183 research outputs found
Universal and measurable entanglement entropy in the spin-boson model
We study the entanglement between a qubit and its environment from the
spin-boson model with Ohmic dissipation. Through a mapping to the anisotropic
Kondo model, we derive the entropy of entanglement of the spin
, where is the dissipation strength, is
the tunneling amplitude between qubit states, and is the level asymmetry.
For and , we show that
the Kondo energy scale controls the entanglement between the qubit and
the bosonic environment ( is a high-energy cutoff). For ,
the disentanglement proceeds as ; for , vanishes as
, up to a logarithmic correction. For a given , the
maximum entanglement occurs at a value of which lies in the crossover
regime . We emphasize the possibility of measuring this entanglement
using charge qubits subject to electromagnetic noise.Comment: 4 pages and 4 figures; updated version to appear in Physical Review
Letter
Probing dynamics of Majorana fermions in quantum impurity systems
We investigate the admittance of a metallic quantum RC circuit with a spinful
single-channel lead or equally with two conducting spin-polarized channels, in
which Majorana fermions play a crucial role in the charge dynamics. We address
how the two-channel Kondo physics and its emergent Majoranas arise. The
existence of a single unscreened Majorana mode results in non-Fermi-liquid
features and we determine the universal crossover function describing the
Fermi-liquid to non-Fermi-liquid region. Remarkably, the same universal form
emerges both at weak transmission and large transmission. We find that the
charge relaxation resistance strongly increases in the non-Fermi-liquid realm.
Our findings can be measured using current technology assuming a large cavity.Comment: 5 pages, 1 fi
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