Continuous coupling of ultracold atoms to an ionic plasma via Rydberg excitation

Weber, Tobias; Niederprüm, Thomas; Manthey, T.; Langer, P.; Guarrera, Vera; Barontini, Giovanni; Ott, Herwig

doi:10.1103/physreva.86.020702

Cited by 16 publications

(22 citation statements)

References 25 publications

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“…We neglect the role of Rydberg-ion interactions, assuming the net charge imbalance is relatively small and the ions are effectively screened by the mobile electrons. This assumption is consistent with our experimental observation that the Rydberg resonance does not significantly shift after plasma formation, but only becomes broadened [16]. On the observed timescale, the repulsive |55S 1/2 atoms are not expected to undergo ionizing Rydberg-Rydberg collisions at a sufficient rate to seed the avalanche [27].…”

Section: Fig 1 (Color Online)supporting

confidence: 91%

Spontaneous Avalanche Ionization of a Strongly Blockaded Rydberg Gas

Robert-De-Saint-Vincent

Hofmann²,

Schempp³

et al. 2013

Phys. Rev. Lett.

110

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We report the sudden and spontaneous evolution of an initially correlated gas of repulsively interacting Rydberg atoms to an ultracold plasma. Under continuous laser coupling we create a Rydberg ensemble in the strong blockade regime, which at longer times undergoes an ionization avalanche. By combining optical imaging and ion detection, we access the full information on the dynamical evolution of the system, including the rapid increase in the number of ions and a sudden depletion of the Rydberg and ground state densities. Rydberg-Rydberg interactions are observed to strongly affect the dynamics of plasma formation. Using a coupled rate-equation model to describe our data, we extract the average energy of electrons trapped in the plasma, and an effective crosssection for ionizing collisions between Rydberg atoms and atoms in low-lying states. Our results suggest that the initial correlations of the Rydberg ensemble should persist through the avalanche. This would provide the means to overcome disorder-induced-heating, and offer a route to enter new strongly-coupled regimes.Ultracold plasmas (UCPs) formed by photo-ionizing ultracold neutral atomic or molecular gases [1,2] offer an ideal laboratory setting to better understand exotic phases of matter such as dense astrophysical plasmas [3] and laser induced plasmas [4]. Experimental and theoretical progress is driven by the potential to reach the so-called strongly-coupled regime [5,6], in which the Coulomb interaction energy dominates over the kinetic energy of the ions, giving rise to collective effects and strong spatial correlations between particles. It is quantified by the coupling parameter Γ = q 2 /4πǫ 0 ak B T ≫ 1, where a is the Wigner-Seitz radius, q the electron charge, and T the ion temperature. In laser-cooled gases, Γ ≈ 0.1 − 2 is readily achieved, which has allowed the observation and driving of collective mechanical modes [7]. Reaching deep into the strongly-coupled regime, however, has remained out of reach partly due to disorder-inducedheating (DIH), where the Coulomb interaction energy due to the initially random distribution of the atoms is converted into kinetic energy of the ions [8,9].Gases of atoms in high-lying (Rydberg) states offer an alternative approach to study UCPs, as they can be easily ionized, and the strong Rydberg-Rydberg interactions lead to dramatic new effects. The spontaneous evolution of an attractively interacting Rydberg gas into an UCP has been observed in several experiments [10,11], which initiated in-depth studies on the ionization mechanisms [12][13][14] and on the electron-ion recombination dynamics towards Rydberg states [15]. Recently [16], the long-term formation of an ionic cloud from attractive and repulsive Rydberg states has been observed, and its back-action onto Rydberg laser-excitation rates has been characterized. At the high densities achievable using optical or magnetic traps, the Rydberg blockade effect [17] gives rise to strong correlations in the initial gas [18]. Since these correlations resemble ...

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Section: Fig 1 (Color Online)supporting

confidence: 91%

Spontaneous Avalanche Ionization of a Strongly Blockaded Rydberg Gas

Robert-De-Saint-Vincent

Hofmann²,

Schempp³

et al. 2013

Phys. Rev. Lett.

