29 research outputs found
Design of a Lambda system for population transfer in superconducting nanocircuits
The implementation of a Lambda scheme in superconducting artificial atoms
could allow detec- tion of stimulated Raman adiabatic passage (STIRAP) and
other quantum manipulations in the microwave regime. However symmetries which
on one hand protect the system against decoherence, yield selection rules which
may cancel coupling to the pump external drive. The tradeoff between efficient
coupling and decoherence due to broad-band colored Noise (BBCN), which is often
the main source of decoherence is addressed, in the class of nanodevices based
on the Cooper pair box (CPB) design. We study transfer efficiency by STIRAP,
showing that substantial efficiency is achieved for off-symmetric bias only in
the charge-phase regime. We find a number of results uniquely due to
non-Markovianity of BBCN, namely: (a) the efficiency for STIRAP depends
essentially on noise channels in the trapped subspace; (b) low-frequency
fluctuations can be analyzed and represented as fictitious correlated
fluctuations of the detunings of the external drives; (c) a simple figure of
merit for design and operating prescriptions allowing the observation of STIRAP
is proposed. The emerging physical picture also applies to other classes of
coherent nanodevices subject to BBCN.Comment: 14 pages, 11 figure
Magneto-optical properties of Au upon the injection of hot spin-polarized electrons across Fe/Au(001) interfaces
We demonstrate a novel method for the excitation of sizable magneto-optical
effects in Au by means of the laser-induced injection of hot spin-polarized
electrons in Au/Fe/MgO(001) heterostructures. It is based on the energy- and
spin-dependent electron transmittance of Fe/Au interface which acts as a spin
filter for non-thermalized electrons optically excited in Fe. We show that
after crossing the interface, majority electrons propagate through the Au layer
with the velocity on the order of 1 nm/fs (close to the Fermi velocity) and the
decay length on the order of 100 nm. Featuring ultrafast functionality and
requiring no strong external magnetic fields, spin injection results in a
distinct magneto-optical response of Au. We develop a formalism based on the
phase of the transient complex MOKE response and demonstrate its robustness in
a plethora of experimental and theoretical MOKE studies on Au, including our ab
initio calculations. Our work introduces a flexible tool to manipulate
magneto-optical properties of metals on the femtosecond timescale that holds
high potential for active magneto-photonics, plasmonics, and spintronics
Magneto-Optical Detection of the Orbital Hall Effect in Chromium
The orbital Hall effect has been theoretically predicted but its direct
observation is a challenge. Here, we report the magneto-optical detection of
current-induced orbital accumulation at the surface of a light 3 transition
metal, Cr. The orbital polarization is in-plane, transverse to the current
direction, and scales linearly with current density, consistent with the
orbital Hall effect. Comparing the thickness-dependent magneto-optical
measurements with calculations, we estimate an orbital
diffusion length in Cr of nm.Comment: 6 pages, 5 figure
Dynamics of a Quantum Particle in Asymmetric Bistable Potential with Environmental Noise
In this work we analyze the dynamics of a quantum particle subject to an asymmetric bistable potential and interacting with a thermal reservoir. We obtain the time evolution of the population distributions in both energy and position eigenstates of the particle, for different values of the coupling strength with the thermal bath. The calculation is carried out using the Feynman-
Vernon functional under the discrete variable representation