20,333 research outputs found
Higgs diphoton rate enhancement from supersymmetric physics beyond the MSSM
We show that supersymmetric "new physics" beyond the MSSM can naturally
accommodate a Higgs mass near 126 GeV and enhance the signal rate in the Higgs
to diphoton channel, while the signal rates in all the other Higgs decay
channels coincide with Standard Model expectations, except possibly the Higgs
to Z-photon channel. The "new physics" that corrects the relevant Higgs
couplings can be captured by two supersymmetric effective operators. We provide
a simple example of an underlying model in which these operators are
simultaneously generated. The scale of "new physics" that generates these
operators can be around 5 TeV or larger, and outside the reach of the LHC.Comment: 24 pages, 4 figure
Fast Single-Charge Sensing with an rf Quantum Point Contact
We report high-bandwidth charge sensing measurements using a GaAs quantum
point contact embedded in a radio frequency impedance matching circuit
(rf-QPC). With the rf-QPC biased near pinch-off where it is most sensitive to
charge, we demonstrate a conductance sensitivity of 5x10^(-6) e^(2)/h Hz^(-1/2)
with a bandwidth of 8 MHz. Single-shot readout of a proximal few-electron
double quantum dot is investigated in a mode where the rf-QPC back-action is
rapidly switched.Comment: related papers available at http://marcuslab.harvard.ed
Cotunneling Spectroscopy in Few-Electron Quantum Dots
Few-electron quantum dots are investigated in the regime of strong tunneling
to the leads. Inelastic cotunneling is used to measure the two-electron
singlet-triplet splitting above and below a magnetic field driven
singlet-triplet transition. Evidence for a non-equilibrium two-electron
singlet-triplet Kondo effect is presented. Cotunneling allows orbital
correlations and parameters characterizing entanglement of the two-electron
singlet ground state to be extracted from dc transport.Comment: related papers available at http://marcuslab.harvard.ed
Wide-angle perfect absorber/thermal emitter in the THz regime
We show that a perfect absorber/thermal emitter exhibiting an absorption peak
of 99.9% can be achieved in metallic nanostructures that can be easily
fabricated. The very high absorption is maintained for large angles with a
minimal shift in the center frequency and can be tuned throughout the visible
and near-infrared regime by scaling the nanostructure dimensions. The stability
of the spectral features at high temperatures is tested by simulations using a
range of material parameters.Comment: Submitted to Phys. Rev. Let
Toward quantum simulations of biological information flow
Recent advances in the spectroscopy of biomolecules have highlighted the
possibility of quantum coherence playing an active role in biological energy
transport. The revelation that quantum coherence can survive in the hot and wet
environment of biology has generated a lively debate across both the physics
and biology communities. In particular, it remains unclear to what extent
non-trivial quantum effects are utilised in biology and what advantage, if any,
they afford. We propose an analogue quantum simulator, based on currently
available techniques in ultra-cold atom physics, to study a model of energy and
electron transport based on the Holstein Hamiltonian By simulating the salient
aspects of a biological system in a tunable laboratory setup, we hope to gain
insight into the validity of several theoretical models of biological quantum
transport in a variety of relevant parameter regimes.Comment: 8 Pages, 2 Figures, Non-technical contributing article for the
Interface Focus Theme Issue `Computability and the Turning centenary'.
Interface Focus
http://rsfs.royalsocietypublishing.org/content/early/2012/03/22/rsfs.2011.0109.shor
Rapid Single-Shot Measurement of a Singlet-Triplet Qubit
We report repeated single-shot measurements of the two-electron spin state in
a GaAs double quantum dot. The readout scheme allows measurement with fidelity
above 90% with a 7 microsecond cycle time. Hyperfine-induced precession between
singlet and triplet states of the two-electron system are directly observed, as
nuclear Overhauser fields are quasi-static on the time scale of the measurement
cycle. Repeated measurements on millisecond to second time scales reveal
evolution of the nuclear environment.Comment: supplemental material at
http://marcuslab.harvard.edu/papers/single_shot_sup.pd
Solid-state circuit for spin entanglement generation and purification
We show how realistic charge manipulation and measurement techniques,
combined with the exchange interaction, allow for the robust generation and
purification of four-particle spin entangled states in electrically controlled
semiconductor quantum dots. The generated states are immunized to the dominant
sources of noise via a dynamical decoherence-free subspace; all additional
errors are corrected by a purification protocol. This approach may find
application in quantum computation, communication, and metrology.Comment: 5 pages, 2 figures; corrected minor typo
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