2,648 research outputs found
Valuation theory, generalized IFS attractors and fractals
Using valuation rings and valued fields as examples, we discuss in which ways the notions of “topological IFS attractor” and “fractal space” can be generalized to cover more general settings
Transform-limited single photons from a single quantum dot
A semiconductor quantum dot mimics a two-level atom. Performance as a single
photon source is limited by decoherence and dephasing of the optical
transition. Even with high quality material at low temperature, the optical
linewidths are a factor of two larger than the transform-limit. A major
contributor to the inhomogeneous linewdith is the nuclear spin noise. We show
here that the nuclear spin noise depends on optical excitation, increasing
(decreasing) with increasing resonant laser power for the neutral (charged)
exciton. Based on this observation, we discover regimes where we demonstrate
transform-limited linewidths on both neutral and charged excitons even when the
measurement is performed very slowly
Epitaxial lift-off for solid-state cavity quantum electrodynamics
We present a new approach to incorporate self-assembled quantum dots into a
Fabry-P\'{e}rot-like microcavity. Thereby a 3/4 GaAs layer containing
quantum dots is epitaxially removed and attached by van der Waals bonding to
one of the microcavity mirrors. We reach a finesse as high as 4,100 with this
configuration limited by the reflectivity of the dielectric mirrors and not by
scattering at the semiconductor - mirror interface, demonstrating that the
epitaxial lift-off procedure is a promising procedure for cavity quantum
electrodynamics in the solid state. As a first step in this direction, we
demonstrate a clear cavity-quantum dot interaction in the weak coupling regime
with a Purcell factor in the order of 3. Estimations of the coupling strength
via the Purcell factor suggests that we are close to the strong coupling
regime.Comment: 6 pages, 4 figure
Electrically-tunable hole g-factor of an optically-active quantum dot for fast spin rotations
We report a large g-factor tunability of a single hole spin in an InGaAs
quantum dot via an electric field. The magnetic field lies in the in-plane
direction x, the direction required for a coherent hole spin. The electrical
field lies along the growth direction z and is changed over a large range, 100
kV/cm. Both electron and hole g-factors are determined by high resolution laser
spectroscopy with resonance fluorescence detection. This, along with the low
electrical-noise environment, gives very high quality experimental results. The
hole g-factor g_xh depends linearly on the electric field Fz, dg_xh/dFz = (8.3
+/- 1.2)* 10^-4 cm/kV, whereas the electron g-factor g_xe is independent of
electric field, dg_xe/dFz = (0.1 +/- 0.3)* 10^-4 cm/kV (results averaged over a
number of quantum dots). The dependence of g_xh on Fz is well reproduced by a
4x4 k.p model demonstrating that the electric field sensitivity arises from a
combination of soft hole confining potential, an In concentration gradient and
a strong dependence of material parameters on In concentration. The electric
field sensitivity of the hole spin can be exploited for electrically-driven
hole spin rotations via the g-tensor modulation technique and based on these
results, a hole spin coupling as large as ~ 1 GHz is expected to be envisaged.Comment: 8 pages, 4 figure
Three-dimensional flow instability in a lid-driven isosceles triangular cavity
Linear three-dimensional modal instability of steady laminar two-dimensional states developing in a lid-driven cavity of isosceles triangular cross-section is investigated theoretically and experimentally for the case in which the equal sides form a rectangular corner. An asymmetric steady two-dimensional motion is driven by the steady motion of one of the equal sides. If the side moves away from the rectangular corner, a stationary three-dimensional instability is found. If the motion is directed towards the corner, the instability is oscillatory. The respective critical Reynolds numbers are identified both theoretically and experimentally. The neutral curves pertinent to the two configurations and the properties of the respective leading eigenmodes are documented and analogies to instabilities in rectangular lid-driven cavities are discussed
Coherent and robust high-fidelity generation of a biexciton in a quantum dot by rapid adiabatic passage
A biexciton in a semiconductor quantum dot is a source of
polarization-entangled photons with high potential for implementation in
scalable systems. Several approaches for non-resonant, resonant and
quasi-resonant biexciton preparation exist, but all have their own
disadvantages, for instance low fidelity, timing jitter, incoherence or
sensitivity to experimental parameters. We demonstrate a coherent and robust
technique to generate a biexciton in an InGaAs quantum dot with a fidelity
close to one. The main concept is the application of rapid adiabatic passage to
the ground state-exciton-biexciton system. We reinforce our experimental
results with simulations which include a microscopic coupling to phonons.Comment: Main manuscript 5 pages and 4 figures, Supplementary Information 5
pages and 3 figures, accepted as a Rapid Communication in PRB. arXiv admin
note: text overlap with arXiv:1701.0130
High resolution coherent population trapping on a single hole spin in a semiconductor
We report high resolution coherent population trapping on a single hole spin
in a semiconductor quantum dot. The absorption dip signifying the formation of
a dark state exhibits an atomic physics-like dip width of just 10 MHz. We
observe fluctuations in the absolute frequency of the absorption dip, evidence
of very slow spin dephasing. We identify this process as charge noise by,
first, demonstrating that the hole spin g-factor in this configuration
(in-plane magnetic field) is strongly dependent on the vertical electric field,
and second, by characterizing the charge noise through its effects on the
optical transition frequency. An important conclusion is that charge noise is
an important hole spin dephasing process
Demonstrating the decoupling regime of the electron-phonon interaction in a quantum dot using chirped optical excitation
Excitation of a semiconductor quantum dot with a chirped laser pulse allows
excitons to be created by rapid adiabatic passage. In quantum dots this process
can be greatly hindered by the coupling to phonons. Here we add a high chirp
rate to ultra-short laser pulses and use these pulses to excite a single
quantum dot. We demonstrate that we enter a regime where the exciton-phonon
coupling is effective for small pulse areas, while for higher pulse areas a
decoupling of the exciton from the phonons occurs. We thus discover a
reappearance of rapid adiabatic passage, in analogy to the predicted
reappearance of Rabi rotations at high pulse areas. The measured results are in
good agreement with theoretical calculations.Comment: Main manuscript 5 pages and 4 figures, Supplementary Information 5
pages and 3 figures, submitted to PR
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