Large conditional single-photon cross-phase modulation

Deterministic optical quantum logic requires a nonlinear quantum process that alters the phase of a quantum optical state by $\pi$ through interaction with only one photon. Here, we demonstrate a large conditional cross-phase modulation between a signal field, stored inside an atomic quantum memory, and a control photon that traverses a high-finesse optical cavity containing the atomic memory. This approach avoids fundamental limitations associated with multimode effects for traveling optical photons. We measure a conditional cross-phase shift of up to $\pi/3$ between the retrieved signal and control photons, and confirm deterministic entanglement between the signal and control modes by extracting a positive concurrence. With a moderate improvement in cavity finesse, our system can reach a coherent phase shift of $\pi$ at low loss, enabling deterministic and universal photonic quantum logic.Comment: 22 pages, 5 figures, 1 table, includes supplementary informatio

Partially Nondestructive Continuous Detection of Individual Traveling Optical Photons

We report the continuous and partially nondestructive measurement of optical photons. For a weak light pulse traveling through a slow-light optical medium (signal), the associated atomic-excitation component is detected by another light beam (probe) with the aid of an optical cavity. We observe strong correlations of $g^{(2)}_{sp}=4.4(5)$ between the transmitted signal and probe photons. The observed (intrinsic) conditional nondestructive quantum efficiency ranges between 13% and 1% (65% and 5%) for a signal transmission range of 2% to 35%, at a typical time resolution of 2.5 $\mu$s. The maximal observed (intrinsic) device nondestructive quantum efficiency, defined as the product of the conditional nondestructive quantum efficiency and the signal transmission, is 0.5% (2.4%). The normalized cross-correlation function violates the Cauchy-Schwarz inequality, confirming the non-classical character of the correlations

Resonator-Aided Single-Atom Detection on a Microfabricated Chip

We use an optical cavity to detect single atoms magnetically trapped on an atom chip. We implement the detection using both fluorescence into the cavity and reduction in cavity transmission due to the presence of atoms. In fluorescence, we register 2.0(2) photon counts per atom, which allows us to detect single atoms with 75% efficiency in 250 microseconds. In absorption, we measure transmission attenuation of 3.3(3)% per atom, which allows us to count small numbers of atoms with a resolution of about 1 atom.Comment: 4.1 pages, 5 figures, and submitted to Physical Review Letter

Quantum network of neutral atom clocks

We propose a protocol for creating a fully entangled GHZ-type state of neutral atoms in spatially separated optical atomic clocks. In our scheme, local operations make use of the strong dipole-dipole interaction between Rydberg excitations, which give rise to fast and reliable quantum operations involving all atoms in the ensemble. The necessary entanglement between distant ensembles is mediated by single-photon quantum channels and collectively enhanced light-matter couplings. These techniques can be used to create the recently proposed quantum clock network based on neutral atom optical clocks. We specifically analyze a possible realization of this scheme using neutral Yb ensembles.Comment: 13 pages, 11 figure

Technologies for trapped-ion quantum information systems

Scaling-up from prototype systems to dense arrays of ions on chip, or vast networks of ions connected by photonic channels, will require developing entirely new technologies that combine miniaturized ion trapping systems with devices to capture, transmit and detect light, while refining how ions are confined and controlled. Building a cohesive ion system from such diverse parts involves many challenges, including navigating materials incompatibilities and undesired coupling between elements. Here, we review our recent efforts to create scalable ion systems incorporating unconventional materials such as graphene and indium tin oxide, integrating devices like optical fibers and mirrors, and exploring alternative ion loading and trapping techniques.Comment: 19 pages, 18 figure

All-Optical Switch and Transistor Gated by One Stored Photon

The realization of an all-optical transistor where one 'gate' photon controls a 'source' light beam, is a long-standing goal in optics. By stopping a light pulse in an atomic ensemble contained inside an optical resonator, we realize a device in which one stored gate photon controls the resonator transmission of subsequently applied source photons. A weak gate pulse induces bimodal transmission distribution, corresponding to zero and one gate photons. One stored gate photon produces fivefold source attenuation, and can be retrieved from the atomic ensemble after switching more than one source photon. Without retrieval, one stored gate photon can switch several hundred source photons. With improved storage and retrieval efficiency, our work may enable various new applications, including photonic quantum gates, and deterministic multiphoton entanglement.Comment: 20 pages, 5 figures. Published in Science. Includes supplemental informatio

Geographical Distribution of Elderly People in Croatia

The authors outlined the geographical distribution of individuals displaying longevity in the Republic of Croatia. Elderly people, aged 80 years and older, have been the subject of this study and were viewed in several aspects including the number of elderly people and age-specific mortality rate by districts. Data for the years 1981 and 1991 were reviewed. In 1981 there were 73,052 (1.6%) persons aged 80 or older. Ten years later in 1991 their number had increased to 107,256, which was 2.2% of the whole population. Most of the elderly people live on the islands, in the district of Dubrovnik and in Lika, which is in the continental part of Croatia. There are more women than men among those aged 80 years and older. Age-specific mortality rate in 1981 in Croatia was 170 and in 1991 151 per 1,000 elderly people. In women the rate was 162 in 1981 and 141 in 1991, per 1,000 elderly people. The death rate was higher in men; in 1981 it was 201 and in 1991, 172 per 1,000 elderly people. We can see that the specific mortality rate had fallen in 1991 compared to 1981. The age specific mortality rate varies from district to district. In 1991 the lowest, 110 per 1,000, was in Lika, and the highest in the districts of Vara`din (182 per 1,000), Bjelovar (178 per 1,000) and Zagorje (175 per 1,000). The death rate was higher amongst elderly men (172.31 per 1,000) than elderly women (141.65 per 1,000). The smallest number of those aged 80 years and older with a high death rate is found in Slavonia. The opposite – a high number of elderly people and a low specific mortality rate – can be seen in the district of Lika. On the islands the number of elderly people is high, especially women, and surprisingly, the specific mortality rate is relatively high as well

Patterns of regional diversity in political elites' attitudes

This chapter examines whether differences in attitudes toward the process of EU integration among members of political elites in various European countries are patterned and to what extent common regional, economic, political, and cultural characteristics of certain country groups influence these attitudes. Results show elites from Southern Europe to be the main proponents of further EU integration, while Eastern European elites are the most cautious. Variables with the strongest influence are economic development (measured by GDP per capita), the prevalent religious denomination (respondents from predominantly Protestant countries are less ready to support stronger EU integration than those from mostly Catholic countries), ethnic homogeneity (increasing level of homogeneity reduces elites' orientation towards stronger EU integration), and the existence of separatist experience (elites from countries with recent independence by secession are less oriented toward EU integration than those from countries without secession problems)

Preparation and Characterization of Some Sodium-, Rubidium-, Cesium- and Ammonium-Oxodiperoxooxalato-Molybdates (VI) and Tungstates (VI)

Potassium derivatives of oxodiperoxooxalato- molybdates and tungstates: were prepared before1>2 studied by infrared Raman3 and X-ray methods4•5 .The crystal structure of corresponding molybdate with literature survey was published recently4