Search

We explore likelihood-free (aka simulation-based) Bayesian model selection to quantify model comparison analyses of reionisation scenarios. We iteratively train the 3D Convolutional Neural Network (CNN) on four toy EoR models based on 21cmFAST simulations with contrasting morphology to obtain summaries of the 21 cm lightcone. Within the pyDelfi framework, we replaced the Emcee sampler with MultiNest to integrate learnt posteriors and produce the Bayesian Evidence. We comfortably distinguish the model used to produce the mock data set in all cases. However, we struggle to produce accurate posterior distributions for outside-in reionisation models. After a variety of cross-checks and alternate analyses we discuss the flexibility of summarising models that differ from precisely the intended network training conditions as this should be more widely scrutinised before CNN can reliably analyse observed data.

We present a scheme for speeding up quantum measurement. The scheme builds on previous protocols that entangle the system to be measured with ancillary systems. In the idealised situation of perfect entangling operations and no decoherence, it gives an exact space-time trade-off meaning the readout speed increases linearly with the number of ancilla. We verify this scheme is robust against experimental imperfections through numerical modelling of gate noise and readout errors, and under certain circumstances our scheme can even lead to better than linear improvement in the speed of measurement with the number of systems measured. This hardware-agnostic approach is broadly applicable to a range of quantum technology platforms and offers a route to accelerate mid-circuit measurement as required for effective quantum error correction., Comment: 14 pages, 8 figures

Long-period radio transients are an emerging class of extreme astrophysical events of which only three are known. These objects emit highly polarised, coherent pulses of typically a few tens of seconds duration and minutes to hour-long periods. While magnetic white dwarfs and magnetars, either isolated or in binary systems, have been invoked to explain these objects, a consensus has not emerged. Here we report on the discovery of ASKAP J193505.1+214841.0 (henceforth ASKAPJ1935+2148) with a period of 53.8 minutes exhibiting three distinct emission states - a bright pulse state with highly linearly polarised pulses with widths of 10-50 seconds; a weak pulse state which is about 26 times fainter than the bright state with highly circularly polarised pulses of widths of approximately 370 milliseconds; and a quiescent or quenched state with no pulses. The first two states have been observed to progressively evolve over the course of 8 months with the quenched state interspersed between them suggesting physical changes in the region producing the emission. A constraint on the radius of the source for the observed period rules out a magnetic white dwarf origin. Unlike other long-period sources, ASKAPJ1935+2148 is the first to exhibit drastic variations in emission modes reminiscent of neutron stars. However, its radio properties challenge our current understanding of neutron star emission and evolution., Comment: Published in Nature Astronomy

Neutral atom arrays have emerged as a versatile platform towards scalable quantum computation and optimization. In this paper we present demonstrations of solving maximum weighted independent set problems on a Rydberg atom array using annealing with local light-shifts. We verify the ability to prepare weighted graphs in 1D and 2D arrays, including embedding a five vertex non-unit disk graph using nine physical qubits and demonstration of a simple crossing gadget. We find common annealing ramps leading to preparation of the target ground state robustly over a substantial range of different graph weightings. This work provides a route to exploring large-scale optimization of non-planar weighted graphs relevant for solving relevant real-world problems., Comment: 7 pages, 5 figures. Methods: 4 pages, 3 figures

Neutral atom quantum processors provide a viable route to scalable quantum computing, with recent demonstrations of high-fidelity and parallel gate operations and initial implementation of quantum algorithms using both physical and logical qubit encodings. In this work we present a characterization of the algorithmic performance of near term Rydberg atom quantum computers through device simulation to enable comparison against competing architectures. We consider three different quantum algorithm related tests, exploiting the ability to dynamically update qubit connectivity and multi-qubit gates. We calculate a quantum volume of $\mathbf{\mathit{V_{Q}}=2^{9}}$ for 9 qubit devices with realistic parameters, which is the maximum achievable value for this device size and establishes a lower bound for larger systems. We also simulate highly efficient implementations of both the Bernstein-Vazirani algorithm with >0.95 success probability for 9 data qubits and 1 ancilla qubit without loss correction, and Grover's search algorithm with a loss-corrected success probability of 0.97 for an implementation of the algorithm using 6 data qubits and 3 ancilla qubits using native multi-qubit $\mathbf{CCZ}$ gates. Our results indicate Rydberg atom processors are a highly competitive near-term platform which, bolstered by the potential for further scalability, can pave the way toward useful quantum computation., Comment: 14 pages, 7 figures