110

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“…The images in Fig. 4 are consistent with the well established avalanche ionization process [31,32], and this is confirmed by the presence of a time threshold in the transmission plots of Fig. 4(h).…”

Section: Charge As Shown Insupporting

confidence: 79%

Ion Imaging via Long-Range Interaction with Rydberg Atoms

Groß

Vogt

2020

Phys. Rev. Lett.

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We demonstrate imaging of ions in an atomic gas with ion-Rydberg atom interaction induced absorption. This is made possible by utilizing a multi-photon electromagnetically induced transparency (EIT) scheme and the extremely large electric polarizability of a Rydberg state with high orbital angular momentum. We process the acquired images to obtain the distribution of ion clouds and to spectroscopically investigate the effect of the ions on the EIT resonance. Furthermore, we show that our method can be employed to image the dynamics of ions in a time resolved way. As an example, we map out the avalanche ionization of a gas of Rydberg atoms. The minimal disruption and the flexibility offered by this imaging technique make it ideally suited for the investigation of cold hybrid ion-atom systems.

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“…The coupled evolution of a Rydberg gas and a plasma has been considered theoretically by several groups [10,11,51]. A related approach was developed for plasma formation in thermal gases in [52].…”

Section: Theoretical Descriptionmentioning

confidence: 99%

Coulomb anti-blockade in a Rydberg gas

et al. 2019

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We perform a comprehensive investigation of the coupling between a Rydberg-dressed atomic gas and an ultra-cold plasma (UCP). Using simultaneous time-resolved measurements of both neutral atoms and ions, we show that plasma formation occurs via a Coulomb anti-blockade mechanism, in which background ions DC Stark shift nearby atoms into resonance at specific distances. The result is a highly correlated growth of the Rydberg population that shares some similarities with that previously observed for van der Waals interactions. We show that a rate equation model that couples the laserdriven Rydberg gas to the UCP via a Coulomb anti-blockade mechanism accurately reproduces both the plasma formation and its subsequent decay. Using long-lived high angular momentum states as a probe, we also find evidence of a crossover from Coulomb anti-blockade to Coulomb blockade at high density. As well as shedding light on loss mechanisms in Rydberg-dressed gases, our results open new ways to create low-entropy states in UCPs. Introduction/motivationHybrid quantum systems of ultracold atoms and ions are emerging as a platform for fundamental research in quantum physics [1]. Recently, Rydberg states have received attention as a way to control the coupling between ionic and atomic systems [2-5], for example, using Coulomb blockade from a single ion to suppress Rydberg excitation [6]. Ultracold mixtures of Rydberg atoms and ions have also been studied in the context of cold Rydberg gases, where it was generally found that ions are almost always present due to processes such as collisions between nearby Rydberg atoms and blackbody photoionization. Indeed, studies using resonant laser excitation of Rydberg states have shown an ultra-cold plasma (UCP) under conditions of strong excitation, both in the pulsed [7-9] and continuously driven [10, 11] regimes.In this paper, we demonstrate that an off-resonant excitation of the Rydberg state can be used to tailor the the interaction between Rydberg atoms and ions in an ultracold gas. We show that plasma formation occurs via a Coulomb anti-blockade mechanism, illustrated in figure 1(b), where background ions DC Stark shift nearby atoms into resonance at specific distances. The result is a highly correlated 'facilitated growth' of the Rydberg population that shares some similarities with that previously observed using van der Waals anti-blockade [12]. A rate equation model that couples the driven Rydberg gas to an UCP via this correlated excitation model accurately reproduces both the initial creation and subsequent decay of the observed ion signal. At longer times, the ionization of long-lived high angular momentum Rydberg states produced in the plasma provides evidence for the interplay between Coulomb blockade [6] and Coulomb anti-blockade in the plasma. In future experiments, controlling this process could provide a route to creating an UCP with a strongly correlated ionic state [13].Our results also provide a strategy for minimising losses due to ionization in cold Rydberg gas experiments, p...

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Continuous coupling of ultracold atoms to an ionic plasma via Rydberg excitation

Cited by 16 publications

References 25 publications

Spontaneous Avalanche Ionization of a Strongly Blockaded Rydberg Gas

Spontaneous Avalanche Ionization of a Strongly Blockaded Rydberg Gas

Ion Imaging via Long-Range Interaction with Rydberg Atoms

Coulomb anti-blockade in a Rydberg gas

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