Research interests:
Theoretical condensed matter physics
The longstanding progress of conventional
semiconductor technology is expected to come to a halt in the next ten
to twenty years. As the size of transistors approach the
nanometer scale, severe problems related to miniaturization and energy
dissipation will hinder further improvement of conventional
devices. This anticipation is motivating the development of
alternative devices that take advantage of the quantum nature at the
atomic scale. A notable example is the quantum computer concept,
where each bit is formed by a single atom or a group of a few atoms,
and the rules of quantum mechanics dictate the way information is
processed. Another interesting alternative is spintronics, where
the spin of the electrons instead of their charge forms the basis for
classical memory and logic, promising much lower rates of energy
dissipation per device. Our research project addresses several
theoretical questions related to the design and optimization of quantum
computer and spintronic devices based on semiconductor, superconductor,
and magnetic nanostructures.
Click here
for a list of publications.
Electrical control of magnetism in Multiferroic materials
We are currently interested
in the
question of electrical control of magnetism in bulk and nanoscale
materials.
One promising direction is to study the so called multiferroic
materials, which possess coexisting ferroelectric and
(anti)ferromagnetic order.
We are investigating novel physical phenomena with these materials with
an eye towards applications to spintronic devices.
Silicon based spintronics and quantum computation
Silicon is the
material of choice in the current microelectronics industry.
Therefore, the development of quantum computing and spintronic devices
based on silicon nanostructures has the advantages of being easily
integrated into existing technology and being compatible
with large scale fabrication techniques. We are currently
interested in spin-dependent effects in silicon nanostructures,
particularly effects leading to the measurement of the spin state of a
single donor impurity in a silicon MOSFET device. This work is in
collaboration with Dr. Thomas Schenkel from the Lawrence Berkeley
National Laboratory, Prof. Jeffrey Bokor from the Dept. of Electrical
Engineering, and Prof. K. Birgitta Whaley from the Dept. of
Chemistry. Click here
to see a recent research news article from Science@Berkeley Lab.
Noise
and decoherence in metallic nanostructures
We are investigating
the physical origin of noise and decoherence affecting quantum
computers based on normal metal and superconducting
nanostructures. Our goal is to control the imperfections
inherent to these devices in order to allow the development of large
scale
fault tolerant quantum hardware.
Recently, we developed a microscopic model
for the noise
on single electron tunneling devices arising due to
the presence of trapping-centers located in the dielectric barrier close to
one of the gate electrodes. The
noise spectrum resulting from coupling to
such trapping-centers is found
to show quite different behavior depending on the relative energy of
the
trapping-center and the Fermi level. When the trap energy
level is close to the Fermi sea and has a linewidth greater than kBT, it
results in an Ohmic noise spectrum, whereas when the linewidth is less than kBT the Lorentzian form expected
from a semiclassical limit is obtained (In the semiclassical limit, trapping-center
noise is well described by a random telegraph noise model). Multiple trap levels above
the Fermi level are shown to lead to a staircase noise spectrum that can be used
to probe the energetics of the trapping-centers, allowing identification
of individual trapping-centers
coupled to a tunneling device [For details, see R. de Sousa,
K.B. Whaley, F.K. Wilhelm, and J. von Delft, Phys.
Rev. Lett. 95, 247006 (2005)].
