Storage Enhanced Nonlinearities in a Cold Atomic Rydberg Ensemble

Abstract

The combination of electromagnetically induced transparency (EIT) with the nonlinear interaction between Rydberg atoms provides an effective interaction between photons. In this paper, we investigate the storage of optical pulses as collective Rydberg atomic excitations in a cold atomic ensemble. By measuring the dynamics of the stored Rydberg polaritons, we experimentally demonstrate that storing a probe pulse as Rydberg polaritons strongly enhances the Rydberg mediated interaction compared to the slow propagation case. We show that the process is characterized by two time scales. At short storage times, we observe a strong enhancement of the interaction due to the reduction of the Rydberg polariton group velocity down to zero. For longer storage times, we observe a further, weaker enhancement dominated by Rydberg induced dephasing of the multiparticle components of the state. In this regime, we observe a non-linear dependence of the Rydberg polariton coherence time with the input photon number. Our results have direct consequences in Rydberg quantum optics and may enable the test of new theories of strongly interacting Rydberg systems.PACS numbers: 32.80. Ee,42.50.Nn,42.50.Gy The possibility to control the interaction between photons provided by highly nonlinear media is a key ingredient to the goal of quantum information processing (QIP) using photons and a unique tool to study the dynamics of many-body correlated systems [1]. Many different systems showing high nonlinear optical response at the single-photon level have been studied during the past years ranging from resonators coupled to single atoms [2-6], atomic ensembles [7], to artificial two-level atoms [8,9].A promising strategy to perform different QIP tasks using photons as carriers is the combination of electromagnetically induced transparency (EIT) [10][11][12][13] and Rydberg atoms [14] (see for example ). Using EIT one maps the state of the photons into atomic coherence in the form of Rydberg dark-state polaritons (DSPs) by means of an auxiliary coupling field. The strong Rydberg dipole-dipole (DD) interaction between neighboring excitations shifts the multiply-excited states from being resonantly coupled when these excitations are closer than a certain length called the blockade radius, r b [25]. This way, only a single excitation can be created inside of a blockaded volume of the atomic cloud (so-called superatom). This phenomenon, known as Rydberg blockade, has been used in combination with EIT to generate quantum states of light [27][28][29], single-photon switches and transistors [30,31,33,34] as well as a π phase shift controlled with single-photon level pulse [36]. These experiments typically require very high atomic densities and high-lying Rydberg states. By switching off and back on the coupling field, photons can be stored as Rydberg excitations and retrieved at later time [26,29]. In this case the DD interaction dephases the collective emission of the multiparticle components of the stored photonic states [37,38]. This feature was ...

Storing single photons emitted by a quantum memory on a highly excited Rydberg state

“…Our result shows (see Methods) N max = 68 ± 8 although the nonlinear dependence of N out with respect to N in appears at a lower number of photons. It should be noted that this result is obtained with a standard magneto-optical trap with a moderate atomic density, and that this result shows a nonlinearity 6 times stronger than the one reported in [27]. As demonstrated in [15,18,19], increasing the density of atomic ensemble with known atomic trapping techniques will allow us to achieve nonlinearity at the single-photon level, as required for applications in quantum information science.…”

“…Finally we prove the highly nonlinear response of the Rydberg ensemble. This is demonstrated by storing for 4 µs weak coherent states with varying mean number of input photon N in and measuring the mean number of photons in the retrieved pulse after storage N out , in a way presented in [27]. For a linear medium N out = T N in where T is the storage efficiency, while here we show ( Figure 5) strong nonlinear dependence.…”

“…First, a single-photon source that matches the frequency and the sub-MHz spectral bandwidth of the Rydberg excitation, and, second, the ability to store and retrieve the input single photon. The latter is of key importance for implementing high-fidelity photonic quantum operations using excited Rydberg states [22,25,26], and, in addition, it has been shown to be beneficial to enhance the nonlinear response of this kind of systems [27]. While storage and retrieval of a single photon transmitted between remote atomic ensembles has been achieved in ground states [28][29][30][31][32] or low-lying Rydberg states [41], storing it in a highly nonlinear Rydberg ensemble presents additional experimental challenges, such as high sensitivity to stray fields, stronger motional-induced dephasing due to the large wavelength mismatch between the single photon and the coupling laser, weak transition oscillator strength requiring higher intensity of the coupling beam, as well as strong focusing of the single-photon needed to achieve non-linearity at low light power.…”

Creation and detection of photonic molecules in Rydberg gases

“…The van der Waals-type interactions between Rydberg states [1] in a gas of three-level atoms can be used to create strong photon-photon interactions for light fields coupling to the atomic medium in an scheme of electromagnetically induced transparency (EIT) [2,3]. Moreover, due to the long-range nature of the Rydberg-Rydberg interactions, also the photon-photon interactions are long-range which makes this setup a promising candidate for creating and analyzing interesting many-body states with applications ranging from quantum computation [4][5][6][7][8] to quantum simulations [9][10][11][12][13].…”

Single-photon source based on Rydberg exciton blockade

“…Rydberg atoms have been used in quantum information applications such as atomic [1] and photonic [3,4,2] quantum computation, as well as for single-photon sources [5,6,7,8]. Furthermore Rydberg atoms have been used in the study of strongly correlated plasmas [9], in quantum non-linear optics [10,11], in ultracold chemistry (e.g. Rydberg molecules) [12], and in the study of exotic quantum phases [13,14] and many-body entangled states [15,16].…”