Coherent backscattering of intense light by cold atoms with degenerate energy levels: Diagrammatic treatment

We present a generalization of the diagrammatic pump-probe approach to coherent backscattering (CBS) of intense laser light for atoms with degenerate energy levels. We employ this approach for a characterization of the double scattering signal from optically pumped atoms with the transition $J_g\rightarrow J_e=J_g+1$ in the helicity preserving polarization channel. We show that, in the saturation regime, the internal degeneracy becomes manifest for atoms with $J_g\geq 1$, leading to a faster decrease of the CBS enhancement factor with increasing saturation parameter than in the non-degenerate case.Comment: 18 pages, 16 figure

Landau-Zener interference at bichromatic driving

We investigate experimentally and theoretically the interference at avoided crossings which are repeatedly traversed as a consequence of an applied ac field. Our model system is a charge qubit in a serial double quantum dot connected to two leads. Our focus lies on effects caused by simultaneous driving with two different frequencies. We work out how the commensurability of the driving frequencies affects the symmetry of the interference patterns both in real space and in Fourier space. For commensurable frequencies, the symmetry depends sensitively on the relative phase between the two modes, whereas for incommensurable frequencies the symmetry of monochromatic driving is always recovered

Fluctuating work in coherent quantum systems: proposals and limitations

One of the most important goals in quantum thermodynamics is to demonstrate advantages of thermodynamic protocols over their classical counterparts. For that, it is necessary to (i) develop theoretical tools and experimental set-ups to deal with quantum coherence in thermodynamic contexts, and to (ii) elucidate which properties are genuinely quantum in a thermodynamic process. In this short review, we discuss proposals to define and measure work fluctuations that allow to capture quantum interference phenomena. We also discuss fundamental limitations arising due to measurement back-action, as well as connections between work distributions and quantum contextuality. We hope the different results summarised here motivate further research on the role of quantum phenomena in thermodynamics.Comment: As a chapter of: F. Binder, L. A. Correa, C. Gogolin, J. Anders, and G. Adesso (eds.), "Thermodynamics in the quantum regime - Recent Progress and Outlook", (Springer International Publishing). Second version: Misspell in the title correcte

Negativity and quantum discord in Davies environments

We investigate the time evolution of negativity and quantum discord for a pair of non-interacting qubits with one being weakly coupled to a decohering Davies--type Markovian environment. At initial time of preparation, the qubits are prepared in one of the maximally entangled pure Bell states. In the limiting case of pure decoherence (i.e. pure dephasing), both, the quantum discord and negativity decay to zero in the long time limit. In presence of a manifest dissipative dynamics, the entanglement negativity undergoes a sudden death at finite time while the quantum discord relaxes continuously to zero with increasing time. We find that in dephasing environments the decay of the negativity is more propitious with increasing time; in contrast, the evolving decay of the quantum discord proceeds weaker for dissipative environments. Particularly, the slowest decay of the quantum discord emerges when the energy relaxation time matches the dephasing time.Comment: submitted for publicatio

Land-ocean connections in organic carbon cycling amid the Early Triassic (Smithian-Spathian) revealed through compound specific isotope analysis

Following the largest mass extinction of the Phanerozoic, the Early Triassic was characterized by a series of carbon cycle perturbations as revealed through multiple global carbon isotope excursions (CIEs). The mechanistic drivers behind these perturbations are a subject of debate due to limited records that differentiate terrestrial and marine carbon cycling processes. In this study, we focus on the Smithian-Spathian boundary, which is characterized by a global positive CIE approximately 2 million years after the onset of the carbon cycle perturbations. We present the results of biomarker molecular distributions (i.e., n-alkanes) and compound-specific carbon isotope analyses (δ13Calkane) for organic matter extracted from shales deposited at the Stensiöfjellet section in Spitsbergen, Norway. The measured middle Smithian δ13Calkane values are among the lowest in the Phanerozoic and potentially indicate high atmospheric pCO2 and a low δ13C value for CO2 as a result of the oxidation of organic carbon. Marine and terrestrial δ13Calkane records show parallel CIEs reflecting that both systems were equally affected by carbon cycle perturbations. Our data suggest the onset of the CIE started in the late middle Smithian, suggesting an earlier perturbation of the carbon cycle than previously recognized. Spathian δ13Calkane values remain elevated and diverge from bulk δ13C trends, reflecting an intrinsic shift in both the marine and terrestrial carbon cycle. Considered together, our compound-specific carbon isotope analyses foster useful insights into the multiple carbon cycle perturbations during an interval of extreme environmental conditions marked by continuous biological radiation and extinction pulses, which might even be analogous to imminent future anthropogenic changes in climate. This study further shows that compound specific carbon isotope analyses can potentially also disentangle deep-time carbon cycle perturbations

