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Physlib.QuantumMechanics.DDimensions.Operators.Commutation

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theorem

[AB,C]=A[B,C]+[A,C]B[A \circ B, C] = A \circ [B, C] + [A, C] \circ B

#leibniz_lie

Let S(Space d,C)\mathcal{S}(\text{Space } d, \mathbb{C}) denote the space of Schwartz functions on a dd-dimensional space. For any continuous linear operators A,B,CA, B, C acting on S(Space d,C)\mathcal{S}(\text{Space } d, \mathbb{C}), the commutator of the composition ABA \circ B with CC satisfies the Leibniz rule: [AB,C]=A[B,C]+[A,C]B [A \circ B, C] = A \circ [B, C] + [A, C] \circ B where [X,Y]=XYYX[X, Y] = X \circ Y - Y \circ X denotes the commutator (Lie bracket) and \circ denotes operator composition.

theorem

Leibniz rule A,BC=BA,C+A,BC\llbracket A, BC \rrbracket = B\llbracket A, C \rrbracket + \llbracket A, B \rrbracket C

#lie_leibniz

Let AA, BB, and CC be continuous linear operators acting on the Schwartz space S(Rd,C)\mathcal{S}(\mathbb{R}^d, \mathbb{C}). The commutator of AA with the composition of BB and CC satisfies the Leibniz rule: A,BC=BA,C+A,BC\llbracket A, B \circ C \rrbracket = B \circ \llbracket A, C \rrbracket + \llbracket A, B \rrbracket \circ C where X,Y=XYYX\llbracket X, Y \rrbracket = X \circ Y - Y \circ X denotes the commutator bracket.

theorem

AB=BA+[A,B]A \circ B = B \circ A + [A, B]

#comp_eq_comp_add_commute

For any two continuous linear operators AA and BB acting on the Schwartz space S(Rd,C)\mathcal{S}(\mathbb{R}^d, \mathbb{C}), the composition ABA \circ B satisfies the identity AB=BA+[A,B]A \circ B = B \circ A + [A, B] where [A,B]=ABBA[A, B] = A \circ B - B \circ A is the commutator of the two operators.

theorem

AB=BA[B,A]A \circ B = B \circ A - [B, A] for operators on Schwartz maps

#comp_eq_comp_sub_commute

Let AA and BB be continuous linear operators on the Schwartz space S(Rd,C)\mathcal{S}(\mathbb{R}^d, \mathbb{C}) of rapidly decreasing functions. Then the composition of AA and BB can be expressed in terms of their commutator as: AB=BA[B,A]A \circ B = B \circ A - [B, A] where [B,A]=BAAB[B, A] = BA - AB denotes the Lie bracket (commutator) of the operators BB and AA.

theorem

[xi,xj]=0[\mathbf{x}_i, \mathbf{x}_j] = 0

#position_commutation_position

For any indices ii and jj, the position operators xi\mathbf{x}_i and xj\mathbf{x}_j acting on the space of Schwartz functions S(Rd,C)\mathcal{S}(\mathbb{R}^d, \mathbb{C}) commute. Their commutator is zero: [xi,xj]=0[\mathbf{x}_i, \mathbf{x}_j] = 0

theorem

xixj=xjxi\mathbf{x}_i \circ \mathbf{x}_j = \mathbf{x}_j \circ \mathbf{x}_i

#position_comp_commute

For any indices ii and jj, the components of the position operator xi\mathbf{x}_i and xj\mathbf{x}_j acting on the Schwartz space S(Rd,C)\mathcal{S}(\mathbb{R}^d, \mathbb{C}) commute under composition: xixj=xjxi\mathbf{x}_i \circ \mathbf{x}_j = \mathbf{x}_j \circ \mathbf{x}_i

theorem

[xi,rϵ,s]=0[\mathbf{x}_i, r_{\epsilon, s}] = 0

#position_commutation_radiusRegPow

In dd-dimensional space, the ii-th component of the position operator xi\mathbf{x}_i commutes with the regularized power of the radius operator rϵ,sr_{\epsilon, s} (where ϵ\epsilon is a regularization parameter and ss is the power). That is, the commutator [xi,rϵ,s]=0[\mathbf{x}_i, r_{\epsilon, s}] = 0.

