Bulletin of the American Physical Society
47th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 61, Number 8
Monday–Friday, May 23–27, 2016; Providence, Rhode Island
Session J9: Rydberg Atoms and Ultracold Plasmas |
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Chair: Michael Noel, Bryn Mawr College Room: 556AB |
Wednesday, May 25, 2016 2:00PM - 2:12PM |
J9.00001: THz Detection and Imaging using Rydberg Atoms Christopher Wade, Nikola Sibalic, Jorge Kondo, Natalia De Melo, Charles Adams, Kevin Weatherill Atoms make excellent electromagnetic field sensors because each atom of the same isotope is identical and has well-studied, permanent properties allowing calibration to SI units. Thus far, atoms have not generally been exploited for terahertz detection because transitions from the atomic ground state are constrained to a limited selection of microwave and optical frequencies. In contrast, highly excited `Rydberg' states allow us access to many strong, electric dipole transitions from the RF to THz regimes. Recent advances in the coherent optical detection of Rydberg atoms have been exploited by a number of groups for precision microwave electrometry Here we report the demonstration of a room-temperature, cesium Rydberg gas as a THz to optical interface. We present two configurations: First, THz-induced fluorescence offers non-destructive and direct imaging of the THz field, providing real-time, single shot images. Second, we convert narrowband terahertz photons to infrared photons with 6{\%} quantum efficiency allowing us to use nano-Watts of THz power to control micro-Watts of laser power on microsecond timescales. Exploiting hysteresis and a room-temperature phase transition in the response of the medium, we demonstrate a latching optical memory for sub pico-Joule THz pulses. [Preview Abstract] |
Wednesday, May 25, 2016 2:12PM - 2:24PM |
J9.00002: Coherent Transfer of Electronic Wavepacket Motion Between Atoms Tao Zhou, B.G. Richards, R.R. Jones We have shown that electron correlations, induced by controlled dipole-dipole (DD) interactions, can enable the coherent transfer of electronic wavepacket motion from atoms to their neighbors. In the experiment, a 5 ns tunable dye laser excites Rb atoms in a MOT to the 25s state in a weak static electric field for which the tunable 25s33s$\leftrightarrow $24p34p DD interaction is resonant. A picosecond THz pulse then further excites each Rydberg atom into a coherent superposition, of 25s and 24p states. The evolution of this mixed-parity wavepacket is characterized by time-dependent oscillations in the electric dipole moment, with a period of 2.9 ps. Approximately 5 ns after the wavepacket creation, a second 5 ns dye-laser promotes a second set of atoms from the 5p level into the 33s state. Because of the DD interaction, the second dye laser actually creates atom pairs whose electronic states are correlated via the resonant DD coupling. A 33s$+$34p wavepacket, oscillating with the same 2.9 ps period as the 25s$+$24p wavepacket, develops on the second set of atoms as a result of the correlation. A second, time-delayed ps THz pulse enables the detection of the coherent wavepacket motion on the two sets of atoms. [Preview Abstract] |
Wednesday, May 25, 2016 2:24PM - 2:36PM |
J9.00003: Strong field radio-frequency measurements using Rydberg states in a vapor cell Stephanie Miller, David Anderson, Georg Raithel There has been a growing interest in using electromagnetically induced transparency with Rydberg atoms in a room-temperature vapor cell as an all-optical readout method for measuring microwave electric fields [1, 2]. We present results from RF-modulating the 60$S_{1/2}$ and 58$D_{5/2}$ Rydberg states of rubidium with 50 MHz and 100 MHz fields, respectively [3]. Weak RF fields AC Stark-shifts the Rydberg states. As the field strength is increased, sidebands appear at even multiples of the driving frequency. When strong fields are applied, the nearby hydrogenic manifold begins to intersect with the shifted levels. Similar investigations have been performed in cesium [4]. Due to the significant amount of state mixing and level structure, Floquet theory is required to describe the level shifts and mixing. By comparing the calculation with the experimental data, we obtain an absolute determination of the RF electric field reaching a maximum field of 296 V/m to within $\pm$0.35$\%$. Additionally, we estimate the shielding of DC fields within the vapor cell. [1] D. A. Anderson et. al., arXiv: 1601.02535 [2] J. A. Sedlacek et. al., Nat. Phys. 8, 819 (2012). [3] S. A. Miller, D. A. Anderson, G. Raithel, arXiv: 1601.06840 [4] Y. Jiao et. al., arXiv: 1601.01748 [Preview Abstract] |
Wednesday, May 25, 2016 2:36PM - 2:48PM |
J9.00004: Study of atomic dipole-dipole interactions via measurement of atom-pair kinetics Nithiwadee Thaicharoen, Lu\'is Felipe Gon\c{c}alves, Georg Raithel We observe atom-pair kinetics due to binary dipolar forces by direct imaging of the center-of-mass positions of the individual Rydberg atoms and pair-correlation analysis. To prepare a highly dipolar quantum state, Rydberg-atom ensembles are switched from a weakly- into a strongly-interacting regime via adiabatic state transformation. The transformed atoms exhibit a large permanent electric dipole moment that is locked to the direction of an applied electric field. The resultant electric dipole-dipole forces reveal dumbbell-shaped pair correlation images that demonstrate the anisotropy of the binary dipolar force. The dipole-dipole interaction coefficient $C_3$, derived from the time dependence of the images, agrees with the value calculated from the known permanent electric-dipole moment of the atoms. The observations also show the dynamics reminiscent of disorder-induced heating in strongly coupled particle systems. [Preview Abstract] |
