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Physlib.QuantumMechanics.RectangularBarrier.Basic

The rectangular potential barrier

i. Overview

The rectangular potential barrier in one dimension provides the simplest example of quantum tunnelling. A particle of mass `m` is subject to a piece-wise constant potential which is `V₀` on a closed interval and zero elsewhere.

ii. Key results

iii. Table of contents

- A. Basic properties - B. Potential function - C. Hilbert space - D. Operators - D.1. Kinetic - D.2. Potential - D.3. Hamiltonian - E. As a quantum system

iv. References

A. Basic properties

B. Potential function

C. Hilbert space

D. Operators

D.1. Kinetic

D.2. Potential

D.3. Hamiltonian

E. As a quantum system

13 declarations

theorem

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

For a rectangular potential barrier system QQ, the mass mm of the particle is strictly positive, satisfying m>0m > 0.

theorem

The mass mm is non-negative (0m0 \le m)

In the context of a rectangular potential barrier system, let mm be the mass of the particle. This theorem states that the mass mm is non-negative, satisfying 0m0 \le m.

theorem

The mass mm is non-zero (m0m \neq 0)

For a particle of mass mm in a rectangular potential barrier system, the mass is non-zero, denoted as m0m \neq 0.

definition

Potential function V(x)V(x) for a rectangular barrier

For a one-dimensional rectangular potential barrier QQ, the potential function V:RRV: \mathbb{R} \to \mathbb{R} maps a position xx to the barrier height V0V_0 if xx lies within the closed interval [a,b][a, b] (defined by the lower bound aa and upper bound bb), and to 00 otherwise. Mathematically, it is defined as V(x)=V01[a,b](x)V(x) = V_0 \cdot \mathbb{1}_{[a, b]}(x).

theorem

The potential function V(x)V(x) for a rectangular barrier equals V01[a,b](x)V_0 \cdot \mathbb{1}_{[a, b]}(x)

For a one-dimensional rectangular potential barrier QQ with barrier height V0V_0, lower bound aa, and upper bound bb, the potential function V:RRV: \mathbb{R} \to \mathbb{R} is defined by the indicator function of the closed interval [a,b][a, b]. Specifically, for a position xx, V(x)=V0V(x) = V_0 if x[a,b]x \in [a, b] and V(x)=0V(x) = 0 otherwise. Mathematically, this is expressed as: V(x)=V01[a,b](x)V(x) = V_0 \cdot \mathbb{1}_{[a, b]}(x) where 1[a,b]\mathbb{1}_{[a, b]} denotes the indicator function on the interval [a,b][a, b].

definition

The potential function VV is a.e. strongly measurable

For a quantum mechanical rectangular barrier, the potential function V:R1RV: \mathbb{R}^1 \to \mathbb{R}, which is defined as V0V_0 on the closed interval [xlower,xupper][x_{\text{lower}}, x_{\text{upper}}] and zero elsewhere, is almost everywhere (a.e.) strongly measurable.

abbrev

Hilbert space L2(R,C)L^2(\mathbb{R}, \mathbb{C}) for the 1D rectangular barrier

The Hilbert space for a one-dimensional rectangular potential barrier is defined as the space L2(R,C)L^2(\mathbb{R}, \mathbb{C}) of square-integrable functions mapping from the 1-dimensional real space to the complex numbers C\mathbb{C}.

definition

Kinetic energy operator T^=p22m\hat{T} = \frac{\mathbf{p}^2}{2m} for the rectangular barrier

For a one-dimensional rectangular potential barrier QQ with particle mass mm, the kinetic energy operator is the partial linear map on the Hilbert space L2(R,C)L^2(\mathbb{R}, \mathbb{C}) defined as 12mp2\frac{1}{2m} \mathbf{p}^2, where p2\mathbf{p}^2 is the momentum-squared operator. In terms of the wavefunction ψ\psi in the domain, this operator acts as 22md2dx2ψ-\frac{\hbar^2}{2m} \frac{d^2}{dx^2} \psi.

definition

Potential operator V^\hat{V} for the rectangular barrier

For a one-dimensional rectangular potential barrier QQ, the potential operator V^\hat{V} is the partially defined linear operator on the Hilbert space L2(R,C)L^2(\mathbb{R}, \mathbb{C}) defined by multiplication by the potential function V(x)V(x). For a wave function ψ(x)\psi(x) in its domain, the operator maps ψ(x)\psi(x) to the product V(x)ψ(x)V(x)\psi(x), where V(x)V(x) is the real-valued potential function of the barrier QQ (mapped to the complex numbers).

definition

The potential operator V^\hat{V} is self-adjoint

In the quantum mechanical model of a one-dimensional rectangular potential barrier, the potential operator V^\hat{V} acting on the system's Hilbert space H\mathcal{H} is self-adjoint.

definition

Hamiltonian H^\hat{H} for the rectangular potential barrier

In the quantum mechanical model of a one-dimensional rectangular potential barrier, the Hamiltonian operator H^\hat{H} is defined as the sum of the kinetic energy operator T^\hat{T} and the potential energy operator V^\hat{V}, acting on the Hilbert space L2(R)L^2(\mathbb{R}).

definition

The Hamiltonian for the rectangular barrier is essentially self-adjoint

The Hamiltonian operator HH associated with a one-dimensional rectangular potential barrier is essentially self-adjoint.

definition

Quantum system of the rectangular potential barrier

The definition characterizes the one-dimensional quantum mechanical system of a particle of mass mm subject to a rectangular potential barrier of height V0V_0. This system is defined by the Hilbert space L2(R)L^2(\mathbb{R}) and its associated self-adjoint Hamiltonian operator H^=T^+V^\hat{H} = \hat{T} + \hat{V}, where T^\hat{T} is the kinetic energy operator and V^\hat{V} is the potential energy operator corresponding to a potential that is V0V_0 on a closed interval and zero elsewhere.