Category Archives: Publications

Precise and robust optical beam steering for space optical instrumentation

G. Drougakis, K. G. Mavrakis, S. Pandey, G. Vasilakis, K. Poulios, D. G. Papazoglou, and W. von Klitzing 
CEAS Space Journal (2019)
http://dx.doi.org/10.1007/s12567-019-00271-x
https://arxiv.org/abs/1907.10425

Abstract

This approach permits much finer adjustments of the beam direc- tion and position when compared to other beam steering techniques of the same mechanical precision. This results in a much increased precision, accu- racy and mechanical stability. A precision of better than 5μrad and 5 μm is demonstrated, resulting in a resolution in coupling efficiency of 0.1%. To- gether with the added flexibility of an additional beam steering element, this allows a great simplification of the design of the fiber coupler, which normally is the most complex and sensitive element on an optical fiber breadboard. We demonstrate a fiber to fiber coupling efficiency of more than 89.8%, with a stability of 0.2% in a stable temperature environment and 2% fluctuations over a temperature range from 10C to 40C over a measurement time of 14 hours. Furthermore, we do not observe any non-reversible change in the coupling efficiency after performing a series of tests over large temperature variations. This technique finds direct application in proposed missions for quantum experiments in space, e.g. where laser beams are used to cool and manipulate atomic clouds.

Our paper on the Fragility of the Laughlin states is accepted in PRA

preprint at arxiv.org (1810.07609) (pdf)

Abstract:
When a Bose-Einstein condensate rotates in a purely harmonic potential with an angular frequency which is close to the trap frequency, its many-body state becomes highly correlated, with the most well-known being the bosonic Laughlin state. To take into account that in a real experiment no trapping potential is ever exactly harmonic, we introduce an additional weak, quartic potential and demonstrate that the Laughlin state is highly sensitive to this extra potential. Our results imply that achieving these states experimentally is essentially impossible, at least for a macroscopic atom number.

Microwave spectroscopy of radio-frequency dressed 87Rb now on arXive

Our latest paper on the spectroscopy between dressed levels of rubidium atoms is out on arXive (pdf).

Abstract:

We study the hyperfine spectrum of atoms of 87Rb dressed by a radio-frequency field, and present experimental results in three different situations: freely falling atoms, atoms trapped in an optical dipole trap and atoms in an adiabatic radio-frequency dressed shell trap. In all cases, we observe several resonant side bands spaced at intervals equal to the dressing frequency, corresponding to transitions enabled by the dressing field. We theoretically explain the main features of the microwave spectrum, using a semi-classical model in the low field limit and the Rotating Wave Approximation. As a proof of concept, we demonstrate how the spectral signal of a dressed atomic ensemble enables an accurate determination of the dressing configuration and the probing microwave field.

Simple precision measurements of optical beam sizes

The paper is in the top 10 most downloaded papers of Applied Optics for November and December 2018.

Applied Optics 57 9863 (2018) 

M. Mylonakis, S. Pandey, K. G. Mavrakis, G. Drougakis, G. Vasilakis, D. G. Papazoglou, and W. von Klitzing 

doi: 10.1364/AO.57.009863 

Abstract: We present a simple high-precision method to quickly and accurately measure the diameters of Gaussian beams, Airy spots, and central peaks of Bessel beams ranging from sub-millimeter to many centimeters without special- ized equipment. By simply moving a wire through the beam and recording the relative losses using an optical power meter, one can easily measure the beam diameters with a precision of 1%. The accuracy of this method has been experimentally verified for Gaussian beams down to the limit of a commercial slit-based beam profiler (3%).

Image of the setup of the beam diameter measurement

Setup of the beam diameter measurement

Plot of the real beam size calculated from the minimum transmitivity.

Real beam size as a function of the minimum transmitivity.

 

Antireflection coated semiconductor laser amplifier for Bose-Einstein condensation experiments

AIP Advances 8 095020 (2018)  

S. Pandey, H. Mas, G. Drougakis, K. G. Mavrakis, M. Mylonakis, G. Vasilakis, V. Bolpasi, and W. von Klitzing 

https://doi.org/10.1063/1.5047839

Abstract

We present a slave laser highly suitable for the preparation and detection of 87Rb Bose-Einstein condensates (BEC). A highly anti-reflection coated laser diode serves as an optical amplifier, which requires neither active temperature stabilization nor dedicated equipment monitoring the spectral purity of the amplified light. The laser power can be controlled with a precision of 10μW in 70mW with relative fluctuations down to 2 × 10^−4. Due to its simplicity and reliability, this slave laser will be a useful tool for laboratory, mobile, or even space-based cold-atom experiments. By the way of demonstration this slave laser was used as the sole 780nm light-source in the production of 3×10^4 BECs in a hybrid magnetic/dipole trap.

