Georg Raithel

Atomic, Molecular and Optical Physics

PhD
38.81

Publications

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    ABSTRACT: We study the repulsive van der Waals interaction of cold rubidium $70S_{1/2}$ Rydberg atoms by analysis of time-delayed pair correlation functions. After excitation, Rydberg atoms are allowed to accelerate under the influence of the van der Waals force. Their positions are then measured using a single-atom imaging technique. From the average pair correlation function of the atom positions we obtain the initial atom-pair separation and the terminal velocity, which yield the van der Waals interaction coefficient $C_{6}$. The measured $C_{6}$ value agrees well with calculations. The experimental method has been validated by simulations. The data hint at anisotropy in the overall expansion, caused by the shape of the excitation volume. Our measurement implies that the interacting entities are individual Rydberg atoms, not groups of atoms that coherently share a Rydberg excitation.
  • Kaitlin Moore, Georg Raithel
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    ABSTRACT: In ponderomotive spectroscopy an amplitude-modulated optical standing wave is employed to probe Rydberg-atom transitions, utilizing a ponderomotive rather than a dipole-field interaction. Here, we engage nonlinearities in the modulation to drive dipole-forbidden transitions up to the fifth order. We reach transition frequencies approaching the sub-THz regime. We also demonstrate magic-wavelength conditions, which result in symmetric spectral lines with a Fourier-limited feature at the line center. Applicability to precision measurement is discussed.
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    ABSTRACT: Multiple adiabatic/diabatic passages through avoided crossings in the Stark map of cesium Rydberg atoms are employed as beam splitters and recombiners in an atom-interferometric measurement of energy-level splittings. We subject cold cesium atoms to laser-excitation, electric-field and detection sequences that constitute an (internal-state) atom interferometer. For the read-out of the interferometer we utilize state-dependent collisions, which selectively remove atoms of one kind from the detected signal. We investigate the dependence of the interferometric signal on timing and field parameters, and find good agreement with time-dependent quantum simulations of the interferometer. Fourier analysis of the interferometric signals yield coherence frequencies that agree with corresponding energy-level differences in calculated Stark maps. The method enables spectroscopy of states that are inaccessible to direct laser-spectroscopic observation, due to selection rules, and has applications in field metrology.
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    ABSTRACT: The passage of cold cesium 49S$_{1/2}$ Rydberg atoms through an electric-field-induced multi-level avoided crossing with nearby hydrogen-like Rydberg levels is employed to prepare a cold, dipolar Rydberg atom gas. When the electric field is ramped through the avoided crossing on time scales on the order of 100~ns or slower, the 49S$_{1/2}$ population adiabatically transitions into high-\emph{l} Rydberg Stark states. The adiabatic state transformation results in a cold gas of Rydberg atoms with large electric dipole moments. After a waiting time of about $1~\mu$s and at sufficient atom density, the adiabatically transformed highly dipolar atoms become undetectable, enabling us to discern adiabatic from diabatic passage behavior through the avoided crossing. We attribute the state-selectivity to $m$-mixing collisions between the dipolar atoms. The data interpretation is supported by numerical simulations of the passage dynamics and of binary $m$-mixing collisions.
    New Journal of Physics 04/2015; 17(6). DOI:10.1088/1367-2630/17/6/063011 · 3.67 Impact Factor
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    ABSTRACT: We discuss a fundamentally new approach for the measurement of electric (E) fields that will lead to the development of a broadband, direct SI-traceable, compact, self-calibrating E-field probe (sensor). This approach is based on the interaction of radio frequency (RF) fields with alkali atoms excited to Rydberg states. The RF field causes an energy splitting of the Rydberg states via the Autler-Townes effect and we detect the splitting via electromagnetically induced transparency. In effect, alkali atoms placed in a vapor cell act like an RF-to-optical transducer, converting an RF E-field strength measurement to an optical frequency measurement. We demonstrate the broadband nature of this approach by showing that one small vapor cell can be used to measure E-field strengths over a wide range of frequencies: 1 GHz to 500 GHz. The technique is validated by comparing experimental data to both numerical simulations and far-field calculations for various frequencies. We also discuss various applications, including: a direct traceable measurement, the ability to measure both weak and strong field strengths, compact form factors of the probe, and sub-wavelength imaging and field mapping.
