13 research outputs found
Laser Scheme for Doppler Cooling of the Hydroxyl Cation (OH)
We report on a cycling scheme for Doppler cooling of trapped OH ions
using transitions between the electronic ground state and the
first excited triplet state . We have identified relevant transitions
for photon cycling and repumping, have found that coupling into other
electronic states is strongly suppressed, and have calculated the number of
photon scatterings required to cool OH to a temperature where Raman
sideband cooling can take over. In contrast to the standard approach, where
molecular ions are sympathetically cooled, our scheme does not require
co-trapping of another species and opens the door to the creation of pure
samples of cold molecular ions with potential applications in quantum
information, quantum chemistry, and astrochemistry. The laser cooling scheme
identified for OH is efficient despite the absence of near-diagonal
Franck-Condon factors, suggesting that broader classes of molecules and
molecular ions are amenable to laser cooling than commonly assumed.Comment: 6 pages, 3 figure
Automated detection of laser cooling schemes for ultracold molecules
One of the demanding frontiers in ultracold science is identifying laser
cooling schemes for complex atoms and molecules, out of their vast spectra of
internal states. Motivated by a need to expand the set of available ultracold
molecules for applications in fundamental physics, chemistry, astrochemistry,
and quantum simulation, we propose and demonstrate an automated graph-based
search approach for viable laser cooling schemes. The method is time efficient
and the outcomes greatly surpass the results of manual searches used so far. We
discover new laser cooling schemes for C, OH, CN, YO, and CO that
can be viewed as surprising or counterintuitive compared to previously
identified laser cooling schemes. In addition, a central insight of this work
is that the reinterpretation of quantum states and transitions between them as
a graph can dramatically enhance our ability to identify new quantum control
schemes for complex quantum systems. As such, this approach will also be
applicable to complex atoms and, in fact, any complex many-body quantum system
with a discrete spectrum of internal states.Comment: 10 pages and 5 figures in the main text + 11 pages and 7 figures in
appendices. Comments and feedback are very welcome. Code is available at
https://github.com/Shmoo137/Detection-Of-Laser-Cooled-Molecule
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Laser cooling scheme for the carbon dimer (12C2)
We report on a scheme for laser cooling of 12 C 2 . We have calculated the branching ratios for cycling and repumping transitions and calculated the number of photon scatterings required to achieve deflection and laser cooling of a beam of C 2 molecules under realistic experimental conditions. Our results demonstrate that C 2 cooling using the Swan ( d 3 Πg ↔ a 3 Πu ) and so-called Duck ( d 3 Πg ↔ c 3 Σ + u ) bands is achievable via techniques similar to state-of-the-art molecular cooling experiments. The Phillips ( A 1 Πu ↔ X 1 Σ + g ) and Ballik-Ramsay ( b 3 Σ − g ↔ a 3 Πu ) bands offer the potential for narrow-line cooling. This work opens up a path to cooling of molecules with carbon-carbon bonds and may pave the way toward quantum control of organic molecules
Collisionally Stable Gas of Bosonic Dipolar Ground State Molecules
Stable ultracold ensembles of dipolar molecules hold great promise for
many-body quantum physics, but high inelastic loss rates have been a
long-standing challenge. Recently, it was shown that gases of fermionic
molecules can be effectively stabilized through external fields. However, many
quantum applications will benefit from molecular ensembles with bosonic
statistics. Here, we stabilize a bosonic gas of strongly dipolar NaCs molecules
against inelastic losses via microwave shielding, decreasing losses by more
than a factor of 200 and reaching lifetimes on the scale of 1 second. We also
measure high elastic scattering rates, a result of strong dipolar interactions,
and observe the anisotropic nature of dipolar collisions. Finally, we
demonstrate evaporative cooling of a bosonic molecular gas to a temperature of
36(5) nK, increasing its phase-space density by a factor of 20. This work is a
critical step towards the creation of a Bose-Einstein condensate of dipolar
molecules.Comment: 13 pages, 10 figure
Ultracold Gas of Dipolar NaCs Ground State Molecules
We report on the creation of bosonic NaCs molecules in their absolute
rovibrational ground state via stimulated Raman adiabatic passage. We create
ultracold gases with up to 22,000 dipolar NaCs molecules at a temperature of
300(50) nK and a peak density of cm. We
demonstrate comprehensive quantum state control by preparing the molecules in a
specific electronic, vibrational, rotational, and hyperfine state. Employing
the tunability and strength of the permanent electric dipole moment of NaCs, we
induce dipole moments of up to 2.6 D. Dipolar systems of NaCs molecules are
uniquely suited to explore strongly interacting phases in dipolar quantum
matter.Comment: 6 pages, 5 figure
Efficient Pathway to NaCs Ground State Molecules
We present a study of two-photon pathways for the transfer of NaCs molecules
to their rovibrational ground state. Starting from NaCs Feshbach molecules, we
perform bound-bound excited state spectroscopy in the wavelength range from
900~nm to 940~nm, covering more than 30 vibrational states of the c \,
^3\Sigma^+, b \, ^3\Pi, and B \, ^1\Pi electronic states. Analyzing the
rotational substructure, we identify the highly mixed c \, ^3\Sigma^+_1 \,
|v=22 \rangle \sim b \, ^3\Pi_1 \, | v=54\rangle state as an efficient bridge
for stimulated Raman adiabatic passage (STIRAP). We demonstrate transfer into
the NaCs ground state with an efficiency of up to 88(4)\%. Highly efficient
transfer is critical for the realization of many-body quantum phases of
strongly dipolar NaCs molecules and high fidelity detection of single
molecules, for example, in spin physics experiments in optical lattices and
quantum information experiments in optical tweezer arrays.Comment: 17 pages, 8 figure
