Physlib.QuantumMechanics.DDimensions.Operators.Position
Position operators
i. Overview
In this module we introduce several position operators for quantum mechanics on `Space d`.
ii. Key results
Definitions: - `positionOperator` : (components of) the position vector operator acting on Schwartz maps `𝓢(Space d, ℂ)` by multiplication by `xᵢ`. - `radiusRegPowOperator` : operator acting on Schwartz maps by multiplication by `(‖x‖² + ε²)^(s/2)`, a smooth regularization of `‖x‖ˢ`. - `positionUnboundedOperator` : a symmetric unbounded operator acting on the Schwartz submodule of the Hilbert space `SpaceDHilbertSpace d`. - `readiusRegPowUnboundedOperator` : a symmetric unbounded operator acting on the Schwartz submodule of the Hilbert space `SpaceDHilbertSpace d`. For `s ≤ 0` this operator is in fact bounded (by `|ε|ˢ`) and has natural domain the entire Hilbert space, but for uniformity we use the same domain for all `s`.
Notation: - `𝐱` for `positionOperator` - `𝐫₀` for `radiusRegPowOperator` - `𝐫` for `radiusPowOperator`
iii. Table of contents
- A. Schwartz operators - A.1. Position vector - A.2. Radius powers (regularized) - A.3. Radius powers - A.3.1. As limit of regularized operators - B. Unbounded operators - B.1. Position vector - B.2. Radius powers (regularized)
iv. References
A. Schwartz operators
A.1. Position vector
A.2. Radius powers (regularized)
A.3. Radius powers
#### A.3.1. As limit of regularized operators
B. Unbounded operators
B.1. Position vector
B.2. Radius powers (regularized)
52 declarations
-th component of the position operator
For a given index , the -th component of the position operator is a continuous linear map from the Schwartz space to itself. It maps a Schwartz function to the product , where is the -th coordinate function on .
Notation for the position operator
The notation is defined to represent the position operator `positionOperator`, which acts as a continuous linear map on the Schwartz space .
Position vector operator in dimension
The notation denotes the position vector operator for a -dimensional space. It acts on the Schwartz space via pointwise multiplication by the coordinate vector , mapping a function to the vector of functions .
For any Schwartz function , the application of the -th component of the position operator to results in the function defined by the pointwise multiplication of the -th coordinate function and . That is, .
For any Schwartz function and any point , the result of applying the -th component of the position operator to and evaluating it at is given by the product of the -th coordinate of and the value of at . That is, .
Regularized norm power function
For a given dimension and real parameters , the function maps a position vector to the value . This function serves as a smooth regularization of the power of the norm .
for non-zero
Let be a natural number and be a non-zero real number. For any vector in the space , the sum of the squared norm of and the square of is strictly positive, i.e.,
for
For any dimension , any non-zero real number , and any real number , the regularized norm power function evaluated at any vector is strictly positive, i.e.,
The regularized norm power function has temperate growth
For any dimension , non-zero real number , and real power , the regularized norm power function on , defined by , has temperate growth.
Regularized radius power operator
For a given dimension , a non-zero real regularization parameter , and an exponent , the regularized radius power operator is the continuous linear map from the Schwartz space to itself defined by the pointwise multiplication of a function by the smooth function . That is, .
Notation for the regularized radius power operator
The notation denotes the regularized radius power operator `radiusRegPowOperator`. For a given dimension , an invertible real regularization parameter , and a power , the operator acts on the Schwartz space by pointwise multiplication with the function .
Pointwise Evaluation of the Regularized Radius Power Operator on Schwartz Functions
For a dimension , an invertible real regularization parameter , and a power , the regularized radius power operator acts on a Schwartz function via pointwise multiplication. Specifically, the value of the resulting function at a point is given by: where denotes the Euclidean norm on .
Notation for the regularized radius power operator
The notation denotes the regularized radius power operator in dimension . This operator acts on functions in the Schwartz space via multiplication by the smooth function , which serves as a regularization of the radius power .
Composition Law for Regularized Radius Power Operators:
Let be the dimension of the space, be a non-zero real regularization parameter, and be real exponents. The regularized radius power operator , acting on the Schwartz space by multiplication by the function , satisfies the composition law: where denotes the composition of continuous linear maps.
