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

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.Peer ReviewedPostprint (published version

Deterministic superresolution with coherent states at the shot noise limit

Interference of light fields plays an important role in various high-precision measurement schemes. It has been shown that super resolving phase measurements beyond the standard coherent state limit can be obtained either by using maximally entangled multi-particle states of light or using complex detection approaches. Here we show that super resolving phase measurements at the shot noise limit can be achieved without resorting to non-classical optical states or to low-efficiency detection processes. Using robust coherent states of light, high-efficiency homodyne detection and a deterministic binarization processing technique, we show a narrowing of the interference fringes that scales with 1/Sqrt{N} where N is the mean number of photons of the coherent state. Experimentally we demonstrate a 12-fold narrowing at the shot noise limit.Comment: 5 pages, 3 figure

Detecting an Itinerant Optical Photon Twice without Destroying It

Nondestructive quantum measurements are central for quantum physics applications ranging from quantum sensing to quantum computing and quantum communication. Employing the toolbox of cavity quantum electrodynamics, we here concatenate two identical nondestructive photon detectors to repeatedly detect and track a single photon propagating through a $60\,\mathrm{m}$ long optical fiber. By demonstrating that the combined signal-to-noise ratio of the two detectors surpasses each single one by about two orders of magnitude, we experimentally verify a key practical benefit of cascaded non-demolition detectors compared to conventional absorbing devices.Comment: 8 pages, 6 figure

Transient dynamics of the quantum light retrieved from Rydberg polaritons

We study the photon statistics of weak coherent pulses propagating through a cold Rydberg atomic ensemble in the regime of Rydberg electromagnetically induced transparency. We show experimentally that the value of the second-order autocorrelation function of the transmitted light strongly depends on the position within the pulse and heavily varies during the transients of the pulse. In particular, we show that the falling edge of the transmitted pulse displays much lower values than the rest of the pulse. We derive a theoretical model that quantitatively predicts our results and explains the physical behavior involved. Finally, we use this effect to generate single photons localized within a pulse from the atomic ensemble. We show that by selecting only the last part of the transmitted pulse, the single photons show an antibunching parameter as low as 0.12 and a generation efficiency per trial larger than possible with probabilistic generation schemes with atomic ensembles.Comment: 21 pages, 11 figure

A quantum light-matter interface with Rydberg polaritons in a cold atomic ensemble

Nonlinear optics at the single-photon level enables deterministic photonphoton interaction, a long-standing goal in quantum photonics science. Besides its implication in fundamental aspects of physics, this would unlock several applications in quantum information science. A relevant example are deterministic Bell state measurements, which find a prominent application in long-distance quantum communications using quantum repeater architecture. Toward this goal, we built a highly nonlinear system based on Rydberg excited states of a cold atomic ensemble and electromagnetically induced transparency (EIT). Our work first focuses on the storage of weak coherent light pulses in the atomic ensemble analysing the resulting nonlinear response of the medium. Then we demonstrate storage and retrieval of a paired single photon by coupling the Rydberg ensemble with a second remote cold atomic based quantum memory. Our set-up is based on magneto-optically trapped 87Rb atoms cooled down to temperature of 50 to 100 μK, with a cloud density of 10 ^(10) cm^(-3). Using EIT, light pulses are slowed down, stored as Rydberg collective atomic excitation and retrieved. We characterize EIT, slow-light and light-storage on a variety of Rydberg states, from the 26S up to the 80S. Depending on the state, the typical storage efficiency observed is of the order of few percents at a storage time of ~200 ns while the typical 1/e coherence time is of ~2us. By studying the optical response at different mean probe photon number, we have examined the Rydberg induced nonlinearity in EIT, slow-light and stored-light case for different Rydberg states. In particular, we have measured the nonlinear Rydberg induced dephasing of a stored collective Rydiberg state. For few microseconds storage time we have measured nonlinear response at the order of tens of photons. Our results show that light-storage enhances the nonlinear response of the atomic ensemble when compared to the slow light case, this possibly facilitating photonic quantum information processing using Rydberg excited atoms. Finally, we have used a separated cold atomic quantum memory to generate pair of correlated single photons. One photon of the pair is stored as single collective Rydberg atomic excitation and we show that non-classical correlations between the two photons and the single-photon statistic persist after the retrieval from the Rydberg ensemble. This result marks an important step towards deterministic photon-photon interactions. At the same time, linking a quantum memory with a highly nonlinear system may enable deterministic distribution of entanglement over long-distance using quantum repeaters.Un dels objectius que la fotònica quàntica persegueix des de temps ençà és la interacció determinista entre fotons, fenomen que podria assolir-se gràcies als avanços en l'òptica no-lineal a nivell de fotó únic. Aquests avanços, a més de les seves implicacions en la física fonamental, possibilitarien diferents aplicacions de la informació quàntica. A mode d'exemple, es podrien portar a terme mesures d'estat de Bell deterministes que facilitessin un funcionament eficient de l'arquitectura dels repetidors quàntics. En aquest projecte, i seguint aquesta línia, hem construït un sistema altament no-lineal basat en estats excitats de Rydberg d'un gas d'àtoms freds i hem aplicat el fenomen de la transparència induïda electromagnèticament (EIT). En un primer moment, ens hem focalitzat en l'emmagatzematge de polsos febles de llum coherent dins el núvol atòmic i en l'anàlisi de la resposta no-lineal del medi. Després, hem demostrat el emmagatzematge i la posterior recuperació d'un fotó emparellat (que forma part d'una parella de fotons correlacionat) gràcies a l'acoblament del nostre sistema d'àtoms Rydberg amb una altra memòria quàntica basada en conjunt diferenciat d'àtoms freds. El nostre dispositiu es compon d'àtoms de 87Rb dins una trampa magneto-òptica que han estat refredats a una temperatura de 50uK amb una densitat de 10^(10) cm^(-3). Utilitzant EIT, alentim els polsos de llum, els emmagatzemem en forma d'excitacions col·lectives a nivells de Rydberg i, posteriorment, els recuperem. Després, caracteritzem la llum lenta i l'emmagatzematge de fotons. Per fer-ho, utilitzem diferents estats de Rydberg: des de el 26S fins al 80S. En funció de l'estat, l'eficiència d'emmagatzematge observada és típicament de l'ordre de 2-8% en un temps ~200 ns, mentre que el temps de coherència 1/e típic és de 2us. A través de l'estudi de la resposta òptica a diferents escales de fotons, hem examinat la no-linealitat induïda per les interaccions dipolo-dipolo entre els estats de Rydberg a l'EIT i quins són els seus efectes, tant en la llum lenta, com en l'emmagatzematge. En concret, hem mesurat el desfasament quàntic induït per les interaccions dipolo-dipolo en els estats col·lectius de Rydberg. Al emmagatzemar-los durant uns microsegons, hem pogut mesurar les respostes no-lineals al nivell de desenes de fotons. Els nostres resultats demostren que l'emmagatzematge de la llum augmenta la resposta no-lineal del sistema atòmic respecte a la mera propagació a través del núvol d'àtoms facilitant, d'aquesta forma, el processament de la informació quàntica amb l'ús d'àtoms de Rydberg excitats. Per últim,hem acoblat el nostre sistema amb una altra memòria quàntica basada en àtoms freds que és capaç de generar parells correlacionats de fotons únics. Així, hem pogut demostrar que tant les correlacions no-clàssiques entre els fotons de la parella, com l'estadística que caracteritza el fotó únic, persisteixen després de l'emmagatzematge i la posterior recuperació d'un dels fotons de la parella dins del conjunt d'àtoms en forma d'excitació col·lectiva de Rydberg. Aquest resultat és un pas important cap a la demostració de les interaccions deterministes entre fotons. A la vegada, el fet d'acoblar una memòria quàntica amb un sistema altament no-lineal podria facilitar la distribució determinista d'entrellaçament a llargues distàncies amb l'ús de repetidors quàntics.Postprint (published version

