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Zheyuan Wu
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# Topic 4: The quantum version of probabilistic concepts
> In mathematics, on often speaks of non-commutative instead of quantum constructions.
## Section 1: Generalities about classical versus quantum systems
In classical physics, we assume that a systema's properties have well-defined values regardless of how we choose to measure them.
### Basic terminology
#### Observables
#### Set of states
The preparation of a system builds a convex set of states as our initial condition for the system.
For a collection of $N$ system. Let procedure $N_1=\lambda P_1$ be a preparation procedure for state $P_1$, and $N_2=(1-\lambda) P_2$ be a preparation procedure for state $P_2$. The state of the collection is $N=\lambda N_1+(1-\lambda) N_2$.
#### Set of effects
The set of effects is the set of all possible outcomes of a measurement. $\Omega=\{\omega_1, \omega_2, \ldots, \omega_n\}$. Where each $\omega_i$ is an associated effect, or some query problems regarding the system. (For example, is outcome $\omega_i$ observed?)
#### Registration of outcomes
A pair of state and effect determines a probability $E_i(P)=p(\omega_i|P)$. By the law of large numbers, this probability shall converge to $N(\omega_i)/N$ as $N$ increases.
**Quantum states, observables, and effects can be represented mathematically by linear operators on a Hilbert space.**
## Section 2: Examples of physical experiment in language of mathematics
### Sten-Gernach experiment
**State preparation:** Silver tams are emitted from a thermal source and collimated to form a beam.
**Measurement:** Silver atoms interact with the field produced by the magnet and impinges on the class plate.
**Registration:** The impression left on the glass pace by the condensed silver atoms.
## Finite probability spaces in the language of Hilbert space and operators
> Superposition is a linear combination of two or more states.
A quantum coin can be represented mathematically by linear combination of $|0\rangle$ and $|1\rangle$.$\alpha|0\rangle+\beta|1\rangle\in\mathscr{H}\cong\mathbb{C}^2$.
> For the rest of the material, we shall take the $\mathscr{H}$ to be vector space over $\mathbb{C}$.

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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",
}