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Pauli matrices
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==== Anticommutation relations==== They also satisfy the [[anticommutator|anticommutation]] relations: :<math>\{\sigma_j, \sigma_k\} = 2 \delta_{j k}\,I,</math> where <math>\{\sigma_j, \sigma_k\}</math> is defined as <math>\sigma_j \sigma_k + \sigma_k \sigma_j,</math> and {{math|''Ξ΄{{sub|jk}}''}} is the [[Kronecker delta]]. {{mvar|I}} denotes the {{math|2 Γ 2}} identity matrix. These anti-commutation relations make the Pauli matrices the generators of a representation of the [[Clifford algebra]] for <math>\mathbb{R}^3,</math> denoted <math>\mathrm{Cl}_3(\mathbb{R}) .</math> The usual construction of generators <math>\sigma_{jk} = \tfrac{1}{4} [\sigma_j, \sigma_k]</math> of <math>\mathfrak{so}(3)</math> using the Clifford algebra recovers the commutation relations above, up to unimportant numerical factors. A few explicit commutators and anti-commutators are given below as examples: {| style="text-align:left;" ! Commutators ! Anticommutators |- | <math>\begin{align} \left[\sigma_1, \sigma_1\right] &= 0 \\ \left[\sigma_1, \sigma_2\right] &= 2i\sigma_3 \\ \left[\sigma_2, \sigma_3\right] &= 2i\sigma_1 \\ \left[\sigma_3, \sigma_1\right] &= 2i\sigma_2 \end{align}</math>{{quad}} | <math>\begin{align} \left\{\sigma_1, \sigma_1\right\} &= 2I \\ \left\{\sigma_1, \sigma_2\right\} &= 0 \\ \left\{\sigma_2, \sigma_3\right\} &= 0 \\ \left\{\sigma_3, \sigma_1\right\} &= 0 \end{align}</math> |}
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