Flexible terabit/s Nyquist-WDM super-channels using a gain-switched comb source

Terabit/s super-channels are likely to become the standard for next-generation optical networks and optical interconnects. A particularly promising approach exploits optical frequency combs for super-channel generation. We show that injection locking of a gain-switched laser diode can be used to generate frequency combs that are particularly well suited for terabit/s super-channel transmission. This approach stands out due to its extraordinary stability and flexibility in tuning both center wavelength and line spacing. We perform a series of transmission experiments using different comb line spacings and modulation formats. Using 9 comb lines and 16QAM signaling, an aggregate line rate (net data rate) of 1.296 Tbit/s (1.109 Tbit/s) is achieved for transmission over 150 km of standard single mode fiber (SSMF) using a spectral bandwidth of 166.5 GHz, which corresponds to a (net) spectral efficiency of 7.8 bit/s/Hz (6.7 bit/s/Hz). The line rate (net data rate) can be boosted to 2.112 Tbit/s (1.867 Tbit/s) for transmission over 300 km of SSMF by using a bandwidth of 300 GHz and QPSK modulation on the weaker carriers. For the reported net data rates and spectral efficiencies, we assume a variable overhead of either 7\% or 20\% for forward- error correction depending on the individual sub-channel quality after fiber transmission

Micromotion-enabled improvement of quantum logic gates with trapped ions

The micromotion of ion crystals confined in Paul traps is usually considered an inconvenient nuisance, and is thus typically minimised in high-precision experiments such as high-fidelity quantum gates for quantum infor- mation processing. In this work, we introduce a particular scheme where this behavior can be reversed, making micromotion beneficial for quantum information processing. We show that using laser-driven micromotion side- bands, it is possible to engineer state-dependent dipole forces with a reduced effect of off-resonant couplings to the carrier transition. This allows one, in a certain parameter regime, to devise entangling gate schemes based on geometric phase gates with both a higher speed and a lower error, which is attractive in light of current efforts towards fault-tolerant quantum information processing. We discuss the prospects of reaching the parameters required to observe this micromotion-enabled improvement in experiments with current and future trap designs

Can different quantum state vectors correspond to the same physical state? An experimental test

A century after the development of quantum theory, the interpretation of a quantum state is still discussed. If a physicist claims to have produced a system with a particular quantum state vector, does this represent directly a physical property of the system, or is the state vector merely a summary of the physicist's information about the system? Assume that a state vector corresponds to a probability distribution over possible values of an unknown physical or 'ontic' state. Then, a recent no-go theorem shows that distinct state vectors with overlapping distributions lead to predictions different from quantum theory. We report an experimental test of these predictions using trapped ions. Within experimental error, the results confirm quantum theory. We analyse which kinds of models are ruled out