Wednesday, May 25, 2016 2:48PM - 3:00PM |
J9.00005: Steady-state bistability and long-range order in optically driven Rydberg gases in the anti-blockade regime Fabian Letscher, Dominik Linzner, Michael Fleischhauer Motivated by recent experiments, we study spatial and temporal correlations of Rydberg excitations of optically driven ultra-cold atoms in the anti-blockade regime. In particular, we discuss the influence of dissipation on the excitation dynamics of a linear chain of atoms, described by the dissipative, transverse-field Ising model. Using t-DMRG simulations of the density matrix we identify parameter regimes with diverging correlation lengths in the coherent regime of weak dissipation. Correlation lengths remain short-ranged in the incoherent regime of strong dissipation, where classical rate equations can be employed. We discuss the different physical mechanisms determining the many-body dynamics in the two regimes and compare theoretical predictions with recent experimental results. In particular we discuss the formation of excitation cluster in the incoherent regime and explain the observed slow-down of the relaxation process due to cluster formation. [Preview Abstract] |
Wednesday, May 25, 2016 3:00PM - 3:12PM |
J9.00006: Simulations Of Laser Cooling In An Ultracold Neutral Plasma Thomas Langin, Trevor Strickler, Thomas Pohl, Daniel Vrinceanu, Thomas Killian Ultracold neutral plasmas (UNPs) generated by photoionization of laser-cooled, magneto-optically trapped neutral gases, are useful systems for studying strongly coupled plasmas. Coupling is parameterized by $\Gamma_{i}$, the ratio of the average nearest neighbor Coulomb interaction energy to the ion kinetic energy. For typical UNPs, $\Gamma_{i}$ is currently limited to $\sim3$. For alkaline earth ions, higher $\Gamma_{i}$ can be achieved by laser-cooling. Using Molecular Dynamics and a quantum trajectories approach, we have simulated laser-cooling of Sr$^{+}$ ions interacting through a Yukawa potential. The simulations include re-pumping from two long-lived D-states, and are conducted at experimentally achievable parameters (density $n=2$\,e+14\,m$^{-3}$, size $\sigma_{0}=4$\,mm, $T_{e}$=19\,K). Laser-cooling is shown to both reduce the temperature by a factor of 2 over relevant timescales (tens of $\mu$\,s) and slow the electron thermal-pressure driven radial expansion of the UNP. We also discuss the unique aspects of laser-cooling in a highly collisional system; in particular, the effect of collisions on dark state formation due to the coupling of the P$_{3/2}$ state to both the S$_{1/2}$ (via the cooling transition) and the D$_{5/2}$ (via a re-pump transition) states. [Preview Abstract] |
Wednesday, May 25, 2016 3:12PM - 3:24PM |
J9.00007: Measurements of the ion velocity distribution in an ultracold neutral plasma derived from a cold, dense Rydberg gas Scott Bergeson, Mary Lyon We report measurements of the ion velocity distribution in an ultracold neutral plasma derived from a dense, cold Rydberg gas in a MOT. The Rydberg atoms are excited using a resonant two-step excitation pathway with lasers of 4 ns duration. The plasma forms spontaneously and rapidly. The rms width of the ion velocity distribution is determined by measuring laser-induced fluorescence (LIF) of the ions. The measured excitation efficiency is compared with a Monte-Carlo wavefunction calculation, and significant differences are observed. We discuss the conditions for blockaded Rydberg excitation and the subsequent spatial ordering of Rydberg atom domains. While the blockade interaction is greater than the Rabi frequency in portions of the atomic sample, no evidence for spatial ordering is observed. [Preview Abstract] |
Wednesday, May 25, 2016 3:24PM - 3:36PM |
J9.00008: Strongly-coupled plasmas formed from laser-heated solids Mary Lyon, Scott Bergeson, Gus Hart, Michael Murillo We present an analysis of ion temperatures in laser-produced plasmas formed from solids with different initial lattice structures. We show that the equilibrium ion temperature is limited by a mismatch between the initial crystallographic configuration and the close-packed configuration of a strongly-coupled plasma, similar to experiments in ultracold neutral plasmas. We propose experiments to demonstrate and exploit this crystallographic heating in order to produce a strongly coupled plasma with a coupling parameter of several hundred. [Preview Abstract] |
Wednesday, May 25, 2016 3:36PM - 3:48PM |
J9.00009: Measurement of Rydberg atom formation in low-density ultracold neutral plasmas Wei-Ting Chen, Craig Witte, Jacob Roberts Rydberg atoms are formed in ultracold neutral plasmas primarily through three-body recombination for typical experimental conditions. At low densities the relative importance of electron-Rydberg state-changing collisions in the dynamical evolution of the Rydberg atom state populations is increased, leading to temperature scalings significantly different from the usual $T^{-9/2}$ scaling associated with the three-body recombination rate. We report our measurement of Rydberg atoms in low-density ultracold neutral plasmas and discuss their utility in calibrating the electron temperature and determining the amount of heating due to continuum lowering that occurs during the formation of the ultracold plasma. [Preview Abstract] |
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