136 research outputs found
Generalized constraints on quantum amplification
We derive quantum constraints on the minimal amount of noise added in linear
amplification involving input or output signals whose component operators do
not necessarily have c-number commutators, as is the case for fermion currents.
This is a generalization of constraints derived for the amplification of
bosonic fields whose components posses c-number commutators.Comment: 4 pages, 1 figure, submitted to Physical Review Letter
Shot-noise in transport and beam experiments
Consider two Fermi gases with the same {\it average} currents: a transport
gas, as in solid-state experiments where the chemical potentials of terminal 1
is and of terminal 2 and 3 is , and a beam, i.e., electrons
entering only from terminal 1 having energies between and . By
expressing the current noise as a sum over single-particle transitions we show
that the temporal current fluctuations are very different: The beam is noisier
due to allowed single-particle transitions into empty states below .
Surprisingly, the correlations between terminals 2 and 3 are the same.Comment: 4 pages, 2 figure
AC-Conductance through an Interacting Quantum Dot
We investigate the linear ac-conductance for tunneling through an arbitrary
interacting quantum dot in the presence of a finite dc-bias. In analogy to the
well-known Meir-Wingreen formula for the dc case, we are able to derive a
general formula for the ac-conductance. It can be expressed entirely in terms
of local correlations on the quantum dot, in the form of a Keldysh block
diagram with four external legs. We illustrate the use of this formula as a
starting point for diagrammatic calculations by considering the ac-conductance
of the noninteracting resonant level model and deriving the result for the
lowest order of electron-phonon coupling. We show how known results are
recovered in the appropriate limits.Comment: 4+ pages, 4 figure
Emission and absorption noise in the fractional quantum Hall effect
We compute the high-frequency emission and absorption noise in a fractional
quantum Hall effect (FQHE) sample at arbitrary temperature. We model the edges
of the FQHE as chiral Luttinger liquids (LL) and we use the non-equilibrium
perturbative Keldysh formalism. We find that the non-symmetrized high frequency
noise contains important signatures of the electron-electron interactions that
can be used to test the Luttinger liquid physics, not only in FQHE edge states,
but possibly also in other one-dimensional systems such as carbon nanotubes. In
particular we find that the emission and absorption components of the excess
noise (defined as the difference between the noise at finite voltage and at
zero voltage) are different in an interacting system, as opposed to the
non-interacting case when they are identical. We study the resonance features
which appear in the noise at the Josephson frequency (proportional to the
applied voltage), and we also analyze the effect of the distance between the
measurement point and the backscattering site. Most of our analysis is
performed in the weak backscattering limit, but we also compute and discuss
briefly the high-frequency noise in the tunneling regime.Comment: 26 pages, 11 figure
Full counting statistics of strongly non-Ohmic transport through single molecules
We study analytically the full counting statistics of charge transport
through single molecules, strongly coupled to a weakly damped vibrational mode.
The specifics of transport in this regime - a hierarchical sequence of
avalanches of transferred charges, interrupted by "quiet" periods - make the
counting statistics strongly non-Gaussian. We support our findings for the
counting statistics as well as for the frequency-dependent noise power by
numerical simulations, finding excellent agreement.Comment: 4+ pages, 2 figures; minor changes, version published in Phys. Rev.
Let
Effective temperature of a dissipative driven mesoscopic system
We study the nonequilibrium dynamics of a mesoscopic metallic ring threaded
by a time-dependent magnetic field and coupled to an electronic reservoir. We
analyze the relation between the (non-stationary) real-time Keldysh and
retarded Green functions and we find that, in the linear response regime with
weak heat transfer to the environment, an effective temperature accounts for
the modification of the equilibrium fluctuation-dissipation relation. We
discuss possible extensions of this analysis.Comment: 4 pages, 4 figures, RevTe
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