Category Archives: Publications

An ultra-bright atom laser

The article has selected the article as a New Journal of Physics Highlight of the year 2014.

Phys.org has published a nice semi-popular article about the paper. The New Scientist has also written a rather popularized article about our atom laser.
Note that we have not been given access to any of these articles before publication and are not responsible for its rather imaginative content.

   

An article in Greek can be found in a number of newspapers, e.g. at Kerdos.gr and in.gr
Article at Kerdos and  Article at In.gr

Sigma Live also have made a video interview in Greek about the atom laser.

Fundamentals of cavity-enhanced polarimetry for parity-nonconserving optical rotation measurements: Application to Xe, Hg, and I

Physical Review A   89   052127 (2014)

L. Bougas, G. E. Katsoprinakis, W. von Klitzing, and T. Rakitzis

http://dx.doi.org/10.1103/PhysRevA.89.052127   or   https://journals.aps.org/pra/abstract/10.1103/PhysRevA.89.052127

Abstract: We present the theoretical basis of a cavity-enhanced polarimetric scheme for the measurement of parity-nonconserving (PNC) optical rotation. We discuss the possibility of detecting PNC optical rotation in accessible transitions in metastable Xe and Hg, and ground state I. In particular, the physics of the PNC optical rotation is presented, and we explore the lineshape effects on the expected PNC optical rotation signals. Furthermore, we present an analysis of the eigenpolarizations of the cavity-enhanced polarimeter, which is necessary for understanding the measurement procedure and the ability of employing robust background subtraction procedures using two novel signal reversals. Using recent atomic structure theoretical calculations, we present simulations of the PNC optical rotation signals for all proposed transitions, assuming a range of experimentally feasible parameters. Finally, the possibility of performing sensitive measurements of the nuclear-spin-dependent PNC effects is investigated, for the odd-neutron nuclei 129Xe and 199Hg, and the odd-proton nucleus 127I.

 

 Cavity frequency polarization spectrum. For the simulations we used θF =13 mad and δ = θF/2 = 6.5 mad and for demonstration purposes φPNC = 0.6 mad. (i) The Faraday effect splits the cavity spectrum into R and L modes by 2ωF = 2θF(c/L) (twofold degeneracy); (ii) the PNC optical rotation splits further the clockwise (CW) and counterclockwise (CCW) modes by 2ωPNC = 2φPNC(c/L), while the cavity modes remain circular polarization states; (iii) in the presence of linear birefringence (δ ̸= 0) the frequency splitting of the eigenmodes increases as ωF′ = 1/qωF and the measured PNC- induced splitting is reduced ωF′ = qωF (0 ≤ q ≤ 1) (see Fig. 3); the eigenmodes transform into elliptical states as observed from the different amplitudes of the output light (see the text for discussion). We also assume that the clockwise input beam was p polarized, while the counterclockwise beam was s polarized. The cavity’s linewidth is exaggerated for demonstration purposes; note that the free spectral range of the cavity is ωFSR = 2π × 40 MHz. In (i)–(iii), the gray dashed line corresponds to the fourfold degenerate axial mode of an isotropic cavity. PBS stands for polarizing beam splitter and BS stands for beam splitter.

Cavity frequency polarization spectrum. For the simulations we used θF =13 mad and δ = θF/2 = 6.5 mad and for demonstration purposes φPNC = 0.6 mad. (i) The Faraday effect splits the cavity spectrum into R and L modes by 2ωF = 2θF(c/L) (twofold degeneracy); (ii) the PNC optical rotation splits further the clockwise (CW) and counterclockwise (CCW) modes by 2ωPNC = 2φPNC(c/L), while the cavity modes remain circular polarization states; (iii) in the presence of linear birefringence (δ ̸= 0) the frequency splitting of the eigenmodes increases as ωF′ = 1/qωF and the measured PNC- induced splitting is reduced ωF′ = qωF (0 ≤ q ≤ 1) (see Fig. 3); the eigenmodes transform into elliptical states as observed from the different amplitudes of the output light (see the text for discussion). We also assume that the clockwise input beam was p polarized, while the counterclockwise beam was s polarized. The cavity’s linewidth is exaggerated for demonstration purposes; note that the free spectral range of the cavity is ωFSR = 2π × 40 MHz. In (i)–(iii), the gray dashed line corresponds to the fourfold degenerate axial mode of an isotropic cavity. PBS stands for polarizing beam splitter and BS stands for beam splitter.

STE-QUEST-test of the universality of free fall using cold atom interferometry

Classical And Quantum Gravity   31   115010 (2014)

D. N. Aguilera et al.

http://dx.doi.org/10.1088/0264-9381/31/11/115010

Abstract: The theory of general relativity describes macroscopic phenomena driven by the influence of gravity while quantum mechanics brilliantly accounts for microscopic effects. Despite their tremendous individual success, a complete unification of fundamental interactions is missing and remains one of the most challenging and important quests in modern theoretical physics. The spacetime explorer and quantum equivalence principle space test satellite mission, proposed as a medium-size mission within the Cosmic Vision program of the European Space Agency (ESA), aims for testing general relativity with high precision in two experiments by performing a measurement of the gravitational redshift of the Sun and the Moon by comparing terrestrial clocks, and by performing a test of the universality of free fall of matter waves in the gravitational field of Earth comparing the trajectory of two Bose–Einstein condensates of 85 Rb and 87 Rb. The two ultracold atom clouds are monitored very precisely thanks to techniques of atom interferometry. This allows to reach down to an uncertainty in the Eötvös parameter of at least 2 × 10 −15 . In this paper, we report about the results of the phase A mission study of the atom interferometer instrument covering the description of the main payload elements, the atomic source concept, and the systematic error sources

