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arXiv:quant-ph/0610127

Noisy Qutrit Channels

Agata Chęcińska, K. Wódkiewicz

Published Oct 16, 2006• 2 citations
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Abstract

We present an analysis of spontaneous emission in a 3-level atom as an example of a qutrit state under the action of noisy quantum channels. We choose a 3-level atom with V-configuration to be the qutrit state. Gell-Mann matrices and a generalized Bloch vector (8-dimensional) are used to describe the qutrit density operator. Using the time-evolution equations of atomic variables we find the Kraus representation of spontaneous emission quantum channel (SE channel). Furthermore, we consider a generalized Werner state of two qutrits and investigate the separability condition. We give similar analysis of spontaneous emission for qubit channels. The influence of spontaneous emission on the separability of Werner states for qutrit and qubit states is compared.

DOI
10.48550/arxiv.quant-ph/0610127

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We present an analysis of spontaneous emission in a 3-level atom as an example of a qutrit state under the action of noisy quantum channels. We choose a 3-level atom with V-configuration to be the qutrit state. Gell-Mann matrices and a generalized Bloch vector (8-dimensional) are used to describe the qutrit density operator. Using the time-evolution equations of atomic variables we find the Kraus representation of spontaneous emission quantum channel (SE channel). Furthermore, we consider a generalized Werner state of two qutrits and investigate the separability condition. We give similar analysis of spontaneous emission for qubit channels. The influence of spontaneous emission on the separability of Werner states for qutrit and qubit states is compared.
We present an analysis of noisy atomic channels involving qutrits. We choose a three-level atom with V\mathsf{V}V configuration to be the qutrit state. Gell-Mann matrices and a generalized Bloch vector (eight-dimensional) are used to describe the qutrit density operator. We introduce quantum quasidistributions for qutrits that provide a simple description of entanglement. Studying the time evolution for the atomic variables we find the Kraus representation of spontaneous emission quantum channel (SE channel). Furthermore, we consider a generalized Werner state of two qutrits and investigate the separability condition in the presence of spontaneous emission noise. The influence of spontaneous emission on the separability of Werner states for qutrit and qubit states is compared.
Two important classes of quantum channels, namely, the Werner-Holevo and the Landau-Streater channels, are known to be related only in three dimensions, i.e., when acting on qutrits. In this work, the definition of the Landau-Streater channel is extended in such a way that it retains its equivalence to the Werner-Holevo channel in all dimensions. This channel is then modified to be representable as a model of noise acting on qudits. We then investigate properties of the resulting noisy channel and determine the conditions under which it cannot be the result of a Markovian evolution. Furthermore, we investigate its different capacities for transmitting classical and quantum information with or without entanglement. In particular, while the pure (or high-noise) Landau-Streater or the Werner-Holevo channel is entanglement breaking and hence has zero capacity, by finding a lower bound for the quantum capacity, we show that when the level of noise is lower than a critical value the quantum capacity will be nonzero. Surprisingly, this value turns out to be approximately equal to 0.4 in all dimensions. Finally, we show that, in even dimensions, this channel has a decomposition in terms of unitary operations. This is in contrast with the three-dimensional, case where it has been proved that such a decomposition is impossible, even in terms of other quantum maps.
Two important classes of quantum channels, namly the Werner-Holevo and the Landau-Streater channels are known to be related only in three dimensions, i.e. when acting on qutrits. In this work, definition of the Landau-Streater channel is extended in such a way which retains its equivalence to the Werner-Holevo channel in all dimensions. This channel is then modified to be representable as a model of noise acting on qudits. We then investigate propeties of the resulting noisy channel and determine the conditions under which it cannot be the result of a Markovian evolution. Furthermore, we investigate its different capacities for transmitting classical and quantum information with or without entanglement. In particular, while the pure (or high noise) Landau-Streater or the Werner-Holevo channel is entanglement breaking and hence has zero capacity, by finding a lower bound for the quantum capacity, we show that when the level of noise is lower than a critical value the quantum capacity will be non-zero. Surprizingly this value turns out to be approximately equal to 0.40.40.4 in all dimensions. Finally we show that, in even dimension, this channel has a decomposition in terms of unitary operations. This is in contrast with the three dimensional case where it has been proved that such a decomposition is impossible, even in terms of other quantum maps.
In the study of d-dimensional quantum channels (d⩾2), an assumption which includes many interesting examples, and which has a natural physical interpretation, is that the corresponding Kraus operators form a representation of a Lie algebra. Physically, this is a symmetry algebra for the interaction Hamiltonian. This paper begins a systematic study of channels defined by representations; the famous Werner-Holevo channel is one element of this infinite class. We show that the channel derived from the defining representation of su(n) is a depolarizing channel for all n, but for most other representations this is not the case. Since the standard Bloch sphere only exists for the qubit representation of su(2), we develop a consistent generalization of Bloch’s technique. By representing the density matrix as a polynomial in Lie algebra generators, we determine a class of positive semidefinite matrices which represent quantum states for various channels defined by finite-dimensional representations of semisimple Lie algebras. We also give a general method for finding positive semidefinite matrices using Lie algebraic trace identities. This includes an analysis of channels based on the exceptional Lie algebra g2 and the Clifford algebra.
In this work, we consider non-interacting atomic two level and three level (qubit-qutrit) systems interacting with a common environment in vacuum state. The interaction with the environment leads to the decoherece of the system due to spontaneous emission of atomic excited states which results in the decay of entanglement and other correlations of the qubit-qutrit system. We study the dynamics of entanglement for different initial class of states and negativity is used as a measure to quantify the degree of entanglement of qubit-qutrit system, the three level systems are considered in V configuration. We construct a class of rank dependant mixed boundary qubit-qutrit states as initial states. We observe entanglement sudden death for higher rank mixed boundary qubit-qutrit states.