Physlib

Physlib.QuantumMechanics.DDimensions.Basic

Single-particle quantum system on `Space d`

i. Overview

In this module we introduce the general notion of a single-particle quantum system on `Space d`.

The structure `SpaceDQuantumSystem` encompasses the basic information needed to specify the system, namely the number of spatial dimensions, the particle's mass and the potential function.

ii. Key results

iii. Table of contents

- A. Basic properties - B. Operators - B.1. Kinetic energy - B.2. Potential energy - B.3. Hamiltonian

iv. References

A. Basic properties

B. Operators

B.1. Kinetic energy

B.2. Potential energy

B.3. Hamiltonian

20 declarations

abbrev

Hilbert space of the quantum system QQ

For a single-particle quantum system QQ with spatial dimension dd, the associated Hilbert space is defined as L2(Space d,C)L^2(\text{Space } d, \mathbb{C}), the space of square-integrable complex-valued functions on the dd-dimensional space Space d\text{Space } d.

theorem

The mass mm of the particle is strictly positive (m>0m > 0)

In a single-particle quantum system QQ as defined in `SpaceDQuantumSystem`, let mm denote the mass of the particle. The mass mm is strictly positive, satisfying 0<m0 < m.

theorem

The mass mm of a quantum system is non-negative: 0m0 \le m

In a single-particle quantum system QQ, the mass mm of the particle is non-negative, satisfying 0m0 \le m.

theorem

Mass m0m \neq 0

For a single-particle quantum system QQ, let mm be the mass of the particle. Then the mass is non-zero, i.e., m0m \neq 0.

definition

Kinetic energy operator 12mp2\frac{1}{2m} \mathbf{p}^2 as a continuous linear map

For a single-particle quantum system QQ with mass mm and spatial dimension dd, the kinetic energy operator is defined as the continuous linear map T:S(Rd,C)S(Rd,C)T: \mathcal{S}(\mathbb{R}^d, \mathbb{C}) \to \mathcal{S}(\mathbb{R}^d, \mathbb{C}) given by: T=12mpp T = \frac{1}{2m} \mathbf{p} \cdot \mathbf{p} where p\mathbf{p} is the momentum operator and S(Rd,C)\mathcal{S}(\mathbb{R}^d, \mathbb{C}) is the Schwartz space of rapidly decreasing functions on the dd-dimensional space.

theorem

The kinetic energy operator T=12mp2T = \frac{1}{2m} \mathbf{p}^2

For a single-particle quantum system QQ with mass mm and spatial dimension dd, the kinetic energy operator TT, defined as a continuous linear map on the Schwartz space S(Rd,C)\mathcal{S}(\mathbb{R}^d, \mathbb{C}), is equal to the momentum operator vector p\mathbf{p} squared divided by twice the mass: T=12mpp T = \frac{1}{2m} \mathbf{p} \cdot \mathbf{p} where pp\mathbf{p} \cdot \mathbf{p} (or p2\mathbf{p}^2) denotes the dot product of the momentum operator with itself.

definition

Kinetic energy operator T=12mp2T = \frac{1}{2m} \mathbf{p}^2

For a single-particle quantum system QQ with mass mm and spatial dimension dd, the kinetic energy operator TT is an unbounded linear operator on the Hilbert space L2(Space d,C)L^2(\text{Space } d, \mathbb{C}) defined by: T=12mp2 T = \frac{1}{2m} \mathbf{p}^2 where p2\mathbf{p}^2 is the momentum-squared operator. The domain of the operator is the Schwartz space S(Space d,C)\mathcal{S}(\text{Space } d, \mathbb{C}).

theorem

Kinetic energy operator T=12mp2T = \frac{1}{2m} \mathbf{p}^2

For a single-particle quantum system QQ with mass mm, the kinetic energy operator TT is equal to the momentum-squared operator p2\mathbf{p}^2 scaled by the factor 12m\frac{1}{2m}: T=12mp2 T = \frac{1}{2m} \mathbf{p}^2

definition

Potential operator on the Schwartz space S(Rd,C)\mathcal{S}(\mathbb{R}^d, \mathbb{C})

For a quantum system QQ in dd dimensions with potential function V:RdRV: \mathbb{R}^d \to \mathbb{R}, the potential operator is the continuous linear map from the Schwartz space S(Rd,C)\mathcal{S}(\mathbb{R}^d, \mathbb{C}) to itself defined by pointwise multiplication. Specifically, for any Schwartz function ψS(Rd,C)\psi \in \mathcal{S}(\mathbb{R}^d, \mathbb{C}), the operator maps ψ\psi to the function xV(x)ψ(x)x \mapsto V(x)\psi(x).

theorem

The potential operator is the multiplication operator by the potential function VV

For a dd-dimensional single-particle quantum system QQ with potential function V:RdRV: \mathbb{R}^d \to \mathbb{R}, the potential operator Q.potentialCLMQ.\text{potentialCLM} (defined as a continuous linear map on the Schwartz space S(Rd,C)\mathcal{S}(\mathbb{R}^d, \mathbb{C})) is equal to the operator of pointwise multiplication by VV. That is, Q.potentialCLM=smulLeftCLMC(ofRealV)Q.\text{potentialCLM} = \text{smulLeftCLM}_{\mathbb{C}}(\text{ofReal} \circ V), where ofRealV\text{ofReal} \circ V denotes the potential function cast into complex values and smulLeftCLM\text{smulLeftCLM} denotes the continuous linear map corresponding to left scalar multiplication.

theorem

The potential operator on Schwartz space is pointwise multiplication by the potential function

