Search

Previous measurements of neutron energy using fast plastic scintillators while operating the Fusion Z Pinch Experiment (FuZE) constrained the energy of any yield-producing deuteron beams to less than $4.65 keV$. FuZE has since been operated at increasingly higher input power, resulting in increased plasma current and larger fusion neutron yields. A detailed experimental study of the neutron energy isotropy in these regimes applies more stringent limits to possible contributions from beam-target fusion. The FuZE device operated at $-25~kV$ charge voltage has resulted in average plasma currents of $370~kA$ and D-D fusion neutron yields of $4\times10^7$ neutrons per discharge. Measurements of the neutron energy isotropy under these operating conditions demonstrates the energy of deuteron beams is less than $7.4 \pm 5.6^\mathrm{(stat)} \pm 3.7^\mathrm{(syst)}~keV$. Characterization of the detector response has reduced the number of free parameters in the fit of the neutron energy distribution, improving the confidence in the forward-fit method. Gamma backgrounds have been measured and the impact of these contributions on the isotropy results have been studied. Additionally, a time dependent measurement of the isotropy has been resolved for the first time, indicating increases to possible deuteron beam energies at late times. This suggests the possible growth of $m$=0 instabilities at the end of the main radiation event but confirms that the majority of the neutron production exhibits isotropy consistent with thermonuclear origin., Comment: 16 pages, 11 figures, submitted to Journal of Nuclear Fusion

We demonstrate Rydberg blockade due to the charge-dipole interaction between a single Rb atom and a single RbCs molecule confined in optical tweezers. The molecule is formed by magnetoassociation of a Rb+Cs atom pair and subsequently transferred to the rovibrational ground state with an efficiency of 91(1)\%. Species-specific tweezers are used to control the separation between the atom and molecule. The charge-dipole interaction causes blockade of the transition to the Rb(52s) Rydberg state, when the atom-molecule separation is set to $310(40)$~nm. The observed excitation dynamics are in good agreement with simulations using calculated interaction potentials. Our results open up the prospect of a hybrid platform where quantum information is transferred between individually trapped molecules using Rydberg atoms., Comment: Main text contains 8 pages, 4 figures. Supplementary material is 13 pages containing 10 figures

Radio frequencies in the HF and VHF (3 MHz to 300 MHz) bands are challenging for Rydberg atom-based detection schemes, as resonant detection requires exciting the atoms to extremely high energy states. We demonstrate a method for detecting and measuring radio frequency (RF) carriers in the HF and VHF bands via a controlled Autler-Townes line splitting. Using a resonant, high-frequency (GHz) RF field, the absorption signal from Townes-Merrit sidebands created by a low frequency, non-resonant RF field can be enhanced. Notably, this technique uses a measurement of the optical frequency separation of an avoided crossing to determine the amplitude of a non-resonant, low frequency RF field. This technique also provides frequency-selective measurements of low frequency RF electric fields. To show this, we demonstrate amplitude modulated signal transduction on a low frequency VHF carrier. We further demonstrate reception of multiple tones simultaneously, creating a Rydberg `spectrum analyzer' over the VHF range., Comment: Data for figures can be found at: https://datapub.nist.gov/od/id/mds2-2852

Atom-light interactions in nano-scale systems hold great promise for novel technologies based on integrated emitters and optical modes. We present the design architecture, construction method, and characterization of an all-glass alkali-metal vapor cell with nanometer-scale internal structure. Our cell has a glue-free design which allows versatile optical access, in particular with high numerical aperture optics, and incorporates a compact integrated heating system in the form of an external deposited ITO layer. By performing spectroscopy in different illumination and detection schemes, we investigate atomic densities and velocity distributions in various nanoscopic landscapes. We apply a two-photon excitation scheme to atoms confined in one dimension within our cells, achieving resonance line-widths more than an order of magnitude smaller than the Doppler width. We also demonstrate sub-Doppler line-widths for atoms confined in two dimensions to micron-sized channels. Furthermore, we illustrate control over vapor density within our cells through nano-scale confinement alone, which could offer a scalable route towards room-temperature devices with single atoms within an interaction volume. Our design offers a robust platform for miniaturized devices that could easily be combined with integrated photonic circuits., Comment: 13 pages, 10 figures

