Improving single-photon sources with Stark tuning

We investigate the use of the Stark shift in atomlike systems in order to control the interaction with a high-Q/V microcavity. By applying a Stark shift pulse to a single atomlike system, in order to affect and control its detuning from a cavity resonance, the cavity QED interaction can be carefully controlled so as to allow stochastic pumping of the emitting state without causing random timing jitter in the output photon. Using a quantum trajectory approach, we conduct simulations that show this technique is capable of producing indistinguishable single photons that exhibit complete Hong-Ou-Mandel interference. Furthermore, Stark tuning control allows for the generation of arbitrary pulse envelopes. We demonstrate this by showing that a simple asymmetric Stark shifting pulse can lead to the emission of symmetric Gaussian single-photon pulse envelopes, rather than the usual exponential decay. These Gaussian pulses also exhibit complete Hong-Ou-Mandel interference. The use of Stark shifting in solid-state systems could ultimately provide the cheap miniature high quality single-photon sources that are currently required for applications such as all-optical quantum computing

Coherent Control of Stationary Light Pulses

We present a detailed analysis of the recently demonstrated technique to generate quasi-stationary pulses of light [M. Bajcsy {\it et al.}, Nature (London) \textbf{426}, 638 (2003)] based on electromagnetically induced transparency. We show that the use of counter-propagating control fields to retrieve a light pulse, previously stored in a collective atomic Raman excitation, leads to quasi-stationary light field that undergoes a slow diffusive spread. The underlying physics of this process is identified as pulse matching of probe and control fields. We then show that spatially modulated control-field amplitudes allow us to coherently manipulate and compress the spatial shape of the stationary light pulse. These techniques can provide valuable tools for quantum nonlinear optics and quantum information processing.Comment: 27 pages, 10 figure

Light storage protocols in Tm:YAG

We present two quantum memory protocols for solids: A stopped light approach based on spectral hole burning and the storage in an atomic frequency comb. These procedures are well adapted to the rare-earth ion doped crystals. We carefully clarify the critical steps of both. On one side, we show that the slowing-down due to hole-burning is sufficient to produce a complete mapping of field into the atomic system. On the other side, we explain the storage and retrieval mechanism of the Atomic Frequency Comb protocol. This two important stages are implemented experimentally in Tm$^{3+}$- doped yttrium-aluminum-garnet crystal

Runaway evaporation for optically dressed atoms

Forced evaporative cooling in a far-off-resonance optical dipole trap is proved to be an efficient method to produce fermionic- or bosonic-degenerated gases. However in most of the experiences, the reduction of the potential height occurs with a diminution of the collision elastic rate. Taking advantage of a long-living excited state, like in two-electron atoms, I propose a new scheme, based on an optical knife, where the forced evaporation can be driven independently of the trap confinement. In this context, the runaway regime might be achieved leading to a substantial improvement of the cooling efficiency. The comparison with the different methods for forced evaporation is discussed in the presence or not of three-body recombination losses

Towards high-speed optical quantum memories

Quantum memories, capable of controllably storing and releasing a photon, are a crucial component for quantum computers and quantum communications. So far, quantum memories have operated with bandwidths that limit data rates to MHz. Here we report the coherent storage and retrieval of sub-nanosecond low intensity light pulses with spectral bandwidths exceeding 1 GHz in cesium vapor. The novel memory interaction takes place via a far off-resonant two-photon transition in which the memory bandwidth is dynamically generated by a strong control field. This allows for an increase in data rates by a factor of almost 1000 compared to existing quantum memories. The memory works with a total efficiency of 15% and its coherence is demonstrated by directly interfering the stored and retrieved pulses. Coherence times in hot atomic vapors are on the order of microsecond - the expected storage time limit for this memory.Comment: 13 pages, 5 figure

Quantum teleportation between light and matter

Quantum teleportation is an important ingredient in distributed quantum networks, and can also serve as an elementary operation in quantum computers. Teleportation was first demonstrated as a transfer of a quantum state of light onto another light beam; later developments used optical relays and demonstrated entanglement swapping for continuous variables. The teleportation of a quantum state between two single material particles (trapped ions) has now also been achieved. Here we demonstrate teleportation between objects of a different nature - light and matter, which respectively represent 'flying' and 'stationary' media. A quantum state encoded in a light pulse is teleported onto a macroscopic object (an atomic ensemble containing 10^12 caesium atoms). Deterministic teleportation is achieved for sets of coherent states with mean photon number (n) up to a few hundred. The fidelities are 0.58+-0.02 for n=20 and 0.60+-0.02 for n=5 - higher than any classical state transfer can possibly achieve. Besides being of fundamental interest, teleportation using a macroscopic atomic ensemble is relevant for the practical implementation of a quantum repeater. An important factor for the implementation of quantum networks is the teleportation distance between transmitter and receiver; this is 0.5 metres in the present experiment. As our experiment uses propagating light to achieve the entanglement of light and atoms required for teleportation, the present approach should be scalable to longer distances.Comment: 23 pages, 8 figures, incl. supplementary informatio