theorem

xirϵ,s=rϵ,sxi\mathbf{x}_i \circ r_{\epsilon, s} = r_{\epsilon, s} \circ \mathbf{x}_i

#position_comp_radiusRegPow_commute

In dd-dimensional space, the ii-th component of the position operator xi\mathbf{x}_i and the regularized radius power operator rϵ,sr_{\epsilon, s} commute under composition. That is, xirϵ,s=rϵ,sxi\mathbf{x}_i \circ r_{\epsilon, s} = r_{\epsilon, s} \circ \mathbf{x}_i where ϵ\epsilon is a regularization parameter and ss is the power.

theorem

[rϵ,s,rϵ,t]=0[\mathbf{r}_{\epsilon, s}, \mathbf{r}_{\epsilon, t}] = 0

#radiusRegPow_commutation_radiusRegPow

The commutator of two regularized radius power operators rϵ,s\mathbf{r}_{\epsilon, s} and rϵ,t\mathbf{r}_{\epsilon, t} in dd-dimensional space is zero, that is, [rϵ,s,rϵ,t]=0 \left[ \mathbf{r}_{\epsilon, s}, \mathbf{r}_{\epsilon, t} \right] = 0 where rϵ,s\mathbf{r}_{\epsilon, s} denotes the operator associated with a regularized power ss of the norm of the position vector with regularization parameter ϵ\epsilon, and [A,B]=ABBA[A, B] = AB - BA is the commutator of operators AA and BB.

theorem

[pi,pj]=0[p_i, p_j] = 0

#momentum_commutation_momentum

For any indices ii and jj, the ii-th and jj-th components of the momentum operator pip_i and pjp_j commute. Their commutator is zero: [pi,pj]=0 [p_i, p_j] = 0 where pk=ikp_k = -i \hbar \partial_k is the momentum operator acting on the space of Schwartz functions S(Rd,C)\mathcal{S}(\mathbb{R}^d, \mathbb{C}).

theorem

pipj=pjpip_i \circ p_j = p_j \circ p_i

#momentum_comp_commute

For any indices ii and jj, the ii-th and jj-th components of the momentum operator pip_i and pjp_j acting on the Schwartz space S(Rd,C)\mathcal{S}(\mathbb{R}^d, \mathbb{C}) commute under composition: pipj=pjpi p_i \circ p_j = p_j \circ p_i where pk=ikp_k = -i \hbar \partial_k denotes the momentum operator in the kk-th direction.

theorem

[p2,pi]=0[\mathbf{p}^2, p_i] = 0

#momentumSqr_commutation_momentum

Let p2\mathbf{p}^2 denote the momentum-squared operator and pip_i denote the ii-th component of the momentum operator acting on the space of Schwartz functions S(Space d,C)\mathcal{S}(\text{Space } d, \mathbb{C}). The commutator of the momentum-squared operator and any component of the momentum operator is zero: [p2,pi]=0 [\mathbf{p}^2, p_i] = 0 where p2=jpjpj\mathbf{p}^2 = \sum_j p_j \circ p_j.

theorem

p2pi=pip2\mathbf{p}^2 \circ p_i = p_i \circ \mathbf{p}^2

#momentumSqr_comp_momentum_commute

Let p2\mathbf{p}^2 denote the momentum-squared operator and pip_i denote the ii-th component of the momentum operator acting on the Schwartz space S(Rd,C)\mathcal{S}(\mathbb{R}^d, \mathbb{C}). These operators commute under composition: p2pi=pip2\mathbf{p}^2 \circ p_i = p_i \circ \mathbf{p}^2 where p2=jpjpj\mathbf{p}^2 = \sum_j p_j \circ p_j is defined as the sum of the squares of the momentum components.

theorem

Canonical Commutation Relation [xi,pj]=iδij1[x_i, p_j] = i \hbar \delta_{ij} \mathbb{1}

#position_commutation_momentum

Let xix_i be the ii-th component of the position operator and pjp_j be the jj-th component of the momentum operator acting on the Schwartz space S(Rd,C)\mathcal{S}(\mathbb{R}^d, \mathbb{C}). The commutator of these operators satisfies the canonical commutation relation: [xi,pj]=iδij1[x_i, p_j] = i \hbar \delta_{ij} \mathbb{1} where ii is the imaginary unit, \hbar is the reduced Planck constant, δij\delta_{ij} is the Kronecker delta, and 1\mathbb{1} is the identity operator on the Schwartz space.

