Experiments

Quantum metrology

Advancements in physics are often motivated/accompanied by advancements in our precision measurements abilities. The current generation of atomic and optical interferometers is limited by shot noise, a fundamental limit when estimating a phase shift with classical light or uncorrelated atoms. In the last years, it has been clarified that the creation of special quantum correlations among particles, which will be called here useful entanglement, can strongly enhance the interferometric sensitivity [1]. Recent pioneer experiments have demonstrated the basic principles [2,3,4]. The focus of our research activity is to find novel interferometric configurations and/or to engineer novel and robust useful entangled states [5] aimed at overcoming the shot noise sensitivity in atomic and optical interferometers. In particular, we study the creation of entangled states in Bose-Einstein condensates (BECs). The large and tuneable nonlinearities of BECs – arising from atom-atom interactions – enable engineering a large variety of entangled states of many particles. Moreover, atoms can be trapped, controlled, and counted. They can couple strongly to external forces, which makes atoms ideal candidates for ultra-precise sensors. All these factors call for generating non-classical atomic states designed for phase estimation in atomic clocks and atom interferometers. In our theory, a key role is played by the Fisher information, a quantity that has been recently experimentally measured with Bose-Einstein condensates [4] and is closely connected to useful many-particles entanglement [1,6]. Finally, it is worth pointing out that quantum interferometers are fascinating toolboxes to learn about foundational questions of quantum mechanics.

[1] L. Pezze’ and A. Smerzi, “Entanglement, Non-linear Dynamics and Heisenberg Limit”. Phys. Rev. Lett. 102, 100401 (2009)
[2] B. Lucke, M. Scherer, J. Kruse, L. Pezze’, F. Deuretzbacher, P. Hyllus, O. Topic, J. Peise, W. Ertmer, J. Arlt, L. Santos, A. Smerzi and C. Klempt “Twin Matter Waves for Interferometry Beyond the Classical Limit”. Science 334, 773 (2011)
[3] R. Krischek, C. Schwemmer, W. Wieczorek, H. Weinfurter, P. Hyllus, L. Pezze’ and A. Smerzi, “Useful Multiparticle Entanglement and Sub-Shot-Noise Sensitivity in Experimental Phase Estimation”. Phys. Rev. Lett. 107, 080504 (2011)
[4] H. Strobel, W. Muessel, D. Linnemann, T. Zibold, D. B. Hume, L. Pezze’, A. Smerzi, M. K. Oberthaler, “Fisher information and entanglement of non- Gaussian spin states”. Science 345, 424 (2014)
[5] L. Pezze’ and A. Smerzi, “Ultrasensitive Two-Mode Interferometry with Single-Mode Number Squeezing”. Phys. Rev. Lett. 110, 163604 (2013)
[6] P. Hyllus, W. Laskowski, R. Krischek, C. Schwemmer, W. Wieczorek, W Witlef, H. Weinfurter, L. Pezze’ and A. Smerzi, “Fisher information and multiparticle entanglement”. Phys. Rev. A 85, 022321 (2012)

Phase sensitivity (normalized by the shot noise) as a function of the phase shift, obtained with a Bose-Einstein condensate [2]. The orange line, reaching values below one, signals entanglement, according to the theory developed in [1].