Global-scale evidence for the refractory nature of riverine black carbon

Author Posting. © The Author(s), 2018. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Nature Geoscience 11 (2018): 584-588, doi:10.1038/s41561-018-0159-8.Wildfires and incomplete combustion of fossil fuel produce large amounts of black carbon. Black carbon production and transport are essential components of the carbon cycle. Constraining estimates of black carbon exported from land to ocean is critical, given ongoing changes in land use and climate, which affect fire occurrence and black carbon dynamics. Here, we present an inventory of the concentration and radiocarbon content (∆14C) of particulate black carbon for 18 rivers around the globe. We find that particulate black carbon accounts for about 15.8 ± 0.9% of river particulate organic carbon, and that fluxes of particulate black carbon co-vary with river-suspended sediment, indicating that particulate black carbon export is primarily controlled by erosion. River particulate black carbon is not exclusively from modern sources but is also aged in intermediate terrestrial carbon pools in several high-latitude rivers, with ages of up to 17,000 14C years. The flux-weighted 14C average age of particulate black carbon exported to oceans is 3,700 ± 400 14C years. We estimate that the annual global flux of particulate black carbon to the ocean is 0.017 to 0.037 Pg, accounting for 4 to 32% of the annually produced black carbon. When buried in marine sediments, particulate black carbon is sequestered to form a long-term sink for CO2.A.C. acknowledges financial support from the University of Zurich Forschungskredit Fellowship and the University of Zurich (grant No. STWF-18-026). M.R., S.A. and M.S. acknowledge support from the University Research Priority Projection Global Change and Biodiversity (URPP-GCB). M.Z. acknowledges support from the National Natural Science Foundation of China (No. 41521064). T.E. acknowledges support from the Swiss National Science Foundation (“CAPS-LOCK” and “CAPS-LOCK2” #200021_140850). V.G. acknowledges financial support from an Independent Study Award from the Woods Hole Oceanographic Institution

Smithian–Spathian carbonate geochemistry in the northern Thaynes Group influenced by multiple styles of diagenesis

The Smithian–Spathian boundary interval is characterised by a positive carbon isotopic excursion in both δ$^{13}$C$_{carb}$ and δ$^{13}$C$_{org}$, concurrent with a major marine ecosystem reorganisation and the resurgence of microbialite facies. While these δ$^{13}$C records have been traditionally interpreted as capturing global carbon cycle behaviour, recent studies have suggested that at least some excursions in early Triassic δ$^{13}$C values may incorporate influences from authigenic or early diagenetic processes. To examine the mechanistic drivers of Smithian–Spathian boundary geochemistry, the carbonate geochemistry of a core from Georgetown, Idaho (USA), was analysed using a coupled δ$^{44/40}$Ca, δ$^{26}$Mg and trace‐metal framework. While the δ$^{13}$C record in the Georgetown core is broadly similar to other Smithian–Spathian boundary sections, portions of the record coincide with substantial shifts in δ$^{44/40}$Ca, δ$^{26}$Mg and trace‐metal compositions that cannot feasibly be interpreted as primary. Furthermore, these geochemical variations correspond with lithology: The δ$^{13}$C record is modulated by variations in the extent of dolomitisation, and the diagenetic styles recognised here coincide with individual lithostratigraphic units. A primary shift in local sea water δ$^{13}$C values is inferred from the most geochemically unaltered strata, from ca 3‰ in the middle Smithian to ca 5‰ in the early Spathian, although the timing and pathway through which this occurs cannot be readily identified nor extrapolated globally. Therefore, the Georgetown core may not directly record exogenic carbon cycle evolution, showing that there is a need for the careful reconsideration of the Smithian–Spathian boundary—and more broadly, Early Triassic—geochemical records to examine potential local and diagenetic influences on sedimentary geochemistry

Palaeoenvironmental variability and carbon cycle perturbations during the Smithian-Spathian (Early Triassic) in Central Spitsbergen

