Helical spin textures in dipolar Bose-Einstein condensates

We numerically study elongated helical spin textures in ferromagnetic spin-1 Bose-Einstein condensates subject to dipolar interparticle forces. Stationary states of the Gross-Pitaevskii equation are solved and analyzed for various values of the helical wave vector and dipolar coupling strength. We find two helical spin textures which differ by the nature of their topological defects. The spin structure hosting a pair of Mermin-Ho vortices with opposite mass flows and aligned spin currents is stabilized for a nonzero value of the helical wave vector.Comment: 7 pages, 6 figure

Elementary excitations in dipolar spin-1 Bose-Einstein condensates

We have numerically solved the low-energy excitation spectra of ferromagnetic Bose-Einstein condensates subject to dipolar interparticle interactions. The system is assumed to be harmonically confined by purely optical means, thereby maintaining the spin degree of freedom of the condensate order parameter. Using a zero-temperature spin-1 model, we solve the Bogoliubov excitations for different spin textures, including a spin-vortex state in the absence of external magnetic fields and a rapidly rotating polarized spin texture in a finite homogeneous field. In particular, we consider the effect of dipolar interactions on excitations characteristic of ferromagnetic condensates. The energies of spin waves and magnetic quadrupole modes are found to increase rapidly with the dipolar coupling strength, whereas the energies of density oscillations change only slightly.Comment: 7 pages, 4 figure

From Rotating Atomic Rings to Quantum Hall States

Considerable efforts are currently devoted to the preparation of ultracold neutral atoms in the emblematic strongly correlated quantum Hall regime. The routes followed so far essentially rely on thermodynamics, i.e. imposing the proper Hamiltonian and cooling the system towards its ground state. In rapidly rotating 2D harmonic traps the role of the transverse magnetic field is played by the angular velocity. For particle numbers significantly larger than unity, the required angular momentum is very large and it can be obtained only for spinning frequencies extremely near to the deconfinement limit; consequently, the required control on experimental parameters turns out to be far too stringent. Here we propose to follow instead a dynamic path starting from the gas confined in a rotating ring. The large moment of inertia of the fluid facilitates the access to states with a large angular momentum, corresponding to a giant vortex. The initial ring-shaped trapping potential is then adiabatically transformed into a harmonic confinement, which brings the interacting atomic gas in the desired quantum Hall regime. We provide clear numerical evidence that for a relatively broad range of initial angular frequencies, the giant vortex state is adiabatically connected to the bosonic $\nu=1/2$ Laughlin state, and we discuss the scaling to many particles.Comment: 9 pages, 5 figure

Stabilization and pumping of giant vortices in dilute Bose-Einstein condensates

Recently, it was shown that giant vortices with arbitrarily large quantum numbers can possibly be created in dilute Bose-Einstein condensates by cyclically pumping vorticity into the condensate. However, multiply quantized vortices are typically dynamically unstable in harmonically trapped nonrotated condensates, which poses a serious challenge to the vortex pump procedure. In this theoretical study, we investigate how the giant vortices can be stabilized by the application of a Gaussian potential peak along the vortex core. We find that achieving dynamical stability is feasible up to high quantum numbers. To demonstrate the efficiency of the stabilization method, we simulate the adiabatic creation of an unsplit 20-quantum vortex with the vortex pump.Comment: 8 pages, 6 figures; to be published in J. Low Temp. Phys., online publication available at http://dx.doi.org/10.1007/s10909-010-0216-

Exotic vortex lattices in two-species Bose-Einstein condensates

We numerically investigate vortex lattices in rotating two-component Bose-Einstein condensates in which the two components have unequal atomic masses and interact attractively with each other. For sufficiently strong attraction, the system is found to exhibit exotic ground-state structures in a harmonic trap, such as lattices having a square geometry or consisting of two-quantum vortices. The obtained states satisfy the Feynman relation, and they can be realized with current experimental techniques.Comment: 7 pages, 4 color figures; the content of v2 is identical to the published articl

Dynamics of Vortex Dipoles in Confined Bose-Einstein Condensates

We present a systematic theoretical analysis of the motion of a pair of straight counter-rotating vortex lines within a trapped Bose-Einstein condensate. We introduce the dynamical equations of motion, identify the associated conserved quantities, and illustrate the integrability of the ensuing dynamics. The system possesses a stationary equilibrium as a special case in a class of exact solutions that consist of rotating guiding-center equilibria about which the vortex lines execute periodic motion; thus, the generic two-vortex motion can be classified as quasi-periodic. We conclude with an analysis of the linear and nonlinear stability of these stationary and rotating equilibria.Comment: 8 pages, 3 figures, to appear in Phys. Lett.

