172 research outputs found
Geometrical Model for Non-Zero theta_13
Based on Friedberg and Lee's geometric picture by which the tribimaximal
Pontecorvo-Maki-Nakawaga-Sakata leptonic mixing matrix is constructed, namely,
corresponding mixing angles correspond to the geometric angles among the sides
of a cube. We suggest that the three realistic mixing angles, which slightly
deviate from the values determined for the cube, are due to a viable
deformation from the perfectly cubic shape. Taking the best-fitted results of
and as inputs, we determine the central value of
should be 0.0238, with a relatively large error tolerance;
this value lies in the range of measurement precision of the Daya Bay
experiment and is consistent with recent results from the T2K Collaboration.Comment: 14 pages, 7 figures. Published version in Phys. Rev.
Dynamical Decoupling of Qubits in Spin Bath under Periodic Quantum Control
We investigate the feasibility for the preservation of coherence and
entanglement of one and two spin qubits coupled to an interacting quantum
spin-1/2 chain within the dynamical decoupling (DD) scheme. The performance is
examined by counting number of computing pulses that can be applied
periodically with period of before qubits become decoherent, while
identical decoupling pulse sequence is applied within each cycle. By
considering pulses with mixed directions and finite width controlled by
magnetic fields, it is shown that pulse-width accumulation degrades the
performance of sequences with larger number of pulses and feasible magnetic
fields in practice restrict the consideration to sequences with number of
decoupling pulses being less than 10 within each cycle. Furthermore, within
each cycle , exact nontrivial pulse sequences are found for the first time
to suppress the qubit-bath coupling to progressively with minimum
number of pulses being for . These sequences, when applied to
all qubits, are shown to preserve both the entanglement and coherence. Based on
time-dependent density matrix renormalization, our numerical results show that
for modest magnetic fields (10-40 Tesla) available in laboratories, the overall
performance is optimized when number of pulses in each cycle is 4 or 7 with
pulse directions be alternating between x and z. Our results provide useful
guides for the preservation of coherence and entanglement of spin qubits in
solid state.Comment: 11 pages, 9 figure
Tunable Dirac Fermion Dynamics in Topological Insulators
Three-dimensional topological insulators are characterized by insulating bulk
state and metallic surface state involving Dirac fermions that behave as
massless relativistic particles. These Dirac fermions are responsible for
achieving a number of novel and exotic quantum phenomena in the topological
insulators and for their potential applications in spintronics and quantum
computations. It is thus essential to understand the electron dynamics of the
Dirac fermions, i.e., how they interact with other electrons, phonons and
disorders. Here we report super-high resolution angle-resolved photoemission
studies on the Dirac fermion dynamics in the prototypical Bi2(Te,Se)3
topological insulators. We have directly revealed signatures of the
electron-phonon coupling in these topological insulators and found that the
electron-disorder interaction is the dominant factor in the scattering process.
The Dirac fermion dynamics in Bi2(Te3-xSex) topological insulators can be tuned
by varying the composition, x, or by controlling the charge carriers. Our
findings provide crucial information in understanding the electron dynamics of
the Dirac fermions in topological insulators and in engineering their surface
state for fundamental studies and potential applications.Comment: 14 Pages, 4 Figure
Unusual Fermi Surface Sheet-Dependent Band Splitting in Sr2RuO4 Revealed by High Resolution Angle-Resolved Photoemission
High resolution angle-resolved photoemission measurements have been carried
out on Sr2RuO4. We observe clearly two sets of Fermi surface sheets near the
(\pi,0)-(0,\pi) line which are most likely attributed to the surface and bulk
Fermi surface splitting of the \beta band. This is in strong contrast to the
nearly null surface and bulk Fermi surface splitting of the \alpha band
although both have identical orbital components. Extensive band structure
calculations are performed by considering various scenarios, including
structural distortion, spin-orbit coupling and surface ferromagnetism. However,
none of them can explain such a qualitative difference of the surface and bulk
Fermi surface splitting between the \alpha and \beta sheets. This unusual
behavior points to an unknown order on the surface of Sr2RuO4 that remains to
be uncovered. Its revelation will be important for studying and utilizing novel
quantum phenomena associated with the surface of Sr2RuO4 as a result of its
being a possible p-wave chiral superconductor and a topological superconductor.Comment: 13 pages, 4 figure
Distinct Fermi Surface Topology and Nodeless Superconducting Gap in (Tl0.58Rb0.42)Fe1.72Se2 Superconductor
High resolution angle-resolved photoemission measurements have been carried
out to study the electronic structure and superconducting gap of the
(TlRb)FeSe superconductor with a T=32 K. The
Fermi surface topology consists of two electron-like Fermi surface sheets
around point which is distinct from that in all other iron-based
compounds reported so far. The Fermi surface around the M point shows a nearly
isotropic superconducting gap of 12 meV. The large Fermi surface near the
point also shows a nearly isotropic superconducting gap of 15
meV while no superconducting gap opening is clearly observed for the inner tiny
Fermi surface. Our observed new Fermi surface topology and its associated
superconducting gap will provide key insights and constraints in understanding
superconductivity mechanism in the iron-based superconductors.Comment: 4 pages, 4 figure
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