The propagation of two-color laser fields through optically thick atomic ensembles is studied. We demonstrate how the interaction between these two fields spawns the formation of co-propagating, two-color soliton-like pulses akin to the simultons found by Konopnicki and Eberly [Phys. Rev. A 24, 2567 (1981)]. For the particular case of thermal Rb atoms, exposed to a combination of a weak cw laser field resonant on the D1 transition and a strong, sub-ns laser pulse resonant on the D2 transition, simulton formation is initiated by an interplay between the 5s_{1/2} -- 5p_{1/2} and 5s_{1/2} -- 5p_{3/2} coherences which amplifies the D1 field at the arrival of the D2 pulse producing sech-squared pulse with a length of less than 10 microns. This amplification is demonstrated in a time-resolved measurement of the light transmitted through a thin thermal cell. We find good agreement between experiment and a model that includes the hyperfine structure of the relevant levels. With the addition of Rydberg dressing, quasi-simultons offer interesting prospects for strong photon-photon interactions in a robust environment.

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 demonstrate a method for measuring atom-surface interactions using transmission spectroscopy of thermal vapors confined in a wedged nano-cell. The wedged shape of the cell allows complementary measurements of both the bulk atomic vapor and atoms close to surfaces experiencing strong van der Waals atom-surface interaction. These are used to tightly constrain the dipole-dipole collisional parameters of a theoretical model for transmission spectra that accounts for atom-surface interactions, cavity effects, collisions with the surface of the cell and atomic motion. We illustrate this method on a cesium vapor in a sapphire cell, find $C_3=1.3\pm0.1$\,kHz.$\mu$m$^3$ and demonstrate that even the weakest of the van der Waals atom-surface interaction coefficients - for ground-state alkali atom transitions - can be determined with a very good precision. This result paves the way towards a precise quantitative characterization of atom-surface interactions in a wide range of atom-based nano-devices., Comment: 5 pages, 4 figures. Supplemental Material (7 pages). Units in Figure 2 and 3 corrected

We demonstrate number-resolved detection of individual strontium atoms in a long working distance low numerical aperture (NA = 0.26) tweezer. Using a camera based on single-photon counting technology, we determine the presence of an atom in the tweezer with a fidelity of 0.989(6) (and loss of 0.13(5)) within a 200 $\mu$s imaging time. Adding continuous narrow-line Sisyphus cooling yields similar fidelity, at the expense of much longer imaging times (30 ms). Under these conditions we determine whether the tweezer contains zero, one or two atoms, with a fidelity $>$0.8 in all cases with the high readout speed of the camera enabling real-time monitoring of the number of trapped atoms. Lastly we show that the fidelity can be further improved by using a pulsed cooling/imaging scheme that reduces the effect of camera dark noise.

We report on the fabrication of an all-glass vapor cell with a thickness varying linearly between (exactly) 0 and ~ 1 {\mu}m. The cell is made in Borofloat glass that allows super polish roughness, a full optical bonding assembling and easy filling with alkali vapors. We detail the challenging manufacture steps and present experimental spectra resulting from off-axis fluorescence and transmission spectroscopy of the Cesium D1 line. The very small surface roughness of 1 Angstr\"om rms is promising to investigate the atom-surface interaction or to minimize parasite stray light., Comment: 5 pages, 5 figures

By measuring the transmission of near-resonant light through an atomic vapor confined in a nano-cell we demonstrate a mesoscopic optical response arising from the non-locality induced by the motion of atoms with a phase coherence length larger than the cell thickness. Whereas conventional dispersion theory -- where the local atomic response is simply convolved by the Maxwell-Boltzmann velocity distribution -- is unable to reproduce the measured spectra, a model including a non-local, size-dependent susceptibility is found to be in excellent agreement with the measurements. This result improves our understanding of light-matter interaction in the mesoscopic regime and has implications for applications where mesoscopic effects may degrade or enhance the performance of miniaturized atomic sensors., Comment: 5 pages, 3 figures; Supplemental material : 9 pages, 4 figures