theorem

pjxi=xipjiδij1p_j \circ x_i = x_i \circ p_j - i \hbar \delta_{ij} \mathbb{1}

#momentum_comp_position_eq

Let xix_i be the ii-th component of the position operator and pjp_j be the jj-th component of the momentum operator acting on the Schwartz space S(Rd,C)\mathcal{S}(\mathbb{R}^d, \mathbb{C}). The composition of these operators satisfies the following relation: pjxi=xipjiδij1p_j \circ x_i = x_i \circ p_j - i \hbar \delta_{ij} \mathbb{1} where ii is the imaginary unit, \hbar is the reduced Planck constant, δij\delta_{ij} is the Kronecker delta, and 1\mathbb{1} is the identity operator on the Schwartz space.

theorem

[xixj,pk]=i(δikxj+δjkxi)[x_i x_j, p_k] = i \hbar (\delta_{ik} x_j + \delta_{jk} x_i)

#position_position_commutation_momentum

Let xix_i and xjx_j be the ii-th and jj-th components of the position operator, respectively, and pkp_k be the kk-th component of the momentum operator acting on the space of Schwartz functions S(Rd,C)\mathcal{S}(\mathbb{R}^d, \mathbb{C}). The commutator of the product (composition) of the position operators xixjx_i x_j with the momentum operator pkp_k is given by: [xixj,pk]=i(δikxj+δjkxi)[x_i x_j, p_k] = i \hbar (\delta_{ik} x_j + \delta_{jk} x_i) where ii is the imaginary unit, \hbar is the reduced Planck constant, and δab\delta_{ab} is the Kronecker delta.

theorem

[xi,pjpk]=i(δikpj+δijpk)[x_i, p_j p_k] = i \hbar (\delta_{ik} p_j + \delta_{ij} p_k)

#position_commutation_momentum_momentum

Let xix_i be the ii-th component of the position operator and pj,pkp_j, p_k be the jj-th and kk-th components of the momentum operator acting on the Schwartz space S(Rd,C)\mathcal{S}(\mathbb{R}^d, \mathbb{C}). The commutator of the position operator xix_i with the product (composition) of the momentum operators pjpkp_j p_k is given by: [xi,pjpk]=i(δikpj+δijpk)[x_i, p_j p_k] = i \hbar (\delta_{ik} p_j + \delta_{ij} p_k) where ii is the imaginary unit, \hbar is the reduced Planck constant, and δab\delta_{ab} is the Kronecker delta.

theorem

[xi,p2]=2ipi[x_i, \mathbf{p}^2] = 2i\hbar p_i

#position_commutation_momentumSqr

Let xix_i be the ii-th component of the position operator and p2\mathbf{p}^2 be the momentum-squared operator (defined as p2=jpj2\mathbf{p}^2 = \sum_j p_j^2) acting on the Schwartz space S(Rd,C)\mathcal{S}(\mathbb{R}^d, \mathbb{C}). The commutator of these operators is given by: [xi,p2]=2ipi[x_i, \mathbf{p}^2] = 2i\hbar p_i where ii is the imaginary unit, \hbar is the reduced Planck constant, and pip_i is the ii-th component of the momentum operator.

theorem

Commutator of regularized radius power and momentum: [rϵs,pi]=isrϵs2xi[r_\epsilon^s, p_i] = i s \hbar r_\epsilon^{s-2} x_i

#radiusRegPow_commutation_momentum

In dd-dimensional space, let rϵs\mathbf{r}_{\epsilon}^s denote the operator of multiplication by the ss-th power of the regularized radius, defined as f(x)=(x2+ϵ2)s/2f(x) = (|x|^2 + \epsilon^2)^{s/2} for a regularization parameter ϵ\epsilon and power ss. Let pip_i be the ii-th component of the momentum operator and xix_i be the ii-th component of the position operator. The commutator of these operators satisfies: [rϵs,pi]=isrϵs2xi \left[ \mathbf{r}_{\epsilon}^s, p_i \right] = i s \hbar \mathbf{r}_{\epsilon}^{s-2} x_i where ii is the imaginary unit and \hbar is the reduced Planck constant.