We present an analysis of interspecies interactions between Rydberg $d$-states of rubidium and cesium. We identify the F\"orster resonance channels offering the strongest interspecies couplings, demonstrating the viability for performing high-fidelity two- and multi-qubit $C_kZ$ gates up to $k=4$, including accounting for blockade errors evaluated via numerical diagonalization of the pair-potentials. Our results show $d$-state orbitals offer enhanced suppression of intraspecies couplings compared to $s$-states, making them well suited for use in large-scale neutral atom quantum processors., Comment: 12 pages, 5 figures

The Australian SKA Pathfinder (ASKAP) is being used to undertake a campaign to rapidly survey the sky in three frequency bands across its operational spectral range. The first pass of the Rapid ASKAP Continuum Survey (RACS) at 887.5 MHz in the low band has already been completed, with images, visibility datasets, and catalogues made available to the wider astronomical community through the CSIRO ASKAP Science Data Archive (CASDA). This work presents details of the second observing pass in the mid band at 1367.5 MHz, RACS-mid, and associated data release comprising images and visibility datasets covering the whole sky south of declination $+$49$^\circ$. This data release incorporates selective peeling to reduce artefacts around bright sources, as well as accurately modelled primary beam responses. The Stokes I images reach a median noise of 198 $\mu$Jy PSF$^{-1}$ with a declination-dependent angular resolution of 8.1 to 47.5 arcsec that fills a niche in the existing ecosystem of large-area astronomical surveys. We also supply Stokes V images after application of a widefield leakage correction, with a median noise of 165 $\mu$Jy PSF$^{-1}$. We find the residual leakage of Stokes I into V to be $\lesssim$ 0.9 to 2.4 % over the survey. This initial RACS-mid data release will be complemented by a future release comprising catalogues of the survey region. As with other RACS data releases, data products from this release will be made available through CASDA., Comment: 39 pages, 85 figure files, accepted for publication in PASA. For associated data see https://doi.org/10.25919/6mr6-rd83

We present new photonics and electronics packages recently developed by M Squared Lasers specifically tailored for scalable neutral atom quantum computing; a high power 1064 nm system for scalable qubit number, a phase locked system for high fidelity single qubit control, and robust cavity locked systems for high fidelity Rydberg operations. We attain driven coherence times competitive with current state-of-the-art for both ground state Raman and ground-Rydberg transitions without cavity filtering, providing an excellent platform for neutral atom quantum computing. These systems are benchmarked by creating entangled Bell states across 7 atom pairs, where we measure a peak raw fidelity of $F\ge0.88(2)$ and a peak SPAM corrected of $F_C\ge0.93(3)$ via a two-qubit $CZ$ gate., Comment: 7 pages, 5 figures

Neutral atoms are a promising platform for scalable quantum computing, however prior demonstration of high fidelity gates or low-loss readout methods have employed restricted numbers of qubits. Using randomized benchmarking of microwave-driven single-qubit gates, we demonstrate average gate errors of $7(2)\times10^{-5}$ on a 225 site atom array using conventional, destructive readout. We further demonstrate a factor of 1.7 suppression of the primary measurement errors via low-loss, non-destructive and state-selective readout on 49 sites whilst achieving gate errors of $2(9)\times10^{-4}$., Comment: 6 pages, 4 figures plus Supplementary Material

Diffuse interstellar bands comprise hundreds of absorption features in the ISM. Most DIBs are observed in the optical, but some are in the IR. We observed 76 early-type stars at R=50,000 and S/N ratios of several hundreds using CRIRES. We measure DIBs around 1318, 1527, 1561, 1565, 1567, 1574 and/or 1624 nm. We detect a total of 6 DIB features and 17 likely stellar features assisted by a CMFGEN model. We also measured the DIBs at 1318 and 1527 nm using X-shooter towards ten Ceph. variables with 3.2 < E(B-V) < 6.5 and 4 stars at low values of water vapour. Correlation coeffs. of 0.73-0.96 are found comparing NIRDIB eq. width vs. E(B-V) and with r > 0.8 when comparing the NIR and optical DIBs 5705, 5780, 6203, 6283 and 6269 A. The 5797 A DIB is less well correlated with the NIDIBs. The "C60+" DIB at 9632 A is not well correlated with the 1318 nm DIB. Partial correlation coefficients using E(B-V) as the covariate were also determined. For stars earlier than B2, the 1318 nm DIB is affected by an emission line on its blue wing, likely stellar in nature, although we cannot rule out interstellar/circumstellar origin for example caused by by a DIB in emission. The 1318 nm DIB has a red wing and is reasonably well fitted by two gaussians. Neither the component ratios nor separation are correlated with 5780/5797 or E(B-V). EW(1318 nm) correlates with HI with EW(1318 nm)/E(B-V) decreasing with f(H2). Five pairs of stars within 1 am show similar 1318 nm DIB profiles. Variation in 1318 nm is seen in HD 145501/145502 and HD 168607/168625 pairs. CRIRES data for 17 stars separated by 6-14 months and 2 X-shooter sightlines separated by 9.9 yr were analysed. No time-variability is detected in the 5780, 5797 A, 1318 nm or 1527 nm DIBs. Tentative time variation is observed in the C60+ DIBs at 9577 and 9632 A towards HD 183143 although very close to the noise level with confirmation required., Comment: Accepted for publicaion in the main journal of Astronomy and Astrophysics on 25th November 2022

