32 research outputs found
Gate Adjustable Coherent Three and Four Level Mixing in a Vertical Quantum Dot Molecule
We study level mixing in the single particle energy spectrum of one of the
constituent quantum dots in a vertical double quantum dot by performing
magneto-resonant-tunneling spectroscopy. The device used in this study differs
from previous vertical double quantum dot devices in that the single side gate
is now split into four separate gates. Because of the presence of natural
perturbations caused by anharmonicity and anistrophy, applying different
combinations of voltages to these gates allows us to alter the effective
potential landscape of the two dots and hence influence the level mixing. We
present here preliminary results from one three level crossing and one four
level crossings high up in the energy spectrum of one of the probed quantum
dots, and demonstrate that we are able to change significantly the energy
dispersions with magnetic field in the vicinity of the crossing regions.Comment: 5 pages, 4 figures. MSS-14 conference proceedings submitted to
Physica
Spin bottleneck in resonant tunneling through double quantum dots with different Zeeman splittings
We investigated the electron transport property of the InGaAs/GaAs double
quantum dots, the electron g-factors of which are different from each other. We
found that in a magnetic field, the resonant tunneling is suppressed even if
one of the Zeeman sublevels is aligned. This is because the other misaligned
Zeeman sublevels limit the total current. A finite broadening of the misaligned
sublevel partially relieves this bottleneck effect, and the maximum current is
reached when interdot detuning is half the Zeeman energy difference.Comment: Added references. Changed conten
Single-dot spectroscopy via elastic single-electron tunneling through a pair of coupled quantum dots
We study the electronic structure of a single self-assembled InAs quantum dot
by probing elastic single-electron tunneling through a single pair of weakly
coupled dots. In the region below pinch-off voltage, the non-linear threshold
voltage behavior provides electronic addition energies exactly as the linear,
Coulomb blockade oscillation does. By analyzing it, we identify the s and p
shell addition spectrum for up to six electrons in the single InAs dot, i.e.
one of the coupled dots. The evolution of shell addition spectrum with magnetic
field provides Fock-Darwin spectra of s and p shell.Comment: 7 pages, 3 figures, Accepted for publication in Phys. Rev. Let
Tunneling Via Individual Electronic States in Ferromagnetic Nanoparticles
We measure electron tunneling via discrete energy levels in ferromagnetic
cobalt particles less than 4 nm in diameter, using non-magnetic electrodes. Due
to magnetic anisotropy, the energy of each tunneling resonance shifts as an
applied magnetic field rotates the particle's magnetic moment. We see both
spin-increasing and decreasing tunneling transitions, but we do not observe the
spin degeneracy at small magnetic fields seen previously in non-magnetic
materials. The tunneling spectrum is denser than predicted for independent
electrons, possibly due to spin-wave excitations.Comment: 4 pages, 4 figures. Improved by comments from referees, to appear in
Phys. Rev. Let
Molecular phases in coupled quantum dots
We present excitation energy spectra of few-electron vertically coupled
quantum dots for strong and intermediate inter-dot coupling. By applying a
magnetic field, we induce ground state transitions and identify the
corresponding quantum numbers by comparison with few-body calculations. In
addition to atomic-like states, we find novel "molecular-like" phases. The
isospin index characterizes the nature of the bond of the artificial molecule
and this we control. Like spin in a single quantum dot, transitions in isospin
leading to full polarization are observed with increasing magnetic field.Comment: PDF file only, 28 pages, 3 tables, 4 color figures, 2 appendices. To
appear in Physical Review B, Scheduled 15 Feb 2004, Vol. 69, Issue
Electrically driven single electron spin resonance in a slanting Zeeman field
The rapidly rising fields of spintronics and quantum information science have
led to a strong interest in developing the ability to coherently manipulate
electron spins. Electron spin resonance (ESR) is a powerful technique to
manipulate spins that is commonly achieved by applying an oscillating magnetic
field. However, the technique has proven very challenging when addressing
individual spins. In contrast, by mixing the spin and charge degrees of freedom
in a controlled way through engineered non-uniform magnetic fields, electron
spin can be manipulated electrically without the need of high-frequency
magnetic fields. Here we realize electrically-driven addressable spin rotations
on two individual electrons by integrating a micron-size ferromagnet to a
double quantum dot device. We find that the electrical control and spin
selectivity is enabled by the micro-magnet's stray magnetic field which can be
tailored to multi-dots architecture. Our results demonstrate the feasibility of
manipulating electron spins electrically in a scalable way.Comment: 25 pages, 6 figure
Swapping and entangling hyperfine coupled nuclear spin baths
We numerically study the hyperfine induced nuclear spin dynamics in a system
of two coupled quantum dots in zero magnetic field. Each of the electron spins
is considered to interact with an individual bath of nuclear spins via
homogeneous coupling constants (all coupling coefficients being equal). In
order to lower the dimension of the problem, the two baths are approximated by
two single long spins. We demonstrate that the hyperfine interaction enables to
utilize the nuclear baths for quantum information purposes. In particular, we
show that it is possible to swap the nuclear ensembles on time scales of
seconds and indicate that it might even be possible to fully entangle them. As
a key result, it turns out that the larger the baths are, the more useful they
become as a resource of quantum information. Interestingly, the nuclear spin
dynamics strongly benefits from combining two quantum dots of different
geometry to a double dot set up.Comment: 6 pages, 7 figure
Current rectification by Pauli exclusion in a weakly coupled double quantum dot system
NRC publication: Ye
Spin selective tunneling and blockade in two-electron double quantum dot
NRC publication: Ye