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arXiv:2010.01128 · Physical Review A

Geometry of symmetric and noninvertible Pauli channels

Katarzyna Siudzińska

Published Dec 30, 2020• 4 citations
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Abstract

We analyze the geometry of positive and completely positive, trace-preserving Pauli maps that are fully determined by up to two distinct parameters. This includes five classes of symmetric and noninvertible Pauli channels. Using the Hilbert-Schmidt metric in the space of the Choi-Jamio\l{}kowski states, we compute the relative volumes of entanglement breaking, time-local generated, and divisible channels. Finally, we find the shapes of the complete positivity regions in relation to the tetrahedron of all Pauli channels.

DOI
10.1103/physreva.102.062615

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We analyze the geometry of positive and completely positive, trace-preserving Pauli maps that are fully determined by up to two distinct parameters. This includes five classes of symmetric and noninvertible Pauli channels. Using the Hilbert-Schmidt metric in the space of the Choi-Jamio\l{}kowski states, we compute the relative volumes of entanglement breaking, time-local generated, and divisible channels. Finally, we find the shapes of the complete positivity regions in relation to the tetrahedron of all Pauli channels.
We analyze the geometrical properties of trace-preserving Pauli maps. Using the Choi-Jamio\l{}kowski isomorphism, we express the Hilbert-Schmidt line and volume elements in terms of the eigenvalues of the Pauli map. We analytically compute the volumes of positive, trace-preserving Pauli maps and Pauli channels. In particular, we find the relative volumes of the entanglement-breaking Pauli channels as well as the channels that can be generated by a time-local generator. Finally, we show what part of the Pauli channels are P\mathrm{P}P- and CP\mathrm{CP}CP-divisible, which is related to the notion of Markovianity.
We analyze the geometry of the generalized Pauli channels constructed from the mutually unbiased bases. The Choi-Jamio\l{}kowski isomorphism allows us to express the Hilbert-Schmidt line and volume elements in terms of the eigenvalues of the generalized Pauli maps. After determining appropriate regions of integration, we analytically compute the volume of generalized Pauli channels and their important subclasses. In particular, we obtain the volumes of the generalized Pauli channels that can be generated by a legitimate generator and are entanglement breaking. We also provide the upper bound for the volume of positive, trace-preserving generalized Pauli maps. This helps us to better understand the structure of high-dimensional sets of quantum channels.
In the space of quantum channels, we establish the geometry that allows us to make statistical predictions about relative volumes of entanglement breaking channels among all the Gaussian quantum channels. The underlying metric is constructed using the Choi-Jamio\l{}kowski isomorphism between the continuous-variable Gaussian states and channels. This construction involves the Hilbert-Schmidt distance in quantum state space. The volume element of the one-mode Gaussian channels can be expressed in terms of local symplectic invariants. We analytically compute the relative volumes of the one-mode Gaussian entanglement breaking and incompatibility breaking channels. Finally, we show that, when given the purities of the Choi-Jamio\l{}kowski state of the channel, one can determine whether or not such channel is incompatibility breaking.
We use symmetric measurement operators to construct quantum channels that provide a further generalization of generalized Pauli channels. The resulting maps are bistochastic but, in general, no longer mixed unitary. We analyze their important properties, such as complete positivity and the ability to break quantum entanglement. In the main part, we consider the corresponding open quantum systems dynamics with time-local generators. From the divisibility properties of dynamical maps, we derive sufficient Markovianity and non-Markovianity conditions. As instructive examples, we present the generators of P-divisible generalized Pauli dynamical maps that allow for more negativity in the decoherence rates.
In matrix algebras, we introduce a class of linear maps that are irreducibly covariant with respect to the finite group generated by the Weyl operators. In particular, we analyze the irreducibly covariant quantum channels, that is, the completely positive and trace-preserving linear maps. Interestingly, imposing additional symmetries leads to the so-called generalized Pauli channels, which were recently considered in the context of the non-Markovian quantum evolution. Finally, we provide examples of irreducibly covariant positive but not necessarily completely positive maps.