Dynamic decoherence control of a solid-state nuclear quadrupole qubit

We report on the application of a dynamic decoherence control pulse sequence on a nuclear quadrupole transition in $Pr^{3+}:Y_2SiO_5$ . Process tomography is used to analyse the effect of the pulse sequence. The pulse sequence was found to increase the decoherence time of the transition to over 30 seconds. Although the decoherence time was significantly increased, the population terms were found to rapidly decay on the application of the pulse sequence. The increase of this decay rate is attributed to inhomogeneity in the ensemble. Methods to circumvent this limit are discussed.Comment: 4 pages, 6 figure

Method of extending hyperfine coherence times in Pr^3+:Y_2SiO_5

In this letter we present a method for increasing the coherence time of praseodymium hyperfine ground state transitions in Pr^3+:Y_2SiO_5 by the application of a specific external magnetic field. The magnitude and angle of the external field is applied such that the Zeeman splitting of a hyperfine transition is at a critical point in three dimensions, making the first order Zeeman shift vanishingly small for the transition. This reduces the influence of the magnetic interactions between the praseodymium ions and the spins in the host lattice on the transition frequency. Using this method a phase memory time of 82ms was observed, a value two orders of magnitude greater than previously reported. It is shown that the residual dephasing is amenable quantum error correction

Methods and guidance to support MRV of livestock emissions: Methods for data collection, analysis and summary results from a pilot baseline survey for the Kenya dairy NAMA

There is increasing interest in mitigation of greenhouse gas (GHG) emissions from the dairy sector in developing countries. However, there is little prior experience with measurement, reporting and verification (MRV) of GHG emissions and emission reductions. A voluntary carbon market methodology, the Smallholder Dairy Methodology, has proposed a methodology for establishing a standardized performance baseline for a region targeted by a GHG mitigation initiative. This working paper reports the first experience of implementing a survey and analyzing survey data to establish a standardized performance baseline using survey data from central Kenya, which is a region targeted by the Kenya dairy NAMA promoted by the Government of Kenya. The publication of this report enables transparent documentation of the baseline setting process for the Kenya dairy NAMA. Data from the survey were also used to characterize dairy production in the intensive production system in Kenya’s Tier 2 GHG inventory for dairy cattle. Publication of the survey data also supports transparency of Kenya’s Tier 2 GHG inventory. The report summarizes the requirements of the Smallholder Dairy Methodology, the methods used for sampling, data collection and data analysis, the main results of data analysis and recommendations for future similar initiatives to quantify standardized baselines for dairy GHG mitigation programs. Appendices present data collection tools, summary statistics, and the data used to estimate parameters in Kenya’s Tier 2 dairy GHG inventory. Analysis of the survey data following the Smallholder Dairy Methodology’s requirements shows that the relationship between GHG intensity (kg CO2e/kg fat and protein corrected milk [FPCM]) and milk yield (kg FPCM per farm per year) can be represented by a power regression: y = 81.868x-0.436. Using this relationship, dairy initiatives in central Kenya need only to measure change in milk yield per farm per year, and can estimate GHG emissions and emission reductions using the relationship published here. The regression has an r2 of 0.43, and an uncertainty of 18.6% as measured by the root mean square error (RMSE) of the regression. The Smallholder Dairy Methodology does not require quantification of uncertainty, but other mitigation initiatives may use estimated uncertainty to discount the GHG emission reductions claimed in order to ensure conservativeness. The baseline survey is representative of 8 counties with a dairy cattle population of about 1.7 million, and data collection and analysis cost about US$ 75,000. The methodology is therefore a cost-effective way to set baselines for an initiative with large numbers of participating farms

A solid state light-matter interface at the single photon level

Coherent and reversible mapping of quantum information between light and matter is an important experimental challenge in quantum information science. In particular, it is a decisive milestone for the implementation of quantum networks and quantum repeaters. So far, quantum interfaces between light and atoms have been demonstrated with atomic gases, and with single trapped atoms in cavities. Here we demonstrate the coherent and reversible mapping of a light field with less than one photon per pulse onto an ensemble of 10 millions atoms naturally trapped in a solid. This is achieved by coherently absorbing the light field in a suitably prepared solid state atomic medium. The state of the light is mapped onto collective atomic excitations on an optical transition and stored for a pre-programmed time up of to 1 mu s before being released in a well defined spatio-temporal mode as a result of a collective interference. The coherence of the process is verified by performing an interference experiment with two stored weak pulses with a variable phase relation. Visibilities of more than 95% are obtained, which demonstrates the high coherence of the mapping process at the single photon level. In addition, we show experimentally that our interface allows one to store and retrieve light fields in multiple temporal modes. Our results represent the first observation of collective enhancement at the single photon level in a solid and open the way to multimode solid state quantum memories as a promising alternative to atomic gases.Comment: 5 pages, 5 figures, version submitted on June 27 200

Spectroscopic investigations of a Ti:Tm:LiNbO3 waveguide for photon-echo quantum memory

We report the fabrication and characterization of a Ti$^{4+}$:Tm$^{3+}$:LiNbO$_3$ optical waveguide in view of photon-echo quantum memory applications. In particular, we investigated room- and cryogenic-temperature properties via absorption, spectral hole burning, photon echo, and Stark spectroscopy. We found radiative lifetimes of 82 $\mu$s and 2.4 ms for the $^3$H$_4$ and $^3$F$_4$ levels, respectively, and a 44% branching ratio from the $^3$H$_{4}$ to the $^3$F$_4$ level. We also measured an optical coherence time of 1.6 $\mu$s for the $^3$H$_6\leftrightarrow{}^3$H$_4$, 795 nm wavelength transition, and investigated the limitation of spectral diffusion to spectral hole burning. Upon application of magnetic fields of a few hundred Gauss, we observed persistent spectral holes with lifetimes up to seconds. Furthermore, we measured a linear Stark shift of 25 kHz$\cdot$cm/V. Our results are promising for integrated, electro-optical, waveguide quantum memory for photons.Comment: 11 pages, 14 figure

Present Status and Future Programs of the n_TOF Experiment

This is an Open Access article distributed under the terms of the Creative Commons Attribution-Noncommercial License 3.0, which permits unrestricted use, distribution, and reproduction in any noncommercial medium, provided the original work is properly citedThe neutron time-of-flight facility n_TOF at CERN, Switzerland, operational since 2001, delivers neutrons using the Proton Synchrotron (PS) 20 GeV/c proton beam impinging on a lead spallation target. The facility combines a very high instantaneous neutron flux, an excellent time of flight resolution due to the distance between the experimental area and the production target (185 meters), a low intrinsic background and a wide range of neutron energies, from thermal to GeV neutrons. These characteristics provide a unique possibility to perform neutron-induced capture and fission cross-section measurements for applications in nuclear astrophysics and in nuclear reactor technology.The most relevant measurements performed up to now and foreseen for the future will be presented in this contribution. The overall efficiency of the experimental program and the range of possible measurements achievable with the construction of a second experimental area (EAR-2), vertically located 20 m on top of the n_TOF spallation target, might offer a substantial improvement in measurement sensitivities. A feasibility study of the possible realisation of the installation extension will be also presented