Dwelling as the life basis of Ukrainians

На прикладі містечок Батурина, Глухова, Борзни та Кролевця у статті розглядається інтер’єр жител населення Чернігово-Сіверщини (друга половина ХVІІІ – середина ХІХ ст.). На основі значного описового матеріалу, стосовно звичаїв і побуту українців, який накопичився в середині і особливо в другій половині ХІХ ст. можна зробити науково-вивірені узагальнення з приводу порівняльної характеристики українців і росіян. Дослідженням цієї теми займалися М. Маркевич, І. Срезнєвський, П. Куліш та ін. Значний внесок до вивчення даної проблематики належить історику М. Костомарову, який виокремив український культурний і традиційно-буттєвий комплекс із загальноросійського, що утрадиційнилось як спільне за понад сторіччя співжиття в рамках однієї імперії. Також у даній статті характеризується поділ оселі на умовні частини та визначаються основні сакральні центри хати. Автор наголошує на глибокому символічному обрядово-ритуальному значенні, яке українці надавали всім предметам хатнього інтер’єру та наголошує на ліричній прив’язаності їх до місця свого проживання.На примере городков Батурина, Глухова, Борзны и Кролевца в статье рассматривается интерьер жилищ населения Чернигово-Северщины во второй половине XVIII – середине XIX вв. На основе материалов, описывающих украинские обычаи и быт, накопившихся в средине, а особенно во второй половине XIX в., можно сделать обобщения по поводу сравнительной характеристики украинцев и русских. Исследованием этой темы занимались Н. Маркевич, И. Срезневский, П. Кулиш и другие ученые. Значительный вклад в изучение данной проблематики принадлежит историку Н. Костомарову, который выделил украинский культурный и традиционно- бытейный комплекс из общероссийского, которые сосуществовали более столетия в границах одной империи. Также в данной статье характеризируется разделение жилища на условные части и определяются основные сакральные центры дома (хаты). Автор отмечает глубокое символическое ритуально-обрядовое значение, которое украинцы придавали всем предметам домашнего интерьера, а также подчеркивает лирическую привязанность населения к месту его проживания.Article deals with the interior of dwellings in Chernihiv-Siverskyi region (in the 2nd half of the ХVІІІ – 1st half of the ХІХ cent.). On the example of towns Baturyn, Glukhiv, Borzna and Krolevets the article deals with the house interiors of the population of Chernihovo-Sivershchyna (the second half of the XVIII – mid. XIX cent.). The analysis is based on considerable descriptive material concerning Ukrainian customs and way of life that has accumulated in the middle and especially in the second half of the XIX cent. and led to scientific adjusted conclusion about the comparative characteristics of Ukrainians and Russians. This topic was researched by M. Markevych, I. Sreznevskyi, P. Kulish and others. A significant contribution to the study of this subject belongs to historian M. Kostomarov, who singled Ukrainian cultural and traditional existential complex out of all-Russian complex, that was considered unified for more than three centuries of coexistence within a single empire. Also, this article characterizes the division of the house on special parts and identifies the main sacred centres of the house. The attention is given to the fact that the Ukrainian housing is associated with many beliefs and rituals. It indicates that the dwelling-house reflects not only people’s ideological and artistic heritage, but also a pragmatic idea. After all, the house seemed a model of nature and the universe, which protected both physically and spiritually. We know that house was not only a place where the family spent most of its life, but it was the family hearth around which ancient and beautiful traditions were preserved. The author emphasizes the deep symbolic ritual value that Ukrainians gave to all subjects of domestic interior and the lyrical attachment to their place of residence. After all, the house had a kind of sacred meaning for its tenants, that is why, to the house and all domestic things people gave some philosophical content. Complexity of representations of the world for humans began from the dwelling and was a dominant through all life. It is revealed that a Ukrainian house with its aesthetic appearance and its interior in particular, is an important factor in the understanding of the Ukrainian people and makes the character unique, and one that is very different from the characteristics of other nations. The author concluded that this topic needs a further study

A quantum information processor with trapped ions

Quantum computers hold the promise to solve certain problems exponentially faster than their classical counterparts. Trapped atomic ions are among the physical systems in which building such a computing device seems viable. In this work we present a small-scale quantum information processor based on a string of [superscript 40]Ca[superscript +] ions confined in a macroscopic linear Paul trap. We review our set of operations which includes non-coherent operations allowing us to realize arbitrary Markovian processes. In order to build a larger quantum information processor it is mandatory to reduce the error rate of the available operations which is only possible if the physics of the noise processes is well understood. We identify the dominant noise sources in our system and discuss their effects on different algorithms. Finally we demonstrate how our entire set of operations can be used to facilitate the implementation of algorithms by examples of the quantum Fourier transform and the quantum order finding algorithm.United States. Office of the Director of National Intelligence (United States. Army Research Office Grant W911NF-10-1-0284

Permutationally invariant state reconstruction

Feasible tomography schemes for large particle numbers must possess, besides an appropriate data acquisition protocol, also an efficient way to reconstruct the density operator from the observed finite data set. Since state reconstruction typically requires the solution of a non-linear large-scale optimization problem, this is a major challenge in the design of scalable tomography schemes. Here we present an efficient state reconstruction scheme for permutationally invariant quantum state tomography. It works for all common state-of-the-art reconstruction principles, including, in particular, maximum likelihood and least squares methods, which are the preferred choices in today's experiments. This high efficiency is achieved by greatly reducing the dimensionality of the problem employing a particular representation of permutationally invariant states known from spin coupling combined with convex optimization, which has clear advantages regarding speed, control and accuracy in comparison to commonly employed numerical routines. First prototype implementations easily allow reconstruction of a state of 20 qubits in a few minutes on a standard computer.Comment: 25 pages, 4 figues, 2 table