17 research outputs found
Bose-Einstein Condensation of Long-Lifetime Polaritons in Thermal Equilibrium
Exciton-polaritons in semiconductor microcavities have been used to
demonstrate quantum effects such as Bose-Einstein condensation, superfluity,
and quantized vortices. However, in these experiments, the polaritons have not
reached thermal equilibrium when they undergo the transition to a coherent
state. This has prevented the verification of one of the canonical predictions
for condensation, namely the phase diagram. In this work, we have created a
polariton gas in a semiconductor microcavity in which the quasiparticles have a
lifetime much longer than their thermalization time. This allows them to reach
thermal equilibrium in a laser-generated confining trap. Their energy
distributions are well fit by equilibrium Bose-Einstein distributions over a
broad range of densities and temperatures from very low densities all the way
up to the threshold for Bose-Einstein condensation. The good fits of the
Bose-Einstein distribution over a broad range of density and temperature imply
that the particles obey the predicted power law for the phase boundary of
Bose-Einstein condensation
Hybrid THz architectures for molecular polaritonics
Physical and chemical properties of materials can be modified by a resonant
optical mode. Such recent demonstrations have mostly relied on a planar cavity
geometry, others have relied on a plasmonic resonator. However, the combination
of these two device architectures have remained largely unexplored, especially
in the context of maximizing light-matter interactions. Here, we investigate
several schemes of electromagnetic field confinement aimed at facilitating the
collective coupling of a localized photonic mode to molecular vibrations in the
terahertz region. The key aspects are the use of metasurface plasmonic
structures combined with standard Fabry-Perot configurations and the deposition
of a thin layer of glucose, via a spray coating technique, within a tightly
focused electromagnetic mode volume. More importantly, we demonstrate enhanced
vacuum Rabi splittings reaching up to 200 GHz when combining plasmonic
resonances, photonic cavity modes and low-energy molecular resonances.
Furthermore, we demonstrate how a cavity mode can be utilized to enhance the
zero-point electric field amplitude of a plasmonic resonator. Our study
provides key insight into the design of polaritonic platforms with organic
molecules to harvest the unique properties of hybrid light-matter states.Comment: 7 pages (5 Figures) + 7 pages Appendix (5 Figures), updated versio
Ku Regulates the Non-Homologous End Joining Pathway Choice of DNA Double-Strand Break Repair in Human Somatic Cells
The repair of DNA double-strand breaks (DSBs) is critical for the maintenance of genomic integrity and viability for all organisms. Mammals have evolved at least two genetically discrete ways to mediate DNA DSB repair: homologous recombination (HR) and non-homologous end joining (NHEJ). In mammalian cells, most DSBs are preferentially repaired by NHEJ. Recent work has demonstrated that NHEJ consists of at least two sub-pathways—the main Ku heterodimer-dependent or “classic” NHEJ (C-NHEJ) pathway and an “alternative” NHEJ (A-NHEJ) pathway, which usually generates microhomology-mediated signatures at repair junctions. In our study, recombinant adeno-associated virus knockout vectors were utilized to construct a series of isogenic human somatic cell lines deficient in the core C-NHEJ factors (Ku, DNA-PKcs, XLF, and LIGIV), and the resulting cell lines were characterized for their ability to carry out DNA DSB repair. The absence of DNA-PKcs, XLF, or LIGIV resulted in cell lines that were profoundly impaired in DNA DSB repair activity. Unexpectedly, Ku86-null cells showed wild-type levels of DNA DSB repair activity that was dominated by microhomology joining events indicative of A-NHEJ. Importantly, A-NHEJ DNA DSB repair activity could also be efficiently de-repressed in LIGIV-null and DNA-PKcs-null cells by subsequently reducing the level of Ku70. These studies demonstrate that in human cells C-NHEJ is the major DNA DSB repair pathway and they show that Ku is the critical C-NHEJ factor that regulates DNA NHEJ DSB pathway choice
Stable switching among high-order modes in polariton condensates
We report multistate optical switching among high-order bouncing-ball modes (“ripples”) and whispering-gallery modes (“petals”) of exciton-polariton condensates in a laser-generated annular trap. By tailoring the diameter and power of the annular trap, the polariton condensate can be switched among different trapped modes, accompanied by redistribution of spatial densities and superlinear increase in the emission intensities, implying that polariton condensates in this geometry could be exploited for an all-optical multistate switch. A model based on non-Hermitian modes of the generalized Gross-Pitaevskii equation reveals that this mode switching arises from competition between pump-induced gain and in-plane polariton loss. The parameters for reproducible switching among trapped modes have been measured experimentally, giving us a phase diagram for mode switching. Taken together, the experimental result and theoretical modeling advance our fundamental understanding of the spontaneous emergence of coherence and move us toward its practical exploitation.United States. Department of Energy. Office of Basic Energy Sciences (Award DE-SC0001088