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Macroscopic quantum entanglement of Kondo cloud at finite temperature

Seung-Sup Lee, Korea Advanced Institute of Science and Technology

27.05.2014 at 09:00 

Macroscopic entanglement, measured by entanglement entropy, characterizes the new aspects of many-body  systems at zero temperature, such as area law, topological order, and quantum criticality. Generalizing the  characterization to finite temperature is desirable. For example, it remains unexplored how the entanglement of Kondo systems, the representative of macroscopic entanglement, thermally decays. However, the generalization  has been obstructed by the impractical cost of computing entanglement in thermal mixed states. Here we develop a variational approach for the computation, using entanglement witness operators (EWs), and compute  the entanglement of formation (EoF), a mixed-state generalization of entanglement entropy, in single- (1CK) and  two-channel Kondo (2CK) systems. The thermal suppression of EoF shows crossover around Kondo temperature, and obeys power-law scaling at low temperature. The scaling exponent is halved from 1CK to 2CK, attributed to a  Majorana fermion, a ''half'' of a complex fermion, emerging in 2CK. Moreover, EoF characterizes the size and  power-law tail of Kondo screening cloud in 1CK.

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