A02: Gravity sensing with very long baseline atom interferometry

 

Owing to the quadratic scaling of the leading order phase shift with increasing free evolution time, atom-interferometric gravimeters and gradiometers operating on baselines of several meters put acceleration resolution in the range of pm/s2 in reach. However, operating these devices with such high sensitivities is not only challenging concerning the production of ultracold atoms but also with respect to the design of the inertial reference and its careful isolation against perturbations from the outside, and the control of the environment along the baseline of the instrument.

By combining extended free evolution times of several seconds with large momentum transfer atomic beam splitters, very long baseline atom interferometers (VLBAIs; figure 01) promise to bring up the next generation of high-accuracy gravimetric base stations with sensitivities in the (nm/s2)/√Hz range as well as testbeds for gravity-gradiometry with unprecedented resolution.

Figure 01: Very Long Baseline Atom Interferometer

In addition, differential operation of two very long baseline atomic gravimeters with different species opens the way to quantum tests of the universality of free fall at the 10-13 level, competing with the current state-of- the-art classical tests (Hartwig et al., 2015) and providing means to surpass these in the future. Finally, macroscopically separated quantum superposition states provide a platform for novel tests of fundamental physics both at the interface between general relativity and quantum mechanics (Kovachy et al., 2015) and the transition between superposition states and macroscopism.

Operating atomic inertial sensors at the aforementioned sensitivity levels puts stringent constraints on the inertial reference. Owing to a low resonance frequency seismic attenuation system, we envisage a vibration-limited short-term sensitivity to accelerations of 10 (nm/s2)/√Hz with a factor of up to 25 improvement when correlating the interferometric signal with a classical inertial sensor in a hybrid setup (Figure 02).

Non-inertial signals can also couple in the interferometric signal via spurious forces on the atoms during their free evolution time, in particular due to magnetic field gradients.

Figure 02

Precision measurements like tests of the universality of free-fall require for example magnetic field gradients below 1.5 nT/m along the 10 meters of the instrument‘s baseline. In addition, differential acceleration of the two atomic species during their free-fall is also impacted by gravity gradients that need to be known better than the 10-7 /s2 level.

In summary, owing to the employed atomic species choice and innovative source concepts as well as the seismic attenuation system and planned atom interferometer geometries, the VLBAI facility is an excellent and worldwide unique tool that will soon open completely new perspectives for geodesy and fundamental research.

PRINCIPAL INVESTIGATORS

Prof. Dr. Wolfgang Ertmer
Board Member, Principal Investigator
Address
c/o Leibniz Universität Hannover
DLR-SI
Callinstraße 36
30167 Hannover
Prof. Dr. Wolfgang Ertmer
Board Member, Principal Investigator
Address
c/o Leibniz Universität Hannover
DLR-SI
Callinstraße 36
30167 Hannover
Prof. Dr. Ernst Rasel
Principal Investigator
Address
Institut für Quantenoptik
Welfengarten 1
30167 Hannover
Room
Prof. Dr. Ernst Rasel
Principal Investigator
Address
Institut für Quantenoptik
Welfengarten 1
30167 Hannover
Room