Accelerating and abruptly autofocusing matter waves

Physical Review A   87   043637 (2013)

N. K. Efremidis, V. Paltoglou, and W. von Klitzing

http://dx.doi.org/10.1103/PhysRevA.87.043637

Abstract: We predict that classes of coherent matter waves can self-accelerate without the presence of an external potential. Such Bose-Einstein condensates can follow arbitrary power-law trajectories and can also take the form of diffraction-free Airy waves. We also show that suitably engineered radially symmetric matter waves can abruptly autofocus in space and time. We suggest different schemes for the preparation of the condensate using laser beams to imprint an amplitude or a phase pattern onto the matter wave. Direct and Fourier space generation of such waves is discussed using continuous and binary masks as well as magnetic mirrors and lenses. We study the effect of interactions and find that independently of the type and strength of the nonlinearity, the dynamics are associated with the generation of accelerating matter waves. In the case of strong attractive interactions, the acceleration is increased while the radiation reorganizes itself in the form of soliton(s).

A simple and highly reliable laser system for cold atom experiments

Optics Communications 290 110-114 (2013)
D. Sahagun, V. Bolpasi, and W. von Klitzing
http://dx.doi.org/10.1016/j.optcom.2012.10.013

Abstract:

The increasing complexity of cold atom experiments puts ever higher demands on the stability and reliability of its components. We present a laser system for atom cooling experiments, which is extremely reliable yet simple to construct and low-cost, thus forming an ideal basis for ultracold atom experiments such as Bose-Einstein condensation and degenerate Fermi gases. The extended cavity (master) diode and slave lasers remain locked over a period of months with a drift in absolute frequency well below 1MHz with a line-width of less than 300kHz. We generate the repumper light by modulating the current of an injection locked slave laser at a frequency of 6.6GHz. The construction of the laser is simple and largely based on off-the-shelf electronic and optomechanical components.

Design

The basic idea of this laser system is to keep the individual elements modular, so that a fault in one part of the system can be repaired by only changing the sub-system with zero changes elsewhere.  Each parts in the graph on the right thus represents a separate bread-board.
The article also describes a very simple diode laser with extraordinary long term stability (depicted here on the right). This master-laser uses simply to machine parts and a commercial mirror mount for holding the grating.  The diode holder and mirror mount are screwed onto an aluminium base plate, which is glued onto a Peltier element, which in turn is glued onto a base.  The whole assembly is then surrounded by thick-walled aluminium box, which has been lined with standard isolation foam.

Another key element are the distribution and AOM breadboards.  They consist of standard 40mm kitchen-top granite plates cut to 300x600mm.  The optical mounts are 1” aluminium posts which are glued onto the base plate using cyanoacrylate adhesive (Loctite 408).  The beam hight is 50mm.

 

A gradient and offset compensated Ioffe–Pritchard trap for Bose–Einstein condensation experiments

Journal of Physics B   45   235301 (2012)

V. Bolpasi, J. Grucker, M. J. Morrissey, and W. von Klitzing

http://dx.doi.org/10.1088/0953-4075/45/23/235301   or   http://doi.org/10.1088/0953-4075/45/23/235301

bolpasi2012jpb-highlightAbstract: The Ioffe–Pritchard trap is the workhorse of modern cold atom physics. Here, we present a novel Ioffe–Pritchard trap coil configuration based purely on circular coils. By eliminating the traditional Ioffe bars one can increase the gradient and thus the radial trapping frequency by almost a factor 2. We also present a method to achieve minimal coupling between the gradient, curvature and offset fields of the trap, thus facilitating the dynamic control of the trapping frequencies and aspect ratio.

This paper was selected by the editors as one of the highlights of 2012 of Journal of Optics B.

Atom number calibration in absorption imaging at very small atom numbers

Central European Journal of Physics 10 1054–1058 (2012)

G. O. Konstantinidis, M. Pappa, G. Wikstroem, P. C. Condylis, D. Sahagun, M. Baker, O. Morizot, and W. von Klitzing

http://dx.doi.org/10.2478/s11534-012-0108-x

Abstract: Cold atom experiments often use images of the atom clouds as their exclusive source of experimental in- formation. The most commonly used technique is absorption imaging, which provides accurate information about the shapes of the atom clouds, but requires care when seeking the absolute atom number for small atom samples. In this paper, we present an independent, absolute calibration of the atom numbers. We di- rectly compare the atom number detected using dark-ground imaging to the one observed by fluorescence imaging of the same atoms in a magneto-optical trap. We normalise the signal using single-atom resolved fluorescence imaging. In order to be able to image the absorption of the very low atom numbers involved, we use diffractive dark-ground imaging as a novel, ultra-sensitive method of in situ imaging for untrapped atom clouds down to only 100 atoms. We demonstrate that the Doppler shift due to the acceleration of the atoms by the probe beam has to be taken into account when measuring the atom-number.