10,639 research outputs found
Nonmonotonic charge occupation in double dots
We study the occupation of two electrostatically-coupled single-level quantum
dots with spinless electrons as a function of gate voltage. While the total
occupation of the double-dot system varies monotonically with gate voltage, we
predict that the competition between tunneling and Coulomb interaction can give
rise to a nonmonotonic filling of the individual quantum dots. This
non-monotonicity is a signature of the correlated nature of the many-body
wavefunction in the reduced Hilbert space of the dots. We identify two
mechanisms for this nonmonotonic behavior, which are associated with changes in
the spectral weights and the positions, respectively, of the excitation spectra
of the individual quantum dots. An experimental setup to test these predictions
is proposed.Comment: 4 pages, 5 figure
Collective Molecular Dynamics in Proteins and Membranes
The understanding of dynamics and functioning of biological membranes and in
particular of membrane embedded proteins is one of the most fundamental
problems and challenges in modern biology and biophysics. In particular the
impact of membrane composition and properties and of structure and dynamics of
the surrounding hydration water on protein function is an upcoming hot topic,
which can be addressed by modern experimental and computational techniques.
Correlated molecular motions might play a crucial role for the understanding
of, for instance, transport processes and elastic properties, and might be
relevant for protein function. Experimentally that involves determining
dispersion relations for the different molecular components, i.e., the length
scale dependent excitation frequencies and relaxation rates. Only very few
experimental techniques can access dynamical properties in biological materials
on the nanometer scale, and resolve dynamics of lipid molecules, hydration
water molecules and proteins and the interaction between them. In this context,
inelastic neutron scattering turned out to be a very powerful tool to study
dynamics and interactions in biomolecular materials up to relevant nanosecond
time scales and down to the nanometer length scale. We review and discuss
inelastic neutron scattering experiments to study membrane elasticity and
protein-protein interactions of membrane embedded proteins
Influence of spin waves on transport through a quantum-dot spin valve
We study the influence of spin waves on transport through a single-level
quantum dot weakly coupled to ferromagnetic electrodes with noncollinear
magnetizations. Side peaks appear in the differential conductance due to
emission and absorption of spin waves. We, furthermore, investigate the
nonequilibrium magnon distributions generated in the source and drain lead. In
addition, we show how magnon-assisted tunneling can generate a fullly
spin-polarized current without an applied transport voltage. We discuss the
influence of spin waves on the current noise. Finally, we show how the magnonic
contributions to the exchange field can be detected in the finite-frequency
Fano factor.Comment: published version, 15 pages, 10 figure
Probing the exchange field of a quantum-dot spin valve by a superconducting lead
Electrons in a quantum-dot spin valve, consisting of a single-level quantum
dot coupled to two ferromagnetic leads with magnetizations pointing in
arbitrary directions, experience an exchange field that is induced on the dot
by the interplay of Coulomb interaction and quantum fluctuations. We show that
a third, superconducting lead with large superconducting gap attached to the
dot probes this exchange field very sensitively. In particular, we find
striking signatures of the exchange field in the symmetric component of the
supercurrent with respect to the bias voltage applied between the ferromagnets
already for small values of the ferromagnets' spin polarization.Comment: published version, 10 pages, 7 figure
A de Finetti representation for finite symmetric quantum states
Consider a symmetric quantum state on an n-fold product space, that is, the
state is invariant under permutations of the n subsystems. We show that,
conditioned on the outcomes of an informationally complete measurement applied
to a number of subsystems, the state in the remaining subsystems is close to
having product form. This immediately generalizes the so-called de Finetti
representation to the case of finite symmetric quantum states.Comment: 22 pages, LaTe
Efficient and spectrally bright source of polarization-entangled photons
We demonstrate an efficient fiber-coupled source of nondegenerate
polarization entangled photons at 795 and 1609 nm using bidirectionally pumped
parametric down-conversion in bulk periodically poled lithium niobate. The
single-mode source has an inferred bandwidth of 50 GHz and a spectral
brightness of 300 pairs/s/GHz/mW of pump power that is suitable for narrowband
applications such as entanglement transfer from photonic to atomic qubits.Comment: 8 pages, 7 figures, submitted to Phys. Rev.
Influence of non-local exchange on RKKY interactions in III-V diluted magnetic semiconductors
The RKKY interaction between substitutional Mn local moments in GaAs is both
spin-direction-dependent and spatially anisotropic. In this Letter we address
the strength of these anisotropies using a semi-phenomenological tight-binding
model which treats the hybridization between Mn d-orbitals and As p-orbitals
perturbatively and accounts realistically for the non-local exchange
interaction between their spins. We show that exchange non-locality,
valence-band spin-orbit coupling, and band-structure anisotropy all play a role
in determining the strength of both effects. We use these results to estimate
the degree of ground-state magnetization suppression due to frustrating
interactions between randomly located Mn ions.Comment: 4 pages RevTeX, 2 figures included, v2: replacement because of font
proble
- …