diff --git a/content/CSE5313/Exam_reviews/CSE5313_F1.md b/content/CSE5313/Exam_reviews/CSE5313_F1.md index 2baee41..e081a89 100644 --- a/content/CSE5313/Exam_reviews/CSE5313_F1.md +++ b/content/CSE5313/Exam_reviews/CSE5313_F1.md @@ -32,241 +32,8 @@ Please refer to the syllabus for our policy regarding the use of GenAI. > > This notation system is annoying since in mathematics, $A^*$ is the transpose of $A$, but since we are using literatures in physics, we keep the notation of $A^*$. In this report, I will try to make the notation consistent as possible and follows the **physics** convention in this report. So every vector you see will be in $\ket{\psi}$ form. And we will avoid using the $\langle v,w\rangle$ notation for inner product as it used in math, we will use $\langle v|w\rangle$ or $\langle v,w\rangle$ to denote the inner product. -A quantum error-correcting code is defined to be a unitary mapping (encoding) of $k$ qubits (two-state quantum systems) into a subspace of the quantum state space of $n$ qubuits such that if any $t$ of the qubits undergo arbitary decoherence, not necessarily independently, the resulting $n$ qubit state can be used to faithfully reconstruct the original quantum state of the $k$ encoded qubits. - -Asymptotic rate $k/n=1-2H_2(2t/n)$, where $H_2$ is the binary entropy function - -$$ -H_2=-p\log_2(p)-(1-p)\log_2(1-p) -$$ - -### Problem setting and motivation - -#### Linear algebra 102 - -The main vector space we are interested in is $\mathbb{C}^n$, therefore, all the linear operator we defined are from $\mathbb{C}^n$ to $\mathbb{C}^n$. - -We denote a vector in vector space as $\ket{\psi}=(z_1,\cdots,z_n)$ (might also be infinite dimensional, and $z_i\in\mathbb{C}$). - -A natural inner product space defined on $\mathbb{C}^n$ is given by the Hermitian inner product: - -$$ -\langle\psi|\varphi\rangle=\sum_{i=1}^n z_i\bar{z}_i -$$ - -This satisfies the following properties: -1. $\bra{\psi}\sum_i \lambda_i\ket{\varphi}=\sum_i \lambda_i \langle\psi|\varphi\rangle$ (linear on the second argument) -2. $\langle\varphi|\psi\rangle=(\langle\psi|\varphi\rangle)^*$ -3. $\langle\psi|\psi\rangle\geq 0$ with equality if and only if $\ket{\psi}=0$ - -Here $\psi$ is just a label for the vector and you don't need to worry about it too much. This is also called the ket, where the counterpart: - -- $\langle\psi\rangle$ is called the bra, used to denote the vector dual to $\psi$, such element is a linear functional if you really wants to know what that is. -- $\langle\psi|\varphi\rangle$ is the inner product between two vectors, and $\bra{\psi} A\ket{\varphi}$ is the inner product between $A\ket{\varphi}$ and $\bra{\psi}$, or equivalently $A^\dagger \bra{\psi}$ and $\ket{\varphi}$. -- Given a complex matrix $A=\mathbb{C}^{n\times n}$, - - $A^*$ is the complex conjugate of $A$. - - i.e., $A=\begin{bmatrix}1+i & 2+i & 3+i\\4+i & 5+i & 6+i\\7+i & 8+i & 9+i\end{bmatrix}$, $A^*=\begin{bmatrix}1-i & 2-i & 3-i\\4-i & 5-i & 6-i\\7-i & 8-i & 9-i\end{bmatrix}$ - - $A^\top$ is the transpose of $A$. - - i.e., $A=\begin{bmatrix}1+i & 2+i & 3+i\\4+i & 5+i & 6+i\\7+i & 8+i & 9+i\end{bmatrix}$, $A^\top=\begin{bmatrix}1+i & 4+i & 7+i\\2+i & 5+i & 8+i\\3+i & 6+i & 9+i\end{bmatrix}$ - - $A^\dagger=(A^*)^\top$ is the complex conjugate transpose, referred to as the adjoint, or Hermitian conjugate of $A$. - - i.e., $A=\begin{bmatrix}1+i & 2+i & 3+i\\4+i & 5+i & 6+i\\7+i & 8+i & 9+i\end{bmatrix}$, $A^\dagger=\begin{bmatrix}1-i & 4-i & 7-i\\2-i & 5-i & 8-i\\3-i & 6-i & 9-i\end{bmatrix}$ - - $A$ is unitary if $A^\dagger A=AA^\dagger=I$. - - $A$ is hermitian (self-adjoint in mathematics literatures) if $A^\dagger=A$. - -#### Motivation of Tensor product - -Recall from the traditional notation of product space of two vector spaces $V$ and $W$, that is, $V\times W$, is the set of all ordered pairs $(\ket{v},\ket{w})$ where $\ket{v}\in V$ and $\ket{w}\in W$. - -The space has dimension $\dim V+\dim W$. - -We want to define a vector space with notation of multiplication of two vectors from different vector spaces. - -That is - -$$ -(\ket{v_1}+\ket{v_2})\otimes \ket{w}=(\ket{v_1}\otimes \ket{w})+(\ket{v_2}\otimes \ket{w}) -$$ -$$ -\ket{v}\otimes (\ket{w_1}+\ket{w_2})=(\ket{v}\otimes \ket{w_1})+(\ket{v}\otimes \ket{w_2}) -$$ - -and enables scalar multiplication by - -$$ -\lambda (\ket{v}\otimes \ket{w})=(\lambda \ket{v})\otimes \ket{w}=\ket{v}\otimes (\lambda \ket{w}) -$$ - -And we wish to build a way associates the basis of $V$ and $W$ to the basis of $V\otimes W$. That makes the tensor product a vector space with dimension $\dim V\times \dim W$. - -#### Definition of linear functional - -> [!TIP] -> -> Note the difference between a linear functional and a linear map. -> -> A generalized linear map is a function $f:V\to W$ satisfying the condition -> -> 1. $f(\ket{u}+\ket{v})=f(\ket{u})+f(\ket{v})$ -> 2. $f(\lambda \ket{v})=\lambda f(\ket{v})$ - -A linear functional is a linear map from $V$ to $\mathbb{F}$. - -#### Definition of bilinear functional - -A bilinear functional is a bilinear function $\beta:V\times W\to \mathbb{F}$ satisfying the condition that $\ket{v}\to \beta(\ket{v},\ket{w})$ is a linear functional for all $\ket{w}\in W$ and $\ket{w}\to \beta(\ket{v},\ket{w})$ is a linear functional for all $\ket{v}\in V$. - -The vector space of all bilinear functionals is denoted by $\mathcal{B}(V,W)$. - -#### Definition of tensor product - -Let $V,W$ be two vector spaces. - -Let $V'$ and $W'$ be the dual spaces of $V$ and $W$, respectively, that is $V'=\{\psi:V\to \mathbb{F}\}$ and $W'=\{\phi:W\to \mathbb{F}\}$, $\psi, \phi$ are linear functionals. - -The tensor product of vectors $v\in V$ and $w\in W$ is the bilinear functional defined by $\forall (\psi,\phi)\in V'\times W'$ given by the notation - -$$ -(v\otimes w)(\psi,\phi)\coloneqq\psi(v)\phi(w) -$$ - -The tensor product of two vector spaces $V$ and $W$ is the vector space $\mathcal{B}(V',W')$ - -Notice that the basis of such vector space is the linear combination of the basis of $V'$ and $W'$, that is, if $\{e_i\}$ is the basis of $V'$ and $\{f_j\}$ is the basis of $W'$, then $\{e_i\otimes f_j\}$ is the basis of $\mathcal{B}(V',W')$. - -That is, every element of $\mathcal{B}(V',W')$ can be written as a linear combination of the basis. - -Since $\{e_i\}$ and $\{f_j\}$ are bases of $V'$ and $W'$, respectively, then we can always find