We study the commutation relations within the Pauli groups built on all decompositions of a given Hilbert space dimension
q, containing a square, into its factors. Illustrative low dimensional examples are the quartit (
q=4) and two-qubit (
q=22) systems, the octit (
q=8), qubit/quartit (
q=2×4) and three-qubit (
q=23) systems, and so on. In the single qudit case, e.g.
q=4,8,12,..., one defines a bijection between the
σ(q) maximal commuting sets [with
σ[q) the sum of divisors of
q] of Pauli observables and the maximal submodules of the modular ring
Zq2, that arrange into the projective line
P1(Zq) and a independent set of size
σ(q)−ψ(q) [with
ψ(q) the Dedekind psi function]. In the multiple qudit case, e.g.
q=22,23,32,..., the Pauli graphs rely on symplectic polar spaces such as the generalized quadrangles GQ(2,2) (if
q=22) and GQ(3,3) (if
q=32). More precisely, in dimension
pn (
p a prime) of the Hilbert space, the observables of the Pauli group (modulo the center) are seen as the elements of the
2n-dimensional vector space over the field
Fp. In this space, one makes use of the commutator to define a symplectic polar space
W2n−1(p) of cardinality
σ(p2n−1), that encodes the maximal commuting sets of the Pauli group by its totally isotropic subspaces. Building blocks of
W2n−1(p) are punctured polar spaces (i.e. a observable and all maximum cliques passing to it are removed) of size given by the Dedekind psi function
ψ(p2n−1). For multiple qudit mixtures (e.g. qubit/quartit, qubit/octit and so on), one finds multiple copies of polar spaces, ponctured polar spaces, hypercube geometries and other intricate structures. Such structures play a role in the science of quantum information.
We study the commutation relations within the Pauli groups built on all decompositions of a given Hilbert space dimension q , containing a square, into its factors. Illustrative low dimensional examples are the quartit ( q = 4) and two-qubit ( q = 2 2 ) systems, the octit ( q = 8), qubit/quartit ( q = 2 × 4) and three-qubit ( q = 2 3 ) systems, and so on. In the single qudit case, e.g. q = 4, 8, 12,..., one defines a bijection between the σ ( q ) maximal commuting sets [with σ[ q )the sum of divisors of q ] of Pauli observables and the maximal submodules of the modular ring q 2 , that arrange into the projective line P 1 ( q ) and a independent set of size σ( q ) − ψ( q ) [with ψ( q ) the Dedekind psi function]. In the multiple qudit case, e.g. q = 2 2 , 2 3 , 3 2 ,..., the Pauli graphs rely on symplectic polar spaces such as the generalized quadrangles GQ (2,2) (if q = 2 2 ) and GQ (3,3) (if q = 3 2 ). More precisely, in dimension p n ( p a prime) of the Hilbert space, the observables of the Pauli group (modulo the center) are seen as the elements of the 2n-dimensional vector space over the field F p . In this space, one makes use of the commutator to define a symplectic polar space W 2 n −1 (p) of cardinality σ ( p 2 n −1 ), that encodes the maximal commuting sets of the Pauli group by its totally isotropic subspaces. Building blocks of W 2 n −1 ( p ) are punctured polar spaces (i.e. a observable and all maximum cliques passing to it are removed) of size given by the Dedekind psi function ψ ( p 2 N −1 ). For multiple qudit mixtures (e.g. qubit/quartit, qubit/octit and so on), one finds multiple copies of polar spaces, ponctured polar spaces, hypercube geometries and other intricate structures. Such structures play a role in the science of quantum information.