theorem

pirϵs=rϵspiisrϵs2xip_i \circ \mathbf{r}_{\epsilon}^s = \mathbf{r}_{\epsilon}^s \circ p_i - i s \hbar \mathbf{r}_{\epsilon}^{s-2} x_i

#momentum_comp_radiusRegPow_eq

Let pip_i be the ii-th component of the momentum operator acting on the Schwartz space S(Rd,C)\mathcal{S}(\mathbb{R}^d, \mathbb{C}). Let rϵs\mathbf{r}_{\epsilon}^s be the operator of multiplication by the ss-th power of the regularized radius, defined by (x2+ϵ2)s/2(|x|^2 + \epsilon^2)^{s/2}. The composition of these operators satisfies the following identity: pirϵs=rϵspiisrϵs2xi p_i \circ \mathbf{r}_{\epsilon}^s = \mathbf{r}_{\epsilon}^s \circ p_i - i s \hbar \mathbf{r}_{\epsilon}^{s-2} \circ x_i where xix_i is the ii-th component of the position operator, ii is the imaginary unit, and \hbar is the reduced Planck constant.

theorem

[rϵs,p2]=2sirϵs2xipi+s(d+s2)2rϵs2ϵ2s(s2)2rϵs4[r_\epsilon^s, \mathbf{p}^2] = 2si\hbar r_\epsilon^{s-2} \sum x_i p_i + s(d+s-2)\hbar^2 r_\epsilon^{s-2} - \epsilon^2 s(s-2)\hbar^2 r_\epsilon^{s-4}

#radiusRegPow_commutation_momentumSqr

In dd-dimensional space, let rϵs\mathbf{r}_{\epsilon}^s denote the operator of multiplication by the function f(x)=(x2+ϵ2)s/2f(x) = (\|x\|^2 + \epsilon^2)^{s/2}, where ϵ\epsilon is a regularization parameter and ss is a power. Let p2=i=1dpi2\mathbf{p}^2 = \sum_{i=1}^d p_i^2 be the momentum-squared operator acting on the Schwartz space S(Rd,C)\mathcal{S}(\mathbb{R}^d, \mathbb{C}). The commutator of these operators is given by the identity: [rϵs,p2]=2sirϵs2i=1dxipi+s(d+s2)2rϵs2ϵ2s(s2)2rϵs4 \left[ \mathbf{r}_{\epsilon}^s, \mathbf{p}^2 \right] = 2 s i \hbar \mathbf{r}_{\epsilon}^{s-2} \sum_{i=1}^d x_i p_i + s(d + s - 2) \hbar^2 \mathbf{r}_{\epsilon}^{s-2} - \epsilon^2 s(s - 2) \hbar^2 \mathbf{r}_{\epsilon}^{s-4} where xix_i and pip_i are the ii-th components of the position and momentum operators respectively, ii is the imaginary unit, and \hbar is the reduced Planck constant.

theorem

[Lij,xk]=i(δikxjδjkxi)[L_{ij}, x_k] = i \hbar (\delta_{ik} x_j - \delta_{jk} x_i)

#angularMomentum_commutation_position

In dd-dimensional space, let LijL_{ij} be the (i,j)(i, j)-th component of the angular momentum operator and xkx_k be the kk-th component of the position operator acting on the Schwartz space S(Rd,C)\mathcal{S}(\mathbb{R}^d, \mathbb{C}). The commutator of these operators is given by: [Lij,xk]=i(δikxjδjkxi) [L_{ij}, x_k] = i \hbar (\delta_{ik} x_j - \delta_{jk} x_i) where ii is the imaginary unit, \hbar is the reduced Planck constant, and δik\delta_{ik} is the Kronecker delta.

