psi,A\phi\rangle$.

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# Math 401, Topic 6: Postulates of quantum theory and measurement operations

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# Math 401, Topic 7: Basic of quantum circuits

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@@ -6,9 +6,18 @@ export default {
Math401_N1: "Math 401, Notes 1",
Math401_N2: "Math 401, Notes 2",
Math401_N3: "Math 401, Notes 3",
"---":{
type: 'separator'
},
Math401_T1: "Math 401, Topic 1: Probability under language of measure theory",
Math401_T2: "Math 401, Topic 2: Finite-dimensional Hilbert spaces",
Math401_T3: "Math 401, Topic 3: Separable Hilbert spaces",
Math401_T4: "Math 401, Topic 4: The quantum version of probabilistic concepts",
Math401_T5: "Math 401, Topic 5: Introducing dynamics: classical and non-commutative",
Math401_T6: "Math 401, Topic 6: Postulates of quantum theory and measurement operations",
Math401_T7: "Math 401, Topic 7: Basic of quantum circuits",
"---":{
type: 'separator'
},
Math401_P1: "Math 401, Paper 1: Concentration of measure effects in quantum information (Patrick Hayden)",
}

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