We present a simple method for producing a low-drift atomic frequency reference based upon the Zeeman effect. Our Zeeman Shifted Atomic Reference `ZSAR' is demonstrated to have tens of GHz tuning range, limited only by the strength of the applied field. ZSAR uses Doppler-free laser spectroscopy in a thermal vapor where the vapor is situated in a large, static and controllable magnetic field. We use a heated $^{85}$Rb vapor cell between a pair of position-adjustable permanent magnets capable of applying magnetic fields up to 1 T. To demonstrate the frequency reference we use a spectral feature from the Zeeman shifted D1 line in $^{85}$Rb at 795 nm to stabilize a laser to the 7S$_{1/2}$ $\longrightarrow$ 23P$_{1/2}$ transition in atomic cesium, which is detuned by approximately 19 GHz from the unperturbed Rb transition. We place an upper bound on the stability of the technique by measuring a 2.5 MHz RMS frequency difference between the two spectral features over a 24 hour period. This versatile method could be adapted easily for use with other atomic species and the tuning range readily increased by applying larger magnetic fields., Comment: 8 pages, 4 figures

We measure the near-resonant transmission of light through a dense medium of potassium vapor confined in a cell with nanometer thickness in order to investigate the origin and validity of the collective Lamb-shift. A complete model including the multiple reflections in the nano-cell accurately reproduces the observed strong asymmetry of the line shape and allows extraction of a density dependent shift of the atomic resonance. We observe an additional, unexpected dependence of this shift with the thickness of the medium. This extra dependence demands further experimental and theoretical investigations.

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)

Collective coupling between dipoles can dramatically modify the optical response of a medium. Such effects depend strongly on the geometry of the medium and the polarization of the light. Using a classical coupled dipole model, here we investigate the simplest case of one dimensional (1D) arrays of interacting atomic dipoles driven by a weak laser field. Changing the polarization and direction of the driving field allows us to separately address superradiant, subradiant, red-shifted, and blue-shifted eigenmodes, as well as observe strong Fano-like interferences between different modes. The cooperative eigenvectors can be characterized by the phase difference between nearest neighbor dipoles, ranging from all oscillating in phase to all oscillating out of phase with their nearest neighbors. Investigating the eigenvalue behavior as a function of atom number and lattice spacing, we find that certain eigenmodes of an infinite atomic chain have the same decay rate as a single atom between two mirrors. The effects we observe provide a framework for collective control of the optical response of a medium, giving insight into the behavior of more complicated geometries, as well as providing further evidence for the dipolar analog of cavity QED., Comment: 14 pages, 9 figures

We measure the resonance line shape of atomic vapor layers with nanoscale thickness confined between two sapphire windows. The measurement is performed by scanning a probe laser through resonance and collecting the scattered light. The line shape is dominated by the effects of Dicke narrowing, self-broadening, and atom-surface interactions. By fitting the measured line shape to a simple model we discuss the possibility to extract information about the atom-surface interaction., Comment: 11 pages, 10 figures

In many areas of physics, the Kramers-Kronig (KK) relations are used to extract information about the real part of the optical response of a medium from its imaginary counterpart. In this paper we discuss an alternative but mathematically equivalent approach based on the Hilbert transform. We apply the Hilbert transform to transmission spectra to find the group and refractive indices of a Cs vapor, and thereby demonstrate how the Hilbert transform allows indirect measurement of the refractive index, group index and group delay whilst avoiding the use of complicated experimental set ups.

We describe a laboratory plasma physics experiment at Los Alamos National Laboratory that uses two merging supersonic plasma jets formed and launched by pulsed-power-driven rail guns. The jets can be formed using any atomic species or mixture available in a compressed-gas bottle and have the following nominal initial parameters at the railgun nozzle exit: $n_e\approx n_i \sim 10^{16}$ cm$^{-3}$, $T_e \approx T_i \approx 1.4$ eV, $V_{\rm jet}\approx 30$-100 km/s, mean charge $\bar{Z}\approx 1$, sonic Mach number $M_s\equiv V_{\rm jet}/C_s>10$, jet diameter $=5$ cm, and jet length $\approx 20$ cm. Experiments to date have focused on the study of merging-jet dynamics and the shocks that form as a result of the interaction, in both collisional and collisionless regimes with respect to the inter-jet classical ion mean free path, and with and without an applied magnetic field. However, many other studies are also possible, as discussed in this paper., Comment: 12 pages, 3 figures, 3 tables; published in J. Plasma Physics

We present experimental observations of atom-light interactions within tens of nanometers (down to 11~nm) of a sapphire surface. Using photon counting we detect the fluorescence from of order one thousand Rb or Cs atoms, confined in a vapor with thickness much less than the optical excitation wavelength. The asymmetry in the spectral lineshape provides a direct read-out of the atom-surface potential. A numerical fit indicates a power-law $-C_{\alpha}/r^{\alpha}$ with $\alpha=3.02\pm0.06$ confirming that the van der Waals interaction dominates over other effects. The extreme sensitivity of our photon-counting technique may allow the search for atom-surface bound states.