theorem

[Lij,rϵs]=0[L_{ij}, r_{\epsilon}^s] = 0

#angularMomentum_commutation_radiusRegPow

In dd-dimensional space, let LijL_{ij} denote the (i,j)(i, j)-th component of the angular momentum operator acting on the Schwartz space S(Rd,C)\mathcal{S}(\mathbb{R}^d, \mathbb{C}). Let rϵsr_{\epsilon}^s denote the regularized radius power operator, which corresponds to the multiplication operator by the function f(x)=(x2+ϵ2)s/2f(x) = (\|x\|^2 + \epsilon^2)^{s/2} for a regularization parameter ϵ\epsilon and power ss. The commutator of these operators is zero: [Lij,rϵs]=0 [L_{ij}, r_{\epsilon}^s] = 0

theorem

Lijrϵs=rϵsLijL_{ij} \circ r_{\epsilon}^s = r_{\epsilon}^s \circ L_{ij}

#angularMomentum_comp_radiusRegPow_commute

In dd-dimensional space, let LijL_{ij} denote the (i,j)(i, j)-th component of the angular momentum operator acting on the Schwartz space S(Rd,C)\mathcal{S}(\mathbb{R}^d, \mathbb{C}). Let rϵsr_{\epsilon}^s denote the regularized radius power operator, which is the multiplication operator by the function f(x)=(x2+ϵ2)s/2f(x) = (\|x\|^2 + \epsilon^2)^{s/2} for a regularization parameter ϵ\epsilon and power ss. The composition of these two operators is commutative: Lijrϵs=rϵsLij L_{ij} \circ r_{\epsilon}^s = r_{\epsilon}^s \circ L_{ij}

theorem

[L2,rϵs]=0[L^2, r_{\epsilon}^s] = 0

#angularMomentumSqr_commutation_radiusRegPow

In dd-dimensional space, let L2L^2 denote the squared angular momentum operator acting on the Schwartz space S(Rd,C)\mathcal{S}(\mathbb{R}^d, \mathbb{C}). Let rϵsr_{\epsilon}^s denote the regularized radius power operator, which acts as the multiplication operator by the function f(x)=(x2+ϵ2)s/2f(x) = (\|x\|^2 + \epsilon^2)^{s/2} for a regularization parameter ϵ\epsilon and power ss. The commutator of the squared angular momentum operator and the regularized radius power operator is zero: [L2,rϵs]=0 [L^2, r_{\epsilon}^s] = 0

theorem

L2rϵs=rϵsL2L^2 \circ r_{\epsilon}^s = r_{\epsilon}^s \circ L^2

#angularMomentumSqr_comp_radiusRegPow_commute

In dd-dimensional space, let L2L^2 denote the squared angular momentum operator acting on the Schwartz space S(Rd,C)\mathcal{S}(\mathbb{R}^d, \mathbb{C}). Let rϵsr_{\epsilon}^s denote the regularized radius power operator, which acts as the multiplication operator by the function f(x)=(x2+ϵ2)s/2f(x) = (\|x\|^2 + \epsilon^2)^{s/2} for a regularization parameter ϵ\epsilon and power ss. The composition of the squared angular momentum operator and the regularized radius power operator is commutative: L2rϵs=rϵsL2 L^2 \circ r_{\epsilon}^s = r_{\epsilon}^s \circ L^2

theorem

[Lij,pk]=i(δikpjδjkpi)[L_{ij}, p_k] = i \hbar (\delta_{ik} p_j - \delta_{jk} p_i)

#angularMomentum_commutation_momentum

Let LijL_{ij} be the components of the angular momentum operator and pkp_k be the kk-th component of the momentum operator acting on the space of Schwartz functions S(Rd,C)\mathcal{S}(\mathbb{R}^d, \mathbb{C}). For any indices i,j,ki, j, k, the commutator of LijL_{ij} and pkp_k is given by: [Lij,pk]=i(δikpjδjkpi) [L_{ij}, p_k] = i \hbar (\delta_{ik} p_j - \delta_{jk} p_i) where ii is the imaginary unit, \hbar is the reduced Planck constant, and δab\delta_{ab} denotes the Kronecker delta.

theorem

pkLij=Lijpki(δikpjδjkpi)p_k \circ L_{ij} = L_{ij} \circ p_k - i \hbar (\delta_{ik} p_j - \delta_{jk} p_i)

#momentum_comp_angularMomentum_eq

Let pkp_k be the kk-th component of the momentum operator and LijL_{ij} be the components of the angular momentum operator, both acting as continuous linear operators on the space of Schwartz functions S(Rd,C)\mathcal{S}(\mathbb{R}^d, \mathbb{C}). For any indices i,j,ki, j, k, the composition of pkp_k and LijL_{ij} satisfies the relation: pkLij=Lijpki(δikpjδjkpi) p_k \circ L_{ij} = L_{ij} \circ p_k - i \hbar (\delta_{ik} p_j - \delta_{jk} p_i) where ii is the imaginary unit, \hbar is the reduced Planck constant, and δab\delta_{ab} denotes the Kronecker delta.

