2,471 research outputs found
The West Point Landscape: 1802–1830
This book chronicles the landscape history of the United States Military Academy\u27s first three decades. Major buildings at West Point are described and maps and illustrations highlight the changes made during the period.https://digitalcommons.usmalibrary.org/books/1043/thumbnail.jp
Cost effective flat plate photovoltaic modules using light trapping
Work in optical trapping in 'thick films' is described to form a design guide for photovoltaic engineers. A thick optical film can trap light by diffusive reflection and total internal reflection. Light can be propagated reasonably long distances compared with layer thicknesses by this technique. This makes it possible to conduct light from inter-cell and intra-cell areas now not used in photovoltaic modules onto active cell areas
How to wire a 1000-qubit trapped ion quantum computer
One of the most formidable challenges of scaling up quantum computers is that
of control signal delivery. Today's small-scale quantum computers typically
connect each qubit to one or more separate external signal sources. This
approach is not scalable due to the I/O limitations of the qubit chip,
necessitating the integration of control electronics. However, it is no small
feat to shrink control electronics into a small package that is compatible with
qubit chip fabrication and operation constraints without sacrificing
performance. This so-called "wiring challenge" is likely to impact the
development of more powerful quantum computers even in the near term. In this
paper, we address the wiring challenge of trapped-ion quantum computers. We
describe a control architecture called WISE (Wiring using Integrated Switching
Electronics), which significantly reduces the I/O requirements of ion trap
quantum computing chips without compromising performance. Our method relies on
judiciously integrating simple switching electronics into the ion trap chip -
in a way that is compatible with its fabrication and operation constraints -
while complex electronics remain external. To demonstrate its power, we
describe how the WISE architecture can be used to operate a fully connected
1000-qubit trapped ion quantum computer using ~ 200 signal sources at a speed
of ~ 40 - 2600 quantum gate layers per second
Suppressing quasiparticle poisoning with a voltage-controlled filter
We study single-electron charging events in an Al/InAs nanowire hybrid system
with deliberately introduced gapless regions. The occupancy of a Coulomb island
is detected using a nearby radio-frequency quantum dot as a charge sensor. We
demonstrate that a 1 micron gapped segment of the wire can be used to
efficiently suppress single electron poisoning of the gapless region and
therefore protect the parity of the island while maintaining good electrical
contact with a normal lead. In the absence of protection by charging energy,
the 1e switching rate can be reduced below 200 per second. In the same
configuration, we observe strong quantum charge fluctuations due to exchange of
electron pairs between the island and the lead. The magnetic field dependence
of the poisoning rate yields a zero-field superconducting coherence length of ~
90 nm
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Towards On-Chip Self-Referenced Frequency-Comb Sources Based on Semiconductor Mode-Locked Lasers.
Miniaturization of frequency-comb sources could open a host of potential applications in spectroscopy, biomedical monitoring, astronomy, microwave signal generation, and distribution of precise time or frequency across networks. This review article places emphasis on an architecture with a semiconductor mode-locked laser at the heart of the system and subsequent supercontinuum generation and carrier-envelope offset detection and stabilization in nonlinear integrated optics
Symmetric Operation of the Resonant Exchange Qubit
We operate a resonant exchange qubit in a highly symmetric triple-dot
configuration using IQ-modulated RF pulses. At the resulting three-dimensional
sweet spot the qubit splitting is an order of magnitude less sensitive to all
relevant control voltages, compared to the conventional operating point, but we
observe no significant improvement in the quality of Rabi oscillations. For
weak driving this is consistent with Overhauser field fluctuations modulating
the qubit splitting. For strong driving we infer that effective voltage noise
modulates the coupling strength between RF drive and the qubit, thereby
quickening Rabi decay. Application of CPMG dynamical decoupling sequences
consisting of up to n = 32 {\pi} pulses significantly prolongs qubit coherence,
leading to marginally longer dephasing times in the symmetric configuration.
This is consistent with dynamical decoupling from low frequency noise, but
quantitatively cannot be explained by effective gate voltage noise and
Overhauser field fluctuations alone. Our results inform recent strategies for
the utilization of partial sweet spots in the operation and long-distance
coupling of triple-dot qubits.Comment: 6 pages, 5 figure
Negative spin exchange in a multielectron quantum dot
By operating a one-electron quantum dot (fabricated between a multielectron
dot and a one-electron reference dot) as a spectroscopic probe, we study the
spin properties of a gate-controlled multielectron GaAs quantum dot at the
transition between odd and even occupation number. We observe that the
multielectron groundstate transitions from spin-1/2-like to singlet-like to
triplet-like as we increase the detuning towards the next higher charge state.
The sign reversal in the inferred exchange energy persists at zero magnetic
field, and the exchange strength is tunable by gate voltages and in-plane
magnetic fields. Complementing spin leakage spectroscopy data, the inspection
of coherent multielectron spin exchange oscillations provides further evidence
for the sign reversal and, inferentially, for the importance of non-trivial
multielectron spin exchange correlations.Comment: 8 pages, including 4 main figures and 2 supplementary figurure
Two types of all-optical magnetization switching mechanisms using femtosecond laser pulses
Magnetization manipulation in the absence of an external magnetic field is a
topic of great interest, since many novel physical phenomena need to be
understood and promising new applications can be imagined. Cutting-edge
experiments have shown the capability to switch the magnetization of magnetic
thin films using ultrashort polarized laser pulses. In 2007, it was first
observed that the magnetization switching for GdFeCo alloy thin films was
helicity-dependent and later helicity-independent switching was also
demonstrated on the same material. Recently, all-optical switching has also
been discovered for a much larger variety of magnetic materials (ferrimagnetic,
ferromagnetic films and granular nanostructures), where the theoretical models
explaining the switching in GdFeCo films do not appear to apply, thus
questioning the uniqueness of the microscopic origin of all-optical switching.
Here, we show that two different all-optical switching mechanisms can be
distinguished; a "single pulse" switching and a "cumulative" switching process
whose rich microscopic origin is discussed. We demonstrate that the latter is a
two-step mechanism; a heat-driven demagnetization followed by a
helicity-dependent remagnetization. This is achieved by an all-electrical and
time-dependent investigation of the all-optical switching in ferrimagnetic and
ferromagnetic Hall crosses via the anomalous Hall effect, enabling to probe the
all-optical switching on different timescales.Comment: 1 page, LaTeX; classified reference number
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