34 research outputs found
CONTROL OF TRAPPED-ION MOTION FOR MOLECULAR SPECTROSCOPY AND QUANTUM INFORMATION PROCESSING
Ph.DDOCTOR OF PHILOSOPH
Quantum absorption refrigerator with trapped ions
Thermodynamics is one of the oldest and well-established branches of physics
that sets boundaries to what can possibly be achieved in macroscopic systems.
While it started as a purely classical theory, it was realized in the early
days of quantum mechanics that large quantum devices, such as masers or lasers,
can be treated with the thermodynamic formalism. Remarkable progress has been
made recently in the miniaturization of heat engines all the way to the single
Brownian particle as well as to a single atom. However, despite several
theoretical proposals, the implementation of heat machines in the fully quantum
regime remains a challenge. Here, we report an experimental realization of a
quantum absorption refrigerator in a system of three trapped ions, with three
of its normal modes of motion coupled by a trilinear Hamiltonian such that heat
transfer between two modes refrigerates the third. We investigate the dynamics
and steady-state properties of the refrigerator and compare its cooling
capability when only thermal states are involved to the case when squeezing is
employed as a quantum resource. We also study the performance of such a
refrigerator in the single shot regime, and demonstrate cooling below both the
steady-state energy and the benchmark predicted by the classical thermodynamics
treatment.Comment: 11 pages, 7 figures, 2 table
Sub-Doppler Cooling and Compressed Trapping of YO Molecules at K Temperatures
Complex molecular structure demands customized solutions to laser cooling by
extending its general set of principles and practices. Yttrium monoxide (YO)
has unique intramolecular interactions. The Fermi-contact interaction dominates
over the spin-rotation coupling, resulting in two manifolds of closely spaced
states, with one of them possessing a negligible Land\'e g-factor. This unique
energy level structure favors dual-frequency DC magneto-optical trapping (MOT)
and gray molasses cooling (GMC). We report exceptionally robust cooling of YO
at 4 K over a wide range of laser intensity, detunings (one and
two-photon), and magnetic field. The magnetic insensitivity enables the spatial
compression of the molecular cloud by alternating GMC and MOT under the
continuous operation of the quadrupole magnetic field. A combination of these
techniques produces a laser-cooled molecular sample with the highest phase
space density in free space.Comment: 9 pages, 6 figure
Extending Our Knowledge about the Th-229 Nuclear Isomer
The first nuclear excited state in Th-229 possesses the lowest excitation energy of all currently known nuclear levels. The energy difference between the ground- and first-excited (isomeric) state (denoted with Th-229m) amounts only to approximate to 8.2 eV (approximate to 151.2 nm), which results in several interesting consequences: Since the excitation energy is in the same energy range as the binding energy of valence electrons, the lifetime of Th-229m is strongly influenced by the electronic structure of the Th atom or ion. Furthermore, it is possible to potentially excite the isomeric state in Th-229 with laser radiation, which led to the proposal of a nuclear clock that could be used to search for new physics beyond the standard model. In this article, we will focus on recent technical developments in our group that will help to better understand the decay mechanisms of Th-229m, focusing primarily on measuring the radiative lifetime of the isomeric state
Regulatory T cells inhibit stable contacts between CD4+ T cells and dendritic cells in vivo
Regulatory T (T reg) cells exert powerful down-modulatory effects on immune responses, but it is not known how they act in vivo. Using intravital two-photon laser scanning microscopy we determined that, in the absence of T reg cells, the locomotion of autoantigen-specific T cells inside lymph nodes is decreased, and the contacts between T cells and antigen-loaded dendritic cells (DCs) are of longer duration. Thus, T reg cells can exert an early effect on immune responses by attenuating the establishment of stable contacts during priming of naive T cells by DCs
Light-Reinforced Key Intermediate for Anticoking To Boost Highly Durable Methane Dry Reforming over Single Atom Ni Active Sites on CeO<sub>2</sub>.
Dry reforming of methane (DRM) has been investigated for more than a century; the paramount stumbling block in its industrial application is the inevitable sintering of catalysts and excessive carbon emissions at high temperatures. However, the low-temperature DRM process still suffered from poor reactivity and severe catalyst deactivation from coking. Herein, we proposed a concept that highly durable DRM could be achieved at low temperatures via fabricating the active site integration with light irradiation. The active sites with Ni-O coordination (NiSA/CeO2) and Ni-Ni coordination (NiNP/CeO2) on CeO2, respectively, were successfully constructed to obtain two targeted reaction paths that produced the key intermediate (CH3O*) for anticoking during DRM. In particular, the operando diffuse reflectance infrared Fourier transform spectroscopy coupling with steady-state isotopic transient kinetic analysis (operando DRIFTS-SSITKA) was utilized and successfully tracked the anticoking paths during the DRM process. It was found that the path from CH3* to CH3O* over NiSA/CeO2 was the key path for anticoking. Furthermore, the targeted reaction path from CH3* to CH3O* was reinforced by light irradiation during the DRM process. Hence, the NiSA/CeO2 catalyst exhibits excellent stability with negligible carbon deposition for 230 h under thermo-photo catalytic DRM at a low temperature of 472 °C, while NiNP/CeO2 shows apparent coke deposition behavior after 0.5 h in solely thermal-driven DRM. The findings are vital as they provide critical insights into the simultaneous achievement of low-temperature and anticoking DRM process through distinguishing and directionally regulating the key intermediate species