We investigate experimentally and theoretically the coherent and incoherent processes in open 3-level ladder systems in room temperature gases and identify in which regime electromagnetically induced transparency (EIT) occurs. The peculiarity of this work lies in the unusual situation where the wavelength of the probe field is shorter than that of the coupling field. The nature of the observed spectral features depends considerably on the total response of different velocity classes, the varying Doppler shifts for bichromatic excitation fields, on optical pumping to additional electronic states and transit time effects. All these ingredients can be absorbed in a model based on optical Bloch equations with only five electronic states., Comment: 7 pages, 7 figures, published version

In this work we propose a hybrid scheme to implement a photonic controlled-z (CZ) gate using photon storage in highly-excited Rydberg states, which controls the effective photon-photon interaction using resonant microwave fields. Our scheme decouples the light propagation from the interaction and exploits the spatial properties of the dipole blockade phenomenon to realize a CZ gate with minimal loss and mode distortion. Excluding the coupling efficiency, fidelities exceeding 95% are achievable and are found to be mainly limited by motional dephasing and the finite lifetime of the Rydberg levels., Comment: 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 present an experimental study of energy transfer in a thermal vapor of atomic rubidium. We measure the fluorescence spectrum in the visible and near infra-red as a function of atomic density using confocal microscopy. At low density we observe energy transfer consistent with the well-known energy pooling process. In contrast, above a critical density we observe a dramatic enhancement of the fluorescence from high-lying states that is not to be expected from kinetic theory. We show that the density threshold for excitation on the D1 and D2 resonance line corresponds to the value at which the dipole-dipole interactions begins to dominate, thereby indicate the key role of these interactions in the enhanced emission., Comment: 8 pages, 7 figures

The dynamics of excitons in a one-dimensional ensemble with partial spatial order are studied. During optical excitation, cold Rydberg atoms spontaneously organize into regular spatial arrangements due to their mutual interactions. This emergent lattice is used as the starting point to study resonant energy transfer triggered by driving a $nS$ to $n^\prime P$ transition using a microwave field. The dynamics are probed by detecting the survival probability of atoms in the $nS$ Rydberg state. Experimental data qualitatively agree with our theoretical predictions including the mapping onto XXZ spin model in the strong-driving limit. Our results suggest that emergent Rydberg lattices provide an ideal platform to study coherent energy transfer in structured media without the need for externally imposed potentials.

We present a fast and Quasideterministic protocol for the production of single ions and electrons from a cloud of laser cooled atoms. The approach is based on a two-step process where first a single Rydberg atom is photo-excited from a dipole-blockade configuration and subsequently ionized by an electric field pulse. We theoretically describe these excitation-ionization cycles via dynamical quantum maps and observe a rich behavior of the ionization dynamics as a function of laser Rabi frequency, pulse duration and particle number. Our results show that a fast sequential heralded production of single charged particles is achievable even from an unstructured and fluctuating atomic ensemble., Comment: 7 pages (including appendix), 4 figures

We report on a scanning microscopy technique for atom-number-resolved imaging of excited-state atoms. A tightly focused laser beam leads to local autoionization, and the resulting ions are counted electronically. Scanning the beam across the cloud builds up an image of the density distribution of excited atoms, with access to the full counting statistics at each spatial sampling point and an overall detection efficiency of 21 %. We apply this technique to the measurement of a spatially inhomogeneous electric field with a spatial resolution of 50 ?m and a sensitivity to electric field gradients of 0.04 V cm$^{-2}$.

