diff --git a/content/Math401/Extending_thesis/Math401_S3.md b/content/Math401/Extending_thesis/Math401_S3.md index 2e7f933..cd0ffa1 100644 --- a/content/Math401/Extending_thesis/Math401_S3.md +++ b/content/Math401/Extending_thesis/Math401_S3.md @@ -1,2 +1,276 @@ # Math 401, Fall 2025: Thesis notes, S3, Coherent states and POVMs +> This section should extends on the reading for +> +> [Holomorphic methods in analysis and mathematical physics]() + + +## Bargmann space (original) + +Also known as Segal-Bargmann space or Bargmann-Fock space. + +It is the space of [holomorphic functions](../../Math416/Math416_L3#definition-28-holomorphic-functions) that is square-integrable over the complex plane. + +> Section belows use [Remarks on a Hilbert Space of Analytic Functions](https://www.jstor.org/stable/71180) as the reference. + +A family of Hilbert spaces, $\mathfrak{F}_n(n=1,2,3,\cdots)$, is defined as follows: + +The element of $\mathfrak{F}_n$ are [entire](../../Math416/Math416_L13#definition-711) [analytic functions](../../Math416/Math416_L9#definition-analytic) in complex Euclidean space $\mathbb{C}^n$. $f:\mathbb{C}^n\to \mathbb{C}\in \mathfrak{F}_n$ + +Let $f,g\in \mathfrak{F}_n$. The inner product is defined by + +$$ +\langle f,g\rangle=\int_{\mathbb{C}^n} \overline{f(z)}g(z) d\mu_n(z) +$$ + +Let $z_k=x_k+iy_k$ be the complex coordinates of $z\in \mathbb{C}^n$. + +The measure $\mu_n$ is the defined by + +$$ +d\mu_n(z)=\pi^{-n}\exp(-\sum_{i=1}^n |z_i|^2)\prod_{k=1}^n dx_k dy_k +$$ + +
+Example + +For $n=2$, + +$$ +\mathfrak{F}_2=\text{ space of entire analytic functions on } \mathbb{C}^2\to \mathbb{C} +$$ + +$$ +\langle f,g\rangle=\int_{\mathbb{C}^2} \overline{f(z)}g(z) d\mu(z),z=(z_1,z_2) +$$ + +$$ +d\mu_2(z)=\frac{1}{\pi^2}\exp(-|z|^2)dx_1 dy_1 dx_2 dy_2 +$$ + +
+ +so that $f$ belongs to $\mathfrak{F}_n$ if and only if $\langle f,f\rangle<\infty$. + +This is absolutely terrible early texts, we will try to formulate it in a more modern way. + +> The section belows are from the lecture notes [Holomorphic method in analysis and mathematical physics](https://arxiv.org/pdf/quant-ph/9912054) + +## Complex function spaces + +### Holomorphic spaces + +Let $U$ be a non-empty open set in $\mathbb{C}^d$. Let $\mathcal{H}(U)$ be the space of holomorphic (or analytic) functions on $U$. + +Let $f\in \mathcal{H}(U)$, note that by definition of holomorphic on several complex variables, $f$ is continuous and holomorphic in each variable with the other variables fixed. + +Let $\alpha$ be a continuous, strictly positive function on $U$. + +$$ +\mathcal{H}L^2(U,\alpha)=\left\{F\in \mathcal{H}(U): \int_U |F(z)|^2 \alpha(z) d\mu(z)<\infty\right\}, +$$ + +where $\mu$ is the Lebesgue measure on $\mathbb{C}^d=\mathbb{R}^{2d}$. + +#### Theorem of holomorphic spaces + +1. For all $z\in U$, there exists a constant $c_z$ such that + $$ + |F(z)|^2\le c_z \|F\|^2_{L^2(U,\alpha)} + $$ + for all $F\in \mathcal{H}L^2(U,\alpha)$. +2. $\mathcal{H}L^2(U,\alpha)$ is a closed subspace of $L^2(U,\alpha)$, and therefore a Hilbert space. + +