The Deeper, Wider, Faster (DWF) program coordinates observations with telescopes across the electromagnetic spectrum, searching for transients on timescales of milliseconds to days. The tenth DWF observing run was carried out in near real-time during September 2021 and consisted of six consecutive days of observations of the NGC 6744 galaxy group and a field containing the repeating fast radio burst FRB190711 with the Australian Square Kilometre Array Pathfinder, the Dark Energy Camera, the Hard X-ray Modulation Telescope and the Parkes 64m "Murriyang" radio telescope. In this work we present the results of an image-domain search for transient, variable and circularly polarised sources carried out with ASKAP using data from the observing run, along with test observations prior to the run and follow-up observations carried out during and after the run. We identified eight variable radio sources, consisting of one pulsar, six stellar systems (five of which exhibit circularly polarised emission) and one previously uncatalogued source. Of particular interest is the detection of pulses from the ultra-cool dwarf SCR J1845-6357 with a period of $14.2\pm 0.3$ h, in good agreement with the known optical rotation period, making this the slowest rotating radio-loud ultra-cool dwarf discovered.

Observations of the 21-cm line from primordial hydrogen promise to be one of the best tools to study the early epochs of the Universe: the Dark Ages, the Cosmic Dawn, and the subsequent Epoch of Reionization. In 2018, the EDGES experiment caught the attention of the cosmology community with a potential detection of an absorption feature in the sky-averaged radio spectrum centred at 78 MHz. The feature is deeper than expected, and, if confirmed, would call for new physics. However, different groups have re-analyzed the EDGES data and questioned the reliability of the signal. The Radio Experiment for the Analysis of Cosmic Hydrogen (REACH) is a sky-averaged 21-cm experiment aiming at improving the current observations by tackling the issues faced by current instruments related to residual systematic signals in the data. The novel experimental approach focuses on detecting and jointly explaining these systematics together with the foregrounds and the cosmological signal using Bayesian statistics. To achieve this, REACH features simultaneous observations with two different antennas, an ultra wideband system (redshift range 7.5 to 28), and a receiver calibrator based on in-field measurements. Simulated observations forecast percent-level constraints on astrophysical parameters, potentially opening up a new window to the infant Universe., Comment: Publication date: 21 July 2022

We demonstrate a native $\mathrm{CNOT}$ gate between two individually addressed neutral atoms based on electromagnetically induced transparency (EIT). This protocol utilizes the strong long-range interactions of Rydberg states to enable conditional state transfer on the target qubit when operated in the blockade regime. An advantage of this scheme is it enables implementation of multi-qubit CNOT$^k$ gates using a pulse sequence independent of qubit number, providing a simple gate for efficient implementation of digital quantum algorithms and stabiliser measurements for quantum error correction. We achieve a loss corrected gate fidelity of $\mathcal{F}_\mathrm{CNOT}^\mathrm{cor} = 0.82(6)$, and prepare an entangled Bell state with $\mathcal{F}_\mathrm{Bell}^\mathrm{cor} = 0.66(5)$, limited at present by laser power. We present a number of technical improvements to advance this to a level required for fault-tolerant scaling., Comment: 6 pages, 5 figures plus Supplementary Material

The formation of deformed liquid marbles via impact of drops onto powder beds is analysed using experimental and computational modelling approaches. Experimentally, particular attention is paid to determining a relationship between the maximum contact area of the spreading drops, which determines how much powder the drop's surface is able to harvest, and the drop's surface area when the powder (potentially) encapsulates and then immobilises (`freezes') the surface of the drop to form a liquid marble. Comparisons between impacts on powder beds to those on rigid and impermeable superhydrophobic substrates show good agreement for a range of parameters and motivate the development of the first mathematical model for the process of liquid marble formation via drop impact. The model utilises experimentally-determined functions to capture encapsulation and freezing thresholds and accounts for the powder's influence on the drop via a surface viscous mechanism. Simulations in the volume-of-fluid framework qualitatively recover many features of the experiments and highlight physical effects that should be incorporated into future analyses., Comment: Accepted in Physical Review Fluids

