20 research outputs found
A Dynamic 'Double Slit' Experiment in a Single Atom
A single-atom 'double-slit' experiment is realized by photo-ionizing Rubidium
atoms using two independent low power lasers. The photoelectron wave of
well-defined energy recedes to the continuum either from the 5P or 6P states in
the same atom, resulting in two-path interference imaged in the far field using
a photoelectron detector. Even though the lasers are independent and not phase
locked, the transitions within the atom impart the phase relationship necessary
for interference. The experiment is designed so that either 5P or 6P states are
excited by one laser, before ionization by the second beam. The measurement
cannot determine which excitation path is taken, resulting in interference in
wave-vector space analogous to Young's double-slit studies. As the lasers are
tunable in both frequency and intensity, the individual excitation-ionization
pathways can be varied, allowing dynamic control of the interference term.
Since the electron wave recedes in the Coulomb potential of the residual ion, a
quantum model is used to capture the dynamics. Excellent agreement is found
between theory and experiment.Comment: 8 pages, 4 figures, accepted in Phys. Rev. Let
Photoelectron emission via time and phase-tailored electromagnetic fields
The energy and the angular distributions of photoelectrons are shown to be
tunable by choosing the time and the spatial phase structure of the driving
fields. These conclusions are derived from quantum mechanical calculations done
within a single-active electron model for an atomic target subjected to a
combination of laser field and a time-asymmetric THz pulse and/or vortex-laser
pulse with a spatially modulated phase of the wavefront.Comment: 7 pages, 4 figures, accepted a JPhys
Ultrafast entanglement switching and singlet-triplet transitions control via structured terahertz pulses
[EN] Terahertz (THz) vector beams with spatially textured polarization are proposed to steer the spin and spatial distributions of two interacting electrons in a quantum dot. We study theoretically the spatiotemporal evolution of the spin and the charge-current densities and quantify the behavior of entanglement by calculating the concurrence. Both aspects are shown to be controllable efficiently and on the picosecond (ps) time scale by the parameters of the driving fields. Analyzing two different materials, GaAs and InGaAs, with different electron g-factors, we study the relationship between the g-factor and type of spin-orbit coupling required to produce efficient interlevel transitions. The results are useful for applications of quantum dots as basic nanoscale hardware elements in quantum information technology and for producing swiftly the appropriate spin and charge currents on demand.ES is supported by the Grant IT986-16 of the Basque Country Government and by the Grant PGC2018-101355-B-I00 funded by MCIN/AEI/10.13039/501100011033 and by 'ERDF A way of making Europe'. JW and JB acknowledge support by the Deutsche Forschungsgemeinschaft (DFG) under SPP1840 and WA 4352/2-1
Entanglement balance of quantum scattering processes
The theory of quantum information constitutes the functional value of the
quantum entanglement, i.e., quantum entanglement is essential for high fidelity
of quantum protocols, while fundamental physical processes behind the formation
of quantum entanglement are less relevant for practical purposes. In the
present work, we explore physical mechanisms leading to the emergence of
quantum entanglement in the initially disentangled system. In particular, we
analyze spin entanglement of outgoing electrons in a nonrelativistic quantum
collision on a target with one active electron. Our description
exploits the time-dependent scattering formalism for typical conditions of
scattering experiments, and contrary to the customary stationary formalism
operates with realistic scattering states. We quantify the spin entanglement in
the final scattering channel through the pair concurrence and express it in
terms of the experimentally measurable spin-resolved triple
differential cross sections. Besides, we consider Bell's inequality and inspect
the regimes of its violation in the final channel. We address both the pure and
the mixed initial spin state cases and uncover kinematical conditions of the
maximal entanglement of the outgoing electron pair. The numerical results for
the pair concurrence, entanglement of formation, and violation of Bell's
inequality obtained for the ionization process of atomic hydrogen show
that the entangled electron pairs indeed can be formed in the
collisions even with spin-unpolarized projectile and target electrons in the
initial channel. The positive entanglement balance---the difference between
entanglements of the initial and final electron pairs---can be measured in the
experiment.Comment: 31 pages, 6 figure