709 research outputs found
Dephasing of entangled electron-hole pairs in a degenerate electron gas
A tunnel barrier in a degenerate electron gas was recently discovered as a
source of entangled electron-hole pairs. Here, we investigate the loss of
entanglement by dephasing. We calculate both the maximal violation E_max of the
Bell inequality and the degree of entanglement (concurrence) C. If the
initially maximally entangled electron-hole pair is in a Bell state, then the
Bell inequality is violated for arbitrary strong dephasing. The same relation
E_max=2\sqrt{1+C^{2}} then holds as in the absence of dephasing. More
generally, for a maximally entangled superposition of Bell states, the Bell
inequality is satisfied for a finite dephasing strength and the entanglement
vanishes for somewhat stronger (but still finite) dephasing strength. There is
then no one-to-one relation between E_max and C.Comment: 7 pages with 3 figures, special style file included; To appear in a
special issue on "Quantum Computation at the Atomic Scale" in Turkish Journal
of Physic
Frequency-dependent transport through a quantum dot in the Kondo regime
We study the AC conductance and equilibrium current fluctuations of a Coulomb
blockaded quantum dot. A relation between the equilibrium spectral function and
the linear AC conductance is derived which is valid for frequencies well below
the charging energy of the quantum dot. Frequency-dependent transport
measurements can thus give experimental access to the Kondo peak in the
equilibrium spectral function of a quantum dot. We illustrate this in detail
for typical experimental parameters using the numerical renormalization group
method in combination with the Kubo formalism.Comment: 4 pages, 4 figure
Hydrodynamic approach to coherent nuclear spin transport
We develop a linear response formalism for nuclear spin diffusion in a
dipolar coupled solid. The theory applies to the high-temperature,
long-wavelength regime studied in the recent experiments of Boutis et al.
[Phys. Rev. Lett. 92, 137201 (2004)], which provided direct measurement of
interspin energy diffusion in such a system. A systematic expansion of Kubo's
formula in the flip-flop term of the Hamiltonian is used to calculate the
diffusion coefficients. We show that this approach is equivalent to the method
of Lowe and Gade [Phys. Rev. 156, 817 (1967)] and Kaplan [Phys. Rev. B 2, 4578
(1970)], but has several calculational and conceptual advantages. Although the
lowest orders in this expansion agree with the experimental results for
magnetization diffusion, this is not the case for energy diffusion. Possible
reasons for this disparity are suggested.Comment: 7 pages, REVTeX4; Published Versio
Quantum teleportation by particle-hole annihilation in the Fermi sea
A tunnel barrier in a degenerate electron gas was recently discovered as a
source of entangled particle-hole excitations. The entanglement is produced by
elastic tunneling events, without requiring electron-electron interactions.
Here we investigate the inverse process, the annihilation of an electron and a
hole by elastic scattering. We find that this process leads to teleportation of
the (unknown) state of the annihilated electron to a second, distant electron
-- if the latter was previously entangled with the annihilated hole. We propose
an experiment, involving low-frequency noise measurements on a two-dimensional
electron gas in a high magnetic field, to detect teleportation of electrons and
holes in the two lowest Landau levels.Comment: 5 pages including 2 figures; [2017: fixed broken postscript figures
Full Counting Statistics of Spin Currents
We discuss how to detect fluctuating spin currents and derive full counting
statistics of electron spin transfers. It is interesting to consider several
detectors in series that simultaneously monitor different components of the
spins transferred. We have found that in general the statistics of the
measurement outcomes cannot be explained with the projection postulate and
essentially depends on the quantum dynamics of the detectors.Comment: twocolumns, 4 pages, 2 figure
DC-transport in superconducting point contacts: a full counting statistics view
We present a comprehensive theoretical analysis of the dc transport
properties of superconducting point contacts. We determine the full counting
statistics for these junctions, which allows us to calculate not only the
current or the noise, but all the cumulants of the current distribution. We
show how the knowledge of the statistics of charge transfer provides an
unprecedented level of understanding of the different transport properties for
a great variety of situations. We illustrate our results with the analysis of
junctions between BCS superconductors, contacts between superconductors with
pair-breaking mechanisms and short diffusive bridges. We also discuss the
temperature dependence of the different cumulants and show the differences with
normal contacts.Comment: revtex4, 20 pages, 15 figure
Inelastic Interaction Corrections and Universal Relations for Full Counting Statistics
We analyze in detail the interaction correction to Full Counting Statistics
(FCS) of electron transfer in a quantum contact originating from the
electromagnetic environment surrounding the contact. The correction can be
presented as a sum of two terms, corresponding to elastic/inelastic electron
transfer. Here we primarily focus on the inelastic correction.
For our analysis, it is important to understand more general -- universal --
relations imposed on FCS only by quantum mechanics and statistics with no
regard for a concrete realization of a contact. So we derive and analyze these
relations. We reveal that for FCS the universal relations can be presented in a
form of detailed balance. We also present several useful formulas for the
cumulants.
To facilitate the experimental observation of the effect, we evaluate
cumulants of FCS at finite voltage and temperature. Several analytical results
obtained are supplemented by numerical calculations for the first three
cumulants at various transmission eigenvalues.Comment: 10 pages, 3 figure
Electron transport and current fluctuations in short coherent conductors
Employing a real time effective action formalism we analyze electron
transport and current fluctuations in comparatively short coherent conductors
in the presence of electron-electron interactions. We demonstrate that, while
Coulomb interaction tends to suppress electron transport, it may {\it strongly
enhance} shot noise in scatterers with highly transparent conducting channels.
This effect of excess noise is governed by the Coulomb gap observed in the
current-voltage characteristics of such scatterers. We also analyze the
frequency dispersion of higher current cumulants and emphasize a direct
relation between electron-electron interaction effects and current fluctuations
in disordered mesoscopic conductors.Comment: 16 pages, 4 figure
Continuous virus inactivation using a packed-bed reactor
A critical unit operation in integrated continuous biomanufacturing is continuous virus inactivation. These reactors must provide sufficient minimum inactivation time and must have a narrow residence time. The narrow residence time is required to avoid a too short or too long incubation. Too short incubation may result in insufficient inactivation, too long may result in partial product destruction. We have developed a packed-bed continuous virus inactivation reactor (CVIR, Figure 1) with significant advantages over other continuous processing approaches, namely scalability, ease of operation and being truly continuous with undisrupted mass flow. The residence time distribution of our reactor is smaller compared to a coiled flow inverter or a jig in a box reactor.
Please click Additional Files below to see the full abstract
- …