Figure 1: Stability of the power of a AR-coated diode lase slave.

 

Matter-wave interferometers using TAAP rings

New Journal of Physics   18   075014 (2016)

P. Navez, S. Pandey, H. Mas, K. Poulios, T. Fernholz, and W. von Klitzing

doi: 10.1088/1367-2630/18/7/075014

Fig 2

Figure 2. Experimental realisation of a ring-shaped TAAP waveguide. The radius of the ring is R = 570 μm.

Abstract: We present two novel matter-wave Sagnac interferometers based on ring-shaped time-averaged adiabatic potentials, where the atoms are put into a superposition of two different spin states and manipulated independently using elliptically polarized rf-fields. In the first interferometer the atoms are accelerated by spin-state-dependent forces and then travel around the ring in a matter-wave guide. In the second one the atoms are fully trapped during the entire interferometric sequence and are moved around the ring in two spin-state-dependent `buckets’.

Figure 6.

Figure 6. Experimental realisation of arbitrary traps. The fitted radius is 440 μm and 450 μm respectively.  Note that (a) and (b) are taken with identical experimental conditions and differ only in the state of the atoms. The axis of the circular rf component and the one of the tilted modulation are not orthogonal.

Corrections to the ideal Sagnac phase are investigated for both cases. We experimentally demonstrate the key atom-optical elements of the interferometer such as the independent manipulation of two different spin states in the ring-shaped potentials under identical experimental conditions.

Towards rotation sensing with a single atomic clock

Proc. SPIE   9900   990007-990007-14 (2016)

T. Fernholz, R. Stevenson, M. R. Hush, I. V. Lesanovsky, T. Bishop, F. Gentile, S. Jammi, T. Pyragius, M. G. Bason, H. Mas, S. Pandey, G. Vasilakis, K. Poulios, and W. von Klitzing

http://dx.doi.org/10.1117/12.2229878

We discuss a scheme to implement a gyroscopic atom sensor with magnetically trapped ultra-cold atoms. Unlike standard light or matter wave Sagnac interferometers no free wave propagation is used. Interferometer operation is controlled only with static, radio-frequency and microwave magnetic fields, which removes the need for interferometric stability of optical laser beams. Due to the confinement of atoms, the scheme may allow the construction of small scale portable sensors. We discuss the main elements of the scheme and report on recent results and efforts towards its experimental realization.

One of the possibilities discussed are state dependent TAAPs:

fernholz2016ps-rotating-rings

fernholz2016ps-ring-trap

However also chip scale solutions are discussed.

 

 

 

 

 

Adiabatic Potentials and Atom Lasers

Rom. Rep. Phys. 67 295 (2015). (link)

V. Bolpasi and W. von Klitzing

Abstract: 
The brightest atom lasers to date are formed by time-dependent adiabatic potentials from magnetic Ioffe-Pritchard traps. We analyse these potentials based on a harmonic trap in the presence of gravity. We present a detailed analytic model of the trap and determine the flux of the atom laser, which we find to be in good agreement with recent experimental data. We also present a novel method for determining the Rabi frequency of the dressing rf-field.

Design of a dual species atom interferometer for space

Experimental Astronomy 39:2 167-206 (2015) (link)  (arXive)
Thilo Schuldt et al.Abstract:
Atom interferometers have a multitude of proposed applications in space including precise measurements of the Earth’s gravitational field, in navigation & ranging, and in fundamental physics such as tests of the weak equivalence principle (WEP) and gravitational wave detection. While atom interferometers are realized routinely in ground-based laboratories, current efforts aim at the development of a space compatible design optimized with respect to dimensions, weight, power consumption, mechanical robustness and radiation hardness. In this paper, we present a design of a high-sensitivity differential dual species 85Rb/87Rb atom interferometer for space, including physics package, laser system, electronics and software. The physics package comprises the atom source consisting of dispensers and a 2D magneto- optical trap (MOT), the science chamber with a 3D-MOT, a magnetic trap based on an atom chip and an optical dipole trap (ODT) used for Bose-Einstein condensate (BEC) creation and interferometry, the detection unit, the vascuum system for 10-11 mbar ultra-high vacuum generation, and the high-suppression factor magnetic shielding as well as the thermal control system. The laser system is based on a hybrid approach using fiber-based telecom components and high-power laser diode technology and includes all laser sources for 2D-MOT, 3D-MOT, ODT, interferometry and detection. Manipulation and switching of the laser beams is carried out on an optical bench using Zerodur bonding technology. The instrument consists of 9 units with an overall mass of 221 kg, an average power consumption of 608 W (819 W peak), and a volume of 470 liters which would well fit on a satellite to be launched with a Soyuz rocket, as system studies have shown.