The Early Triassic Smithian and Spathian time intervals are characterized by perturbations in the global carbon cycle, fluctuations in sea surface temperature, high turnover rates of marine nekton, and a change in terrestrial vegetation. Despite the importance of this time interval, comprehensive multiproxy investigations from Early Triassic high and middle latitude regions remain scarce due to the difficulty in accessing sections. The objective of this study is to increase our understanding of regional and local palaeoenvironmental and carbon cycle perturbations from a middle Smithian to late Spathian middle latitude section from Central Spitsbergen. Geochemical analyses show an increase in phosphorus and nitrogen just at and above the Smithian–Spathian boundary (SSB). High primary productivity led to increasingly anoxic conditions in bottom waters during the middle and late Spathian, enhancing the preservation of organic matter in the sediments. Anoxic conditions restrain phosphorus remineralization, allowing it to be recycled within the water column. This increase in anoxia is consistent with observations in other Arctic basins, demonstrating larger regional similarities in palaeoenvironmental conditions. The fluctuations in isostatic and eustatic sea levels affected organic carbon sequestration by regulating organic matter mineral interactions via the control of grain size within the sediment. This study demonstrates that local organic carbon sequestration in the Barents Sea shelf during the Spathian was influenced by a multitude of factors, including sedimentology, redox conditions, nutrient availability, and primary productivity. □ Vikinghøgda Formation, bulk rock geochemistry, particulate organic matter, extinction recovery, carbon isotopes, Stensiöfjellet Franziska R. Blattmann ✉ [[email protected]], Zoneibe A.S. Luz [[email protected]] and Torsten W. Vennemann [[email protected]], Institute of Earth Surface Dynamics, University of Lausanne, Quartier UNIL-Mouline, 1015 Lausanne, Switzerland; Elke Schneebeli-Hermann [[email protected]] and Hugo F.R. Bucher [[email protected]], Department of Palaeontology, University of Zürich, Karl-Schmid-Strasse 4, 8006 Zürich, Switzerland; Thierry Adatte [[email protected]], Institute of Earth Sciences, University of Lausanne, Quartier UNIL-Mouline, CH-1015 Lausanne, Switzerland; Christian Vérard [[email protected]], Section of Earth and Environmental Sciences, University of Geneva, Rue des Maraîchers 13, CH-1205 Geneva, Switzerland; Øyvind Hammer [[email protected]], Natural History Museum, University of Oslo, Pb. 1172 Blindern, 0318 Oslo, Norway; manuscript received on 08/08/2023; manuscript accepted on 02/02/2024; manuscript published on 20/06/2024 in Lethaia 57(2)

Smithian–Spathian carbonate geochemistry in the northern Thaynes Group influenced by multiple styles of diagenesis

The Smithian–Spathian boundary interval is characterised by a positive carbon isotopic excursion in both δ13Ccarb and δ13Corg, concurrent with a major marine ecosystem reorganisation and the resurgence of microbialite facies. While these δ13C records have been traditionally interpreted as capturing global carbon cycle behaviour, recent studies have suggested that at least some excursions in early Triassic δ13C values may incorporate influences from authigenic or early diagenetic processes. To examine the mechanistic drivers of Smithian–Spathian boundary geochemistry, the carbonate geochemistry of a core from Georgetown, Idaho (USA), was analysed using a coupled δ44/40Ca, δ26Mg and trace-metal framework. While the δ13C record in the Georgetown core is broadly similar to other Smithian–Spathian boundary sections, portions of the record coincide with substantial shifts in δ44/40Ca, δ26Mg and trace-metal compositions that cannot feasibly be interpreted as primary. Furthermore, these geochemical variations correspond with lithology: The δ13C record is modulated by variations in the extent of dolomitisation, and the diagenetic styles recognised here coincide with individual lithostratigraphic units. A primary shift in local sea water δ13C values is inferred from the most geochemically unaltered strata, from ca 3‰ in the middle Smithian to ca 5‰ in the early Spathian, although the timing and pathway through which this occurs cannot be readily identified nor extrapolated globally. Therefore, the Georgetown core may not directly record exogenic carbon cycle evolution, showing that there is a need for the careful reconsideration of the Smithian–Spathian boundary—and more broadly, Early Triassic—geochemical records to examine potential local and diagenetic influences on sedimentary geochemistry

Fourier synthesis of radio frequency nanomechanical pulses with different shapes

The concept of Fourier synthesis is heavily employed in both consumer electronic products and fundamental research. In the latter, pulse shaping is key to dynamically initialize, probe and manipulate the state of classical or quantum systems. In nuclear magnetic resonance, for instance, shaped pulses have a long-standing tradition and the underlying fundamental concepts have subsequently been successfully extended to optical frequencies and even to implement quantum gate operations. Transferring these paradigms to nanomechanical systems requires tailored nanomechanical waveforms. Here, we report on an additive Fourier synthesizer for nanomechanical waveforms based on monochromatic surface acoustic waves. As a proof of concept, we electrically synthesize four different elementary nanomechanical waveforms from a fundamental surface acoustic wave at $f_1 \sim 150$ MHz using a superposition of up to three discrete harmonics $f_n$. We employ these shaped pulses to interact with an individual sensor quantum dot and detect their deliberately and temporally modulated strain component via the opto-mechanical quantum dot response. Importantly, and in contrast to the direct mechanical actuation by bulk piezoactuators, surface acoustic waves provide much higher frequencies (> 20 GHz) to resonantly drive mechanical motion. Thus, our technique uniquely allows coherent mechanical control of localized vibronic modes of optomechanical crystals, even in the quantum limit when cooled to the vibrational ground state.Comment: 18 pages - final manuscript and supporting materia