umu.sePublications
Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Characterisation of a three-dimensional Brownian motor in optical lattices
Umeå University, Faculty of Science and Technology, Department of Physics.
Umeå University, Faculty of Science and Technology, Department of Physics.
Umeå University, Faculty of Science and Technology, Department of Physics.
Umeå University, Faculty of Science and Technology, Department of Physics.
Show others and affiliations
2007 (English)In: European Physical Journal D: Atomic, Molecular and Optical Physics, ISSN 1434-6060, E-ISSN 1434-6079, Vol. 44, no 2, 381-388 p.Article in journal (Refereed) Published
Abstract [en]

We present here a detailed study of the behaviour of a three dimensional Brownian motor based on cold atoms in a double optical lattice [P. Sjölund et al., Phys. Rev. Lett. 96, 190602 (2006)]. This includes both experiments and numerical simulations of a Brownian particle. The potentials used are spatially and temporally symmetric, but combined spatiotemporal symmetry is broken by phase shifts and asymmetric transfer rates between potentials. The diffusion of atoms in the optical lattices is rectified and controlled both in direction and speed along three dimensions. We explore a large range of experimental parameters, where irradiances and detunings of the optical lattice lights are varied within the dissipative regime. Induced drift velocities in the order of one atomic recoil velocity have been achieved.

Place, publisher, year, edition, pages
Springer Verlag , 2007. Vol. 44, no 2, 381-388 p.
National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
URN: urn:nbn:se:umu:diva-16377DOI: 10.1140/epjd/e2007-00233-3OAI: oai:DiVA.org:umu-16377DiVA: diva2:156050
Available from: 2010-03-08 Created: 2007-09-18 Last updated: 2010-12-21Bibliographically approved
In thesis
1. Laser cooling mechanisms and Brownian motors in optical lattices
Open this publication in new window or tab >>Laser cooling mechanisms and Brownian motors in optical lattices
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [sv]

Denna avhandling innefattar såväl experimentella som numeriska studier av laserkylda atomer i optiska kristallgitter. Bland annat har laserkylningsprocesser studerats, där atomers rörelser i optiska kristallgitter har uppvisat andra typer av bakomliggande mekanismer än de som tidigare förutsågs genom “Sisyfoskylningsmodellen”. Sedan atomer kylda till några mikrokelvin först realiserades (sent 60-tal) så har Sisyfoskylningsmodellen varit hörnstenen för förståelsen av laserkylda och lokaliserade atomer i dissipativa optiska kristallgitter. I dissipativa optiska kristallgitter finns det en balans mellan den uppvärmande diffusionen och den kylande friktionen. Studier i denna avhandling visar att laserkylningsprocesser är mer komplexa än vad denna modell innefattar. Både experimentella och numeriska resultat visar att atomer i optiska kristallgitter har två hastighetsfördelningar där en “kallare” och en “varmare” mod av atomer omfördelas mellan moderna. Speciellt så visar det sig att varma atomer dels värms och diffunderar ut ur gittret, men samtidigt populeras den kalla moden med en tidsutveckling som inte förändrar dess temperatur nämnvärt. I detta arbete presenteras också resultat från den första realiserade tredimensionella Brownska motorn baserad på ljus-atom-växelverkan. Det unika med denna Brownska motor är att den är kontrollerbar både vad gäller dess hastighet som dess riktning. Den underliggande principen för denna Brownska motor är tämligen generell och den kan därför vara applicerbar inom andra vetenskapliga discipliner såsom nanoteknik, biologi, kemi och elektronik. Generellt så är förståelsen av Brownska motorer viktigt eftersom de återfinns i vår omgivning, från exempelvis härkomsten av muskelsammandragningar och materialtransporter i levande celler till rörelsen hos bakterier och mindre organismer. Det flesta av de experimentella resultaten presenterade i denna avhandling har varit möjliga genom utveckling och förbättringar av den experimentella uppställningen. Framförallt så har kvaliten och reproducerbarheten vid de olika mätningar som gjorts blivit avsevärt förbättrade jämfört med tidigare vilket utgör en bra grund för framtida studier av ultrakalla atomer.

