dc.description.abstract |
Quantum Sensors, like atom interferometers (AI), can be employed for
high-precision measurements of inertial forces, including their application
as gravimeters, gradiometers, accelerometers, and gyroscopes.
Their measurement principle relies on ultracold atoms that are prepared
in quantum-mechanical superposition states in external degrees
of freedom. These states can be prepared by a momentum transfer of
a Raman laser. Then the superposition state senses the effect of an inertial
force, which induce a corresponding relative phase. The phase is
read out by a final coupling which converts the interferometric phase
into a atom number difference between the two states. The difference
provides an estimate of the interferometric phase and the corresponding
quantity of interest. The quantum mechanical noise of the atomic
ensemble cause a fundamental uncertainty of this estimation, which I
analyze for generic AIs. For small atomic densities, the quantum phase
noise of the ensemble limits the interferometric sensitivity. For large
densities, quantum number fluctuations generate density fluctuations,
which generates phase noise. I show that these two competing effects
result in an optimal atom number with a maximal interferometer resolution.
Squeezed atomic samples allow for a reduction of the quantum
noise of one quantity at the expense of an increased noise along of a
conjugate quantity. Phase and number are such quantities which obey
to a variant of Heisenberg’s uncertainty principle. Neither phase nor
number squeezing can improve the maximal interferometer resolution.
As one main result of this thesis, I show how an optimal squeezing
in between number and phase squeezing, allows for a fundamental
improvement. I evaluate possible experimental paths to implement
the proposed protocol.
Concepts for a squeezing-enhanced operation of external-degree
AIs have not yet been demonstrated. I propose and implement an
atomic gravimeter, which is designed to accept spin-squeezed atomic
states as input states. The interferometer is designed such that the
interferometer couplings are performed in spin space, while the phase
accumulation is performed in momentum states. For this interferometer,
the squeezed input can be directly obtained from spin dynamics
in spinor Bose-Einstein condensates. The main noise contributions in
the experiment are analyzed, which results in a factor of 84 above
the relevant quantum limit, preventing a squeezing enhancement so
far. I outline a suppression of the main noise source, uncontrolled
AC Stark shift on the squeezed mode and propose future important
applications, including test of spontaneous collapse theories and an
improvement of large-scale, high-precision gradiometers. |
eng |