28 research outputs found
Non-Markovian quantum state diffusion for an open quantum system in fermionic environments
Non-Markovian quantum state diffusion (NMQSD) provides a powerful approach to
the dynamics of an open quantum system in bosonic environments. Here we develop
an NMQSD method to study the open quantum system in fermionic environments.
This problem involves anticommutative noise functions (i.e., Grassmann
variables) that are intrinsically different from the noise functions of bosonic
baths. We obtain the NMQSD equation for quantum states of the system and the
non-Markovian master equation. Moreover, we apply this NMQSD method to single
and double quantum-dot systems.Comment: 9 pages, 1 figur
Accessing nanotube bands via crossed electric and magnetic fields
We investigate the properties of conduction electrons in single-walled
armchair carbon nanotubes in the presence of mutually orthogonal electric and
magnetic fields transverse to the tube's axis. We find that the fields give
rise to an asymmetric dispersion in the right- and left-moving electrons along
the tube as well as a band-dependent interaction. We predict that such a
nanotube system would exhibit spin-band-charge separation and a band-dependant
tunneling density of states. We show that in the quantum dot limit, the fields
serve to completely tune the quantum states of electrons added to the nanotube.
For each of the predicted effects, we provide examples and estimates that are
relevant to experiment.Comment: 4 pages, 2 figure
Quantum integrability of sigma models on AII and CII symmetric spaces
Exact massive S-matrices for two dimensional sigma models on symmetric spaces
SU(2N)/Sp(N) and Sp(2P)/Sp(P)*Sp(P) are conjectured. They are checked by
comparison of perturbative and non perturbative TBA calculations of free energy
in a strong external field. We find the mass spectrum of the models and
calculate their exact mass gap.Comment: 11 p., minor correction
Chiral Disorder and QCD at Finite Chemical Potential
We investigate the effects of a finite chemical potential in QCD viewed
as a disordered medium. In the quenched approximation, induces a
complex electric Aharonov-Bohm effect that causes the diagonal contribution to
the quark return probability to vanish at (half the pion mass).
In two-color QCD, the weak-localization contribution to the quark return
probability remains unaffected causing a mutation in the spectral statistics.
In full QCD, the complex electric flux is screened and the light quarks are
shown to diffuse asymmetrically with a substantial decrease in the conductivity
along the `spatial' directions. Mean-field arguments suggest that a d=1
percolation transition may take place in the range ,
where is nuclear matter density.Comment: 4 page
Quantum Diagrammatic Theory of the Extrinsic Spin Hall Effect in Graphene
We present a rigorous microscopic theory of the extrinsic spin Hall effect in disordered graphene based on a nonperturbative quantum diagrammatic treatment incorporating skew scattering and anomalous---impurity concentration-independent---quantum corrections on equal footing. The leading skew scattering contribution to the spin Hall conductivity is shown to quantitatively agree with Boltzmann transport theory over a wide range of parameters. Our self-consistent approach---where all topologically equivalent noncrossing diagrams are resummed---unveils that the skewness generated by spin--orbit-active impurities deeply influences the anomalous component of the spin Hall conductivity, even in the weak scattering regime. This seemingly counterintuitive result is explained by the rich sublattice structure of scattering potentials in graphene, for which traditional Gaussian disorder approximations fail to capture the intricate correlations between skew scattering and side jumps generated through diffusion. Finally, we assess the role of quantum interference corrections by evaluating an important subclass of crossing diagrams recently considered in the context of the anomalous Hall effect, the and diagrams [Ado et al., EPL 111, 37004 (2015)]. We show that diagrams---encoding quantum coherent skew scattering---display a strong Fermi energy dependence, dominating the anomalous spin Hall component away from the Dirac point. Our findings have direct implications for nonlocal transport experiments in spin--orbit-coupled graphene systems