Efficient and long-lived quantum memory with cold atoms inside a ring cavity

Quantum memories are regarded as one of the fundamental building blocks of linear-optical quantum computation and long-distance quantum communication. A long standing goal to realize scalable quantum information processing is to build a long-lived and efficient quantum memory. There have been significant efforts distributed towards this goal. However, either efficient but short-lived or long-lived but inefficient quantum memories have been demonstrated so far. Here we report a high-performance quantum memory in which long lifetime and high retrieval efficiency meet for the first time. By placing a ring cavity around an atomic ensemble, employing a pair of clock states, creating a long-wavelength spin wave, and arranging the setup in the gravitational direction, we realize a quantum memory with an intrinsic spin wave to photon conversion efficiency of 73(2)% together with a storage lifetime of 3.2(1) ms. This realization provides an essential tool towards scalable linear-optical quantum information processing.Comment: 6 pages, 4 figure

Delay of Squeezing and Entanglement using Electromagnetically Induced Transparency in a Vapour Cell

We demonstrate experimentally the delay of squeezed light and entanglement using Electromagnetically Induced Transparency (EIT) in a rubidium vapour cell. We perform quadrature amplitude measurements of the probe field and find no appreciable excess noise from the EIT process. From an input squeezing of 3.1 dB at low sideband frequencies, we observed the survival of 2 dB of squeezing at the EIT output. By splitting the squeezed light on a beam-splitter, we generated biased entanglement between two beams. We transmit one of the entangled beams through the EIT cell and correlate the quantum statistics of this beam with its entangled counterpart. We experimentally observed a 2 $\mu$s delay of the biased entanglement and obtained a preserved degree of wavefunction inseparability of 0.71, below the unity value for separable states.Comment: 8 pages, 5 figure

Prévalence des événements indésirables associés aux soins en ambulatoire

International audienceContexte Selon l'étude PHARE, 2,7 % des médicaments prescrits en médecine générale entraînaient un événement indésirable lié aux soins (EIS), soit environ 2 événements par jour et par médecin1. La revue de S.-V. Taché et al. estimait la prévalence des EIS en soins ambulatoires à 12,8 %2. Pour estimer la prévalence des EIS en soins ambulatoires, il faudrait également intégrer les EIS découverts aux urgences et qui ont entraîné des hospitalisations. Objectifs Estimer la prévalence des événements indésirables associés aux soins ambulatoires. Étudier les différentes méthodes des études de prévalence et leur influence sur les résultats

Factors contributing to patient safety incidents in primary care: a descriptive analysis of patient safety incidents in a French study using CADYA (categorization of errors in primary care)

Abstract Background Patient safety incidents (PSIs) frequently occur in primary care and are often considered to be preventable. Better knowledge of factors contributing to PSIs is required to build safer care. The aim of this work was to describe the underlying factors, specifically the human factors, that are associated with PSIs in primary care using CADYA (“CAtégorisation des DYsfonctionnements en Ambulatoire” or “Categorization of Errors in Primary Care”). Methods We followed a mixed method with content analysis and coding in CADYA of PSIs reported in the ESPRIT study, a French cross-sectional survey of primary care. For each incident, a main contributing factor (MD) and, if applicable, a secondary contributing factor (SD) were identified. Several descriptive keywords from an incremental glossary have been suggested to describe each identified human factor (attitudes or behaviours). A descriptive statistical analysis was then conducted. Results Among the 482 PSIs reported in the ESPRIT study, from 13,438 acts reported by 127 participating general practitioners (GPs), we identified 590 contributing factors (482 MDs and 178 SDs). Overall, 35% were related to the care process, 30% to human factors, 22% to the healthcare environment and 13% to technical factors. The contributing factors, in decreasing order of frequency, were communication errors (13.7%), human factors related to healthcare providers (12.9%) and human factors related to patients (12.9%). The human factors were mainly related to ‘lack of attention’, ‘stress’, ‘anger’ and ‘fatigue’. Conclusions Our results tend to prove that human factors are often involved in PSIs in primary care, with GPs and patients being equally responsible. Beyond the identification of communication errors, often found in other international research, we have described the attitudes and behaviours contributing to unsafe care. Further research exploring the links between working conditions and human factors is required