We report on the immersion of a spin qubit encoded in a single trapped ion into a spin-polarized neutral atom environment, which possesses both continuous (motional) and discrete (spin) degrees of ...freedom. The environment offers the possibility of a precise microscopic description, which allows us to understand dynamics and decoherence from first principles. We observe the spin dynamics of the qubit and measure the decoherence times (T(1) and T(2)), which are determined by the spin-exchange interaction as well as by an unexpectedly strong spin-nonconserving coupling mechanism.
The Pamir Plateau, a result of the India‐Asia collision, contains extensive exposures of Cenozoic middle to lower crust in domes exhumed by north‐south crustal extension. Titanite grains from 60 ...igneous and metamorphic rocks were investigated with U‐Pb + trace element petrochronology (including Zr thermometry) to constrain the timing and temperatures of crustal thickening and exhumation. Titanite from the Pamir domes records thickening from ~44 to 25 Ma. Retrograde titanite from the Yazgulem, Sarez, and Muskol‐Shatput domes records a transition from thickening to exhumation at ~20–16 Ma, whereas titanite from the Shakhadara dome records prolonged exhumation from ~20 to 8 Ma. The synchronous onset of exhumation may have been initiated by breakoff of the Indian slab and possible convective removal of the Asian lower crust and/or mantle lithosphere. The prolonged exhumation of the Shakhdara and Muztaghata‐Kongur Shan domes may have been driven by continued rollback of the Asian lithosphere concurrent with shortening and northwestward translation of the Pamir Plateau.
Key Points
Titanite ages record different durations of gneiss dome exhumation from 20 to 8 Ma
Independent exhumation was driven by two tectonic events rather than GPE alone
Titanite retained Pb and Zr > 650 C for ~25 Myr
Although frequency multiplexing of information has revolutionized the field of classical communications, the color degree of freedom (DOF) has been used relatively little for quantum applications. We ...experimentally demonstrate a new hybrid quantum gate that transfers polarization entanglement of nondegenerate photons onto the color DOF. We create, for the first time, high-quality, discretely color-entangled states (with energy band gap up to 8.4 THz) without any spectrally selective filtering, and unambiguously verify and quantify the amount of entanglement (tangle, 0.611 +/- 0.009) by reconstructing a restricted density matrix; we generate a range of maximally entangled states, including a set of mutually unbiased bases for an encoded qubit space. The technique can be generalized to transfer polarization entanglement onto other photonic DOFs, like orbital angular momentum.
We demonstrate the parallel and nondestructive readout of the hyperfine state for optically trapped ^{87}Rb atoms. The scheme is based on state-selective fluorescence imaging and achieves detection ...fidelities >98% within 10 ms, while keeping 99% of the atoms trapped. For the readout of dense arrays of neutral atoms in optical lattices, where the fluorescence images of neighboring atoms overlap, we apply a novel image analysis technique using Bayesian inference to determine the internal state of multiple atoms. Our method is scalable to large neutral atom registers relevant for future quantum information processing tasks requiring fast and nondestructive readout and can also be used for the simultaneous readout of quantum information stored in internal qubit states and in the atoms' positions.
Fabry–Perot interferometers have stimulated numerous scientific and technical applications ranging from high-resolution spectroscopy over metrology, optical filters, to interfaces of light and matter ...at the quantum limit and more. End facet machining of optical fibers has enabled the miniaturization of optical Fabry–Perot cavities. Integration with fiber wave guide technology allows for small yet open devices with favorable scaling properties including mechanical stability and compact mode geometry. These fiber Fabry–Perot cavities (FFPCs) are stimulating extended applications in many fields including cavity quantum electrodynamics, optomechanics, sensing, nonlinear optics and more. Here we summarize the state of the art of devices based on FFPCs, provide an overview of applications and conclude with expected further research activities.
Fiber Fabry–Perot cavities, formed by micro-machined mirrors on the end-facets of optical fibers, are used in an increasing number of technical and scientific applications, where they typically ...require precise stabilization of their optical resonances. Here, we study two different approaches to construct fiber Fabry–Perot resonators and stabilize their length for experiments in cavity quantum electrodynamics with neutral atoms. A piezo-mechanically actuated cavity with feedback based on the Pound–Drever–Hall locking technique is compared to a novel rigid cavity design that makes use of the high passive stability of a monolithic cavity spacer and employs thermal self-locking and external temperature tuning. Furthermore, we present a general analysis of the mode matching problem in fiber Fabry–Perot cavities, which explains the asymmetry in their reflective line shapes and has important implications for the optimal alignment of the fiber resonators. Finally, we discuss the issue of fiber-generated background photons. We expect that our results contribute toward the integration of high-finesse fiber Fabry–Perot cavities into compact and robust quantum-enabled devices in the future.
