165 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
Scattering theory of plasmon-assisted entanglement transfer and distillation
We analyse the quantum mechanical limits to the plasmon-assisted entanglement
transfer observed by E. Altewischer, M.P. van Exter, and J.P. Woerdman [Nature,
418, 304 (2002)]. The maximal violation S of Bell's inequality at the
photodetectors behind two linear media (such as the perforated metal films in
the experiment) can be described by two ratio's tau_1, tau_2 of
polarization-dependent transmission probabilities. A fully entangled incident
state is transferred without degradation for tau_1=tau_2, but a relatively
large mismatch of tau_1 and tau_2 can be tolerated with a small reduction of S.
We predict that fully entangled Bell pairs can be distilled out of partially
entangled radiation if tau_1 and tau_2 satisfy a pair of inequalities.Comment: 4 pages including 2 figures; two references added, plasmon model
include
Entanglement detection for electrons via witness operators
We discuss an implementation of the entanglement witness, a method to detect
entanglement with few local measurements, in systems where entangled electrons
are generated both in the spin and orbital degrees of freedom.
We address the efficiency of this method in various setups, including two
different particle-hole entanglement structures, and we demonstrate that it can
also be used to infer information on the possible dephasing afflicting the
devices.Comment: 12 pages, 5 figures; published versio
Production and detection of entangled electron-hole pairs in a degenerate electron gas
We demonstrate theoretically that the shot noise produced by a tunnel barrier
in a two-channel conductor violates a Bell inequality. The non-locality is
shown to originate from entangled electron-hole pairs created by tunneling
events -- without requiring electron-electron interactions. The degree of
entanglement (concurrence) equals 2(T_1 T_2)^1/2 (T_1+T_2)^-1, with T_1,T_2 <<
1 the transmission eigenvalues. A pair of edge channels in the quantum Hall
effect is proposed as experimental realization.Comment: 4 pages including 1 figure; three comments have been added to the
reference list, addressing the entanglement of formation, the Clauser-Horne
inequality, and the dephasing effect of a finite voltag
Proposal for production and detection of entangled electron-hole pairs in a degenerate electron gas
Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe
Clauser-Horne inequality and decoherence in mesoscopic conductors
We analyze the effect of decoherence on the violation of the Clauser-Horne
(CH) inequality for the full electron counting statistics in a mesoscopic
multiterminal conductor. Our setup consists of an entangler that emits a flux
of entangled electrons into two conductors characterized by a scattering matrix
and subject to decoherence. Loss of phase memory is modeled phenomenologically
by introducing fictitious extra leads. The outgoing electrons are detected
using spin-sensitive electron counters. Given a certain average number of
incoming entangled electrons, the CH inequality is evaluated as a function of
the numbers of detected particles and on the various quantities characterizing
the scattering matrix. When decoherence is turned on, we show that the amount
of violation of the CH inequality is effectively reduced. Interestingly we find
that, by adjusting the parameters of the system, there exists a protected
region of values for which violation holds for arbitrary strong
decoherence.Comment: 14 pages, 10 figures. Published versio
Hamiltonian dynamics of the two-dimensional lattice phi^4 model
The Hamiltonian dynamics of the classical model on a two-dimensional
square lattice is investigated by means of numerical simulations. The
macroscopic observables are computed as time averages. The results clearly
reveal the presence of the continuous phase transition at a finite energy
density and are consistent both qualitatively and quantitatively with the
predictions of equilibrium statistical mechanics. The Hamiltonian microscopic
dynamics also exhibits critical slowing down close to the transition. Moreover,
the relationship between chaos and the phase transition is considered, and
interpreted in the light of a geometrization of dynamics.Comment: REVTeX, 24 pages with 20 PostScript figure
Production and detection of three-qubit entanglement in the Fermi sea
Building on a previous proposal for the entanglement of electron-hole pairs
in the Fermi sea, we show how 3 qubits can be entangled without using
electron-electron interactions. As in the 2-qubit case, this electronic scheme
works even if the sources are in (local) thermal equilibrium -- in contrast to
the photonic analogue. The 3 qubits are represented by 4 edge-channel
excitations in the quantum Hall effect (2 hole excitations plus 2 electron
excitations with identical channel index). The entangler consists of an
adiabatic point contact flanked by a pair of tunneling point contacts. The
irreducible 3-qubit entanglement is characterized by the tangle, which is
expressed in terms of the transmission matrices of the tunneling point
contacts. The maximally entangled Greenberger-Horne-Zeilinger (GHZ) state is
obtained for channel-independent tunnel probabilities. We show how
low-frequency noise measurements can be used to determine an upper and lower
bound to the tangle. The bounds become tighter the closer the electron-hole
state is to the GHZ state.Comment: 8 pages including 4 figures; [2017: fixed broken postscript figures
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