Following the reported detection of an absorption profile associated with the 21~cm sky-averaged signal from the Cosmic Dawn by the EDGES experiment in 2018, a number of experiments have been set up to verify this result. This paper discusses the design process used for global 21~cm experiments, focusing specifically on the Radio Experiment for the Analysis of Cosmic Hydrogen (REACH). This experiment will seek to understand and compensate for systematic errors present using detailed modelling and characterization of the instrumentation. There is detailed the quantitative figures of merit and numerical modelling used to assist the design process of the REACH dipole antenna (one of the 2 antenna designs for REACH Phase I). This design process produced a 2.5:1 frequency bandwidth dipole. The aim of this design was to balance spectral smoothness and low impedance reflections with the ability to describe and understand the antenna response to the sky signal to inform the critically important calibration during observation and data analysis., Comment: 32 pages, 30 figures, to be submitted to the Journal of Astronomical Instrumentation

We present results from a search for the radio counterpart to the possible neutron star-black hole merger GW190814 with the Australian Square Kilometre Array Pathfinder. We have carried out 10 epochs of observation spanning 2-655 days post-merger at a frequency of 944 MHz. Each observation covered 30 deg$^2$, equivalent to 87% of the event localisation. We conducted an untargeted search for radio transients in the field, as well as a targeted search for transients associated with known galaxies. We find one radio transient, ASKAP J005022.3-230349, but conclude that it is unlikely to be associated with the merger. We use our observations to place constraints on the inclination angle of the merger and the density of the surrounding environment by comparing our non-detection to model predictions for radio emission from compact binary coalescences. This survey is also the most comprehensive widefield search (in terms of sensitivity and both areal and temporal coverage) for radio transients to-date and we calculate the radio transient surface density at 944 MHz.

The Rapid ASKAP Continuum Survey (RACS) is the first large sky survey using the Australian Square Kilometre Array Pathfinder (ASKAP), covering the sky south of +41$^\circ$ declination. With ASKAP's large, instantaneous field of view, $\sim 31$ deg$^2$, RACS observed the entire sky at a central frequency of 887.5 MHz using 903 individual pointings with 15 minute observations. This has resulted in the deepest radio survey of the full Southern sky to date at these frequencies. In this paper, we present the first Stokes I catalogue derived from the RACS survey. This catalogue was assembled from 799 tiles that could be convolved to a common resolution of 25$^{\prime\prime}$, covering a large contiguous region in the declination range $\delta=-$80$^\circ$ to +30$^\circ$. The catalogue provides an important tool for both the preparation of future ASKAP surveys and for scientific research. It consists of $\sim$2.1 million sources and excludes the $|b|<5^\circ$ region around the Galactic plane. This provides a first extragalactic catalogue with ASKAP covering the majority of the sky ($\delta<+30^\circ$). We describe the methods to obtain this catalogue from the initial RACS observations and discuss the verification of the data, to highlight its quality. Using simulations, we find this catalogue detects 95% of point sources at an integrated flux density of $\sim$5 mJy. Assuming a typical sky source distribution model, this suggests an overall 95% point source completeness at an integrated flux density $\sim$3 mJy. The catalogue will be available through the CSIRO ASKAP Science Data Archive (CASDA)., Comment: Accepted for Publication in PASA; 29 pages, 20 figures, 6 tables

Gravitational waves from coalescing neutron stars encode information about nuclear matter at extreme densities, inaccessible by laboratory experiments. The late inspiral is influenced by the presence of tides, which depend on the neutron star equation of state. Neutron star mergers are expected to often produce rapidly-rotating remnant neutron stars that emit gravitational waves. These will provide clues to the extremely hot post-merger environment. This signature of nuclear matter in gravitational waves contains most information in the 2-4 kHz frequency band, which is outside of the most sensitive band of current detectors. We present the design concept and science case for a neutron star extreme matter observatory (NEMO): a gravitational-wave interferometer optimized to study nuclear physics with merging neutron stars. The concept uses high circulating laser power, quantum squeezing and a detector topology specifically designed to achieve the high-frequency sensitivity necessary to probe nuclear matter using gravitational waves. Above one kHz, the proposed strain sensitivity is comparable to full third-generation detectors at a fraction of the cost. Such sensitivity changes expected event rates for detection of post-merger remnants from approximately one per few decades with two A+ detectors to a few per year, and potentially allows for the first gravitational-wave observations of supernovae, isolated neutron stars, and other exotica., Comment: Accepted for publication in PASA

