ResearchResearch Area A
Research propject A02

Project A02: Non-Gaussian atomic states for tests of nature’s quantum character

Many-particle entangled states are a valuable resource for experimentally testing fundamental properties of nature. In this project, such highly non-classical states are generated by spin-changing collisions in Bose-Einstein condensates and used for fundamental tests. A main goal is a Bell test with neutral atoms, which offers the possibility to test quantum mechanics with multi-particle states and under the influence of surrounding gravity. As the project progresses, we will continue to increase the number of entangled particles in order to explore the transition to the classical regime of highly entangled states.

INTRODUCTION

At ultracold temperatures, neutral atoms can form a Bose-Einstein condensate (BEC). Such condensates can be manipulated with high accuracy and are used as the core of high-precision sensors and for the investigation of fundamental physical effects. In a dipole trap generated by a red detuned laser, atoms with any spin orientation can be trapped. Thus, the condensates gain a further degree of freedom and are referred to as Spinor condensates.

In project A02, spin-changing collisions in such a Spinor condensate are used to generate entanglement between the atoms. Different entangled states can be prepared. In the case of spin squeezed states, entanglement reduces quantum noise: The variance of a measured spin distribution can be below the classical shot noise. However, highly entangled states show non-Gaussian distributions and are generally more difficult to characterize. We investigate the generation and application of these complex atomic states.

RESULTS

In our experiment we created entanglement between two spatially separated clouds. We prepared a twin-Fock state in the first excited mode of the dipole trap. This mode divides naturally into two spatially separated clouds. We have developed a criterion to describe the entanglement between the two clouds and to prove it experimentally. Since the clouds could be addressed individually, our experiments open a way to use the available highly entangled states of indistinguishable particles for quantum information applications.

Visualization of the entanglement between the two separated atomic clouds.

If the boundary conditions of the quantum vacuum change over time, quantum field theory predicts that real, observable particles can occupy the initially empty modes. This process is called the dynamic Casimir effect. In our experiment we were able to realize this effect by periodically changing the boundary conditions of our Spinor BEC, that is the external homogeneous magnetic field. We could observe that initially unoccupied space and spin modes were occupied by entangled pairs of atoms. 

In addition, we were able to demonstrate the application of spin-squeezed states in an atomic clock, develop criteria for the characterization of multi-particle entanglement in our states, and showed that spin-changing collisions are also capable of reducing the influence of technical noise in the detection of the atoms.

FUTURE

We plan to use the current setup for the development of quantum logic techniques for state preparation of molecular ions that will be implemented using MgH+-ions. For that purpose, we will set up a high power, far detuned Raman laser to couple the molecule’s internal state to the shared motional degree of freedom. Simultaneous cooling of the motion via the logic ion provides a dissipation channel to eventually cool the molecules internal states.

In parallel we are working on a new experimental setup, where we plan to implement high precision quantum logic spectroscopy of molecular oxygen ions on a vibrational transition to infer a limit on a possible temporal variation of the proton-to-electron mass ratio.   


PUBLICATIONS

  • Anders F., Pezzè L., Smerzi A., Klempt C. (2018): Phase magnification by two-axis counter-twisting for detection noise robust interferometry
    DOI: 10.1103/PhysRevA.97.043813
  • Feldmann P., Gessner M., Gabbrielli M., Klempt C., Santos L., Pezzè L., Smerzi A. (2018): Interferometric sensitivity and entanglement by scanning through quantum phase transitions in spinor Bose-Einstein condensatesPhys. Rev. A 97, 032339
    DOI: 10.1103/PhysRevA.97.032339
  • K. Lange, J. Peise, B. Lücke, T. Gruber, A. Sala, A. Polls, W. Ertmer, B. Juliá-Díaz, L. Santos, C. Klempt (2018): Creation of entangled atomic states by an analogue of the Dynamical Casimir EffectNew J. Phys. 20 103017 (2018) More Info
    DOI: 10.1088/1367-2630/aae116
    arXiv: 1805.02560
  • Lange K., Peise J., Lücke B., Kruse I., Vitagliano G., Apellaniz I., Kleinmann M., Toth G., Klempt C. (2018): Entanglement between two spatially separated atomic modesScience 360, 416–418
    DOI: 10.1126/science.aao2035
  • Deuretzbacher, F.; Becker, D.; Bjerlin, J.; Reimann, S. M.; Santos, L. (2017): Spin-chain model for strongly interacting one-dimensional Bose-Fermi mixturesPhys. Rev. A 95, 043630
    DOI: 10.1103/PhysRevA.95.043630
  • Vitagliano G., Apellaniz I., Kleinmann M., Lücke B., Klempt C., Tòth G. (2017): Entanglement and extreme spin squeezing of unpolarized statesNew J. Phys. 19 , 013027 (2017).
    DOI: 10.1088/1367-2630/19/1/013027
  • Kruse, I.; Lange, K.; Peise, J.; Luecke, B.; Pezze, L.; Arlt, J.; Ertmer, W.; Lisdat, C.; Santos, L.; Smerzi, A.; Klempt, C. (2016): Improvement of an Atomic Clock using Squeezed VacuumPhys. Rev. Lett. 117, 143004
    DOI: 10.1103/PhysRevLett.117.143004
All publications of the Collaborative Research Centre

PROJECT LEADER

apl. Prof. Dr. Carsten Klempt
Address
Welfengarten 1
30167 Hannover
Building
Room
Address
Welfengarten 1
30167 Hannover
Building
Room
Prof. Dr. Luis Santos
Address
Appelstraße 2
30167 Hannover
Building
Room
249
Address
Appelstraße 2
30167 Hannover
Building
Room
249
Prof. Dr. Wolfgang Ertmer
Address
Welfengarten 1
30167 Hannover
Building
Room
Address
Welfengarten 1
30167 Hannover
Building
Room

STAFF

Alexander Idel
Alexander Idel
Fabian Anders
Fabian Anders