We report experimental results on the parameters, structure, and evolution of high-Mach-number (M) argon plasma jets formed and launched by a pulsed-power-driven railgun. The nominal initial average jet parameters in the data set analyzed are density \approx 2 x 10^(16) cm^(-3), electron temperature \approx 1.4 eV, velocity \approx 30 km/s, M \approx 14, ionization fraction \approx 0.96, diameter \approx 5 cm, and length \approx 20 cm. These values approach the range needed by the Plasma Liner Experiment (PLX), which is designed to use merging plasma jets to form imploding spherical plasma liners that can reach peak pressures of 0.1-1 Mbar at stagnation. As these jets propagate a distance of approximately 40 cm, the average density drops by one order of magnitude, which is at the very low end of the 8-160 times drop predicted by ideal hydrodynamic theory of a constant-M jet., Comment: 35 pages, 2 tables, 14 figures, accepted for publication in Physics of Plasmas (12/11/2012)

We present an experimental measurement of the refractive index of high density Rb vapor in a gaseous atomic nanolayer. We use heterodyne interferometry to measure the relative phase shift between two copropagating laser beams as a function of the laser detuning and infer a peak index n = 1.26 \pm 0.02, close to the theoretical maximum of 1.31. The large index has a concomitant large index gradient creating a region with steep anomalous dispersion where a sub-nanosecond optical pulse is advanced by >100 ps over a propagation distance of 390 nm, corresponding to a group index of -1x10^5, the largest negative group index measured to date.

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

A light, compact optical isolator using an atomic vapor in the hyperfine Paschen-Back regime is presented. Absolute transmission spectra for experiment and theory through an isotopically pure 87Rb vapor cell show excellent agreement for fields of 0.6 T. We show \pi/4 rotation for a linearly polarized beam in the vicinity of the D2 line and achieve an isolation of 30 dB with a transmission > 95 %.

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 investigate, theoretically and experimentally, absorption on an excited-state atomic transition in a thermal vapor where the lower state is coherently pumped. We find that the transition linewidth can be sub-natural, i.e. less than the combined linewidth of the lower and upper state. For the specific case of the 6P_{3/2} -> 7S_{1/2} transition in room temperature cesium vapor, we measure a minimum linewidth of 6.6 MHz compared with the natural width of 8.5 MHz. Using perturbation techniques, an expression for the complex susceptibility is obtained which provides excellent agreement with the measured spectra., Comment: 9 pages, 5 figures

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

Electrometry near a dielectric surface is performed using Rydberg electromagnetically induced transparency (EIT). The large polarizability of high n-state Rydberg atoms gives this method extreme sensitivity. We show that adsorbates on the dielectric surface produce a significant electric field that responds to an applied field with a time constant of order one second. For transient applied fields (with a time scale of < 1 s) we observe good agreement with calculations based on numerical solutions of Laplace's equation using an effective dielectric constant to simulate the bulk dielectric., Comment: 5 pages, 6 figures

One-dimensional radiation-hydrodynamic simulations are performed to develop insight into the scaling of stagnation pressure with initial conditions of an imploding spherical plasma shell or "liner." Simulations reveal the evolution of high-Mach-number (M), annular, spherical plasma flows during convergence, stagnation, shock formation, and disassembly, and indicate that cm- and {\mu}s-scale plasmas with peak pressures near 1 Mbar can be generated by liners with initial kinetic energy of several hundred kilo-joules. It is shown that radiation transport and thermal conduction must be included to avoid non-physical plasma temperatures at the origin which artificially limit liner convergence and thus the peak stagnation pressure. Scalings of the stagnated plasma lifetime ({\tau}stag) and average stagnation pressure (Pstag, the pressure at the origin, averaged over {\tau}stag) are determined by evaluating a wide range of liner initial conditions. For high-M flows, {\tau}stag L0/v0, where L0 and v0 are the initial liner thickness and velocity, respectively. Furthermore, for argon liners, Pstag scales approximately as v0^(15/4) over a wide range of initial densities (n0), and as n0^(1/2) over a wide range of v0. The approximate scaling Pstag ~ M 3/2 is also found for a wide range of liner-plasma initial conditions., Comment: 28 pages, 12 figures, accepted by Physics of Plasmas (June 23, 2011)

We use the technique of electro-magnetically induced transparency (EIT) to probe the effect of attractive dipole-dipole interactions in a highly excited Rydberg gas. The transient character of the EIT response is investigated by rapidly scanning the probe laser through resonance. We characterize the resulting cooperative optical non-linearity as a function of probe strength, density and scan direction. For the 58D$_{5/2}$ Rydberg state, an atom density of $1.6\times10^{10} $cm$^{-3}$ and a positive frequency scan we measure a third-order non-linearity of $\chi^{(3)}=5\times 10^{-7}$ m$^2$V$^{-2}$. For the reverse scan we observe a second order non-linearity of $\chi^{(2)}=5\times 10^{-6}$ mV$^{-1}$. The contrasting behaviour can be explained in terms of motional effects and resonant excitation of Rydberg pairs., Comment: 11 pages, 5 figure