This topical review addresses how Rydberg atoms can serve as building blocks for emerging quantum technologies. Whereas the fabrication of large numbers of artificial quantum systems with the uniformity required for the most attractive applications is difficult if not impossible, atoms provide stable quantum systems which, for the same species and isotope, are all identical. Whilst atomic ground-states provide scalable quantum objects, their applications are limited by the range over which their properties can be varied. In contrast, Rydberg atoms offer strong and controllable atomic interactions that can be tuned by selecting states with different principal quantum number or orbital angular momentum. In addition Rydberg atoms are comparatively long-lived, and the large number of available energy levels and their separations allow coupling to electromagnetic fields spanning over 6 orders of magnitude in frequency. These features make Rydberg atoms highly desirable for developing new quantum technologies. After giving a brief introduction to how the properties of Rydberg atoms can be tuned, we give several examples of current areas where the unique advantages of Rydberg atom systems are being exploited to enable new applications in quantum computing, electromagnetic field sensing, and quantum optics., Comment: 24 pages, 7 figures

We apply Bayesian statistics to perform model selection on different reionisation scenarios via the Multinest algorithm. Initially, we recover the results shown by 21CMMC for the parameter estimation of 21cmFAST models. We proceed to test several toy models of the Epoch of Reionisation (EoR) defined in contrasting morphology and scale. We find that LOFAR observations are unlikely to allow model selection even with long integration times. HERA would require 61 dipoles to perform the same analysis in 1080 hours, and becomes comparable to the SKA with 217 dipoles. We find the SKA requires only 324 hours of observation to conclusively distinguish between our models. Once model selection is achievable, an analysis of observational priors is performed finding that neutral fraction checks at specific redshifts add little to no inference. We show the difficulties in model selection at the level of distinguishing fiducial parameters within a model or distinguishing galaxies with a constant versus power law mass-to-light ratio. Finally, we explore the use of the Savage-Dickey density ratio to show the redundancy of the parameter Rmfp within 21cmFAST., Comment: 20 pages, 16 figures - Accepted for publication by MNRAS

The Square Kilometre Array (SKA) is a planned large radio interferometer designed to operate over a wide range of frequencies, and with an order of magnitude greater sensitivity and survey speed than any current radio telescope. The SKA will address many important topics in astronomy, ranging from planet formation to distant galaxies. However, in this work, we consider the perspective of the SKA as a facility for studying physics. We review four areas in which the SKA is expected to make major contributions to our understanding of fundamental physics: cosmic dawn and reionisation; gravity and gravitational radiation; cosmology and dark energy; and dark matter and astroparticle physics. These discussions demonstrate that the SKA will be a spectacular physics machine, which will provide many new breakthroughs and novel insights on matter, energy and spacetime., Comment: 69 pages, PASA, in press

We report results of a ground-state entanglement protocol for a pair of Cs atoms separated by 6~$\mu$m, combining the Rydberg blockade mechanism with a two-photon Raman transitions to prepare the $\vert\Psi^+\rangle=(\vert 10\rangle+\vert 01\rangle)/\sqrt{2}$ Bell state with a loss-corrected fidelity of 0.81(5), equal to the best demonstrated fidelity for atoms trapped in optical tweezers but without the requirement for dynamically adjustable interatomic spacing. Qubit state coherence is also critical for quantum information applications, and we characterise both ground-state and ground-Rydberg dephasing rates using Ramsey spectroscopy. We demonstrate transverse dephasing times $T_2^*=10(1)$~ms and $T_2'=0.14(1)$~s for the qubit levels and achieve long ground-Rydberg coherence times of $T_2^*=17(2)~\mu$s as required for implementing high-fidelity multi-qubit gate sequences where a control atom remains in the Rydberg state while applying local operations on neighbouring target qubits., Comment: 6 pages, 5 figures

We gathered more than 1130 high-resolution optical spectra for more than 250 Galactic classical Cepheids. The spectra were collected with different optical spectrographs: UVES at VLT, HARPS at 3.6m, FEROS at 2.2m MPG/ESO, and STELLA. To improve the effective temperature estimates, we present more than 150 new line depth ratio (LDR) calibrations that together with similar calibrations already available in the literature allowed us to cover a broad range in wavelength (between 5348 and 8427 angstrom) and in effective temperatures (between 3500 and 7700 K). This means the unique opportunity to cover both the hottest and coolest phases along the Cepheid pulsation cycle and to limit the intrinsic error on individual measurements at the level of ~100 K. Thanks to the high signal-to-noise ratio of individual spectra we identified and measured hundreds of neutral and ionized lines of heavy elements, and in turn, have the opportunity to trace the variation of both surface gravity and microturbulent velocity along the pulsation cycle. The accuracy of the physical parameters and the number of Fe I (more than one hundred) and Fe II (more than ten) lines measured allowed us to estimate mean iron abundances with a precision better than 0.1 dex. Here we focus on 14 calibrating Cepheids for which the current spectra cover either the entire or a significant portion of the pulsation cycle. The current estimates of the variation of the physical parameters along the pulsation cycle and of the iron abundances agree quite well with similar estimates available in the literature. Independent homogeneous estimates of both physical parameters and metal abundances based on different approaches that can constrain possible systematics are highly encouraged., Comment: 25 pages, 9 figures, 5 tables

