Abstract
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 laser-driven 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.
Highlights
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
Our interpretation is that the correlated growth of Rydberg excitation due to the DC Stark shifts from nearby ions eventually leads to the runaway formation of an ultra-cold plasma (UCP), leading to rapid ionization of most the remaining Rydberg atoms
Charges created within the cloud can DC Stark shift nearby atoms into resonance with the excitation laser, leading to strong Rydberg excitation
Summary
The experiments began with the formation of a MOT of 88Sr atoms operating on the narrow 5s2 1S0 « 5s5p 3P1 transition. A MOT beam detuning of dMOT 2p » -175 kHz and an intensity per beam of IMOT = 3–50 Isat (where Isat is the saturation intensity of the transition) resulted in 1/e2 cloud radii of 30–60 μm (100–200 μm) in the vertical (z) (horizontal (x)) direction, and temperature Tz = 1 μK. Atoms in the MOT were subsequently coupled to the Rydberg state by off-resonantly driving the 5s5p 3P1 5s36d 3D1 transition using 50 mW of 319 nm light [33] with a beam waist of 160 μm (120 μm) in the vertical (horizontal) direction, resulting in a peak coupling beam Rabi frequency of Ω/2π = 4 MHz. The coupling beam detuning was varied from Δ/2π = −20 to +20 MHz, allowing observation of the attractive van der Waals interaction of the 36d 3D1 state for negative detunings, and the DC Stark shift due to nearby ions for positive detunings, illustrated in figure 1(b). We do not correct measured Q parameters for detection efficiency
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