The possibility to overcome the standard quantum limit (SQL) by engineering specific quantum correlations between the atoms is attracting increasing interest in the field of atom interferometry. Recently, Bose-Einstein condensates (BECs) have been pinpointed as optimal candidates for the realization of entanglement-enhanced atom interferometers with spatially separated arms either in trapped  or free-fall  configurations. However, either due to the presence of residual interactions during the interferometer sequence or due to the fast expansion of the BEC during the state preparation, only a modest sub-SQL sensitivity gain is predicted.
To overcome these problems, we recently proposed a novel method we refer to as Delta-Kick Squeezing (DKS) . This method involves the rapid action of an external trap focusing the matter-waves to significantly increase the atomic densities during a preparation stage. This method is explored in the two relevant cases of Raman or Bragg scattering light pulses. In the second case, we demonstrated the possibility to implement a non-linear readout scheme making the sub-SQL sensitivity highly robust against imperfect atom counting detection [4,5]. We predict more than 30 dB of sensitivity gain beyond the SQL, assuming realistic parameters and millions of atoms in the BEC.
 R. Corgier, L.Pezzè and A. Smerzi, PRA 103 (2021).
Nonlinear Bragg interferometer with a trapped Bose-Einstein condensate
 S. S. Szigeti, S. P. Nolan, J. D. Close, and S. A. Haine, PRL 125 (2020).
High Precision quantum-enhanced gravimetry with a Bose-Einstein condensate
 R. Corgier, N. Gaaloul, A. Smerzi and L.Pezzè, PRL 127 (2021).
 E. Davis, G. Bentsen, and M. Schleier-Smith, PRL 116, 053601 (2016).
Approaching the Heisenberg limit without single-particle detection.
 O. Hosten, R. Krishnakumar, N. J. Engelsen, and M. A. Kasevich, Science 352 (2016).
Quantum phase magnification