a set of linear functionals $\{\phi_i\}$ and $\{\psi_j\}$ such that $\phi_i(e_j)=\delta_{ij}$ and $\psi_j(f_i)=\delta_{ij}$. - -Here $\delta_{ij}=\begin{cases} -1 & \text{if } i=j \\ -0 & \text{otherwise} -\end{cases}$ is the Kronecker delta. - -$$ -V\otimes W=\left\{\sum_{i=1}^n \sum_{j=1}^m a_{ij} \phi_i(v)\psi_j(w): \phi_i\in V', \psi_j\in W'\right\} -$$ - -Note that $\sum_{i=1}^n \sum_{j=1}^m a_{ij} \phi_i(v)\psi_j(w)$ is a bilinear functional that maps $V'\times W'$ to $\mathbb{F}$. - -This enables basis free construction of vector spaces with proper multiplication and scalar multiplication. - -This vector space is equipped with the unique inner product $\langle v\otimes w, u\otimes x\rangle_{V\otimes W}$ defined by - -$$ -\langle v\otimes w, u\otimes x\rangle=\langle v,u\rangle_V\langle w,x\rangle_W -$$ - -In practice, we ignore the subscript of the vector space and just write $\langle v\otimes w, u\otimes x\rangle=\langle v,u\rangle\langle w,x\rangle$. - -> [!NOTE] -> -> All those definitions and proofs can be found in Linear Algebra Done Right by Sheldon Axler. - -#### Definition of two-state quantum system - -The finite dimensional Hilbert space $\mathcscr{H} - -#### Definition of Coherent states from the view of physics - -#### Side node: Why quantum error-correcting code is hard - -Decoherence process - -#### No-cloning theorem - -> Reference from P.532 of the book - -Suppose we have a quantum system with two slots $A$, and $B$, the data slot, starts out in an unknown but pure quantum state $\ket{\psi}$. This is the state which is to be copied into slot $B$m the target slot. We assume that the target slot starts out in some standard pure state $\ket{s}$. Thus the initial state of the copying machine is $\ket{\psi}\otimes \ket{s}$. - -Assume there exists some unitary operator $U$ such that $U(\ket{\psi}\otimes \ket{s})=\ket{\psi}\otimes \ket{\psi}$. - -Consider two pure states $\ket{\psi}$ and $\ket{\varphi}$, such that $U(\ket{\psi}\otimes \ket{s})=\ket{\psi}\otimes \ket{\psi}$ and $U(\ket{\varphi}\otimes \ket{s})=\ket{\varphi}\otimes \ket{\varphi}$. The inner product of the two equation yields: - -$$ -\langle \psi|\varphi\rangle =(\langle \psi|\varphi\rangle)^2 -$$ - -This equation has only two solutions, either $\langle \psi|\varphi\rangle=0$ or $\langle \psi|\varphi\rangle=1$. - -If $\langle \psi|\varphi\rangle=0$, then $\ket{\psi}=\ket{\varphi}$, no cloning for trivial case. - -If $\langle \psi|\varphi\rangle=1$, then $\ket{\psi}$ and $\ket{\varphi}$ are orthogonal. - -#### Proposition: Encoding 8 to 9 that correct 1 errors - -Recover 1 qubit from a 9 qubit quantum system. (Shor code, 1995) - -![Shore code](https://notenextra.trance-0.com/CSE5313/Shore_code.png) - -### Tools and related topics - -#### Theoretical upper bound for quantum error-correcting code - -From quantum information capacity of a quantum channel - -$$ -\min\{1-H_2(2t/3n),H_2(\frac{1}{2}+\sqrt{(1-t/n)t/n})\} -$$ - -#### Definition of quantum error-correcting code from binary linear error-correcting code - -All the operations will be done in $\mathbb{F}_2=\{0,1\}$. - -Consider two binary vectors $v=[v_1,...,v_n],v_i\in\{0,1\}$ and $w=[w_1,...,w_n],w_i\in\{0,1\}$ with size $n$. - -Recall from our lecture that - -$d$ denotes the Hamming weight of a vector. - -$d_H(v,w)=\sum_{i=1}^{n}\begin{cases} 0 & \text{if } v_i=w_i \\ 1 & \text{if } v_i\neq w_i \end{cases}$ denotes the Hamming distance between $v$ and $w$. - -$\operatorname{supp}(v)=\{i\in[n]:v_i\neq 0\}$ denotes the support of $v$. - -$v|_S$ denotes the projection of $v$ onto the subspace $S$, we usually denote the $S$ by a set of coordinates, that is $S\subseteq[n]$. - -When projecting a vector $v$ onto a another vector $w$, we usually write $v|_E\coloneqq v|_{\operatorname{supp} w}$. - -When we have two vector we may use $v\leqslant w$ (Note that this is different than $\leq$ sign) to mean $\operatorname{supp}(v)\subseteq \operatorname{supp}(w)$. - -
-Example - -Let $v=[1,0,0,1,1,1,1]$ and $w=[1,0,0,1,0,0,1]$, then $\operatorname{supp}(v)=\{1,4,5,6,7\}$, $\operatorname{supp}(w)=\{1,4,7\}$. Therefore $w\leqslant v$. - -$v|_w=[v_1,v_4,v_7]=[1,1,0]$ -
- -$\mathcal{C}$ denotes the code, a set of arbitrary binary vectors with length $n$. - -$d(\mathcal{C})=\{d(v,w)|v,w\in\mathcal{C}\}$ denotes the minimum distance of the code. - -If $\mathcal{C}$ is linear then the minimum distance is the minimum Hamming weight of a non-zero codeword. - -A $[n,k,d]$ linear code is a linear code of $n$ bits codeword with $k$ message bits that can correct $d$ errors. - -$R\coloneqq\frac{\operatorname{dim}\mathcal{C}}{n}$ is the rate of code $\mathcal{C}$. - -$\mathcal{C}^{\perp}\coloneqq\{v\in\mathbb{F}_2^n:v\cdot w=0\text{ for all }w\in\mathcal{C}\}$ is the dual code of a code $\mathcal{C}$. From linear algebra, we know that $\dim\mathcal{C}^{\perp}+\dim\mathcal{C}=n$. - -
-Example used in the paper - -Consider the $[7,4,3]$ Hamming code with generator matrix $G$. - -
- -#### Proposition: Encoding $k$ to $n$ that correct $t$ errors - -### Evaluation of paper - -### Limitation and suggestions - -### Further direction and research - -#### Toric code, surface code - -This is the topic I really want to dig into. - -This method gives a [2nm+n+m+1, 1, min(n,m)] error correcting code with only needs local stabilizer checks and really interests me. - -### References \ No newline at end of file + diff --git a/content/Math401/Extending_thesis/Math401_R4.md b/content/Math401/Extending_thesis/Math401_R4.md index 958dbf6..b813d2c 100644 --- a/content/Math401/Extending_thesis/Math401_R4.md +++ b/content/Math401/Extending_thesis/Math401_R4.md @@ -53,4 +53,4 @@ $$ This part is intentionally left blank and may be filled near the end of the semester, by assignments given in CSE5313. -[Link to self-contained report](../../CSE5313/Exam_reviews/CSE5313_F1.md) \ No newline at end of file +[Link to self-contained report](https://notenextra.trance-0.com/CSE5313/Exam_reviews/CSE5313_F1/) \ No newline at end of file diff --git a/content/Math401/Math401_H1.md b/content/Math401/Math401_H1.md index 7dfbc24..5ab693a 100644 --- a/content/Math401/Math401_H1.md +++ b/content/Math401/Math401_H1.md @@ -4,6 +4,7 @@ I made this little book for my Honor Thesis, showing the relevant parts of my wo Contents updated as displayed and based on my personal interest and progress with Prof.Feres. +