20 research outputs found
Squeezing light with Majorana fermions
Coupling a semiconducting nanowire to a microwave cavity provides a powerfull
means to assess the presence or absence of isolated Majorana fermions in the
nanowire. These exotic bound states can cause a significant cavity frequency
shift but also a strong cavity nonlinearity leading for instance to light
squeezing. The dependence of these effects on the nanowire gate voltages gives
direct signatures of the unique properties of Majorana fermions, such as their
self-adjoint character and their exponential confinement.Comment: long version: 11 pages, 5 figure
Direct cavity detection of Majorana pairs
No experiment could directly test the particle/antiparticle duality of
Majorana fermions, so far. However, this property represents a necessary
ingredient towards the realization of topological quantum computing schemes.
Here, we show how to complete this task by using microwave techniques. The
direct coupling between a pair of overlapping Majorana bound states and the
electric field from a microwave cavity is extremely difficult to detect due to
the self-adjoint character of Majorana fermions which forbids direct energy
exchanges with the cavity. We show theoretically how this problem can be
circumvented by using photo-assisted tunneling to fermionic reservoirs. The
absence of direct microwave transition inside the Majorana pair in spite of the
light-Majorana coupling would represent a smoking gun for the Majorana
self-adjoint character.Comment: 6 pages, 4 figure
Production of non-local quartets and phase-sensitive entanglement in a superconducting beam splitter
Three BCS superconductors S_a, S_b, and S and two short normal regions N_a
and N_b in a three-terminal S_aN_aSN_bS_b set-up provide a source of non-local
quartets spatially separated as two correlated pairs in S_a and S_b, if the
distance between the interfaces N_aS and SN_b is comparable to the coherence
length in S. Low-temperature dc-transport of non-local quartets from S to S_a
and S_b can occur in equilibrium, and also if S_a and S_b are biased at
opposite voltages. At higher temperatures, thermal excitations result in
correlated current fluctuations which depend on the superconducting phases
phi_a and phi_b in S_a and S_b. Phase-sensitive entanglement is obtained at
zero temperature if N_a and N_b are replaced by discrete levels.Comment: 4 pages, 2 figures; technical details attached in ancillary file
http://arxiv.org/src/1102.2355v4/anc/EPAPS_Freyn_2011.pdf; higher versions:
minor corrections, cleanup and corrected reference
Finite frequency noise of a superconductor/ferromagnet quantum point contact
We have calculated the finite-frequency current noise of a
superconductor-ferromagnet quantum point contact (SF QPC). This signal is
qualitatively affected by the spin-dependence of interfacial phase shifts
(SDIPS) acquired by electrons upon reflection on the QPC. For a weakly
transparent QPC, noise steps appear at frequencies or voltages determined
directly by the SDIPS. These steps can occur at experimentally accessible
temperatures and frequencies. Finite frequency noise is thus a promising tool
to characterize the scattering properties of a SF QPC.Comment: 5 pages, 3 figures, revised version, to appear in Phys. Rev. Let
Aharonov-Bohm cages in two-dimensional structures
We present an extreme localization mechanism induced by a magnetic field for
tight-binding electrons in two-dimensional structures. This spectacular
phenomenon is investigated for a large class of tilings (periodic,
quasiperiodic, or random). We are led to introduce the Aharonov-Bohm cages
defined as the set of sites eventually visited by a wavepacket that can, for
particular values of the magnetic flux, be bounded. We finally discuss the
quantum dynamics which exhibits an original pulsating behaviour.Comment: 4 pages Latex, 3 eps figures, 1 ps figur
Pairing of Cooper Pairs in a Fully Frustrated Josephson Junction Chain
We study a one-dimensional Josephson junction chain embedded in a magnetic
field. We show that when the magnetic flux per elementary loop equals half the
superconducting flux quantum , a local \nbZ_2 symmetry arises.
This symmetry is responsible for a nematic Luttinger liquid state associated to
bound states of Cooper pairs. We analyze the phase diagram and we discuss some
experimental possibilities to observe this exotic phase.Comment: 4 pages, 4 EPS figure
Nesting Induced Precursor Effects: a Renormalization Group Approach
We develop a controlled weak coupling renormalization group (RG) approach to
itinerant electrons. Within this formalism we rederive the phase diagram for
two-dimensional (2D) non-nested systems. Then we study how nesting modifies
this phase diagram. We show that competition between p-p and p-h channels,
leads to the manifestation of unstable precursor fixed points in the RG flow.
This effect should be experimentally measurable, and may be relevant for an
explanation of pseudogaps in the high temperature superconductors (HTC), as a
crossover phenomenon.Comment: 4 pages, 4 figures, 1 tabl
How to escape Aharonov-Bohm cages ?
We study the effect of disorder and interactions on a recently proposed
magnetic field induced localization mechanism. We show that both partially
destroy the extreme confinement of the excitations occuring in the pure case
and give rise to unusual behavior. We also point out the role of the edge
states that allows for a propagation of the electrons in these systems.Comment: 22 pages, 20 EPS figure
Strongly correlated hopping and many-body bound states
We study a system in which the quantum dynamics of electrons depend on the
particle density in their neighborhood. For any on-site repulsive interaction,
we show that the exact two-body and three-body ground states are bound states.
We also discuss the finite density case in a mean-field framework and we show
that the system can undergo an unusual transition from an effective attractive
interaction to a repulsive one, when varying the electron density.Comment: 6 pages, 6 EPS figures, minor modifications and references adde