+Proof + +First we check part 1. + +Let $z=(z_1,z_2,\cdots,z_d)\in U, z_k\in \mathbb{C}$. Let $P_s(z)$ be the "polydisk"of radius $s$ centered at $z$ defined as + +$$ +P_s(z)=\{v\in \mathbb{C}^d: |v_k-z_k|1$, we can use the same argument to show that + +Let $\mathbb{I}_{P_s(z)}(v)=\begin{cases}1 & v\in P_s(z) \\0 & v\notin P_s(z)\end{cases}$ be the indicator function of $P_s(z)$. + +$$ +\begin{aligned} +F(z)&=(\pi s^2)^{-d}\int_{U}\mathbb{I}_{P_s(z)}(v)\frac{1}{\alpha(v)}F(v)\alpha(v) d\mu(v)\\ +&=(\pi s^2)^{-d}\langle \mathbb{I}_{P_s(z)}\frac{1}{\alpha},F\rangle_{L^2(U,\alpha)} +\end{aligned} +$$ + +By definition of inner product. + +So $\|F(z)\|^2\leq (\pi s^2)^{-2d}\|\mathbb{I}_{P_s(z)}\frac{1}{\alpha}\|^2_{L^2(U,\alpha)} \|F\|^2_{L^2(U,\alpha)}$. + +All the terms are bounded and finite. + +For part 2, we need to show that $\forall z\in U$, we can find a neighborhood $V$ of $z$ and a constant $d_z$ such that + +$$ +|F(z)|^2\leq d_z \|F\|^2_{L^2(U,\alpha)} +$$ + +Suppose we have a sequence $F_n\in \mathcal{H}L^2(U,\alpha)$ such that $F_n\to F$, $F\in L^2(U,\alpha)$. + +Then $F_n$ is a cauchy sequence in $L^2(U,\alpha)$. So, + +$$ +\sup_{v\in V}|F_n(v)-F_m(v)|\leq \sqrt{d_z}\|F_n-F_m\|_{L^2(U,\alpha)}\to 0\text{ as }n,m\to \infty +$$ + +So the sequence $F_m$ converges locally uniformly to some limit function which must be $F$ ($\mathbb{C}^d$ is Hausdorff, unique limit point). + +Locally uniform limit of holomorphic functions is holomorphic. (Use Morera's Theorem to show that the limit is still holomorphic in each variable.) So the limit function $F$ is actually in $\mathcal{H}L^2(U,\alpha)$, which shows that $\mathcal{H}L^2(U,\alpha)$ is closed. + +which shows that $\mathcal{H}L^2(U,\alpha)$ is closed. + +
+ +> [!TIP] +> +> [1.] states that point-wise evaluation of $F$ on $U$ is continuous. That is, for each $z\in U$, the map $\varphi: \mathcal{H}L^2(U,\alpha)\to \mathbb{C}$ that takes $F\in \mathcal{H}L^2(U,\alpha)$ to $F(z)$ is a continuous linear functional on $\mathcal{H}L^2(U,\alpha)$. This is false for ordinary non-holomorphic functions, e.g. $L^2$ spaces. + +#### Reproducing kernel + +Let $\mathcal{H}L^2(U,\alpha)$ be a holomorphic space. The reproducing kernel of $\mathcal{H}L^2(U,\alpha)$ is a function $K:U\times U\to \mathbb{C}$, $K(z,w),z,w\in U$ with the following properties: + +1. $K(z,w)$ is holomorphic in $z$ and anti-holomorphic in $w$. + $$ + K(w,z)=\overline{K(z,w)} + $$ + +2. For each fixed $z\in U$, $K(z,w)$ is a square integrable $d\alpha(w)$. For all $F\in \mathcal{H}L^2(U,\alpha)$, + $$ + F(z)=\int_U K(z,w)F(w) \alpha(w) dw + $$ + +3. If $F\in L^2(U,\alpha)$, let $PF$ denote the orthogonal projection of $F$ onto closed subspace $\mathcal{H}L^2(U,\alpha)$. Then + $$ + PF(z)=\int_U K(z,w)F(w) \alpha(w) dw + $$ + +4. For all $z,u\in U$, + $$ + \int_U K(z,w)K(w,u) \alpha(w) dw=K(z,u) + $$ + +5. For all $z\in U$, + $$ + |F(z)|^2\leq K(z,z) \|F\|^2_{L^2(U,\alpha)} + $$ + +