•The Kontinentale Tiefbohrung reveals defects of the apatite fission-track method.•Near-isothermal holding lasts since the Late Cretaceous to Palaeocene exhumation.•Fossil tracks in natural apatite ...do not etch as induced tracks in annealed apatite.•Surface-intersecting and confined fission tracks are sampled with different bias.•None of the annealing models can claim decisive support from geological data.
Deep boreholes serve as natural laboratories for testing thermochronometers under geological conditions. The Kontinentale Tiefbohrung (KTB) is an interesting candidate because the geological evidence suggests that approximate isothermal holding since the last documented exhumation in the Late Cretaceous to Palaeocene is a reasonable assumption for the thermal histories of the KTB samples. We report 30 new apatite fission-track ages and 50 new mean confined track lengths determined on cores from the 4km deep pilot hole. The ϕ- and ζ-external detector ages are consistent with the population ages from earlier studies and together define a clear age profile. The mean track lengths from this and earlier studies reveal the effects of experimental factors. The measured age and length profiles are compared with the predictions of 24 annealing models for isothermal holding. There are clear discrepancies between the measured and calculated profiles. Down to 1.5km depth, the measured mean track lengths are shorter than the predicted. The balance of methodological evidence indicates that this is due to seasoning, i.e., a shortening of the fossil confined tracks without attendant age reduction. From 2.5 to 4.0km depth, the mean track lengths are longer than the predictions. This suggests that the bias model that weights the probabilities of observing tracks of different length and which is based on experiments relating surface track densities to mean track lengths is not appropriate for confined tracks. Experimental and methodological factors are sometimes difficult to disentangle, but present a sufficient margin for there to be no need to go against the independent geological evidence. Unknown geological events cannot be ruled out but their existence cannot be inferred from the fission-track data alone, much less can the nature or magnitude of such events be specified.
SUMMARY
Utilizing seismic refraction/wide‐angle reflection data from 11 approximately in‐line earthquakes, 2‐D P‐ and S‐velocity models and a Poisson's ratio model of the crust and uppermost mantle ...beneath the southern Tien Shan and the Pamir have been derived along the 400‐km long main profile of the TIPAGE (TIen shan—PAmir GEodynamic program) project. These models show that the crustal thickness varies from about 65.5 km close to the southern end of the profile beneath the South Pamir through about 73.6 km under Lake Karakul in the North Pamir, to about 57.7 km, 50 km south of the northern end of the profile in the southern Tien Shan. Average crustal P velocities are low with respect to the global average, varying from 6.26 to 6.30 km s−1. The average crustal S velocity varies from 3.54 to 3.70 km s−1 along the profile and thus average crustal Poisson's ratio (σ) varies from 0.23 beneath the central Pamir in the south central part of the profile to 0.265 towards the northern end of the profile beneath the southern Tien Shan. The main layer of the upper crust extending from about 2 km below the Earth's surface to 27 km depth below sea level (b.s.l.) has average P velocities of about 6.05–6.1 km s−1, except beneath the south central part of the profile where they decrease to around 5.95 km s−1. This is in contrast to the S velocities which range from 3.4 to 3.6 km s−1 and exhibit the highest values of 3.55–3.6 km s−1 where the P velocity is lowest. Thus, σ for the main layer of the upper crust is 0.26 beneath the profile except beneath the south central part of the profile where it decreases to 0.22. The low value of 0.22 for σ under the central Pamir, the along‐strike equivalent of the Qiangtang terrane in Tibet, is similar to that within the corresponding layer beneath the northern Lhasa and southern Qiangtang terranes in central Tibet and is indicative of felsic rocks rich in quartz in the α state. The lower crust below 27 km b.s.l. has P velocities ranging from 6.1 km s−1 at the top to 7.1 km s−1 at the base. Further, σ for this layer is 0.27–0.28 towards the northern end of the profile but is low at about 0.24 beneath the central and southern parts of the profile, which is similar to the situation found in the northeast Tibetan plateau. The low values can be explained by felsic schists and gneisses in the upper part of the lower crust transitioning to granulite‐facies and possibly also eclogite‐facies metapelites in the lower part. Within the uppermost mantle, the average P velocity is about 8.10–8.15 km s−1 and σ is about 0.26. Assuming an isotropic situation, then a relatively cool (700–800°C) uppermost mantle beneath the profile is indicated. This would in turn indicate an intact mantle lid beneath the profile. An upper mantle reflector dipping from 104 km b.s.l., 120 km from the southern end of the profile to 86 km b.s.l., 155 km from the northern end of the profile has also been identified. The preferred model presented here for the crustal and lithospheric mantle structure beneath the Pamir calls for nearly horizontal underthrusting of relatively cool Indian mantle lithosphere, the leading edge of which is outlined by the Pamir seismic zone. This cool Indian mantle lithosphere is overlain by significantly shortening, warm Asian crust. The Moho trough that is a feature seen beneath some other orogenic belts, for example the Alps and the Urals, beneath the northern Pamir may mark the southern tip of the actively underthrusting Tien Shan crust along the Main Pamir thrust.