Quantum information processing using atomic qubits requires narrow linewidth lasers with long-term stability for high fidelity coherent manipulation of Rydberg states. In this paper, we report on the construction and characterization of three continuous-wave (CW) narrow linewidth lasers stabilized simultaneously to an ultra-high finesse Fabry-Perot cavity made of ultra-low expansion (ULE) glass, with a tunable offset-lock frequency. One laser operates at 852~nm while the two locked lasers at 1018~nm are frequency doubled to 509~nm for excitation of $^{133}$Cs atoms to Rydberg states. The optical beatnote at 509~nm is measured to be 260(5)~Hz. We present measurements of the offset between the atomic and cavity resonant frequencies using electromagnetically induced transparency (EIT) for high-resolution spectroscopy on a cold atom cloud. The long-term stability is determined from repeated spectra over a period of 20 days yielding a linear frequency drift of $\sim1$~Hz/s., Comment: 13 pages, 6 figures

Context: Cepheids are excellent tracers of young stellar populations. They play a crucial role in astrophysics as standard candles. The chemistry of classical Cepheids in the Milky Way is now quite well-known. Despite a much larger sample, the chemical composition of Magellanic Cepheids has been only scarcely investigated. Aims: For the first time, we study the chemical composition of several Cepheids located in the same populous cluster: NGC 1866, in the Large Magellanic Cloud (LMC). To also investigate the chemical composition of Cepheids at lower metallicity, four targets are located in the Small Magellanic Cloud (SMC). Our sample allows us to increase the number of Cepheids with known metallicities in the LMC/SMC by 20%/25% and the number of Cepheids with detailed chemical composition in the LMC/SMC by 46%/50%. Methods: We use canonical spectroscopic analysis to determine the chemical composition of Cepheids and provide abundances for a good number of $\alpha$, iron-peak and neutron-capture elements. Results: We find that six Cepheids in the LMC cluster NGC 1866 have a very homogeneous chemical composition, also consistent with red giant branch (RGB) stars in the cluster. Period--age relations that include no or average rotation indicate that all the Cepheids in NGC 1866 have a similar age and therefore belong to the same stellar population. Our results are in good agreement with theoretical models accounting for luminosity and radial velocity variations. Using distances based on period-luminosity relations in the near- or mid-infrared, we investigate for the first time the metallicity distribution of the young population in the SMC in the depth direction. Preliminary results show no metallicity gradient along the SMC main body, but our sample is small and does not contain Cepheids in the inner few degrees of the SMC., Comment: Accepted in A&A

Single atom imaging requires discrimination of weak photon count events above background and has typically been performed using either EMCCD cameras, photomultiplier tubes or single photon counting modules. sCMOS provides a cost effective and highly scalable alternative to other single atom imaging technologies, offering fast readout and larger sensor dimensions. We demonstrate single atom resolved imaging of two site-addressable single atom traps separated by 10~$\mu$m using an sCMOS camera, offering a competitive signal-to-noise ratio at intermediate count rates to allow high fidelity readout discrimination (error $<10^{-6}$) and sub-$\mu$m spatial resolution for applications in quantum technologies., Comment: 4 pages, 4 figures

We present an object-oriented Python library for computation of properties of highly-excited Rydberg states of alkali atoms. These include single-body effects such as dipole matrix elements, excited-state lifetimes (radiative and black-body limited) and Stark maps of atoms in external electric fields, as well as two-atom interaction potentials accounting for dipole and quadrupole coupling effects valid at both long and short range for arbitrary placement of the atomic dipoles. The package is cross-referenced to precise measurements of atomic energy levels and features extensive documentation to facilitate rapid upgrade or expansion by users. This library has direct application in the field of quantum information and quantum optics which exploit the strong Rydberg dipolar interactions for two-qubit gates, robust atom-light interfaces and simulating quantum many-body physics, as well as the field of metrology using Rydberg atoms as precise microwave electrometers., Comment: 15 pages, 7 figures, code and documentation available online (see Ref. [18] and Ref. [21] for more details)

We present a pair of optimized objective lenses with long working distances of 117~mm and 65~mm respectively that offer diffraction limited performance for both Cs and Rb wavelengths when imaging through standard vacuum windows. The designs utilise standard catalog lens elements to provide a simple and cost-effective solution. Objective 1 provides $\mathrm{NA}=0.175$ offering 3~$\mu$m resolution whilst objective 2 is optimized for high collection efficiency with $\mathrm{NA}=0.29$ and 1.8~$\mu$m resolution. This flexible design can be further extended for use at shorter wavelengths by simply re-optimising the lens separations., Comment: 4 pages, 5 figures