Abstract [en]

In this thesis, detailed experimental studies and numerical simulations are presented of laser cooling mechanisms in dissipative optical lattices and results of the first realized three dimensional Brownian motor in optical lattices. A dissipative optical lattice is a periodic light shift potential, created in the interference patterns of laser beams. In this, atoms can be both cooled and trapped, and the most important relaxation mechanism is generally considered to be “Sisyphus cooling”. However, careful experimental and theoretical investigations indicate the presence of other cooling processes as well. This is studied by varying different parameters such as irradiance and frequency of the lattice light. The time evolution of atoms in optical lattices show strong evidence of a bimodal velocity distribution, where a population transfer between one mode containing “hot” atoms and one mode containing “cold” atoms is evident. The normal diffusion of atoms in optical lattices is characterized by isotrop random fluctuations and exhibit the nature of Brownian motion. We have realized a technique where this motion is rectified and controlled. This is done in a three dimensional double optical lattice. This Brownian motor has control properties for both its speed and its direction in three dimensions. Our three dimensional double optical lattice is created by using laser light, exploiting two transitions, in the D2 line of cesium. Two three dimensional optical lattices are spatially overlapped; each optical lattice traps atoms in one of two hyperfine ground states. The controllability comes about by inducing phase shifts in the lattice laser beams, which displace the lattices relative to each other. This type of highly controlled Brownian motor is of fundamental interest since Brownian motion is present in almost all systems and for the role they play in protein motors and the function of living cells, and for the potential applications in nanotechnology. Brownian motors of this kind also open the way to possible studies of quantum Brownian motors and quantum resonances that are predicted for atomic ratchets. Optical lattices, and especially double optical lattices, have also been suggested as a platform for quantum state manipulations due to the good isolation from environment and ambient effects. Most of the work in this thesis is a first step towards the implementation of quantum manipulation schemes in a double optical lattice.

Place, publisher, year, edition, pages
Umeå: Fysik, 2007. 93 p.
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:umu:diva-1127 (URN)978-91-7264-321-5 (ISBN)
Public defence
2007-05-31, MA121, MIT Huset, Umeå Universitet, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2007-05-10 Created: 2007-05-10 Last updated: 2012-01-26Bibliographically approved
2. Atomic transport in optical lattices
Open this publication in new window or tab >>Atomic transport in optical lattices
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis includes both experimental and theoretical investigations of fluctuation-induced transport phenomena, presented in a series of nine papers, by studies of the dynamics of cold atoms in dissipative optical lattices.

With standard laser cooling techniques about 108 cesium atoms are accumulated, cooled to a few μK, and transferred into a dissipative optical lattice. An optical lattice is a periodic light-shift potential, and in dissipative optical lattice the light field is sufficiently close to resonance for incoherent light scattering to be of importance. This provides the system with a diffusive force, but also with a friction through laser cooling mechanisms.

In the dissipative optical lattices the friction and the diffusive force will eventually reach a steady state. At steady state, the thermal energy is low enough, compared to the potential depth, for the atoms to be localized close to the potential minima, but high enough for the atoms to occasionally make inter-well flights. This leads to a Brownian motion of the atoms in the optical lattices. In the normal case these random walks average to zero, leading to a symmetric, isotropic diffusion of the atoms.

If the optical lattices are tilted, the symmetry is broken and the diffusion will be biased. This leads to a fluctuation-induced drift of the atoms. In this thesis an investigation of such drifts, for an optical lattice tilted by the gravitational force, is presented. We show that even though the tilt over a potential period is small compared to the potential depth, it clearly affect the dynamics of the atoms, and despite the complex details of the system it can, to a good approximation, be described by the Langevin equation formalism for a particle in a periodic potential. The linear drifts give evidence of stop-and-go dynamics where the atoms escape the potential wells and travel over one or more wells before being recaptured.

Brownian motors open the possibility of creating fluctuation-induced drifts in the absence of bias forces, if two requirements are fulfilled: the symmetry has to be broken and the system has to be brought out of thermal equilibrium. By utilizing two distinguishable optical lattices, with a relative spatial phase and unequal transfer rates between them, these requirements can be fulfilled. In this thesis, such a Brownian motor is realized, and drifts in arbitrary directions in 3D are demonstrated. We also demonstrate a real-time steering of the transport as well as drifts along pre-designed paths. Moreover, we present measurements and discussions of performance characteristics of the motor, and we show that the required asymmetry can be obtained in multiple ways.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, Institutionen för fysik, 2010. 83 p.
Keyword
Ultra-cold atoms, optical lattice, laser cooling, directed transport, Brownian motor, Brownian motion
Identifiers
urn:nbn:se:umu:diva-38648 (URN)978-91-7459-123-1 (ISBN)
Public defence
2011-01-21, Naturvetarhuset, N200, Umeå universitet, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2010-12-21 Created: 2010-12-20 Last updated: 2011-05-16Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full text

Search in DiVA

By author/editor
Dion, ClaudeHagman, HenningKastberg, Anders
By organisation
Department of Physics
In the same journal
European Physical Journal D: Atomic, Molecular and Optical Physics
Atom and Molecular Physics and Optics

Search outside of DiVA

GoogleGoogle Scholar

doi
urn-nbn

Altmetric score

doi
urn-nbn
Total: 123 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf