862 research outputs found
Trapping ultracold atoms at 100 nm from a chip surface in a 0.7-micrometer-period magnetic lattice
We report the trapping of ultracold 87Rb atoms in a 0.7 micron-period 2D
triangular magnetic lattice on an atom chip. The magnetic lattice is created by
a lithographically patterned magnetic Co/Pd multilayer film plus bias fields.
Rubidium atoms in the F=1, mF=-1 low-field seeking state are trapped at
estimated distances down to about 100 nm from the chip surface and with
calculated mean trapping frequencies as high as 800 kHz. The measured lifetimes
of the atoms trapped in the magnetic lattice are in the range 0.4 - 1.7 ms,
depending on distance from the chip surface. Model calculations suggest the
trap lifetimes are currently limited mainly by losses due to surface-induced
thermal evaporation following loading of the atoms from the Z-wire trap into
the very tight magnetic lattice traps, rather than by fundamental loss
processes such as surface interactions, three-body recombination or spin flips
due to Johnson magnetic noise. The trapping of atoms in a 0.7 micrometer-period
magnetic lattice represents a significant step towards using magnetic lattices
for quantum tunneling experiments and to simulate condensed matter and
many-body phenomena in nontrivial lattice geometries.Comment: 11 pages, 7 figure
The value of designers' creative practice within complex collaborations
This paper reports a case study investigating the productive value of designers' creative practice within complex academic-industrial collaborations in which a designer's practice had a formative role. Adopting a pragmatic approach, collaborators' experiences of this project were reconstructed through interviews and ‘annotated timelines.’ Collaborators were found to value the designer's work in responding to their particular concerns whilst also opening up new possibilities. This paper discusses how such benefit is attributable to the ‘designerly thinking’ of skilled designers, shifting the focus of work from problem-solving to problematisation and enabling participants to collectively formulate concerns, roles, and potentialities. The paper concludes that designers' creative practice can enable collaborative projects to build upon and transcend participants' expertise and expectations through ‘creative exchange.
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
Noise suppression using symmetric exchange gates in spin qubits
We demonstrate a substantial improvement in the spin-exchange gate using
symmetric control instead of conventional detuning in GaAs spin qubits, up to a
factor-of-six increase in the quality factor of the gate. For symmetric
operation, nanosecond voltage pulses are applied to the barrier that controls
the interdot potential between quantum dots, modulating the exchange
interaction while maintaining symmetry between the dots. Excellent agreement is
found with a model that separately includes electrical and nuclear noise
sources for both detuning and symmetric gating schemes. Unlike exchange control
via detuning, the decoherence of symmetric exchange rotations is dominated by
rotation-axis fluctuations due to nuclear field noise rather than direct
exchange noise.Comment: 5 pages main text (4 figures) plus 5 pages supplemental information
(3 figures
Role of ionotropic glutamate receptors in long-term potentiation in rat hippocampal CA1 oriens-lacunosum moleculare interneurons
Some interneurons of the hippocampus exhibit NMDA receptor-independent long-term potentiation (LTP) that is induced by presynaptic glutamate release when the postsynaptic membrane potential is hyperpolarized. This "anti-Hebbian" form of LTP is prevented by postsynaptic depolarization or by blocking AMPA and kainate receptors. Although both AMPA and kainate receptors are expressed in hippocampal interneurons, their relative roles in anti-Hebbian LTP are not known. Because interneuron diversity potentially conceals simple rules underlying different forms of plasticity, we focus on glutamatergic synapses onto a subset of interneurons with dendrites in stratum oriens and a main ascending axon that projects to stratum lacunosum moleculare, the oriens-lacunosum moleculare (O-LM) cells. We show that anti-Hebbian LTP in O-LM interneurons has consistent induction and expression properties, and is prevented by selective inhibition of AMPA receptors. The majority of the ionotropic glutamatergic synaptic current in these cells is mediated by inwardly rectifying Ca(2+)-permeable AMPA receptors. Although GluR5-containing kainate receptors contribute to synaptic currents at high stimulus frequency, they are not required for LTP induction. Glutamatergic synapses on O-LM cells thus behave in a homogeneous manner and exhibit LTP dependent on Ca(2+)-permeable AMPA receptors
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