+Proof + +For part 1, By [Riesz Theorem](../../Math429/Math429_L27#theorem-642-riesz-representation-theorem), the linear functional evaluation at $z\in U$ on $\mathcal{H}L^2(U,\alpha)$ can be represented uniquely as inner product with some $\phi_z\in \mathcal{H}L^2(U,\alpha)$. + +$$ +F(z)=\langle F,\phi_z\rangle_{L^2(U,\alpha)}=\int_U F(w)\overline{\phi_z(w)} \alpha(w) dw +$$ + +And assume part 2 is true, then we have + +$K(z,w)=\overline{\phi_z(w)}$ + +So part 1 is true. + +For part 2, we can use the same argument + +$$ +\phi_z(w)=\langle \phi_z,\phi_w\rangle_{L^2(U,\alpha)}=\overline{\langle \phi_w,\phi_z\rangle_{L^2(U,\alpha)}}=\overline{\phi_w(z)} +$$ + +... continue if needed. + +
+ +#### Construction of reproducing kernel + +Let $\{e_j\}$ be any orthonormal basis of $\mathcal{H}L^2(U,\alpha)$. Then for all $z,w\in U$, + +$$ +\sum_{j=1}^{\infty} |e_j(z)\overline{e_j(w)}|<\infty +$$ + +and + +$$ +K(z,w)=\sum_{j=1}^{\infty} e_j(z)\overline{e_j(w)} +$$ + +### Bargmann space + +The Bargmann spaces are the holomorphic spaces + +$$ +\mathcal{H}L^2(\mathbb{C}^d,\mu_t) +$$ + +where + +$$ +\mu_t(z)=(\pi t)^{-d}\exp(-|z|^2/t) +$$ + +> For this research, we can tentatively set $t=1$ and $d=2$ for simplicity so that you can continue to read the next section. + +#### Reproducing kernel for Bargmann space + +For all $d\geq 1$, the reproducing kernel of the space $\mathcal{H}L^2(\mathbb{C}^d,\mu_t)$ is given by + +$$ +K(z,w)=\exp(z\cdot \overline{w}/t) +$$ + +where $z\cdot \overline{w}=\sum_{k=1}^d z_k\overline{w_k}$. + +This gives the pointwise bounds + +$$ +|F(z)|^2\leq \exp(\|z\|^2/t) \|F\|^2_{L^2(\mathbb{C}^d,\mu_t)} +$$ + +For all $F\in \mathcal{H}L^2(\mathbb{C}^d,\mu_t)$, and $z\in \mathbb{C}^d$. + +> Proofs are intentionally skipped, you can refer to the lecture notes for details. + +#### Lie bracket of vector fields + +Let $X,Y$ be two vector fields on a smooth manifold $M$. The Lie bracket of $X$ and $Y$ is an operator $[X,Y]:C^\infty(M)\to C^\infty(M)$ defined by + +$$ +[X,Y](f)=X(Y(f))-Y(X(f)) +$$ + +This operator is a vector field. + +> Continue here for quantization of Coherent states and POVMs \ No newline at end of file diff --git a/content/Math401/Extending_thesis/Math401_S4.md b/content/Math401/Extending_thesis/Math401_S4.md index 62c10f8..d7d3acd 100644 --- a/content/Math401/Extending_thesis/Math401_S4.md +++ b/content/Math401/Extending_thesis/Math401_S4.md @@ -1,272 +1,4 @@ -# Math 401, Fall 2025: Thesis notes, S4, Complex function spaces and complex manifold - -## Bargmann space (original) - -Also known as Segal-Bargmann space or Bargmann-Fock space. - -It is the space of [holomorphic functions](../../Math416/Math416_L3#definition-28-holomorphic-functions) that is square-integrable over the complex plane. - -> Section belows use [Remarks on a Hilbert Space of Analytic Functions](https://www.jstor.org/stable/71180) as the reference. - -A family of Hilbert spaces, $\mathfrak{F}_n(n=1,2,3,\cdots)$, is defined as follows: - -The element of $\mathfrak{F}_n$ are [entire](../../Math416/Math416_L13#definition-711) [analytic functions](../../Math416/Math416_L9#definition-analytic) in complex Euclidean space $\mathbb{C}^n$. $f:\mathbb{C}^n\to \mathbb{C}\in \mathfrak{F}_n$ - -Let $f,g\in \mathfrak{F}_n$. The inner product is defined by - -$$ -\langle f,g\rangle=\int_{\mathbb{C}^n} \overline{f(z)}g(z) d\mu_n(z) -$$ - -Let $z_k=x_k+iy_k$ be the complex coordinates of $z\in \mathbb{C}^n$. - -The measure $\mu_n$ is the defined by - -$$ -d\mu_n(z)=\pi^{-n}\exp(-\sum_{i=1}^n |z_i|^2)\prod_{k=1}^n dx_k dy_k -$$ - -
-Example - -For $n=2$, - -$$ -\mathfrak{F}_2=\text{ space of entire analytic functions on } \mathbb{C}^2\to \mathbb{C} -$$ - -$$ -\langle f,g\rangle=\int_{\mathbb{C}^2} \overline{f(z)}g(z) d\mu(z),z=(z_1,z_2) -$$ - -$$ -d\mu_2(z)=\frac{1}{\pi^2}\exp(-|z|^2)dx_1 dy_1 dx_2 dy_2 -$$ - -
- -so that $f$ belongs to $\mathfrak{F}_n$ if and only if $\langle f,f\rangle<\infty$. - -This is absolutely terrible early texts, we will try to formulate it in a more modern way. - -> The section belows are from the lecture notes [Holomorphic method in analysis and mathematical physics](https://arxiv.org/pdf/quant-ph/9912054) - -## Complex function spaces - -### Holomorphic spaces - -Let $U$ be a non-empty open set in $\mathbb{C}^d$. Let $\mathcal{H}(U)$ be the space of holomorphic (or analytic) functions on $U$. - -Let $f\in \mathcal{H}(U)$, note that by definition of holomorphic on several complex variables, $f$ is continuous and holomorphic in each variable with the other variables fixed. - -Let $\alpha$ be a continuous, strictly positive function on $U$. - -$$ -\mathcal{H}L^2(U,\alpha)=\left\{F\in \mathcal{H}(U): \int_U |F(z)|^2 \alpha(z) d\mu(z)<\infty\right\}, -$$ - -where $\mu$ is the Lebesgue measure on $\mathbb{C}^d=\mathbb{R}^{2d}$. - -#### Theorem of holomorphic spaces - -1. For all $z\in U$, there exists a constant $c_z$ such that - $$ - |F(z)|^2\le c_z \|F\|^2_{L^2(U,\alpha)} - $$ - for all $F\in \mathcal{H}L^2(U,\alpha)$. -2. $\mathcal{H}L^2(U,\alpha)$ is a closed subspace of $L^2(U,\alpha)$, and therefore a Hilbert space. - -
-Proof - -First we check part 1. - -Let $z=(z_1,z_2,\cdots,z_d)\in U, z_k\in \mathbb{C}$. Let $P_s(z)$ be the "polydisk"of radius $s$ centered at $z$ defined as - -$$ -P_s(z)=\{v\in \mathbb{C}^d: |v_k-z_k|1$, we can use the same argument to show that - -Let $\mathbb{I}_{P_s(z)}(v)=\begin{cases}1 & v\in P_s(z) \\0 & v\notin P_s(z)\end{cases}$ be the indicator function of $P_s(z)$. - -$$ -\begin{aligned} -F(z)&=(\pi s^2)^{-d}\int_{U}\mathbb{I}_{P_s(z)}(v)\frac{1}{\alpha(v)}F(v)\alpha(v) d\mu(v)\\ -&=(\pi s^2)^{-d}\langle \mathbb{I}_{P_s(z)}\frac{1}{\alpha},F\rangle_{L^2(U,\alpha)} -\end{aligned} -$$ - -By definition of inner product. - -So $\|F(z)\|^2\leq (\pi s^2)^{-2d}\|\mathbb{I}_{P_s(z)}\frac{1}{\alpha}\|^2_{L^2(U,\alpha)} \|F\|^2_{L^2(U,\alpha)}$. - -All the terms are bounded and finite. - -For part 2, we need to show that $\forall z\in U$, we can find a neighborhood $V$ of $z$ and a constant $d_z$ such that - -$$ -|F(z)|^2\leq d_z \|F\|^2_{L^2(U,\alpha)} -$$ - -Suppose we have a sequence $F_n\in \mathcal{H}L^2(U,\alpha)$ such that $F_n\to F$, $F\in L^2(U,\alpha)$. - -Then $F_n$ is a cauchy sequence in $L^2(U,\alpha)$. So, - -$$ -\sup_{v\in V}|F_n(v)-F_m(v)|\leq \sqrt{d_z}\|F_n-F_m\|_{L^2(U,\alpha)}\to 0\text{ as }n,m\to \infty -$$ - -So the sequence $F_m$ converges locally uniformly to some limit function which must be $F$ ($\mathbb{C}^d$ is Hausdorff, unique limit point). - -Locally uniform limit of holomorphic functions is holomorphic. (Use Morera's Theorem to show that the limit is still holomorphic in each variable.) So the limit function $F$ is actually in $\mathcal{H}L^2(U,\alpha)$, which shows that $\mathcal{H}L^2(U,\alpha)$ is closed. - -which shows that $\mathcal{H}L^2(U,\alpha)$ is closed. - -
- -> [!TIP] -> -> [1.] states that point-wise evaluation of $F$ on $U$ is continuous. That is, for each $z\in U$, the map $\varphi: \mathcal{H}L^2(U,\alpha)\to \mathbb{C}$ that takes $F\in \mathcal{H}L^2(U,\alpha)$ to $F(z)$ is a continuous linear functional on $\mathcal{H}L^2(U,\alpha)$. This is false for ordinary non-holomorphic functions, e.g. $L^2$ spaces. - -#### Reproducing kernel - -Let $\mathcal{H}L^2(U,\alpha)$ be a holomorphic space. The reproducing kernel of $\mathcal{H}L^2(U,\alpha)$ is a function $K:U\times U\to \mathbb{C}$, $K(z,w),z,w\in U$ with the following properties: - -1. $K(z,w)$ is holomorphic in $z$ and anti-holomorphic in $w$. - $$ - K(w,z)=\overline{K(z,w)} - $$ - -2. For each fixed $z\in U$, $K(z,w)$ is a square integrable $d\alpha(w)$. For all $F\in \mathcal{H}L^2(U,\alpha)$, - $$ - F(z)=\int_U K(z,w)F(w) \alpha(w) dw - $$ - -3. If $F\in L^2(U,\alpha)$, let $PF$ denote the orthogonal projection of $F$ onto closed subspace $\mathcal{H}L^2(U,\alpha)$. Then - $$ - PF(z)=\int_U K(z,w)F(w) \alpha(w) dw - $$ - -4. For all $z,u\in U$, - $$ - \int_U K(z,w)K(w,u) \alpha(w) dw=K(z,u) - $$ - -5. For all $z\in U$, - $$ - |F(z)|^2\leq K(z,z) \|F\|^2_{L^2(U,\alpha)} - $$ - -
-Proof - -For part 1, By [Riesz Theorem](../../Math429/Math429_L27#theorem-642-riesz-representation-theorem), the linear functional evaluation at $z\in U$ on $\mathcal{H}L^2(U,\alpha)$ can be represented uniquely as inner product with some $\phi_z\in \mathcal{H}L^2(U,\alpha)$. - -$$ -F(z)=\langle F,\phi_z\rangle_{L^2(U,\alpha)}=\int_U F(w)\overline{\phi_z(w)} \alpha(w) dw -$$ - -And assume part 2 is true, then we have - -$K(z,w)=\overline{\phi_z(w)}$ - -So part 1 is true. - -For part 2, we can use the same argument - -$$ -\phi_z(w)=\langle \phi_z,\phi_w\rangle_{L^2(U,\alpha)}=\overline{\langle \phi_w,\phi_z\rangle_{L^2(U,\alpha)}}=\overline{\phi_w(z)} -$$ - -... continue if needed. - -