The regularized radius power operator is the identity operator
For any dimension and any non-zero real regularization parameter , the regularized radius power operator with exponent is equal to the identity operator on the Schwartz space .
Action of the regularized radius power operator on Schwartz functions
For any dimension , a non-zero real regularization parameter , and a real exponent , the regularized radius power operator applied to a Schwartz function is equal to the function .
Pointwise Action of the Regularized Radius Power Operator
For any dimension , a non-zero real regularization parameter , and a real exponent , the value of the regularized radius power operator applied to a Schwartz function and evaluated at a point is given by .
For a given dimension , a non-zero real regularization parameter , and exponents , the composition of the regularized radius power operators and acting on the Schwartz space satisfies: where is the operator defined by pointwise multiplication by the function .
For any dimension and any non-zero real regularization parameter , the regularized radius power operator for the exponent is equal to the identity continuous linear map on the Schwartz space . That is, .
For any dimension and any non-zero real regularization parameter , the sum of the squares of the -th components of the position operator on the Schwartz space satisfies the identity: where denotes the composition , is the regularized radius power operator for (which acts as multiplication by ), and is the identity operator on the Schwartz space.
Radius power operator
Given a real number , the radius power operator is a -linear map from the Schwartz space to the space of functions . For a Schwartz function , the operator is defined by , where denotes the Euclidean norm of the position vector .
Notation for the radius power operator
The symbol is the mathematical notation for the radius power operator. For a parameter , the operator (formally defined as `radiusPowOperator s`) acts on a Schwartz function by pointwise multiplication by the -th power of the Euclidean norm of the position vector, specifically .
For any dimension , real exponent , and Schwartz function , the radius power operator applied to is the function defined by , where denotes the Euclidean norm of the position vector .
For any dimension , real power , and Schwartz function , the radius power operator applied to is the function , where is the Euclidean norm of .
For any dimension , real exponent , Schwartz function , and position vector , the radius power operator applied to and evaluated at satisfies , where denotes the Euclidean norm of .
is at
For any dimension , real exponent , and Schwartz function , the function is of class at any point such that , for any .
is Strongly Measurable
For any dimension , real exponent , and Schwartz function , the function is strongly measurable, where denotes the Euclidean norm on .
is square-integrable for
For any dimension and real exponent such that , the function defined by is square-integrable for any Schwartz function . That is, belongs to the Hilbert space .
Neighborhood filter of in
The filter on the set of non-zero real numbers (the units of ) defined as the preimage of the neighborhood filter of in under the inclusion map . A set belongs to this filter if there exists an such that the punctured neighborhood is contained in .
The filter of punctured neighborhoods of in is non-trivial
Let denote the set of non-zero real numbers. The filter of punctured neighborhoods of in (defined as the neighborhood filter of in the subspace ) is non-trivial, meaning it is not the bottom filter and thus every set in the filter is non-empty.
as for
For any dimension , real exponent , and Schwartz function , let be a position vector such that . Then the value of the regularized radius power operator converges to the value of the radius power operator as the regularization parameter approaches through non-zero real values.
Pointwise convergence as for or
For any dimension , real exponent , and Schwartz function , if either or the function vanishes at the origin (), then the regularized radius power function converges pointwise to the radius power function as the regularization parameter approaches through non-zero real values.
almost everywhere as
For a positive dimension , a real exponent , and a Schwartz function , the value of the regularized radius power operator converges to the value of the radius power operator as the regularization parameter approaches (through non-zero real values) for almost every . Here, and .
Pointwise almost everywhere limit of as is iff a.e.
For a positive dimension , real exponent , Schwartz function , and function , the regularized radius power function converges pointwise to for almost every as the regularization parameter approaches through non-zero real values if and only if is equal to the radius power function almost everywhere with respect to the Lebesgue measure.
-th component of the position operator on the Schwartz submodule
For a given index , the -th component of the position operator on the Schwartz submodule is a linear map from the Schwartz submodule of the Hilbert space to itself. It maps a Schwartz function to the product , where is the -th coordinate function on . This definition specifically realizes the position operator as an operator acting within the context of the Schwartz space as a dense subspace of the system's Hilbert space.
The position operator is symmetric
For a given index , the -th component of the position operator , acting as a linear operator on the Schwartz submodule of the Hilbert space , is symmetric. That is, for any two functions and in the Schwartz submodule, the inner product satisfies .
