11 research outputs found
Two-Photon Spectroscopy of the NaLi Triplet Ground State
We employ two-photon spectroscopy to study the vibrational states of the
triplet ground state potential () of the NaLi
molecule. Pairs of Na and Li atoms in an ultracold mixture are photoassociated
into an excited triplet molecular state, which in turn is coupled to
vibrational states of the triplet ground potential. Vibrational state binding
energies, line strengths, and potential fitting parameters for the triplet
ground potential are reported. We also observe rotational
splitting in the lowest vibrational state.Comment: 7 pages, 3 figure
Collisional Cooling of Ultracold Molecules
Since the original work on Bose-Einstein condensation, quantum degenerate
gases of atoms have allowed the quantum emulation of important systems from
condensed matter and nuclear physics, as well as the study of novel many-body
states with no analog in other fields of physics. Ultracold molecules in the
micro- and nano-Kelvin regimes promise to bring powerful new capabilities to
quantum emulation and quantum computing, thanks to their rich internal degrees
of freedom compared to atoms. They also open new possibilities for precision
measurement and the study of quantum chemistry. Quantum gases of atoms were
made possible by collision-based cooling schemes, such as evaporative cooling.
For ultracold molecules, thermalization and collisional cooling have not been
realized. With other techniques such as supersonic jets and cryogenic buffer
gases, studies have been limited to temperatures above 10 mK. Here we show
cooling of NaLi molecules at micro- and nano-Kelvin temperatures through
collisions with ultracold Na atoms, both prepared in their stretched hyperfine
spin states. We find a lower bound on the elastic to inelastic collision ratio
between molecules and atoms greater than 50 -- large enough to support
sustained collisional cooling. By employing two stages of evaporation, we
increase the phase-space density (PSD) of the molecules by a factor of 20,
achieving temperatures as low as 220 nK. The favorable collisional properties
of a Na and NaLi mixture show great promise for making deeply quantum
degenerate dipolar molecules and suggest the potential for such cooling in
other systems
Long-Lived Ultracold Molecules with Electric and Magnetic Dipole Moments
We create fermionic dipolar NaLi molecules in their triplet ground
state from an ultracold mixture of Na and Li. Using
magneto-association across a narrow Feshbach resonance followed by a two-photon
STIRAP transfer to the triplet ground state, we produce
ground state molecules in a spin-polarized state. We observe a lifetime of
in an isolated molecular sample, approaching the -wave
universal rate limit. Electron spin resonance spectroscopy of the triplet state
was used to determine the hyperfine structure of this previously unobserved
molecular state.Comment: 5 pages, 5 figure
Photoassociation of Ultracold NaLi
We perform photoassociation spectroscopy in an ultracold Na-Li
mixture to study the excited triplet molecular potential. We
observe 50 vibrational states and their substructure to an accuracy of 20 MHz,
and provide line strength data from photoassociation loss measurements. An
analysis of the vibrational line positions using near-dissociation expansions
and a full potential fit is presented. This is the first observation of the
potential, as well as photoassociation in the NaLi system.Comment: 6 pages, 3 figure
Spectrum of Feshbach resonances in NaLi Na collisions
Collisional resonances of molecules can offer a deeper understanding of
interaction potentials and collision complexes, and allow control of chemical
reactions. Here, we experimentally map out the spectrum of Feshbach resonances
in collisions between ultracold triplet ro-vibrational ground-state NaLi
molecules and Na atoms over a range of 1400 G. Preparation of the
spin-stretched state puts the system initially into the non-reactive quartet
potential. A total of 25 resonances are observed, in agreement with
quantum-chemistry calculations using a coupled-channels approach. Although the
theory cannot predict the positions of resonances, it can account for several
experimental findings and provide unprecedented insight into the nature and
couplings of ultracold, strongly interacting complexes. Previous work has
addressed only weakly bound complexes. We show that the main coupling mechanism
results from spin-rotation and spin-spin couplings in combination with the
anisotropic atom-molecule interaction, and that the collisional complexes which