    IEEE Transactions on Antennas and Propagation 12/2014; 62(12):6169-6182. DOI:10.1109/TAP.2014.2360208 · 2.46 Impact Factor
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    ABSTRACT: We investigate two-photon Autler-Townes splitting and strong-field effects of Rb-85 Rydberg atoms in a room-temperature vapor cell. To observe the level structure we employ electromagnetically induced transparency. We first study the two-photon 62S(1/2)-63S(1/2) microwave transition using an electric-field reference measurement obtained with the one-photon 62S(1/2)-62P(3/2) transition. We then study the 61D(5/2)-62D(5/2) transition where the microwave electric-field range is extended up to similar to 40 V/m. A Floquet analysis is used to model field-induced level shifts and state-mixing effects present in the strongly driven quantum systems under consideration. Calculations are found to be in good agreement with experimental observations.
    Physical Review A 10/2014; 90(4):043419. DOI:10.1103/PhysRevA.90.043419 · 2.99 Impact Factor
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    ABSTRACT: We study the effects of Rydberg-atom interactions on Autler-Townes (AT) spectra in a dense gas of ultracold cesium atoms. The 6S(1/2) and 6P(3/2) levels of cesium are strongly coupled (Rabi frequency Omega(c)), and the resultant AT spectra are probed via excitation into a Rydberg level. Van der Waals interactions between the atoms in the probe Rydberg level give rise to a dephasing rate (gamma(3)). The interaction-induced dephasing is found to cause characteristic changes in the AT spectra, including a reduction or elimination of the AT splitting, an increase in the critical Omega(c) above which AT splitting occurs, and an increase in the width of the AT spectral lines. Rydberg-atom interactions are controlled by varying the principal quantum number n of the probe Rydberg level; larger values of n correspond to higher dephasing rates gamma(3). Results of numerical calculations are in good agreement with the experiments.
    Physical Review A 10/2014; 90(4). DOI:10.1103/PhysRevA.90.043849 · 2.99 Impact Factor
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    ABSTRACT: Spectroscopy is an essential tool in understanding and manipulating quantum systems, such as atoms and molecules. The model describing spectroscopy includes a multipole-field interaction, which leads to established spectroscopic selection rules, and an interaction that is quadratic in the field, which is often neglected. However, spectroscopy using the quadratic (ponderomotive) interaction promises two significant advantages over spectroscopy using the multipole-field interaction: flexible transition rules and vastly improved spatial addressability of the quantum system. For the first time, we demonstrate ponderomotive spectroscopy by using optical-lattice-trapped Rydberg atoms, pulsating the lattice light at a microwave frequency, and driving a microwave atomic transition that would otherwise be forbidden by established spectroscopic selection rules. This new ability to measure frequencies of previously inaccessible transitions makes possible improved determinations of atomic characteristics and constants underlying physics. In the spatial domain, the resolution of ponderomotive spectroscopy is orders of magnitude better than the transition frequency (and the corresponding diffraction limit) would suggest, promising single-site addressability in a dense particle array for quantum control and computing applications. Future advances in technology may allow ponderomotive spectroscopy to be extended to ground-state atoms and trapped molecules.
    Nature Communications 09/2014; 6. DOI:10.1038/ncomms7090 · 10.74 Impact Factor
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    ABSTRACT: We study angular-momentum couplings in $^{87}$Rb$_2$ Rydberg molecules formed between Rydberg and 5S$_{1/2}$ ground-state atoms. We use a Fermi model that includes S-wave and P-wave singlet and triplet scattering of the Rydberg electron with the 5S$_{1/2}$ atom, along with the fine structure coupling of the Rydberg atom and hyperfine structure coupling of the 5S$_{1/2}$ atom. We discuss the effects of these couplings on the adiabatic molecular potentials. We obtain bound-state energies, lifetimes, and electric and magnetic dipole moments for the vibrational ground states of the $^{87}$Rb$(n$D$+5$S$_{1/2})$ molecules in all adiabatic potentials, with fine and hyperfine structure included. We also study the effect of the hyperfine structure on the deep $^3$S-wave- and $^3$P-wave-dominated adiabatic molecular potentials, which support high-$\ell$ $^{87}$Rb$_2$ Rydberg molecules.
    Physical Review A 09/2014; 90(6). DOI:10.1103/PhysRevA.90.062518 · 2.99 Impact Factor
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    ABSTRACT: We present a technique for measuring radio-frequency (RF) electric field strengths with sub-wavelength resolution. We use Rydberg states of rubidium atoms to probe the RF field. The RF field causes an energy splitting of the Rydberg states via the Autler-Townes effect, and we detect the splitting via electromagnetically induced transparency (EIT). We use this technique to measure the electric field distribution inside a glass cylinder with applied RF fields at 17.04 GHz and 104.77 GHz. We achieve a spatial resolution of ≈100 μm, limited by the widths of the laser beams utilized for the EIT spectroscopy. We numerically simulate the fields in the glass cylinder and find good agreement with the measured fields. Our results suggest that this technique could be applied to image fields on a small spatial scale over a large range of frequencies, up into the sub-terahertz regime.