We describe the design and characterization of superconducting coplanar waveguide cavities tailored to facilitate strong coupling between superconducting quantum circuits and single trapped Rydberg atoms. For initial superconductor-atom experiments at 4.2 K, we show that resonator quality factors above $10^4$ can be readily achieved. Furthermore, we demonstrate that the incorporation of thick-film copper electrodes at a voltage antinode of the resonator provides a route to enhance the zero-point electric fields of the resonator in a trapping region that is 40 $\mu$m above the chip surface, thereby minimizing chip heating from scattered trap light. The combination of high resonator quality factor and strong electric dipole coupling between the resonator and the atom should make it possible to achieve the strong coupling limit of cavity quantum electrodynamics with this system., Comment: 4 pages, 4 figures

Concerted effort is currently ongoing to open up the Epoch of Reionization (EoR) ($z\sim$15-6) for studies with IR and radio telescopes. Whereas IR detections have been made of sources (Lyman-$\alpha$ emitters, quasars and drop-outs) in this redshift regime in relatively small fields of view, no direct detection of neutral hydrogen, via the redshifted 21-cm line, has yet been established. Such a direct detection is expected in the coming years, with ongoing surveys, and could open up the entire universe from $z\sim$6-200 for astrophysical and cosmological studies, opening not only the EoR, but also its preceding Cosmic Dawn ($z\sim$30-15) and possibly even the later phases of the Dark Ages ($z\sim$200-30). All currently ongoing experiments attempt statistical detections of the 21-cm signal during the EoR, with limited signal-to-noise. Direct imaging, except maybe on the largest (degree) scales at lower redshifts, as well as higher redshifts will remain out of reach. The Square Kilometre Array(SKA) will revolutionize the field, allowing direct imaging of neutral hydrogen from scales of arc-minutes to degrees over most of the redshift range $z\sim$6-28 with SKA1-LOW, and possibly even higher redshifts with the SKA2-LOW. In this SKA will be unique, and in parallel provide enormous potential of synergy with other upcoming facilities (e.g. JWST). In this chapter we summarize the physics of 21-cm emission, the different phases the universe is thought to go through, and the observables that the SKA can probe, referring where needed to detailed chapters in this volume (Abridged)., Comment: Accepted for publication in the SKA Science Book 'Advancing Astrophysics with the Square Kilometre Array', to appear in 2015. PoS(AASKA14)001

We investigate the impact of sinks of ionizing radiation on the reionization-era 21-cm signal, focusing on 1-point statistics. We consider sinks in both the intergalactic medium and inside galaxies. At a fixed filling factor of HII regions, sinks will have two main effects on the 21-cm morphology: (i) as inhomogeneous absorbers of ionizing photons they result in smaller and more widespread cosmic HII patches; and (ii) as reservoirs of neutral gas they contribute a non-zero 21-cm signal in otherwise ionized regions. Both effects damp the contrast between neutral and ionized patches during reionization, making detection of the epoch of reionization with 21-cm interferometry more challenging. Here we systematically investigate these effects using the latest semi-numerical simulations. We find that sinks dramatically suppress the peak in the redshift evolution of the variance, corresponding to the midpoint of reionization. As previously predicted, skewness changes sign at midpoint, but the fluctuations in the residual HI suppress a late-time rise. Furthermore, large levels of residual HI dramatically alter the evolution of the variance, skewness and power spectrum from that seen at lower levels. In general, the evolution of the large-scale modes provides a better, cleaner, higher signal-to-noise probe of reionization., Comment: Minor edits to agree with MNRAS published version

We report measurements of the absolute excitation frequencies of $^{165}$Ho $4f^{11}6sns$ and $4f^{11}6snd$ odd-parity Rydberg series. The states are detected through depletion of a magneto-optical trap via a two-photon excitation scheme. Measurements of 162 Rydberg levels in the range $n=40-101$ yield quantum defects well described by the Rydberg-Ritz formula. We observe a strong perturbation in the $ns$ series around $n=51$ due to an unidentified interloper at 48515.47(4) cm$^{-1}$. From the series convergence, we determine the first ionization potential $E_\mathrm{IP}=48565.939(4)$ cm$^{-1}$, which is three orders of magnitude more accurate than previous work. This work represents the first time such spectroscopy has been done in Holmium and is an important step towards using Ho atoms for collective encoding of a quantum register., Comment: 6 figures