support the resonances have a size of 30-40 . This study illustrates the
potential of a combined experimental and theoretical approach
Ab initio calculation of the spectrum of Feshbach resonances in NaLi + Na collisions
We present a combined experimental and theoretical study of the spectrum of
magnetically tunable Feshbach resonances in NaLi Na
collisions. In the accompanying paper, we observe experimentally 8 and 17
resonances occur between and ~G in upper and lower spin-stretched
states, respectively. Here, we perform ab initio calculations of the NaLi
Na interaction potential and describe in detail the coupled-channel scattering
calculations of the Feshbach resonance spectrum. The positions of the
resonances cannot be predicted with realistic uncertainty in the
state-of-the-art ab initio potential, but our calculations yield a typical
number of resonances that is in near-quantitative agreement with experiment. We
show that the main coupling mechanism results from spin-rotation and spin-spin
couplings in combination with the anisotropic atom-molecule interaction. The
calculations furthermore explain the qualitative difference between the numbers
of resonances in either spin state
Electrical Control of Plasmon Resonance with Graphene
Surface plasmon, with its unique capability to concentrate light into
sub-wavelength volume, has enabled great advances in photon science, ranging
from nano-antenna and single-molecule Raman scattering to plasmonic waveguide
and metamaterials. In many applications it is desirable to control the surface
plasmon resonance in situ with electric field. Graphene, with its unique
tunable optical properties, provides an ideal material to integrate with
nanometallic structures for realizing such control. Here we demonstrate
effective modulation of the plasmon resonance in a model system composed of
hybrid graphene-gold nanorod structure. Upon electrical gating the strong
optical transitions in graphene can be switched on and off, which leads to
significant modulation of both the resonance frequency and quality factor of
plasmon resonance in gold nanorods. Hybrid graphene-nanometallic structures, as
exemplified by this combination of graphene and gold nanorod, provide a general
and powerful way for electrical control of plasmon resonances. It holds promise
for novel active optical devices and plasmonic circuits at the deep
subwavelength scale
Control of reactive collisions by quantum interference
In this study, we achieved magnetic control of reactive scattering in an ultracold mixture of
23
Na atoms and
23
Na
6
Li molecules. In most molecular collisions, particles react or are lost near short range with unity probability, leading to the so-called universal rate. By contrast, the Na + NaLi system was shown to have only ~4% loss probability in a fully spin-polarized state. By controlling the phase of the scattering wave function via a Feshbach resonance, we modified the loss rate by more than a factor of 100, from far below to far above the universal limit. The results are explained in analogy with an optical Fabry-Perot resonator by interference of reflections at short and long range. Our work demonstrates quantum control of chemistry by magnetic fields with the full dynamic range predicted by our models.
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Electrical Control of Optical Plasmon Resonance with Graphene
Surface plasmon has the unique capability to concentrate
light
into subwavelength volume.− Active plasmon devices using electrostatic gating can enable flexible
control of the plasmon excitations, which
has been demonstrated recently in terahertz plasmonic structures.− Controlling plasmon resonance at optical frequencies, however, remains
a significant challenge because gate-induced free electrons have very
weak responses at optical frequencies. Here we achieve efficient control of near-infrared plasmon resonance
in a hybrid graphene-gold nanorod system. Exploiting the uniquely
strong, and gate-tunable optical transitions, of graphene, we are able to significantly modulate both the resonance
frequency and quality factor of gold nanorod plasmon. Our analysis
shows that the plasmon–graphene coupling is remarkably strong:
even a single electron in graphene at the plasmonic hotspot could
have an observable effect on plasmon scattering intensity. Such hybrid
graphene–nanometallic structure provides a powerful way for
electrical control of plasmon resonances at optical frequencies and
could enable novel plasmonic sensing down to single charge transfer
events