theorem

[Lij,p2]=0[L_{ij}, \mathbf{p}^2] = 0

#angularMomentum_commutation_momentumSqr

Let LijL_{ij} be the components of the angular momentum operator and p2\mathbf{p}^2 be the momentum-squared operator acting on the space of Schwartz functions S(Rd,C)\mathcal{S}(\mathbb{R}^d, \mathbb{C}). For any indices ii and jj, the commutator of LijL_{ij} and p2\mathbf{p}^2 is zero: [Lij,p2]=0 [L_{ij}, \mathbf{p}^2] = 0 where [A,B]=ABBA[A, B] = A \circ B - B \circ A denotes the commutator bracket.

theorem

p2Lij=Lijp2\mathbf{p}^2 \circ L_{ij} = L_{ij} \circ \mathbf{p}^2

#momentumSqr_comp_angularMomentum_commute

Let p2\mathbf{p}^2 be the momentum-squared operator and LijL_{ij} be the (i,j)(i, j)-th component of the angular momentum operator, both acting as continuous linear operators on the space of Schwartz functions S(Rd,C)\mathcal{S}(\mathbb{R}^d, \mathbb{C}). For any indices ii and jj, the composition of these operators is commutative: p2Lij=Lijp2 \mathbf{p}^2 \circ L_{ij} = L_{ij} \circ \mathbf{p}^2

theorem

[L2,p2]=0[\mathbf{L}^2, \mathbf{p}^2] = 0

#angularMomentumSqr_commutation_momentumSqr

Let L2\mathbf{L}^2 be the angular momentum-squared operator and p2\mathbf{p}^2 be the momentum-squared operator acting on the space of Schwartz functions S(Rd,C)\mathcal{S}(\mathbb{R}^d, \mathbb{C}). The commutator of L2\mathbf{L}^2 and p2\mathbf{p}^2 is zero: [L2,p2]=0 [\mathbf{L}^2, \mathbf{p}^2] = 0 where [A,B]=ABBA[A, B] = A \circ B - B \circ A denotes the commutator bracket.

theorem

[Lij,Lkl]=i(δikLjlδilLjkδjkLil+δjlLik)[L_{ij}, L_{kl}] = i \hbar (\delta_{ik} L_{jl} - \delta_{il} L_{jk} - \delta_{jk} L_{il} + \delta_{jl} L_{ik})

#angularMomentum_commutation_angularMomentum

Let LijL_{ij} be the (i,j)(i, j)-th component of the angular momentum operator acting on the space of Schwartz functions S(Rd,C)\mathcal{S}(\mathbb{R}^d, \mathbb{C}). For any indices i,j,k,l{1,,d}i, j, k, l \in \{1, \dots, d\}, the commutator of the angular momentum operators LijL_{ij} and LklL_{kl} is given by: [Lij,Lkl]=i(δikLjlδilLjkδjkLil+δjlLik) [L_{ij}, L_{kl}] = i \hbar (\delta_{ik} L_{jl} - \delta_{il} L_{jk} - \delta_{jk} L_{il} + \delta_{jl} L_{ik}) where ii is the imaginary unit, \hbar is the reduced Planck constant, and δab\delta_{ab} denotes the Kronecker delta. This relation shows that the angular momentum operators generate the so(d)\mathfrak{so}(d) algebra.

theorem

[L2,Lij]=0[L^2, L_{ij}] = 0

#angularMomentumSqr_commutation_angularMomentum

Let L2L^2 be the total angular momentum squared operator and LijL_{ij} be the (i,j)(i, j)-th component of the angular momentum operator, both acting on the space of Schwartz functions S(Rd,C)\mathcal{S}(\mathbb{R}^d, \mathbb{C}). For any indices i,j{1,,d}i, j \in \{1, \dots, d\}, the commutator of L2L^2 and LijL_{ij} vanishes: [L2,Lij]=0 [L^2, L_{ij}] = 0 where [,][\cdot, \cdot] denotes the Lie bracket (commutator) of operators.