233 research outputs found
Andreev-like reflections with cold atoms
We propose a setup in which Andreev-like reflections predicted for 1D transport systems could be observed time dependently using cold atoms in a 1D optical lattice. Using time-dependent density matrix renormalization group methods we analyze the wave packet dynamics as a density excitation propagates across a boundary in the interaction strength. These phenomena exhibit good correspondence with predictions from Luttinger liquid models and could be observed in current experiments in the context of the Bose-Hubbard model
Fractional Wigner crystal in the helical Luttinger liquid
The properties of the strongly interacting edge states of two dimensional
topological insulators in the presence of two particle backscattering are
investigated. We find an anomalous behavior of the density-density correlation
functions, which show oscillations that are neither of Friedel nor of Wigner
type: they instead represent a Wigner crystal of fermions of fractional charge
e/2, with e the electron charge. By studying the Fermi operator, we show that
the state characterized by such fractional oscillations still bears the
signatures of spin momentum locking. Finally, we compare the spin-spin
correlation functions and the density-density correlation functions to argue
that the fractional Wigner crystal is characterized by a non trivial spin
texture.Comment: 5 pages, 2 figure
Fractional charge in the noise of Luttinger liquid systems
The current noise of a voltage biased interacting quantum wire adiabatically
connected to metallic leads is computed in presence of an impurity in the wire.
We find that in the weak backscattering limit the Fano factor characterizing
the ratio between shot noise and backscattering current crucially depends on
the noise frequency relative to the ballistic frequency v_F/gL, where v_F is
the Fermi velocity, g the Luttinger liquid interaction parameter, and L the
length of the wire. In contrast to chiral Luttinger liquids, the noise is not
only due to the Poissonian backscattering of fractionally charged
quasiparticles at the impurity, but also depends on Andreev-type reflections of
plasmons at the contacts, so that the frequency dependence of the noise needs
to be analyzed to extract the fractional charge e*=e g of the bulk excitations.
We show that the frequencies needed to see interaction effects in the Fano
factor are within experimental reach.Comment: 9 pages, 4 figures, conference proceedings of Fluctuations and Noise
2005, Austin, Texa
Spin Hall effect at interfaces between HgTe/CdTe quantum wells and metals
We study the spin-dependent transmission through interfaces between a
HgTe/CdTe quantum well (QW) and a metal - both for the normal metal and the
superconducting case. Interestingly, we discover a new type of spin Hall effect
at these interfaces that happens to exist even in the absence of structure and
bulk inversion asymmetry within each subsystem (i.e. the QW and the metal).
Thus, this is a pure boundary spin Hall effect which can be directly related to
the existence of exponentially localized edge states at the interface. We
demonstrate how this effect can be measured and functionalized for an
all-electric spin injection into normal metal leads.Comment: 7 pages, 6 figure
Entangled microwave photons from quantum dots
We describe a mechanism for the production of polarisation-entangled
microwaves using intra-band transitions in a pair of quantum dots. This
proposal relies neither on spin-orbit coupling nor on control over
electron-electron interactions. The quantum correlation of microwave
polarisations is obtained from orbital degrees of freedom in an external
magnetic field. We calculate the concurrence of emitted microwave photon pairs,
and show that a maximally entangled Bell pair is obtained in the limit of weak
inter-dot coupling.Comment: 4 pages, 5 figure
Appearance of fractional charge in the noise of non-chiral Luttinger liquids
The current noise of a voltage biased interacting quantum wire adiabatically
connected to metallic leads is computed in presence of an impurity in the wire.
We find that in the weak backscattering limit the Fano factor characterizing
the ratio between noise and backscattered current crucially depends on the
noise frequency relative to the ballistic frequency , where
is the Fermi velocity, the Luttinger liquid interaction parameter,
and the length of the wire. In contrast to chiral Luttinger liquids the
noise is not only due to the Poissonian backscattering of fractionally charged
quasiparticles at the impurity, but also depends on Andreev-type reflections at
the contacts, so that the frequency dependence of the noise needs to be
analyzed to extract the fractional charge of the bulk excitations.Comment: 4 pages, 2 figures, final version, to appear in PR
Optimal spin-entangled electron-hole pair pump
A nonperturbative theory is presented for the creation by an oscillating
potential of spin-entangled electron-hole pairs in the Fermi sea. In the weak
potential limit, considered earlier by Samuelsson and Buttiker, the
entanglement production is much less than one bit per cycle. We demonstrate
that a strong potential oscillation can produce an average of one Bell pair per
two cycles, making it an efficient source of entangled flying qubits.Comment: 6 pages including 1 figure -- Two appendices contain material that is
not in the Journal version: A) Gaussian elimination for fermions; B) class of
optimal pump cycle
Photon-assisted electron transport in graphene
Photon-assisted electron transport in ballistic graphene is analyzed using
scattering theory. We show that the presence of an ac signal (applied to a gate
electrode in a region of the system) has interesting consequences on electron
transport in graphene, where the low energy dynamics is described by the Dirac
equation. In particular, such a setup describes a feasible way to probe energy
dependent transmission in graphene. This is of substantial interest because the
energy dependence of transmission in mesoscopic graphene is the basis of many
peculiar transport phenomena proposed in the recent literature. Furthermore, we
discuss the relevance of our analysis of ac transport in graphene to the
observability of zitterbewegung of electrons that behave as relativistic
particles (but with a lower effective speed of light).Comment: 5 pages, 2 figure
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