270 research outputs found
Frustrated three-leg spin tubes: from spin 1/2 with chirality to spin 3/2
Motivated by the recent discovery of the spin tube
[(CuCltachH)Cl]Cl, we investigate the properties of a frustrated
three-leg spin tube with antiferromagnetic intra-ring and inter-ring couplings.
We pay special attention to the evolution of the properties from weak to strong
inter-ring coupling and show on the basis of extensive density matrix
renormalization group and exact diagonalization calculations that the system
undergoes a first-order phase transition between a dimerized gapped phase at
weak coupling that can be described by the usual spin-chirality model and a
gapless critical phase at strong coupling that can be described by an effective
spin-3/2 model. We also show that there is a magnetization plateau at 1/3 in
the gapped phase and slightly beyond. The implications for
[(CuCltachH)Cl]Cl are discussed, with the conclusion that this
system behaves essentially as a spin-3/2 chain.Comment: 8 pages, 9 figures, revised versio
Enhanced molecular yield from a cryogenic buffer gas beam source via excited state chemistry
We use narrow-band laser excitation of Yb atoms to substantially enhance the brightness of a cold beam of YbOH, a polyatomic molecule with high sensitivity to physics beyond the standard model (BSM). By exciting atomic Yb to the metastable ³P₁ state in a cryogenic environment, we significantly increase the chemical reaction cross-section for collisions of Yb with reactants. We characterize the dependence of the enhancement on the properties of the laser light, and study the final state distribution of the YbOH products. The resulting bright, cold YbOH beam can be used to increase the statistical sensitivity in searches for new physics utilizing YbOH, such as electron electric dipole moment and nuclear magnetic quadrupole moment experiments. We also perform new quantum chemical calculations that confirm the enhanced reactivity observed in our experiment and compare reaction pathways of Yb(³P) with the reactants H₂O and H₂O₂. More generally, our work presents a broad approach for improving experiments that use cryogenic molecular beams for laser cooling and precision measurement searches of BSM physics
Strategisch manoeuvreren in medische consultatie: een pragma-dialectische analyse van autoriteitsargumentatie van de arts
In dit artikel wordt autoriteitsargumentatie van de arts in medische consultatie geanalyseerd als strategische manoeuvre. Het doel van deze analyse is ten eerste om te laten zien hoe de institutionele context van het medische consult een argumentatieve discussie tussen een arts en een patiënt kan beïnvloeden, en ten tweede om een uitgangspunt te bieden voor de evaluatie van de deugdelijkheid van autoriteitsargumentatie van de arts in medische consultatie. Om deze doelen te verwezenlijken, zal eerst een argumentatieve karakterisering van medische consultatie worden gegeven. Vervolgens zal autoriteitsargumentatie van de arts worden geanalyseerd aan de hand van de uitgebreide pragma-dialectische argumentatietheorie.FGW – Publications not associated with a particular research are
Direct measurement of high-lying vibrational repumping transitions for molecular laser cooling
Molecular laser cooling and trapping requires addressing all spontaneous
decays to excited vibrational states that occur at the level, which is accomplished by driving repumping transitions out of
these states. However, the transitions must first be identified
spectroscopically at high-resolution. A typical approach is to prepare
molecules in excited vibrational states via optical cycling and pumping, which
requires multiple high-power lasers. Here, we demonstrate a general method to
perform this spectroscopy without the need for optical cycling. We produce
molecules in excited vibrational states by using optically-driven chemical
reactions in a cryogenic buffer gas cell, and implement frequency-modulated
absorption to perform direct, sensitive, high-resolution spectroscopy. We
demonstrate this technique by measuring the spectrum of the
band in YbOH.
We identify the specific vibrational repump transitions needed for photon
cycling, and combine our data with previous measurements of the
band to determine all
of the relevant spectral constants of the state.
This technique achieves high signal-to-noise, can be further improved to
measure increasingly high-lying vibrational states, and is applicable to other
molecular species favorable for laser cooling.Comment: 14 pages, 5 figure
Enhanced molecular yield from a cryogenic buffer gas beam source via excited state chemistry
We use narrow-band laser excitation of Yb atoms to substantially enhance the brightness of a cold beam of YbOH, a polyatomic molecule with high sensitivity to physics beyond the standard model (BSM). By exciting atomic Yb to the metastable ³P₁ state in a cryogenic environment, we significantly increase the chemical reaction cross-section for collisions of Yb with reactants. We characterize the dependence of the enhancement on the properties of the laser light, and study the final state distribution of the YbOH products. The resulting bright, cold YbOH beam can be used to increase the statistical sensitivity in searches for new physics utilizing YbOH, such as electron electric dipole moment and nuclear magnetic quadrupole moment experiments. We also perform new quantum chemical calculations that confirm the enhanced reactivity observed in our experiment and compare reaction pathways of Yb(³P) with the reactants H₂O and H₂O₂. More generally, our work presents a broad approach for improving experiments that use cryogenic molecular beams for laser cooling and precision measurement searches of BSM physics
Stub model for dephasing in a quantum dot
As an alternative to Buttiker's dephasing lead model, we examine a dephasing
stub. Both models are phenomenological ways to introduce decoherence in chaotic
scattering by a quantum dot. The difference is that the dephasing lead opens up
the quantum dot by connecting it to an electron reservoir, while the dephasing
stub is closed at one end. Voltage fluctuations in the stub take over the
dephasing role from the reservoir. Because the quantum dot with dephasing lead
is an open system, only expectation values of the current can be forced to
vanish at low frequencies, while the outcome of an individual measurement is
not so constrained. The quantum dot with dephasing stub, in contrast, remains a
closed system with a vanishing low-frequency current at each and every
measurement. This difference is a crucial one in the context of quantum
algorithms, which are based on the outcome of individual measurements rather
than on expectation values. We demonstrate that the dephasing stub model has a
parameter range in which the voltage fluctuations are sufficiently strong to
suppress quantum interference effects, while still being sufficiently weak that
classical current fluctuations can be neglected relative to the nonequilibrium
shot noise.Comment: 8 pages with 1 figure; contribution for the special issue of J.Phys.A
on "Trends in Quantum Chaotic Scattering
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