1,219 research outputs found

### Electronic spin precession and interferometry from spin-orbital entanglement in a double quantum dot

A double quantum dot inserted in parallel between two metallic leads allows
to entangle the electron spin with the orbital (dot index) degree of freedom.
An Aharonov-Bohm orbital phase can then be transferred to the spinor
wavefunction, providing a geometrical control of the spin precession around a
fixed magnetic field. A fully coherent behaviour is obtained in a mixed
orbital/spin Kondo regime. Evidence for the spin precession can be obtained,
either using spin-polarized metallic leads or by placing the double dot in one
branch of a metallic loop.Comment: Final versio

### Tunneling Spectroscopy of Two-level Systems Inside Josephson Junction

We consider a two-level (TL) system with energy level separation Omega_0
inside a Josephson junction. The junction is shunted by a resistor R and is
current I (or voltage V = RI) biased. If the TL system modulates the Josephson
energy and/or is optically active, it is Rabi driven by the Josephson
oscillations in the running phase regime near the resonance 2eV = Omega_0. The
Rabi oscillations, in turn, translate into oscillations of current and voltage
which can be detected in noise measurements. This effect provides an option to
fully characterize the TL systems and to find the TL's contribution to the
decoherence when the junction is used as a qubit.Comment: 4 page

### Quantum Tunneling Detection of Two-photon and Two-electron Processes

We analyze the operation of a quantum tunneling detector coupled to a
coherent conductor. We demonstrate that in a certain energy range the output of
the detector is determined by two-photon processes, two-electron processes and
the interference of the two. We show how the individual contributions of these
processes can be resolved in experiments.Comment: 4 pages, 4 figure

### Tunneling into Multiwalled Carbon Nanotubes: Coulomb Blockade and Fano Resonance

Tunneling spectroscopy measurements of single tunnel junctions formed between
multiwalled carbon nanotubes (MWNTs) and a normal metal are reported. Intrinsic
Coulomb interactions in the MWNTs give rise to a strong zero-bias suppression
of a tunneling density of states (TDOS) that can be fitted numerically to the
environmental quantum-fluctuation (EQF) theory. An asymmetric conductance
anomaly near zero bias is found at low temperatures and interpreted as Fano
resonance in the strong tunneling regime.Comment: 4 pages, 4 figure

### A one-channel conductor in an ohmic environment: mapping to a TLL and full counting statistics

It is shown that a one-channel mesoscopic conductor in an ohmic environment
can be mapped to the problem of a backscattering impurity in a
Tomonaga-Luttinger liquid (TLL). This allows to determine non perturbatively
the effect of the environment on $I-V$ curves, and to find an exact
relationship between dynamic Coulomb blockade and shot noise. We investigate
critically how this relationship compares to recent proposals in the
literature. The full counting statistics is determined at zero temperature.Comment: 5 pages, 2 figures, shortened version for publication in Phys. Rev.
Let

### Loss of quantum coherence due to non-stationary glass fluctuations

Low-temperature dynamics of insulating glasses is dominated by a macroscopic
concentration of tunneling two-level systems (TTLS). The distribution of the
switching/relaxation rates of TTLS is exponentially broad, which results in
non-equilibrium state of the glass at arbitrarily long time-scales. Due to the
electric dipolar nature, the switching TTLS generate fluctuating
electromagnetic fields. We study the effect of the non-thermal slow fluctuators
on the dephasing of a solid state qubit. We find that at low enough
temperatures, non-stationary contribution can dominate the stationary (thermal)
one, and discuss how this effect can be minimized.Comment: 4 page

### Inverse proximity effect in superconductors near ferromagnetic material

We study the electronic density of states in a mesoscopic superconductor near
a transparent interface with a ferromagnetic metal. In our tunnel spectroscopy
experiment, a substantial density of states is observed at sub-gap energies
close to a ferromagnet. We compare our data with detailed calculations based on
the Usadel equation, where the effect of the ferromagnet is treated as an
effective boundary condition. We achieve an excellent agreement with theory
when non-ideal quality of the interface is taken into account.Comment: revised, 7 pages, 3 figure

### Resonant Tunneling in a Dissipative Environment

We measure tunneling through a single quantum level in a carbon nanotube
quantum dot connected to resistive metal leads. For the electrons tunneling
to/from the nanotube, the leads serve as a dissipative environment, which
suppresses the tunneling rate. In the regime of sequential tunneling, the
height of the single-electron conductance peaks increases as the temperature is
lowered, although it scales more weekly than the conventional 1/T. In the
resonant tunneling regime (temperature smaller than the level width), the peak
width approaches saturation, while the peak height starts to decrease. Overall,
the peak height shows a non-monotonic temperature dependence. We associate this
unusual behavior with the transition from the sequential to the resonant
tunneling through a single quantum level in a dissipative environment.Comment: 5 pages, 5 figure

### The Influence of Electro-Mechanical Effects on Resonant Electron Tunneling Through Small Carbon Nano-Peapods

The influence of a fullerene molecule trapped inside a single-wall carbon
nanotube on resonant electron transport at low temperatures and strong
polaronic coupling is theoretically discussed. Strong peak to peak fluctuations
and anomalous temperature behavior of conductance amplitudes are predicted and
investigated. The influence of the chiral properties of carbon nanotubes on
transport is also studied.Comment: 17 pages, 3 figures. Replaced with published version. Important
changes. Open access: http://stacks.iop.org/1367-2630/10/04304

### Tunneling into Nonequilibrium Luttinger Liquid with Impurity

We evaluate tunneling rates into/from a voltage biased quantum wire
containing weak backscattering defect. Interacting electrons in such a wire
form a true nonequilibrium state of the Luttinger liquid (LL). This state is
created due to inelastic electron backscattering leading to the emission of
nonequilibrium plasmons with typical frequency $\hbar \omega \leq U$. The
tunneling rates are split into two edges. The tunneling exponent at the Fermi
edge is positive and equals that of the equilibrium LL, while the exponent at
the side edge $E_F-U$ is negative if Coulomb interaction is not too strong.Comment: 4+ pages, 5 figure

- …