A High Phase-Space Density Gas of NaCs Feshbach Molecules
We report on the creation of ultracold gases of bosonic Feshbach molecules of
NaCs. The molecules are associated from overlapping gases of Na and Cs using a
Feshbach resonance at 864.12(5) G. We characterize the Feshbach resonance using
bound state spectroscopy, in conjunction with a coupled-channel calculation. By
varying the temperature and atom numbers of the initial atomic mixtures, we
demonstrate the association of NaCs gases over a wide dynamic range of molecule
numbers and temperatures, reaching 70 nK for our coldest systems and a
phase-space density (PSD) near 0.1. This is an important stepping-stone for the
creation of degenerate gases of strongly dipolar NaCs molecules in their
absolute ground state.Comment: 6 pages, 5 figures, supplemental materia
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Reaching the Bose-Einstein Condensation of Dipolar Molecules: a Journey from Ultracold Atoms to Molecular Quantum Control
Achieving the quantum control of ever more complex systems has been a driving force of atomic, molecular, and optical physics. This goal has materialized in the harnessing of systems with increasingly rich structures and interactions: the more sophisticated the system, the more faceted and fascinating its application to fields as varied as quantum simulation, quantum information, many body physics, metrology, and quantum chemistry. One of the current frontiers of quantum control is ultracold dipolar molecules. They present rich internal structures and long-range, anisotropic dipole-dipole interactions which promise to revolutionize AMO physics, for example by realizing realistic Hamiltonians in quantum simulation, by providing a new platform for quantum information, and by achieving a novel kind of quantum liquid.
Despite its promises, the full quantum control of dipolar molecules has been over a decade in the making. The difficulties in either directly laser cooling molecules or in collisionally stabilizing their bulk samples have been major roadblocks that have hampered the development of this quantum system. The realization of a Bose-Einstein condensate of dipolar molecules has been a particularly elusive milestone. In this thesis, I report on the first observation of this quantum state of matter.
The work that brought us to this achievement parallels the historical evolution of AMO physics in the last thirty years. To reach a BEC of molecules, we initially constructed a dual species experiment capable of realizing the simultaneous Bose-Einstein condensation of atomic sodium (Na) and cesium (Cs). Individual BECs of sodium and cesium were first reported in 1995 and 2003 respectively, while our experiment was the first instance of their concurrent condensation. The study of the Na-Cs interatomic scattering properties in an homogeneous magnetic field showed us the path to the Feshbach association of loosely-bound sodium-cesium (NaCs) molecules, a technique first demonstrated in 2006 for heteronuclear molecules but never attempted on our species. Following the Feschbach association, we determined a novel pathway to the molecular electronic, vibrational and rotational ground state using STIRAP.
From this point, we found ourselves at the forefront of the field: bulk samples of bosonic molecules such as NaCs had neither been stabilized against collisional losses nor evaporatively cooled. At first, we successfully applied a single-frequency microwave shielding approach to decrease in-bulk losses by a factor of 200 and reach lifetimes on the order of 2 s, allowing us to measure high elastic scattering rates and characterize their dipolar anisotropy. Moreover, we demonstrated the first evaporative cooling of a bosonic molecular gas by increasing its phase-spacedensity by a factor of 20 and reaching a temperature of 36(5) nK. Since this proved insufficient to achieve Bose-Einstein condensation due to unexpected three-body losses, we introduced an enhanced microwave shielding technique, double microwave shielding. This further decreased loss rates enabling efficient evaporative cooling of our sample to a long-lived Bose-Einstein condensate of dipolar molecules. This new double microwave shielding technique also allows the tunability of the strength of dipole-dipole interaction, establishing ultracold bosonic dipolar molecules as a new quantum liquid for the exploration of many body physics.
In addition to the experimental work on dipolar NaCs, we have theoretically explored the field of direct molecular laser cooling. Our aim was twofold: we aimed to expand the category of molecules that can be laser cooled and to simplify the identification of laser cycling schemes. For the former goal, we lifted the widespread assumption that only molecules with diagonal Franck-Condon factors could be laser cooled. For the latter, we decided to employ publicly available repositories of molecular transitions. A second consequence of the use of these databases is that they contain data on molecules of interest to other scientific fields, further establishing direct laser cooling as a technique that could be of interest beyond AMO physics. Our work was successful in that we identified laser cycling schemes for Câ‚‚ and OH+. To simplify the determination of laser cycling schemes, we developed a graph-based algorithm form their identification starting from spectroscopic data
Laser Cooling Scheme for the Carbon Dimer (C)
We report on a scheme for laser cooling of C. We have calculated
the branching ratios for cycling and repumping transitions and calculated the
number of photon scatterings required to achieve deflection and laser cooling
of a beam of molecules under realistic experimental conditions. Our
results demonstrate that C cooling using the Swan () and Duck () bands is achievable via techniques similar to
state-of-the-art molecular cooling experiments. The Phillips () and Ballik-Ramsay () bands offer the potential for narrow-line
cooling. This work opens up a path to cooling of molecules with carbon-carbon
bonds and may pave the way toward quantum control of organic molecules.Comment: 7 pages, 5 figure