Reinforcement Learning based Omnidirectional Vision Agent for Mobile Robot Navigation

This paper presents an Omnidirectional Vision Agent able to learn to navigate a mobile robot in its working environment. The novelty of the work is the application of Reinforcement Learning paradigm to Vision Agents aiming to develop a totally autonomous system able to learn control policies by on-line learning, to deal with changing environment and to improve its performance dur- ing lifetime. SARSA(\u3bb) method is used by the Vision Agent to learn the con- trol policy for the robot. The LEM strategy is also applied to speed up learning. The knowledge acquired by one Vision Agent is then \u201ccopied\u201d to another Vision Agent in a network of cameras implementing a Distributed Vision System (DVS). By copying the knowledge the aim is both reducing learning time and exploiting the knowledge already learned. Since our prime interest was to investigate how the Vision Agent learns the knowledge by using SARSA(\u3bb) and to evaluate its performance, we carried out the experimentation in simulation. The good results obtained during the experimental phase are very encouraging to transfer all the experimentation in a real context

Time Entanglement between a Photon and a Spin Wave in a Multimode Solid-State Quantum Memory

The generation and distribution of entanglement are key resources in quantum repeater schemes. Temporally multiplexed systems offer time-bin encoding of quantum information which provides robustness against decoherence in fibers, crucial in long distance communication. Here we demonstrate the direct generation of entanglement in time between a photon and a collective spin excitation in a rare earth ion doped ensemble. We analyze the entanglement by mapping the atomic excitation onto a photonic qubit and by using time-bin qubits analyzers implemented with another doped crystal using the atomic frequency comb technique. Our results provide a solid-state source of entangled photons with embedded quantum memory. Moreover, the quality of the entanglement is high enough to enable a violation of a Bell inequality by more than two standard deviations.Comment: 8 pages and 10 figure

Storage enhanced nonlinearities in a cold atomic Rydberg ensemble: experimental data

The data show number of input/output photons under different conditions when coherent pulses of light undergo electromagnetically induced transparency (EIT) in a cold cloud of Rubidium 87 atoms via a ladder system connecting the ground state of 87-Rubidium and different Rydberg levels via (see more details in Distante et al. Phys. Rev. Lett. 117, 113001 (2016) or in the preprint https://arxiv.org/abs/1605.07478) This is the pre-analysed data from which the results in the paper are derived. The ODS file contains different sheets which correspond to Rydberg states with different principal quantum numbers The PDF contains useful information regarding the conditions of the experiment under which the data was obtained, such as the optical depth (OD) of the cloud, its dimensions, and the Rabi frequency of the coupling beam

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

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.Peer Reviewe