We study electromagnetically induced transparency (EIT) in the 5s$\rightarrow$5p$\rightarrow$46s ladder system of a cold $^{87}$Rb gas. We show that the resonant microwave coupling between the 46s and 45p states leads to an Autler-Townes splitting of the EIT resonance. This splitting can be employed to vary the group index by $\pm 10^5$ allowing independent control of the propagation of dark state polaritons. We also demonstrate that microwave dressing leads to enhanced interaction effects. In particular, we present evidence for a $1/R^3$ energy shift between Rydberg states resonantly coupled by the microwave field and the ensuing breakdown of the pair-wise interaction approximation., Comment: 12 pages, 5 figures and 1 table

We report on the magnetic merging of ultracold atomic gases of $^{85}$Rb and $^{87}$Rb by the controlled overlap of two initially spatially-separated magnetic traps. We present a detailed analysis of the combined magnetic field potential as the two traps are brought together which predicts a clear optimum trajectory for the merging. We verify this prediction experimentally using $^{85}$Rb and find that the final atom number in the merged trap is maximised with minimal heating by following the predicted optimum trajectory. Using the magnetic merging approach allows us to create variable ratio isotopic Rb mixtures with a single laser cooling setup by simply storing one isotope in a magnetic trap before jumping the laser frequencies to the transitions necessary to laser cool the second isotope. This offers a simple and cost effective way to achieve suitable starting conditions for sympathetic cooling of $^{85}$Rb by $^{87}$Rb towards quantum degeneracy., Comment: 18 pages, 7 figures; http://link.aps.org/doi/10.1103/PhysRevA.83.053633

We present a design for a switchable nanomagnetic atom mirror formed by an array of 180{\deg} domain walls confined within Ni80Fe20 planar nanowires. A simple analytical model is developed which allows the magnetic field produced by the domain wall array to be calculated. This model is then used to optimize the geometry of the nanowires so as to maximize the reflectivity of the atom mirror. We then describe the fabrication of a nanowire array and characterize its magnetic behavior using magneto-optic Kerr effect magnetometry, scanning Hall probe microscopy and micromagnetic simulations, demonstrating how the mobility of the domain walls allow the atom mirror to be switched "on" and "off" in a manner which would be impossible for conventional designs. Finally, we model the reflection of 87Rb atoms from the atom mirror's surface, showing that our design is well suited for investigating interactions between domain walls and cold atoms., Comment: To appear in Journal of Applied Physics. Volume 108, issue 3

We present a simple technique for stabilization of a laser frequency off resonance using the Faraday effect in a heated vapor cell with an applied magnetic field. In particular we demonstrate stabilization of a 780 nm laser detuned up to 14 GHz from the 85Rb D2 5 2S_1/2 F = 2 to 5 2P_3/2 F' = 3 transition. Control of the temperature of the vapor cell and the magnitude of the applied magnetic field allows locking ~6-14 GHz red and blue detuned from the atomic line. We obtain an rms fluctuation of 16(1) MHz over one hour without stabilization of the cell temperature or magnetic field., Comment: 3 pages, 4 figures

By coupling a probe transition to a Rydberg state using electro-magnetically induced transparency (EIT) we map the strong dipole-dipole interactions onto an optical field. We characterize the resulting cooperative optical non-linearity as a function of probe strength and density. We show that the effect of dipole blockade cannot be described using a mean-field but requires an $N$-atom cooperative model. Good quantitative agreement is obtained for three atoms per blockade with the $n=60$ Rydberg state. We place an upper-limit on the dephasing rate of the blockade spheres of $<110$ kHz., Comment: 4 pages, 4 figures

We demonstrate a cooperative optical non-linearity caused by dipolar interactions between Rydberg atoms in an ultra-cold atomic ensemble. By coupling a probe transition to the Rydberg state we map the strong dipole-dipole interactions between Rydberg pairs onto the optical field. We characterize the non-linearity as a function of electric field and density, and demonstrate the enhancement of the optical non-linearity due to cooperativity., Comment: 4 pages, 5 figures, updated references

