Storing interacting photons in ensembles of highly excited Rydberg atoms makes it possible to realize photon-photon gates. The efficiency of stopping and retrieving pairs of single-photon pulses in any Rydberg medium is, however, significantly influenced by their mutual interaction. The corresponding dynamical process is rather complicated due to the interaction constantly changing with the relative positions of photon pulses and the associated dissipation. Applying the numerical calculations based on first principles, we reveal the detail of such a dynamical process by showing how the interacting pulses evolve in various situations. Other important issues, such as the use of nonadiabatic passage for stopping photons and the optimal way to regenerate photons, are also investigated.
Storing interacting photons in ensembles of highly excited Rydberg atoms makes it possible to realize photon-photon gates. The efficiency of stopping and retrieving pairs of single-photon pulses in any Rydberg medium is, however, significantly influenced by their mutual interaction. The corresponding dynamical process is rather complicated due to the interaction constantly changing with the relative positions of photon pulses and the associated dissipation. Applying the numerical calculations based on first principles, we reveal the detail of such a dynamical process by showing how the interacting pulses evolve in various situations. Other important issues, such as the use of nonadiabatic passage for stopping photons and the optimal way to regenerate photons, are also investigated.
Stopping and regenerating a pair of single-photon pulses at adjacent locations in coherently prepared Rydberg atomic ensembles are significantly affected by their effective interaction mediated by Rydberg excitations, and the similar processes can differ notably from the one exhibiting the common Rydberg blockade as with the stationary propagation of multi-photon light beams in the same medium. Based on the complete dynamics, we reveal the detailed features in such processes by finding how the profiles of the involved quantum fields evolve in various situations. The findings help to determine the proper regimes for implementing photonic gates and transistors. In addition, we discuss the non-adiabatic corrections associated with quickly changing control fields, and illustrate a method that restores the photon pulses' original amplitude during their retrieval unless they are heavily damped before storage.
Strong interaction between two single photons is a long standing and important goal in quantum photonics. This would enable a new regime of nonlinear optics and unlock several applications in quantum information science, including photonic quantum gates and deterministic Bell-state measurements. In the context of quantum networks, it would be important to achieve interactions between single photons from independent photon pairs storable in quantum memories. So far, most experiments showing nonlinearities at the single-photon level have used weak classical input light. Here we demonstrate the storage and retrieval of a paired single photon emitted by an ensemble quantum memory in a strongly nonlinear medium based on highly excited Rydberg atoms. We show that nonclassical correlations between the two photons persist after retrieval from the Rydberg ensemble. Our result is an important step towards deterministic photon-photon interactions, and may enable deterministic Bell-state measurements with multimode quantum memories.
Summary form only given. Strong interaction between two single photons [1], is a long standing and important goal in quantum photonics. This would enable a new regime of nonlinear optics and unlock several applications in quantum information science, including photon-photon gates and deterministic Bell-state measurements for quantum networking. In the context of quantum networks [2], a particularly important case is to achieve strong interaction between single photons from independent photon pairs that can be stored in quantum memories. So far, most of the efforts towards nonlinear effects at the single-photon level have been realized using weak classical input light.In this contribution, we demonstrate the storage and retrieval of a paired single photon emitted by an ensemble quantum memory in a strongly nonlinear medium based on highly excited Rydberg atomic excitations [3,4]. We demonstrate that non-classical correlations between the two photons persist after the retrieval from the Rydberg ensemble. We show that our Rydberg cold atomic ensemble displays optical nonlinearity with input pulses containing few tens of photons. Our results [5], mark an important step towards deterministic photonphoton interactions, and may enable deterministic Bell-state measurement with multimode quantum memories.
Photons are very good candidates to carry quantum information due to their negligible interactions. However, photon-photon interactions are needed to process photonic quantum information. This is very useful for quantum repeater applications [1], in which the success probability of entanglement swapping can be highly increased if the Bell-state measurement is performed deterministically. In the case of photons, it requires mapping them in a non-linear medium at the single-photon level. This strong non-linearity has been demonstrated by using Rydberg atoms, which are atoms excited to states with a high principal quantum number. However, previous experiments with Rydberg atoms have been implemented with weak coherent input states of light [2, 3]. Hence, the mapping of true single photons to a medium with strong single-photon non-linearity is, so far, an outstanding goal. In this work, we have demonstrated the storage and retrieval of a paired single photon on a highly non-linear medium based on atoms excited to Rydberg levels. More recently, we have also enhanced the non-linearity of our ensemble to the single photon-level, as witnessed by the antibunching of a stored and retrieved incoming coherent field [3]. This will allow the storage of a single photon in a medium with single-photon non-linearity.
