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Quantum Information and Computation

Cohering power and decohering power of Gaussian unitary operations

Yangyang Wang, Xiaofei Qi, Jinchuan Hou, Rufen Ma

Published Jun 1, 2019• 1 citation
Publisher

Abstract

Having a suitable measure to quantify the coherence of quantum states, a natural task is to evaluate the power of quantum channels for creating or destroying the coherence of input quantum states. In the present paper, by introducing the maximal coherent Gaussian states based on the relative entropy measure of coherence, we propose the (generalized) cohering power and the (generalized) decohering power of Gaussian unitary operations for continuous-variable systems. Some basic properties are obtained and the cohering power and decohering power of two special kinds of Gaussian unitary operations are calculated.

DOI
10.26421/qic19.7-8-3

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Having a suitable measure to quantify the coherence of quantum states, a natural task is to evaluate the power of quantum channels for creating or destroying the coherence of input quantum states. In the present paper, by introducing the maximal coherent Gaussian states based on the relative entropy measure of coherence, we propose the (generalized) cohering power and the (generalized) decohering power of Gaussian unitary operations for continuous-variable systems. Some basic properties are obtained and the cohering power and decohering power of two special kinds of Gaussian unitary operations are calculated.
We introduce the concepts of cohering and decohering power of quantum channels. Using the axiomatic definition of the coherence measure, we show that the optimization required for calculations of these measures can be restricted to pure input states and hence greatly simplified. We then use two examples of this measure, one based on the skew information and the other based on the l1{l}_{1}l1​ norm; we find the cohering and decohering measures of a number of one-, two-, and nnn-qubit channels. Contrary to the view at first glance, it is seen that quantum channels can have cohering power. It is also shown that a specific property of a qubit unitary map is that it has equal cohering and decohering power in any basis. Finally, we derive simple relations between cohering and decohering powers of unitary qubit gates and their tensor products, results which have physically interesting implications.
The coherence power of a quantum channel, that is, its maximum ability to increase the coherence of input states, is a fundamental concept within the framework of the resource theory of coherence. In this note we discuss various possible definitions of coherence power and coherence rate and their basic properties. Then we prove that the coherence power of a unitary operator acting on a qubit, computed with respect to the l1-coherence measure, can be calculated by maximizing its coherence gain over pure incoherent states. We proceed to show that this result fails in the general case, that is, the maximal coherence gain is found when acting on a state with non-vanishing coherence in the case of the l1-coherence and dimension N > 2, the relative entropy of coherence and the geometric measure of coherence.
Abstract Quantum coherence stems from the superposition principle of states. It shows an essential feature of quantum systems which is different from the classical phenomena. We investigate the concept of cohering and decohering power of single-mode quantum Gaussian noises. For this purpose, we use the Hellinger distance-based and Bures distance-based measure to quantify the coherence of single-mode quantum Gaussian states. We will show that both Hellinger and Bures distance-based measures are the same when quantifying the quantum coherence of pure single-mode quantum Gaussian states. In this work we will study the cohering and decohering power of single-mode attenuation and amplification noise. We will investigate the effects of the amplification parameter k and attenuation parameter on the cohering and decohering power of corresponding channels. We find that for single-mode amplification noise the cohering power is increased by increasing k , while the decohering power is decreased by increasing k . Conversely, we will see that for a single-mode attenuation channel the cohering power is decreased by increasing the attenuation parameter , while in general the decohering power is increased by increasing . We also investigate the effect of the mean photon number of the environment N on the cohering and decohering power of single-mode attenuation and amplification noises. For both of the channels the cohering power is increased, while the decohering power is decreased, by increasing N .
In this paper, we consider the cohering power of unitary operation, which is defined by the maximum coherence caused by an unitary operation acting on incoherent states. We obtain that the optimizations can be reduced to a simple discrete set that depends only on the fixed reference basis. Then, we investigate that the de-cohering power of quantum channel, which is defined by the maximum decay of coherence caused by quantum channel acting on the maximally coherent states. Based on the relative entropy, we discuss the cohering power of 1-qubit and 2-qubit unitary operations and the de-cohering power of quantum channel on 1-qubit system. Finally, we study the relation between the coherence and the discord via incoherent operation.
Abstract In this paper, we investigate the cohering and decohering power of the one-qubit Markovian channels with respect to coherence measures based on the l 1 - norm, the Rényi α - relative entropy and the Tsallis α - relative entropy of coherence, respectively. The amplitude damping channel, phase damping channel, depolarizing channel, and flip channels are analytically calculated. It shows that the decohering power of the amplitude damping channel on the x , y , and z basis is equal to each other. The same phenomenon can be seen for the phase damping channel and the flip channels. The cohering power for the phase damping channel and the flip channels on the x , y basis also equals to that on the z basis. However, the cohering and decohering power of the depolarizing channel is independent to the reference basises. And the cohering power of the amplitude damping channel on the x , y basis is different to that on the z basis.