  We present possible design concepts for a tractor atom interferometer (TAI)
based on three-dimensional confinement and transport of ultracold atoms. The
confinement reduces device size and wave-packet dispersion, enables arbitrary
holding times, and facilitates control to create complex trajectories that
allow for optimization to cancel unwanted sensitivity, fast splitting and
recombination, and suppression of detrimental nonadiabatic excitation. Thus,
the design allows for further advancement of compact, high-sensitivity, quantum
sensing technology. In particular, we focus on the implementation of
quantum-enhanced accelerometers and gyroscopes. We discuss TAI protocols for
both spin-dependent and scalar trapping potentials. Using optimal control
theory, we demonstrate the splitting of the wave function on a time scale two
orders of magnitude shorter than the previous proposal using adiabatic
dynamics, thus maximizing the time spent at full separation, where the
interferometric phase is accumulated. Lastly, we explore the possibility of
including non-classical correlations between the atoms to improve sensitivity.
The performance estimates for TAI give a promising perspective for
atom-interferometry-based sensing, significantly exceeding the sensitivities of
current state-of-the-art devices.