We present the crustal resistivity structure of the Pamir and Southern Tian Shan orogenic belts at the northwestern promontory of the India–Asia collision zone. The magnetotelluric (MT) data were ...recorded along a roughly north–south trending, 350 km long corridor from the Pamir Plateau in southern Tajikistan across the Pamir frontal ranges, the Alai Valley and the southwestern Tian Shan to Osh in the Kyrgyz part of the Fergana Basin. In total, we measured at 178 sites, whereof 26 combine broad band and long period recordings. One of the most intriguing features of the 2-D and 3-D inversion results is a laterally extended zone of high electrical conductivity below the Pamir Plateau, with resistivities below 1 Ωm, starting at a depth of ∼10–15 km. The high conductivity can be explained with the presence of partially molten rocks at middle to lower crustal levels, possibly related to ongoing migmatization and/or middle/lower crustal flow underneath the Southern Pamir. This interpretation is consistent with a low velocity zone found from local earthquake tomography, relatively high v
p
/v
s
ratios, elevated surface heat flow, and thermomechanical modelling suggesting that melting temperatures are reached in the felsic middle crust. In the upper crust of the Pamir and Tian Shan, the Palaeozoic–Mesozoic suture zones appear as electrically conductive, whereas the compact metamorphic rocks of the Muskol-Shatput Dome of the Central Pamir are highly resistive. The intra-montane basin of the Alai Valley—sandwiched between the Pamir and Tian Shan—exhibits a generally conductive upper crust that bifurcates into two conductors at depth. One of them connects to the active Main Pamir Thrust, which is absorbing most of today's convergence between the Pamir and the Tian Shan. Several deeper zones of high conductivity in the middle and lower crust of Central and Northern Pamir likely record fluid release due to metamorphism associated with active continental subduction/delamination.
An inclined zone of intermediate-depth seismicity beneath the Pamir orogen in Central Asia has been interpreted as southward subduction of a slab of Asian lithosphere. However, it is not known ...whether Asian lithosphere subducts intact or only partially. We used arrival times of shallow and intermediate-depth earthquakes, recorded with a temporary (2008–2010) seismic network in this region, to invert for 3D models of seismic velocities in an attempt to answer this question. With local seismicity reaching depths of up to 240 km, the deep structure of the Pamir could be illuminated with high resolution.
The resulting velocity models show a north–south contrast in crustal seismic velocities in the Pamir, with very low P velocities (5.7–5.9 km/s at 15–30 km depth), coupled with relatively low vp/vs (<1.70), at mid-crustal levels in the southern part of the orogen. At sub-Moho depths, we image an arcuate high-velocity (8.2–8.6 km/s) slab dipping south in the eastern Pamir and east in the Pamirʼs southwest, underlying the intermediate-depth earthquakes. On top of the high-velocity slab and just above the onset of deep seismicity, between a depth of 60 to 100 km, very low compressional wavespeeds (around 7.1 km/s) and high vp/vs ratios (⩾1.80) attest to subducted crustal rocks. Additionally, we carried out 2D numerical thermomechanical modeling of the continental collision in the Pamir, focusing on the fate of the crust and mantle lithosphere of the Asian and Indian plates. Seismic velocities were computed from the modeling results, and the resulting images were compared with the velocity distributions obtained from seismic traveltimes.
Combining tomography and modeling results, we infer that a substantial amount of crustal material is pulled down beneath the Pamir by cold mantle lithosphere to depths of at least 80–100 km. From there on, only lower crust and mantle lithosphere continue their subduction, and earthquakes occur inside the lower crustal layer probably due to metamorphic reactions. The buoyant Asian upper and middle crust does not penetrate deeper into the mantle, but pools at this depth level, from where it might eventually exhume or relaminate.
•Subduction of continental crust beneath the Pamir.•Lower crust recycled into mantle atop mantle lithospheric slab.•More felsic crustal material initially subducted, pools at 80–100 km depth.•Intermediate-depth earthquakes occur in continental lower crust.
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