Optimized Dynamical Decoupling in a Model Quantum Memory

We present experimental measurements on a model quantum system that demonstrate our ability to dramatically suppress qubit error rates by the application of optimized dynamical decoupling pulse sequences in a variety of experimentally relevant noise environments. We provide the first demonstration of an analytically derived pulse sequence developed by Uhrig, and find novel sequences through active, real-time experimental feedback. These new sequences are specially tailored to maximize error suppression without the need for a priori knowledge of the ambient noise environment. We compare these sequences against the Uhrig sequence, and the well established CPMG-style spin echo, demonstrating that our locally optimized pulse sequences outperform all others under test. Numerical simulations show that our locally optimized pulse sequences are capable of suppressing errors by orders of magnitude over other existing sequences. Our work includes the extension of a treatment to predict qubit decoherence under realistic conditions, including the use of finite-duration, square $\pi$ pulses, yielding strong agreement between experimental data and theory for arbitrary pulse sequences. These results demonstrate the robustness of qubit memory error suppression through dynamical decoupling techniques across a variety of qubit technologies.Comment: Subject to press embarg

EnSaCo - TEKES Green Mining projekti 2013 - 2015:loppuraportti - 30.10.2015

abstract This report describes the tests done in TEKES Green Mining program research project called Energy and Chemicals Saving Flotation Concentration (EnSaCo). The report presents the action, ie. the theory and practical work in accordance with the project objectives. During the project many different kind of ore and side rock types were tested using laboratory scale mechanical and flotation tests. Outcomes from several tests during this project are presented as a pictures and tables in appendixes (38 pieces). In introduction of this report the project partners and objectives are presented, the present state of comminution and development requirements are described and also the theory of micro cracks formation in material and their effect on material breakage are gone through. In Research material paragraph the companies where the studied material was got are shortly presented, geology and mineralogy of the ore deposits are described and the ore and the rock samples are presented. Standard tests leading principles are shortly described and new Geometallurgical Comminution Test and devices used for the researched material tests are gathered the in Experimental devices and methods section. In following paragraphs the devices and methods for analyzing samples of this project are presented, like FESEM in electronic microscopy. Moreover the software for monitoring, studying and managing measurement data of experiments and modelling the enrichment process are presented. Execution of experiments describes how analyses and tests of this research are done in practice, followed by the results and conclusions in Results and discussion. At the end of this report theory and all test results are summarized in Conclusion paragraph. As a result of this project a lot of information and data from researched material has been collected and obtained from literature and experimentation. Most of the practical test results verify the theoretical behaviour, nature and substance of material. Outcome of mineralogical study of ore is that from researched material can be said that texture characteristics affect mechanical behaviour of rock (for example direction of schistosity and occurrence of hard minerals affect fractional strength). LIF and hyperspectral imaging methods gives information about rock and it can be analyzed and further processed. Handled data can be utilized in controlling and managing grinding processes, for example in sorting stage. In this research, preliminary tests of laboratory grinding mill monitoring have been done. In tests have been occurred that grinding efficiency of the rod mill can be measured and monitored with the help of energy consumption, vibrations and voice. Grinding of the material in batch grinding was observed by acceleration sensors data and sieve analyses. Combining the measuring parameters data it is possible to observe and