We report high resolution spectral observations of the yellow symbiotic star V417 Cen obtained in 2004. We find that the equivalent widths of the emission lines decreased, while the brightness increased. The FWHMs and wavelengths of the emission lines do not change. We estimated the interstellar extinction towards V417 Cen as $E_{B-V}$ = 0.95 $\pm$0.10, using the KI interstellar line. Using the [O III] lines, we obtain a rough estimation of the density and the temperature in the forbidden lines region $\log N_e \approx 4.5 \pm$ 0.5 and $T_e=100000 \pm 25000$~K. Tidal interaction in this binary is also discussed., Comment: 11 pages, 4 figures, submitted to BAJ

We outline the prospects for performing pioneering radio weak gravitational lensing analyses using observations from a potential forthcoming JVLA Sky Survey program. A large-scale survey with the JVLA can offer interesting and unique opportunities for performing weak lensing studies in the radio band, a field which has until now been the preserve of optical telescopes. In particular, the JVLA has the capacity for large, deep radio surveys with relatively high angular resolution, which are the key characteristics required for a successful weak lensing study. We highlight the potential advantages and unique aspects of performing weak lensing in the radio band. In particular, the inclusion of continuum polarisation information can greatly reduce noise in weak lensing reconstructions and can also remove the effects of intrinsic galaxy alignments, the key astrophysical systematic effect that limits weak lensing at all wavelengths. We identify a VLASS "deep fields" program (total area ~10-20 square degs), to be conducted at L-band and with high-resolution (A-array configuration), as the optimal survey strategy from the point of view of weak lensing science. Such a survey will build on the unique strengths of the JVLA and will remain unsurpassed in terms of its combination of resolution and sensitivity until the advent of the Square Kilometre Array. We identify the best fields on the JVLA-accessible sky from the point of view of overlapping with existing deep optical and near infra-red data which will provide crucial redshift information and facilitate a host of additional compelling multi-wavelength science., Comment: Submitted in response to NRAO's recent call for community white papers on the VLA Sky Survey (VLASS)

We propose a novel hybrid quantum gate between an atom and a microwave photon in a superconducting coplanar waveguide cavity by exploiting the strong resonant microwave coupling between adjacent Rydberg states. Using experimentally achievable parameters gate fidelities $> 0.99$ are possible on sub-$\mu$s timescales for waveguide temperatures below 40 mK. This provides a mechanism for generating entanglement between two disparate quantum systems and represents an important step in the creation of a hybrid quantum interface applicable for both quantum simulation and quantum information processing., Comment: 4 pages, 4 figures

A microwave field is used to control the interaction between pairs of optical photons stored in highly excited collective states (Rydberg polaritons). We show that strong dipole-dipole interactions induced by the microwave field destroy the coherence of polariton modes with more than one Rydberg excitation. Consequently single-polariton modes, which correspond to single stored photons, are preferentially retrieved from the sample. Measurements of the photon statistics of the retrieved light field also reveal non-trivial propagation dynamics of the interacting polaritons., Comment: 6 pages, 3 figures

We use a microwave field to control the quantum state of optical photons stored in a cold atomic cloud. The photons are stored in highly excited collective states (Rydberg polaritons) enabling both fast qubit rotations and control of photon-photon interactions. Through the collective read-out of these pseudo-spin rotations it is shown that the microwave field modifies the long-range interactions between polaritons. This technique provides a powerful interface between the microwave and optical domains, with applications in quantum simulations of spin liquids, quantum metrology and quantum networks., Comment: 7 pages, 4 figures

We report the first demonstration of an inductively coupled magnetic ring trap for cold atoms. A uniform, ac magnetic field is used to induce current in a copper ring, which creates an opposing magnetic field that is time-averaged to produce a smooth cylindrically symmetric ring trap of radius 5 mm. We use a laser-cooled atomic sample to characterise the loading efficiency and adiabaticity of the magnetic potential, achieving a vacuum-limited lifetime in the trap. This technique is suitable for creating scalable toroidal waveguides for applications in matterwave interferometry, offering long interaction times and large enclosed areas., Comment: 12 pages, 6 figures

The implementation of electromagnetically induced transparency (EIT) in a cold Rydberg gas provides an attractive route towards strong photon--photon interactions and fully deterministic all-optical quantum information processing. In this brief review we discuss the underlying principles of how large single photon non-linearities are achieved in this system and describe experimental progress to date., Comment: 50 pages, 21 figures. Preprint of book chapter submitted to the Annual Review of cold atoms and molecules \copyright (2012) [copyright World Scientific Publishing Company]

We consider three level atoms driven by two resonant light fields in a ladder scheme where the upper level is a highly excited Rydberg state. We show that the dipole--dipole interactions between Rydberg excited atoms prevents the formation of single particle dark states and leads to strongly correlated photon emission from atoms separated by distances large compared to the emission wavelength. For two atoms, correlated photon pairs are emitted with an angular distribution given by a coherent sum of the independent dipolar fields., Comment: 4 pages, 4 figures