For a quantum system QQ in dd dimensions with potential function V:RdRV: \mathbb{R}^d \to \mathbb{R}, if VV has temperate growth, then the potential operator potentialCLM\text{potentialCLM} applied to a Schwartz function ψS(Rd,C)\psi \in \mathcal{S}(\mathbb{R}^d, \mathbb{C}) is the function given by pointwise multiplication: (potentialCLM ψ)(x)=V(x)ψ(x) (\text{potentialCLM } \psi)(x) = V(x) \psi(x) for all xRdx \in \mathbb{R}^d.

theorem

Pointwise evaluation of the potential operator (Vopψ)(x)=V(x)ψ(x)(V_{\text{op}} \psi)(x) = V(x) \psi(x)

Let QQ be a single-particle quantum system in dd dimensions with a potential function V:RdRV: \mathbb{R}^d \to \mathbb{R}. If VV has temperate growth, then for any wave function ψ\psi in the Schwartz space S(Rd,C)\mathcal{S}(\mathbb{R}^d, \mathbb{C}) and any point xRdx \in \mathbb{R}^d, the potential operator VopV_{\text{op}} applied to ψ\psi and evaluated at xx is given by the pointwise product: (Vopψ)(x)=V(x)ψ(x) (V_{\text{op}} \psi)(x) = V(x) \psi(x) where V(x)ψ(x)V(x) \psi(x) denotes the scalar multiplication of the potential value at xx and the value of the wave function at xx.

definition

Potential operator V^\hat{V} as a multiplication operator MV\mathcal{M}_V

For a single-particle quantum system QQ in dd dimensions with a real-valued potential function V:Space dRV: \text{Space } d \to \mathbb{R}, the potential operator V^\hat{V} (denoted by `potentialOperator`) is the partially defined (unbounded) linear operator on the Hilbert space L2(Space d,C)L^2(\text{Space } d, \mathbb{C}) that maps a wave function ψ\psi to the pointwise product VψV \cdot \psi. The domain of this operator is the set of all ψL2(Space d,C)\psi \in L^2(\text{Space } d, \mathbb{C}) such that the resulting product VψV \cdot \psi is also square-integrable.

theorem

The potential operator V^\hat{V} is the multiplication operator MV\mathcal{M}_V

For a single-particle quantum system QQ in dd dimensions with a real-valued potential function V:Space dRV: \text{Space } d \to \mathbb{R}, the potential operator V^\hat{V} is defined as the multiplication operator MV\mathcal{M}_V associated with the complex-valued function obtained by embedding VV into the complex numbers.

theorem

The potential operator V^\hat{V} is self-adjoint if the potential VV is almost everywhere strongly measurable

For a single-particle quantum system QQ in dd dimensions with a real-valued potential function V:Space dRV: \text{Space } d \to \mathbb{R}, if VV is almost everywhere strongly measurable, then the potential operator V^\hat{V} (the multiplication operator MV\mathcal{M}_V acting on the Hilbert space L2(Space d,C)L^2(\text{Space } d, \mathbb{C})) is self-adjoint.

theorem

The Schwartz space S(Space d,C)\mathcal{S}(\text{Space } d, \mathbb{C}) is contained in the domain of the potential operator V^\hat{V} for potential functions with temperate growth

For a single-particle quantum system QQ in dd dimensions with potential function V:Space dRV: \text{Space } d \to \mathbb{R}, if VV has temperate growth, then the Schwartz space S(Space d,C)\mathcal{S}(\text{Space } d, \mathbb{C}) is contained within the domain of the potential operator V^\hat{V}.

definition

Hamiltonian operator H=T+VH = T + V on Schwartz space S(Rd,C)\mathcal{S}(\mathbb{R}^d, \mathbb{C})

For a single-particle quantum system QQ in dd dimensions, the Hamiltonian operator HH is the continuous linear map from the Schwartz space S(Rd,C)\mathcal{S}(\mathbb{R}^d, \mathbb{C}) to itself defined as the sum of the kinetic energy operator TT and the potential energy operator VV: H=T+V H = T + V where TT is the kinetic energy operator `kineticCLM` and VV is the potential energy operator `potentialCLM`. This definition assumes the potential function has temperate growth to ensure the operator is well-defined on the Schwartz space.

theorem

Hamiltonian Operator H=T+VH = T + V on Schwartz Space

For a single-particle quantum system QQ in dd dimensions, the Hamiltonian operator HH is equal to the sum of the kinetic energy operator TT and the potential energy operator VV, where each is defined as a continuous linear map on the Schwartz space S(Rd,C)\mathcal{S}(\mathbb{R}^d, \mathbb{C}): H=T+V H = T + V Here, TT represents the operator 12mp2\frac{1}{2m} \mathbf{p}^2 and VV represents the operator of pointwise multiplication by the potential function.

definition

Hamiltonian operator H=T+VH = T + V

For a single-particle quantum system QQ with spatial dimension dd, the Hamiltonian operator HH is the unbounded linear operator on the Hilbert space L2(Space d,C)L^2(\text{Space } d, \mathbb{C}) defined as the sum of the kinetic energy operator TT and the potential energy operator VV: H=T+V H = T + V This operator is a symmetric unbounded operator on the system's Hilbert space.

theorem

The Hamiltonian operator HH equals T+VT + V

For a single-particle quantum system QQ in dd dimensions, the Hamiltonian operator HH is equal to the sum of the kinetic energy operator TT and the potential energy operator VV: H=T+V H = T + V These operators are defined as unbounded linear operators on the system's Hilbert space L2(Space d,C)L^2(\text{Space } d, \mathbb{C}).