20 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
Scanning NV magnetometry of focused-electron-beam-deposited cobalt nanomagnets
Focused-electron-beam-induced deposition is a promising technique for
patterning nanomagnets for spin qubit control in a single step. We fabricate
cobalt nanomagnets in such a process, obtaining cobalt contents and saturation
magnetizations comparable to or higher than those typically obtained using
electron-beam lithography. We characterize the nanomagnets using transmission
electron microscopy and image their stray magnetic field using scanning NV
magnetometry, finding good agreement with micromagnetic simulations. The
magnetometry reveals the presence of magnetic domains and halo side-deposits,
which are common for this fabrication technique. Finally, we estimate dephasing
times for electron spin qubits in the presence of disordered stray fields due
to these side-deposits
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
A compact and versatile cryogenic probe station for quantum device testing
Fast feedback from cryogenic electrical characterization measurements is key
for the development of scalable quantum computing technology. At room
temperature, high-throughput device testing is accomplished with a probe-based
solution, where electrical probes are repeatedly positioned onto devices for
acquiring statistical data. In this work we present a probe station that can be
operated from room temperature down to below 2K. Its small size makes it
compatible with standard cryogenic measurement setups with a magnet. A large
variety of electronic devices can be tested. Here, we demonstrate the
performance of the prober by characterizing silicon fin field-effect
transistors as a host for quantum dot spin qubits. Such a tool can massively
accelerate the design-fabrication-measurement cycle and provide important
feedback for process optimization towards building scalable quantum circuits
A fiber-coupled quantum-dot on a photonic tip
International audienc
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
Identification of osteolineage cell-derived extracellular vesicle cargo implicated in hematopoietic support
Osteolineage cell-derived extracellular vesicles (EVs) play a regulatory role in hematopoiesis and have been shown to promote the ex vivo expansion of human hematopoietic stem and progenitor cells (HSPCs). Here, we demonstrate that EVs from different human osteolineage sources do not have the same HSPC expansion promoting potential. Comparison of stimulatory and non-stimulatory osteolineage EVs by next-generation sequencing and mass spectrometry analyses revealed distinct microRNA and protein signatures identifying EV-derived candidate regulators of ex vivo HSPC expansion. Accordingly, the treatment of umbilical cord blood-derived CD34+ HSPCs with stimulatory EVs-altered HSPC transcriptome, including genes with known roles in cell proliferation. An integrative bioinformatics approach, which connects the HSPC gene expression data with the candidate cargo in stimulatory EVs, delineated the potentially targeted biological functions and pathways during hematopoietic cell expansion and development. In conclusion, our study giv