control the behaviour of grinding process. In this project the effect of feed amount and fine fraction on flotation results has been researched by flotation tests. From gold ore results it can be concluded that the best outcome was when process feed was 38 t/h. In both researched ore cases the fine fraction contains plenty of valuable minerals. In flotation process especially floatability of the fine material fraction should be taken into account. Oulu Mining School minipilot enrichment process has been modelled using HSC Sim software. Models have been done for steady-state and dynamic process behaviour and they based on experimental operations. Using these models the behaviour of process can be studied and they can be used as an aid tools for controlling the process.Tiivistelmä Tässä raportissa kerrotaan TEKES Green Mining -ohjelman tutkimusprojektin Energiaa ja kemikaaleja säästävä vaahdotusrikastus, Energy and Chemicals Saving Flotation Concentration (EnSaCo) tutkimuksista. Raportissa esitellään projektin tavoitteiden mukaisia toimia eli teoriaa ja käytännön tekemistä. Projektin aikana toteutettiin monentyyppistä malmien ja sivukivien testaamista laboratoriomitassa mekaanisten testien ja vaahdotuskokeiden avulla. Projektissa tehtyjen monien erilaisten testaamisten tuloksia on esitetty kuvina ja taulukoina liitteissä (38 kpl). Johdannossa esitellään projektin osapuolet ja tavoitteet, kerrotaan hienonnuksen nykytilasta ja kehittämistarpeesta sekä käydään läpi teoriaa mikrohalkeamien muodostumisesta materiaaliin ja niiden vaikutuksesta materiaalin rikkoutumiseen. Tutkittava materiaali -kappaleessa esitellään lyhyesti yritykset, joista projektin tutkittavat materiaalit saatiin, kerrotaan malmiesiintymien geologiasta ja mineralogiasta sekä käydään läpi tutkimuksissa käytettävät malmi- ja kivinäytteet. Koelaitteet ja –menetelmät -osiossa esitellään tutkittavien materiaalien testauksissa käytettävien laitteiden lisäksi lyhyesti standardimenetelmien pääperiaatteita ja esitellään uusi geometallurginen hienonnustesti. Seuraavissa kappaleissa esitellään projektissa tehtyjen näytteiden analysointiin käytetyt laitteet ja menetelmät, kuten elektronimikroskopiaan käytetty FESEM, ja esitellään ohjelmistot, joilla tarkasteltiin ja käsiteltiin saatuja mittaustietoja sekä mallinnettiin rikastusprosessia. Kokeiden suorituksessa käydään läpi miten tutkimuksessa tehdyt analyysit ja testaukset käytännössä tehtiin, jonka jälkeen tulokset ja johtopäätökset kerrotaan Tulokset ja niiden tarkastelu -kappaleessa. Raportin lopuksi teoria ja kaikkien kokeiden tulokset kootaan yhteen Johtopäätökset-kappaleessa. Projektin tuloksena tutkittavista materiaaleista on kerätty ja saatu laajasti tietoa kirjallisuudesta ja koetoiminnasta. Suurin osa käytännön kokeiden tuloksista vahvistaa materiaalin teorioiden mukaista käyttäytymistä ja olemusta. Malmin mineralogisen tarkastelun tuloksena materiaaleista voidaan todeta, että tekstuuriominaisuudet vaikuttavat kiven mekaaniseen käyttäytymiseen (esim. liuskeisuuden suunta ja kovien mineraalien esiintyminen murtolujuuteen). LIF- ja hyperspektrikuvausmenetelmillä kivestä saadaan tietoa, jota voidaan jatkokäsitellä (analysoida) niin, että sitä voidaan käyttää hyödyksi jopa hienonnusprosessin ohjauksessa (esim. lajittelussa). Tässä tutkimuksessa on tehty alustavia testauksia jauhatusmyllyn monitorointiin liittyen. Kokeissa on havaittu, että jauhatusmyllyn jauhatustehokkuutta voidaan mitata ja monitoroida energian, tärinän ja äänen avulla. Kiihtyvyysanturien datan ja seula-analyysien avulla on seurattu materiaalin hienontumista panosjauhatuksessa. Mittausparametrien tietojen yhdistämisellä on mahdollista tarkkailla ja ohjata jauhatusprosessin käyttäytymistä. Tämän projektin vaahdotuskokeilla on tutkittu syöttömäärän ja hienoaineen vaikutusta vaahdotustulokseen. Kultamalmin osalta tuloksista voidaan todeta, että paras tulos saadaan prosessisyötöllä 38 t/h ja että hienoaines sisältää molempien malmien tapauksessa paljon arvoainesta. Vaahdotuksessa hienoaineksen vaahdottumiseen tulisi kiinnittää erityistä huomiota. OMS minipilot-rikastusprosessia on mallinnettu HSC Sim -ohjelmiston avulla. Mallit on tehty rikastusprosessin tasapainotilan ja dynaamisesta käyttäytymisestä, jotka perustuvat kokeelliseen toimintaan. Mallien avulla voidaan tutkia prosessin käyttäytymistä ja niitä voidaan käyttää prosessin hallinnan apuvälineenä