Gravitational Waves (GWs) were observed for the first time in 2015, one century after Einstein predicted their existence. There is now growing interest to extend the detection bandwidth to low frequency. The scientific potential of multi-frequency GW astronomy is enormous as it would enable to obtain a more complete picture of cosmic events and mechanisms. This is a unique and entirely new opportunity for the future of astronomy, the success of which depends upon the decisions being made on existing and new infrastructures. The prospect of combining observations from the future space-based instrument LISA together with third generation ground based detectors will open the way towards multi-band GW astronomy, but will leave the infrasound (0.1 Hz to 10 Hz) band uncovered. GW detectors based on matter wave interferometry promise to fill such a sensitivity gap. We propose the European Laboratory for Gravitation and Atom-interferometric Research (ELGAR), an underground infrastructure based on the latest progress in atomic physics, to study space-time and gravitation with the primary goal of detecting GWs in the infrasound band. ELGAR will directly inherit from large research facilities now being built in Europe for the study of large scale atom interferometry and will drive new pan-European synergies from top research centers developing quantum sensors. ELGAR will measure GW radiation in the infrasound band with a peak strain sensitivity of 3.3×10-22/√Hz at 1.7 Hz. The antenna will have an impact on diverse fundamental and applied research fields beyond GW astronomy, including gravitation, general relativity, and geology.
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.
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.
Our latest paper on the spectroscopy between dressed levels of rubidium atoms is out on arXive (pdf).
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.
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%).
Setup of the beam diameter measurement
Real beam size as a function of the minimum transmitivity.
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.
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. 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.
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:
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.