- -#### Construction of reproducing kernel - -Let $\{e_j\}$ be any orthonormal basis of $\mathcal{H}L^2(U,\alpha)$. Then for all $z,w\in U$, - -$$ -\sum_{j=1}^{\infty} |e_j(z)\overline{e_j(w)}|<\infty -$$ - -and - -$$ -K(z,w)=\sum_{j=1}^{\infty} e_j(z)\overline{e_j(w)} -$$ - -### Bargmann space - -The Bargmann spaces are the holomorphic spaces - -$$ -\mathcal{H}L^2(\mathbb{C}^d,\mu_t) -$$ - -where - -$$ -\mu_t(z)=(\pi t)^{-d}\exp(-|z|^2/t) -$$ - -> For this research, we can tentatively set $t=1$ and $d=2$ for simplicity so that you can continue to read the next section. - -#### Reproducing kernel for Bargmann space - -For all $d\geq 1$, the reproducing kernel of the space $\mathcal{H}L^2(\mathbb{C}^d,\mu_t)$ is given by - -$$ -K(z,w)=\exp(z\cdot \overline{w}/t) -$$ - -where $z\cdot \overline{w}=\sum_{k=1}^d z_k\overline{w_k}$. - -This gives the pointwise bounds - -$$ -|F(z)|^2\leq \exp(\|z\|^2/t) \|F\|^2_{L^2(\mathbb{C}^d,\mu_t)} -$$ - -For all $F\in \mathcal{H}L^2(\mathbb{C}^d,\mu_t)$, and $z\in \mathbb{C}^d$. - -> Proofs are intentionally skipped, you can refer to the lecture notes for details. - -#### Lie bracket of vector fields - -Let $X,Y$ be two vector fields on a smooth manifold $M$. The Lie bracket of $X$ and $Y$ is an operator $[X,Y]:C^\infty(M)\to C^\infty(M)$ defined by - -$$ -[X,Y](f)=X(Y(f))-Y(X(f)) -$$ - -This operator is a vector field. +# Math 401, Fall 2025: Thesis notes, S4, Complex manifolds ## Complex Manifolds @@ -312,6 +44,40 @@ A **holomorphic line bundle** is a holomorphic vector bundle with rank 1. > Intuitively, a holomorphic line bundle is a complex vector bundle with a complex structure on each fiber. +### Simplicial, Sheafs, Cohomology and homology + +What is homology and cohomology? + +> This section is based on extension for conversation with Professor Feres on [11/05/2025]. + +#### Definition of meromorphic function + +Let $Y$ be an open subset of $X$. A function $f$ is called meromorphic function on $Y$, if there exists a non-empty open subset $Y'\subset Y$ such that + +1. $f:Y'\to \mathbb{C}$ is a holomorphic function. +2. $A=Y\setminus Y'$ is a set of isolated points (called the set of poles) +3. $\lim_{x\to p}|f(x)|=+\infty$ for all $p\in A$ + +> Basically, a local holomorphic function on $Y$. + +#### De Rham Theorem + +This is analogous to the Stoke's Theorem on chains, $\int_c d\omega=\int_{\partial c} \omega$. + +$$ +H_k(X)\cong H^k(X) +$$ + +Where $H_k(X)$ is the $k$-th homology of $X$, and $H^k(X)$ is the $k$-th cohomology of $X$. + +#### Simplicial Cohomology + +Riemann surfaces admit triangulations. The triangle are 2 simplices. The edges are 1 simplices. the vertices are 0 simplices. + +Our goal is to build global description of Riemann surfaces using local description on each triangulation. + +#### Singular Cohomology + ### Riemann-Roch Theorem (Theorem 9.64) Suppose $M$ is a connected compact Riemann surface of genus $g$, and $L\to M$ is a holomorphic line bundle. Then diff --git a/content/Math401/Extending_thesis/_meta.js b/content/Math401/Extending_thesis/_meta.js index 2996d95..037fab7 100644 --- a/content/Math401/Extending_thesis/_meta.js +++ b/content/Math401/Extending_thesis/_meta.js @@ -1,3 +1,4 @@ export default { index: "Math 401, Fall 2025: Overview of thesis", + } \ No newline at end of file