    Applied Physics Letters 06/2014; 104(24):244102-244102-5. DOI:10.1063/1.4883635 · 3.52 Impact Factor
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    ABSTRACT: In this paper we demonstrate the detection of millimeter waves via Autler-Townes splitting in 85Rb Rydberg atoms. This method may provide an independent, atom-based, SI-traceable method for measuring mm-wave electric fields, which addresses a gap in current calibration techniques in the mm-wave regime. The electric- field amplitude within a rubidium vapor cell in the WR-10 waveguide band is measured for frequencies of 93 GHz, and 104 GHz. Relevant aspects of Autler-Townes splitting originating from a four-level electromagnetically induced transparency scheme are discussed. We measure the E-field generated by an open-ended waveguide using this technique. Experimental results are compared to a full-wave finite element simulation.
    Applied Physics Letters 06/2014; 105(2). DOI:10.1063/1.4890094 · 3.52 Impact Factor
  • Yun-Jhih Chen, Stefan Zigo, Georg Raithel
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    ABSTRACT: We use a near-concentric optical cavity at 1064 nm to generate trapping potentials for cold atoms. The cavity exhibits nondegenerate Hermite-Gaussian modes. Using just a few-milliwatt trap laser power, the cavity readily generates one-and higher-dimensional optical traps that replicate the mode functions. We spectroscopically characterize the optical trapping potentials and laser-cooling limits under continuous loading conditions. We use absorption images to measure atom densities and to compare the spatial profiles of trapped-atom samples with calculated mode functions. Steady-state fluorescence images reveal bright radiation emerging from the ends of the elongated, cavity-trapped atom clouds, providing evidence for radiation guiding.
    Physical Review A 06/2014; 89(6). DOI:10.1103/PhysRevA.89.063409 · 2.99 Impact Factor
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    ABSTRACT: We discuss a fundamentally new approach for the measurement of electric (E) fields that will lead to the development of a broadband, direct SI-traceable, compact, self-calibrating E-field probe (sensor). This approach is based on the interaction of radio frequency (RF) fields with alkali atoms excited to Rydberg states. The RF field causes an energy splitting of the Rydberg states via the Autler-Townes effect and we detect the splitting via electromagnetically induced transparency (EIT). In effect, alkali atoms placed in a vapor cell act like an RF-to-optical transducer, converting an RF E-field strength measurement to an optical frequency measurement. We demonstrate the broadband nature of this approach by showing that one small vapor cell can be used to measure E-field strengths over a wide range of frequencies: 1 GHz to 500 GHz. The technique is validated by comparing experimental data to both numerical simulations and far-field calculations for various frequencies. We also discuss various applications, including: a direct traceable measurement, the ability to measure both weak and strong field strengths, compact form factors of the probe, and sub-wavelength imaging and field mapping.
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    D A Anderson, S A Miller, G Raithel
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    ABSTRACT: We observe long-range homonuclear diatomic nD Rydberg molecules photoassociated out of an ultracold gas of Rb87 atoms for 34≤n≤40. The measured ground-state binding energies of Rb87(nD+5S1/2) molecular states are larger than those of their Rb87(nS+5S1/2) counterparts, which shows the dependence of the molecular bond on the angular momentum of the Rydberg atom. We exhibit the transition of Rb87(nD+5S1/2) molecules from a molecular-binding-dominant regime at low n to a fine-structure-dominant regime at high n [akin to Hund's cases (a) and (c), respectively]. In the analysis, the fine structure of the nD Rydberg atom and the hyperfine structure of the 5S1/2 atom are included.
    Physical Review Letters 04/2014; 112(16):163201. DOI:10.1103/PhysRevLett.112.163201 · 7.73 Impact Factor
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    ABSTRACT: We study steady-state evaporation in an atom guide via Monte Carlo simulations. The evaporation surface follows a specific profile as a function of longitudinal guide location. We demonstrate that the choice of evaporation profile significantly impacts the performance of the evaporation. Our simulations also demonstrate a significant performance boost in the evaporation when using a longitudinally compressed guide. We show that for a purely pressure-driven atom beam, it should be possible to reach degeneracy within a $0.5~\m$ guide for experimentally feasible, albeit challenging, loading conditions.
