  Using a trapped quintessence model, a series of time-of-flight (TOF)
experiments with a different frequency of probe light were designed and
performed. The varying-frequency TOF (VFTOF) experiments demonstrated that the
fall acceleration of test atoms is dependent on the detuning of the probe light
frequency with respect to the atomic transition frequency. In appropriately
designed experiments, if the scalar field in the model accounts for the
accelerated expansion of the Universe entirely, the field will result in an
observable fifth force. Meanwhile, the trapped quintessence model still
satisfies all experimental bounds on deviations from general relativity due to
both the saturation effect and the short interaction range of the scalar field.
The scalar saturates at a value corresponding to the cosmological constant when
the microscopic nonrelativistic matter density is large enough. The interaction
range of the scalar is inversely proportional to the square root of the
microscopic nonrelativistic matter density. The interaction range has been
estimated to be several $\mu \rm{m}$ in the current cosmic density. The
Universe is assumed to be permeated with fuzzy dark matter, which means that
the microscopic nonrelativistic matter density defined through the quantum
wavefunctions of the ultralight particles can be used on the cosmic scale.
  By measuring the fall acceleration of the test atoms with the TOF method
step-by-step in the detuning frequency domain of the probe light, we derived
the dispersion curves of the measured acceleration versus the frequency
detuning of the probe light. When the nonrelativistic matter density of the
source increased due to the energy gained from the laser light, the test atoms
were pulled to the center of the source, and vice versa.
