10 research outputs found
Optimized single-shot laser ablation of concave mirror templates on optical fibers
We realize mirror templates on the tips of optical fibers using a single-shot
CO laser ablation procedure. We perform a systematic study of the influence
of the pulse power, pulse duration, and laser spot size on the radius of
curvature, depth, and diameter of the mirror templates. We find that these
geometrical characteristics can be tuned to a larger extent than has been
previously reported, and notably observe that compound convex-concave shapes
can be obtained. This detailed investigation should help further the
understanding of the physics of CO laser ablation processes and help
improve current models. We additionally identify regimes of ablation parameters
that lead to mirror templates with favorable geometries for use in cavity
quantum electrodynamics and optomechanics
Fast Long-Distance Control of Spin Qubits by Photon Assisted Cotunneling
We investigate theoretically the long-distance coupling and spin exchange in
an array of quantum dot spin qubits in the presence of microwaves. We find that
photon assisted cotunneling is boosted at resonances between photon and
energies of virtually occupied excited states and show how to make it spin
selective. We identify configurations that enable fast switching and spin echo
sequences for efficient and non-local manipulation of spin qubits. We devise
configurations in which the near-resonantly boosted cotunneling provides
non-local coupling which, up to certain limit, does not diminish with distance
between the manipulated dots before it decays weakly with inverse distance.Comment: 17 pages (including 8 pages of Appendices), 2 figure
Coherent two-mode dynamics of a nanowire force sensor
Classically coherent dynamics analogous to those of quantum two-level systems
are studied in the setting of force sensing. We demonstrate quantitative
control over the coupling between two orthogonal mechanical modes of a nanowire
cantilever, through measurement of avoided crossings as we deterministically
position the nanowire inside an electric field. Furthermore, we demonstrate
Rabi oscillations between the two mechanical modes in the strong coupling
regime. These results give prospects of implementing coherent two-mode control
techniques for force sensing signal enhancement.Comment: 16 pages, 4 figure
Ultrafast Hole Spin Qubit with Gate-Tunable Spin-Orbit Switch
A key challenge in quantum computation is the implementation of fast and
local qubit control while simultaneously maintaining coherence. Qubits based on
hole spins offer, through their strong spin-orbit interaction, a way to
implement fast quantum gates. Strikingly, for hole spins in one-dimensional
germanium and silicon devices, the spin-orbit interaction has been predicted to
be exceptionally strong yet highly tunable with gate voltages. Such electrical
control would make it possible to switch on demand between qubit idling and
manipulation modes. Here, we demonstrate ultrafast and universal quantum
control of a hole spin qubit in a germanium/silicon core/shell nanowire, with
Rabi frequencies of several hundreds of megahertz, corresponding to
spin-flipping times as short as ~1 ns - a new record for a single-spin qubit.
Next, we show a large degree of electrical control over the Rabi frequency,
Zeeman energy, and coherence time - thus implementing a switch toggling from a
rapid qubit manipulation mode to a more coherent idling mode. We identify an
exceptionally strong but gate-tunable spin-orbit interaction as the underlying
mechanism, with a short associated spin-orbit length that can be tuned over a
large range down to 3 nm for holes of heavy-hole mass. Our work demonstrates a
spin-orbit qubit switch and establishes hole spin qubits defined in
one-dimensional germanium/silicon nanostructures as a fast and highly tunable
platform for quantum computation
Single, double, and triple quantum dots in Ge/Si nanowires
\u3cp\u3eWe report highly tunable control of holes in Ge/Si core/shell nanowires. We demonstrate the ability to create single quantum dots of various sizes, with low hole occupation numbers and clearly observable excited states. For the smallest dot size, we observe indications of single-hole occupation. Moreover, we create double and triple tunnel-coupled quantum dot arrays. In the double quantum dot configuration, we observe Pauli spin blockade. These results open the way to perform hole spin qubit experiments in these devices.\u3c/p\u3
The big picture All eight topics under one roof
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