Electrical Readout for Coherent Phenomena Involving Rydberg Atoms in Thermal Vapor Cells

Abstract

We present a very sensitive and scalable method to measure the population of highly excited Rydberg states in a thermal vapor cell of rubidium atoms. We detect the Rydberg ionization current in a 5 mm electrically contacted cell. The measured current is found to be in excellent agreement with a theory for the Rydberg population based on a master equation for the three level problem including an ionization channel and the full Doppler distributions at the corresponding temperatures. The signal-to-noise ratio of the current detection is substantially better than purely optical techniques.PACS numbers: 32.80. Rm, 03.67.Lx, 42.50.Gy Coherent phenomena involving strongly interacting Rydberg atoms have recently led to the demonstration of first quantum devices like quantum logic gates [1][2][3] and single photon sources [4] based on ultracold atoms. All these experiments require precise control over the highly excited states populations, which can be probed directly by field ionization [5,6] or by fluorescence techniques involving Rydberg shielding [7]. Since the strong vdW interaction has recently also been observed in vapor cells [8], scalable quantum devices based on the Rydberg blockade in above room temperature ensembles seem to be also within reach [9]. However, ion detectors as electron multipliers or multi-channel plates cannot be used in dense thermal vapors. For this reason, in thermal cells, most studies today use an indirect measurement of the excited state population by analyzing light fields leaving the atomic ensemble. Nevertheless, it is desirable to study not only the back-action of the vapor on the light, typically via electromagnetically induced transparency (EIT) [10], but also to measure directly the number of excited Rydberg states. One method, developed almost a century ago [11,12], makes use of thermionic diodes [13][14][15]. There, one of the electrodes is heated to emit electrons, which produce space charge limited gain for the amplification of ionized Rydberg atoms. The need of long ion trapping times requires large geometries for the space charge region, and an additional shielded excitation region to minimize the effect of disturbing electric fields during excitation of the highly polarizable Rydberg atoms. Despite its high sensitivity, this drawback sets a practical limitation for further applications where size and scalability play a role.Here we demonstrate that, in a symmetric configuration of atomic vapor between two transparent field plates, sizable currents in the nA regime reflect directly the Rydberg population and can be used as a probe with very good signal-to-noise ratio. This opens unique possibilities to probe very efficiently small spectroscopic features involving Rydberg states in thermal vapor but also might be used to stabilize lasers. By extending this concept to an array of pixel-wise arranged electrodes, high resolution spatial information on the Rydberg population can be obtained.The experiments were performed with the setup schematically shown in Fig. 1. The Rb va...

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Proof of concept for an optogalvanic gas sensor for NO based on Rydberg excitations

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“…alkali atoms [22]. We collect the emerging charges using two metallic electrodes [22][23][24] and convert this current to a voltage using a customdesigned transimpedance amplifier (TIA) [25]. The advantage of exciting a transition, which is only close to the ionization continuum and ionizes only subsequently is that we gain a much higher selectivity compared to a direct photoionization.…”