A number of recent experiments with nearly pure atomic Bose-Einstein condensates have confirmed the predicted dark soliton oscillations when under harmonic trapping. However, a dark soliton propagating in an inhomogeneous condensate has also been predicted to be unstable to the emission of sound waves. Although harmonic trapping supports an equilibrium between the co-existing soliton and sound, we show that the ensuing dynamics are sensitive to trap anharmonicities. Such anharmonicities can break the soliton-sound equilibrium and lead to the net decay of the soliton on a considerably shorter timescale than other dissipation mechanisms. Thus, we propose how small realistic modifications to existing experimental set-ups could enable the experimental observation of this decay channel., Comment: 10 pages, 9 figures

The formation of rf-dressed Rydberg dark states in thermal Rb vapour is demonstrated. It is shown that such states exhibit enhanced sensitivity to dc electric fields compared to their bare counterparts and enable precise measurement of the dc field independent of laser frequency fluctuations., Comment: 10 pages, 5 figures

We present a viewport for use in Ultra-high vacuum (UHV) based upon the preflattened solder seal design presented in earlier work, Cox et al. Rev. Sci. Inst. 74, 3185 (2003). The design features significant modifications to improve long term performance. The windows have been leak tested to less than 10^-10 atm cm^3/s . From atom number measurements in an optical dipole trap loaded from a vapor cell magneto-optical trap (MOT) inside a vacuum chamber accommodating these viewports, we measure a trap lifetime of 9.5s suggesting a pressure of around 10^-10 Torr limited by background Rubidium vapor pressure. We also present a simplified design where the UHV seal is made directly to a vacuum pipe

We demonstrate laser frequency stabilization to excited state transitions using cascade electromagnetically induced transparency (EIT). Using a room temperature Rb vapor cell as a reference, we stabilize a first diode laser to the D2 transition and a second laser to a transition from the intermediate state to a Rydberg state with principal quantum number n=19 - 70. A combined laser linewidth of 280 kHz over a 0.1 ms time period is achieved. This method may be applied generally to any cascade system and allows laser stabilization to an atomic reference in the absence of strong optical transitions., Comment: 3 pages, 4 figures, with corrections

We study the effect of a control beam on a Lambda electromagnetically induced transparency (EIT) system in 87Rb. The control beam couples one ground state to another excited state forming a four level N-system. Phase coherent beams to drive the N-system are produced using a double injection scheme. We show that the control beam can be used to Stark shift or split the EIT resonance. Finally, we show that the when the control beam is on-resonance one observes a Doppler-free and sub-natural absorptive resonance with a width of order 100 kHz. Crucially, this narrow absorptive resonance only occurs when atoms with a range of velocities are present, as is the case in a room temperature vapour., Comment: 9 pages, 6 figures

We describe a simple strontium vapor cell for laser spectroscopy experiments. Strontium vapor is produced using an electrically heated commercial dispenser source. The sealed cell operates at room temperature, and without a buffer gas or vacuum pump. The cell was characterised using laser spectroscopy, and was found to offer stable and robust operation, with an estimated lifetime of >10,000 hours. By changing the dispenser, this technique can be readily extended to other alkali and alkaline earth elements., Comment: 8 pages, 3 figures

We study electromagnetically induced transparency (EIT) of a weakly interacting cold Rydberg gas. We show that the onset of interactions is manifest as a depopulation of the Rydberg state and numerically model this effect by adding a density-dependent non-linear term to the optical Bloch equations. In the limit of a weak probe where the depopulation effect is negligible, we observe no evidence of interaction induced decoherence and obtain a narrow Rydberg dark resonance with a linewidth of <600 kHz, limited by the Rabi frequency of the coupling beam, Comment: 4 pages, 4 figures

The electro-optic effect, where the refractive index of a medium is modified by an electric field, is of central importance in non-linear optics, laser technology, quantum optics and optical communications. In general, electro-optic coefficients are very weak and a medium with a giant electro-optic coefficient would have profound implications for non-linear optics, especially at the single photon level, enabling single photon entanglement and switching. Here we propose and demonstrate a giant electro-optic effect based on polarizable dark states. We demonstrate phase modulation of the light field in the dark state medium and measure an electro-optic coefficient that is more than 12 orders of magnitude larger than in other gases. This enormous Kerr non-linearity also creates the potential for precision electrometry and photon entanglement., Comment: To appear in Nature Physics