Photons are good candidates for carrying quantum information because they are very stable particles: they interact weakly with the medium and barely with each other. However, this has drawbacks when you want to process the information because, in this case, it is preferable to have photon-photon interactions. For example, for applications in quantum repeaters, such interactions would allow deterministic Bell state measurements, increasing the entanglement distribution rate between two remote nodes. Getting two photons to interact with each other efficiently requires mapping them into a nonlinear medium at the single-photon level, that is, a medium that reacts differently when it interacts with a single photon than when it does with two. Such strong nonlinearity has been demonstrated with Rydberg atoms, which are atoms excited to a state with a high principal quantum number.
In this thesis we have performed nonlinear quantum optics experiments using an ensemble of cold Rydberg atoms, where we have studied the properties of the quantum light emitted by these atoms. First, we demonstrated nonlinearities at the single-photon level. To reach this stage, we made several improvements to the previous experimental setup available in the group, of which the implementation of a dipole trap was especially relevant. We evidence quantum nonlinearity by measuring photon antibunching for the transmitted light after interacting with the Rydberg state under electromagnetically induced transparency (EIT). We also showed the generation of single photons on-demand after storing weak coherent states of light pulses as collective Rydberg excitations.
Then, we studied the variation of the light statistic throughout the output pulse after propagating through the medium as Rydberg polaritons, which are superposition states of light and Rydberg excitations. We showed that the properties at the beginning and the end of the pulse were different from those of the steady state. In particular, the light detected after the input pulse was abruptly turned off gave much stronger suppression of two-photon events. Then, we investigated how to exploit this effect to generate single photons on demand. To do this, we analyzed the quality of the single photons detected at the end of the pulse as a function of the detection probability and compared the results with those obtained by storing the input pulse as collective Rydberg excitations. We showed that the photons were generated more efficiently when increasing the detection window at the cost of deteriorating the single photons statistics.
Finally, we investigated the indistinguishability of the photons emitted by our Rydberg atomic ensemble, a crucial property for using Rydberg atoms as nodes in quantum networks. We also compared the single photons generated after storage under EIT conditions with those obtained using a two-photon Raman excitation to the Rydberg state. We measured the indistinguishability by making them interfere with weak coherent states of light in a Hong-Ou-Mandel experiment. And we showed that, although we obtained better photon statistics under EIT conditions, the indistinguishability from those obtained with Raman excitation was significantly higher.
Interacting Rydberg excitations in cold atomic ensembles can exhibit large quantum nonlinearities that enable engineering of strong interactions between individual photons. Consequently, Rydberg ensembles are a promising platform for quantum information applications and the study of more fundamental physics of few- and many-body phenomena with interacting photons. This thesis presents a series of experiments that study and exploit different regimes of Rydberg-mediated interactions. We report the realization of an efficient on-demand single-photon source. The strong long-range Rydberg interactions allow the excitation of only a single collective Rydberg state within the entire atomic medium. The collective excitation can be subsequently retrieved as a single-photon. We use this scheme to generate highly pure and highly indistinguishable photons, which are suitable for scalable quantum information applications. These photons can be compatible with other atomic systems due to their narrow bandwidth, which makes building practical hybrid quantum systems feasible. Here, we demonstrate high visibility two-photon quantum interference between our Rydberg-produced photons, and photons emitted by a remote single-trapped ion. We also study Rydberg atoms under electromagnetically induced transparency conditions, where coherent superpostions of photons and Rydberg excitations propagate through the atomic medium as lossless dark-state polaritons. In the experiment, we use the external control fields to tune the interactions to a many-body regime where we can observe resonant scattering of dark-state polaritons to lossy channels. We show that the enhanced scattering process arises as a pure three-body effect.