1,854 research outputs found
Measurements of strongly-anisotropic g-factors for spins in single quantum states
We have measured the full angular dependence, as a function of the direction
of magnetic field, for the Zeeman splitting of individual energy states in
copper nanoparticles. The g-factors for spin splitting are highly anisotropic,
with angular variations as large as a factor of five. The angular dependence
fits well to ellipsoids. Both the principal-axis directions and g-factor
magnitudes vary between different energy levels within one nanoparticle. The
variations agree quantitatively with random-matrix theory predictions which
incorporate spin-orbit coupling.Comment: 4 pages, 3 figures, 2 in colo
Single charge sensing and transport in double quantum dots fabricated from commercially grown Si/SiGe heterostructures
We perform quantum Hall measurements on three types of commercially available
modulation doped Si/SiGe heterostructures to determine their suitability for
depletion gate defined quantum dot devices. By adjusting the growth parameters,
we are able to achieve electron gases with charge densities 1-3 X 10^{11}/cm^2
and mobilities in excess of 100,000 cm^2/Vs. Double quantum dot devices
fabricated on these heterostructures show clear evidence of single charge
transitions as measured in dc transport and charge sensing and exhibit electron
temperatures of 100 mK in the single quantum dot regime.Comment: Related papers at http://pettagroup.princeton.ed
Effect of Exchange Interaction on Spin Dephasing in a Double Quantum Dot
We measure singlet-triplet dephasing in a two-electron double quantum dot in
the presence of an exchange interaction which can be electrically tuned from
much smaller to much larger than the hyperfine energy. Saturation of dephasing
and damped oscillations of the spin correlator as a function of time are
observed when the two interaction strengths are comparable. Both features of
the data are compared with predictions from a quasistatic model of the
hyperfine field.Comment: see related papers at http://marcuslab.harvard.ed
Measurement of Temporal Correlations of the Overhauser Field in a Double Quantum Dot
In quantum dots made from materials with nonzero nuclear spins, hyperfine
coupling creates a fluctuating effective Zeeman field (Overhauser field) felt
by electrons, which can be a dominant source of spin qubit decoherence. We
characterize the spectral properties of the fluctuating Overhauser field in a
GaAs double quantum dot by measuring correlation functions and power spectra of
the rate of singlet-triplet mixing of two separated electrons. Away from zero
field, spectral weight is concentrated below 10 Hz, with 1/f^2 dependence on
frequency, f. This is consistent with a model of nuclear spin diffusion, and
indicates that decoherence can be largely suppressed by echo techniques.Comment: related papers available at http://marcuslab.harvard.ed
Dynamic Nuclear Polarization with Single Electron Spins
We polarize nuclear spins in a GaAs double quantum dot by controlling
two-electron spin states near the anti-crossing of the singlet (S) and m_S=+1
triplet (T+) using pulsed gates. An initialized S state is cyclically brought
into resonance with the T+ state, where hyperfine fields drive rapid rotations
between S and T+, 'flipping' an electron spin and 'flopping' a nuclear spin.
The resulting Overhauser field approaches 80 mT, in agreement with a simple
rate-equation model. A self-limiting pulse sequence is developed that allows
the steady-state nuclear polarization to be set using a gate voltage.Comment: related papers available at http://marcuslab.harvard.ed
Manipulation of a single charge in a double quantum dot
We manipulate a single electron in a fully tunable double quantum dot using
microwave excitation. Under resonant conditions, microwaves drive transitions
between the (1,0) and (0,1) charge states of the double dot. Local quantum
point contact charge detectors enable a direct measurement of the
photon-induced change in occupancy of the charge states. From charge sensing
measurements, we find T1~16 ns and a lower bound estimate for T2* of 400 ps for
the charge two-level system.Comment: related articles at http://marcuslab.harvard.ed
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