Position unbounded operator
For a given dimension and an index , the -th component of the position operator is an unbounded operator on the Hilbert space (represented by `SpaceDHilbertSpace d`). It is defined with the Schwartz space as its dense domain. The operator acts by mapping a Schwartz function to the product , where is the -th coordinate function. This definition utilizes the symmetry of the position operator on the Schwartz submodule to establish it as a symmetric unbounded operator on the entire Hilbert space.
Regularized radius power operator on the Schwartz submodule
For a given dimension , a non-zero real regularization parameter , and an exponent , the regularized radius power operator on the Schwartz submodule is a -linear map from the Schwartz submodule of the Hilbert space to itself. This operator acts on a function by pointwise multiplication with the smooth regularization of the radius power function, .
The regularized radius power operator on the Schwartz submodule is symmetric
For any dimension , any non-zero real regularization parameter , and any real exponent , the regularized radius power operator on the Schwartz submodule of —defined by the pointwise multiplication of a function by the function —is a symmetric operator.
Regularized radius power unbounded operator on
For a given dimension , a non-zero real regularization parameter , and a real exponent , the regularized radius power unbounded operator is an unbounded operator on the Hilbert space . It is defined with the dense submodule of Schwartz functions as its domain, acting on a function by pointwise multiplication: . The operator is constructed as a symmetric operator using the fact that this multiplication map is symmetric on the Schwartz space.
Notation for the regularized radius power operator
The notation (rendered as `𝐫₀` in code) denotes the regularized radius power operator. For a non-zero real regularization parameter and a real exponent , this operator acts on functions in the Schwartz space by pointwise multiplication: .
Notation for the regularized radius power operator
This definition introduces the notation for the regularized radius power operator. For a given power and regularization parameter , the operator acts on the Schwartz space via multiplication by the smooth function , which serves as a regularization of the potentially singular function .
The regularized radius power operator has a dense domain
For a given dimension , a non-zero real regularization parameter , and an exponent , the regularized radius power operator has a dense domain in the Hilbert space . This operator is defined on the Schwartz space by the pointwise multiplication .
The regularized radius power operator is self-adjoint
For any dimension , non-zero real regularization parameter , and exponent , the regularized radius power operator is self-adjoint. This operator is defined on a dense subdomain of the Hilbert space by the pointwise multiplication of functions by the map .
The regularized radius power operator is an unbounded operator
For any dimension , non-zero real regularization parameter , and exponent , the regularized radius power operator is an unbounded operator on the Hilbert space . This operator is defined by its action on the Schwartz space as the pointwise multiplication .
Notation for the radius power operator
This definition establishes the syntax for the notation (or ), which represents the radius power operator. This operator acts on the space of Schwartz functions in -dimensional space by pointwise multiplication by for a given real power .
Notation for the radius operator
This definition provides the mathematical notation for the radius power operator (represented in the library as ). In the context of quantum mechanics on a -dimensional space, this operator acts on the Schwartz space via multiplication by the function , where denotes the Euclidean norm of the position vector . It is mathematically defined as the limit of the regularized radius operators which multiply by as the regularization parameter approaches zero.
The operator has a dense domain
For any real number , the radius power operator (defined by multiplication by ) acting on the Schwartz space has a dense domain in the Hilbert space .
The Radius Power Operator is Self-Adjoint
For any real number , the radius power operator , which acts as multiplication by on functions in the Schwartz space , is a self-adjoint operator on the Hilbert space . Here, denotes the Euclidean norm of the position vector .
The radius power operator is an unbounded operator
For any real number , the radius power operator , which acts on the Schwartz space by multiplication by (where ), is an unbounded operator on the Hilbert space .
The radius power is square-integrable for in the polynomially-bounded Schwartz submodule of index
For any dimension and any real exponent , let be a natural number. If is an element of the polynomially-bounded Schwartz submodule of the Hilbert space , then the function obtained by multiplying its corresponding Schwartz map (where ) by the radius power is square-integrable. That is,
The domain of contains the polynomially-bounded Schwartz submodule with index
For any dimension and any real exponent , the domain of the radius power operator (which acts by multiplication by ) on the Hilbert space contains the polynomially-bounded Schwartz submodule with index . That is, any Schwartz function that satisfies the growth condition at the origin for all natural numbers is in the domain of .