    Physical Review A 04/2014; 90(4). DOI:10.1103/PhysRevA.90.043612 · 2.99 Impact Factor
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    ABSTRACT: We present a technique for measuring radio-frequency (RF) electric field strengths with sub-wavelength resolution. We use Rydberg states of rubidium atoms to probe the RF field. The RF field causes an energy splitting of the Rydberg states via the Autler-Townes effect, and we detect the splitting via electromagnetically induced transparency (EIT). We use this technique to measure the electric field distribution inside a glass cylinder with applied RF fields at 17.04 GHz and 104.77 GHz. We achieve a spatial resolution of $\bf{\approx}$100 $\bf{\mu}$m, limited by the widths of the laser beams utilized for the EIT spectroscopy. We numerically simulate the fields in the glass cylinder and find good agreement with the measured fields. Our results suggest that this technique could be applied to image fields on a small spatial scale over a large range of frequencies, up into the sub-THz regime.
  • Sarah E Anderson, Georg Raithel
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    ABSTRACT: When electromagnetic radiation induces atomic transitions, the size of the atom is usually much smaller than the wavelength of the radiation, allowing the spatial variation of the radiation field's phase to be neglected in the description of transition rates. Somewhat unexpectedly, this approximation, known as the electric dipole approximation, is still valid for the ionization of micrometre-sized atoms in highly excited Rydberg states by laser light with a wavelength of about the same size. Here we employ a standing-wave laser field as a spatially resolving probe within the volume of a Rydberg atom to show that the photoionization process only occurs near the nucleus, within a volume that is small with respect to both the atom and the laser wavelength. This evidence resolves the apparent inconsistency of the electric dipole approximation's validity for photoionization of Rydberg atoms, and it verifies the theory of light-matter interaction in a limiting case.
    Nature Communications 12/2013; 4:2967. DOI:10.1038/ncomms3967 · 10.74 Impact Factor
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    ABSTRACT: We use direct spatial ion imaging of cold Rb-85 Rydberg atom clouds to measure the Rydberg-Rydberg correlation function, with and without light-shift potentials generated by an optical dipole trap. We find that the blockade radius depends on laser detunings and spatially varying light shifts. At certain laser detunings the probability of exciting Rydberg atoms at particular separations is enhanced, which we interpret to be a result of direct two-photon excitation of Rydberg atom pairs. The results are in accordance with predictions [F. Robicheaux and J. V. Hernandez, Phys. Rev. A 72, 063403 (2005)] and a model we develop that accounts for a one-dimensional dipole-trap potential.
    Physical Review A 12/2013; 88(6):061406. DOI:10.1103/PhysRevA.88.061406 · 2.99 Impact Factor
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    ABSTRACT: Cold circular Rydberg atoms are produced and magnetically trapped. The trap is characterized by direct spatial imaging of ion distributions, ion counting, and state-selective field ionization. At room temperature, we observe about 70% of the trapped atoms remaining after 6 ms. We measure a trap oscillation frequency increase of the circular Rydberg atom trap relative to the ground-state atom trap due to the larger magnetic moment of the circular Rydberg atoms. Simulations of the center-of-mass and internal-state evolution of circular states in our magnetic trap are performed and results are in good agreement with experimental observations.
    Physical Review A 09/2013; 88(3):31401-. DOI:10.1103/PhysRevA.88.031401 · 2.99 Impact Factor
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    ABSTRACT: We study cold rubidium Rydberg atoms, initially prepared in state 59D 5/2 , guided along a two-wire magnetic atom guide. The evolution of the atoms is driven by the combined effects of internal-state transitions and dipole forces acting on the center-of-mass degree of freedom. State-selective field ionization, applied at a variable delay time, is used to investigate the evolution of the internal-state distribution. We observe a broadening of the field ionization spectrum caused by population transfer between Rydberg states. At late times, the distribution of the remaining Rydberg atoms becomes biased toward states with high principal quantum numbers. The population transfer is attributed to thermal transitions and, to a lesser extent, initial state mixing due to Rydberg-Rydberg collisions. Characteristic components in spatially and temporally resolved distributions of the ion signal are interpreted in the context of the underlying physics. The system is simulated with a model in which the center-of-mass dynamics are treated classically, while the internal-state dynamics are treated quantum mechanically. The simulation qualitatively reproduces most experimental findings and provides experimentally inaccessible information.
    Physical Review A 05/2013; 87(5):053418. DOI:10.1103/PhysRevA.87.053418 · 2.99 Impact Factor

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