Project A02: Entanglement in momentum space

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

In the beginning of the second funding period, the generation of highly entangled states was mainly restricted to the creation of spin correlations, where the external degrees of freedom remain untouched. However, the creation of entanglement in external degrees of freedom is highly desirable: Entangled atomic states in external degrees of freedom can improve inertially sensitive atom interferometers beyond the Standard Quantum Limit (SQL). Entangled ensembles of ultra-cold atoms provide an ideal source for highest-precision atom interferometry, as they offer perfect mode control and low densities to suppress systematic effects, and offer a superior phase resolution for a given atomic flux. Furthermore, they constitute fascinating quantum-mechanical probes for tests of fundamental physics, most prominently in their interaction with gravitational fields.

Results

Our generation of high-fidelity Twin-Fock states enabled sub-SQL interferometry, featuring a high degree of entanglement. However, the employed process led to strong fluctuations of the total number of particles. The fluctuations are unwanted for the application of Twin-Fock states in atom interferometry, where a steady atom number is desirable. Based on our study in the first funding period and previous work, we have implemented the adiabatic generation of entangled states.

We have constructed a Raman laser system, where the laser intensities of the two beams and the relative phase between them is actively stabilized. Because of the intensity stabilisation, the Raman laser can be precisely operated on the specific intensity ratio, where it is insensitive to first-order intensity drifts, enabling an unprecedented contrast close to 100%.

Based on the adiabatic generation of Twin-Fock states and the developed Raman laser system, we were able to create Twin-Fock states in spin space and transfer them to momentum space. This achievement presents an important requirement for entanglement-enhanced gravimetry.

We have used our system of Bose-Einstein condensates with spin degree of freedom for an investigation of excited-state quantum phases, as proposed for the second funding phase. The ground-state phases of a quantum many-body system are characterised by an order parameter, which changes abruptly at quantum phase transitions when an external control parameter is varied. Interestingly, these concepts may be extended to excited states, for which it is possible to define equivalent excited-state quantum phase transitions. However, the experimental mapping of a phase diagram of excited quantum states was not realized so far. We were able to demonstrate the experimental determination of the excited-state phase diagram in our spinor Bose-Einstein condensates, where, crucially, the excitation energy is one of the control parameters.


Publications

Showing results 1 - 13 out of 13

Meyer-Hoppe B, Baron M, Cassens C, Anders F, Idel A, Peise J et al. Dynamical low-noise microwave source for cold-atom experiments. Review of Scientific Instruments. 2023 Jul;94(7):074705. doi: 10.48550/arXiv.2003.10989, 10.1063/5.0160367
Meyer-Hoppe B, Anders F, Feldmann P, Santos L, Klempt C. Excited-State Phase Diagram of a Ferromagnetic Quantum Gas. Physical Review Letters. 2023 Dec;131(24):243402. Epub 2023 Dec 13. doi: 10.48550/arXiv.2301.10655, 10.1103/PhysRevLett.131.243402
Vitagliano G, Fadel M, Apellaniz I, Kleinmann M, Lücke B, Klempt C et al. Number-phase uncertainty relations and bipartite entanglement detection in spin ensembles. Quantum. 2023 Feb 9;7:914. Epub 2021 Apr 12. doi: 10.48550/arXiv.2104.05663, 10.22331/q-2023-02-09-914
Anders F, Idel A, Feldmann P, Bondarenko D, Loriani S, Lange K et al. Momentum Entanglement for Atom Interferometry. Physical Review Letters. 2021 Oct 1;127(14):140402. Epub 2021 Sept 29. doi: 10.1103/PhysRevLett.127.140402
Feldmann P, Klempt C, Smerzi A, Santos L, Gessner M. Interferometric Order Parameter for Excited-State Quantum Phase Transitions in Bose-Einstein Condensates. Physical review letters. 2021 Jun 10;126(23):230602. doi: 10.1103/PhysRevLett.126.230602
Chu A, Will J, Arlt J, Klempt C, Rey AM. Simulation of XXZ spin models using sideband transitions in trapped bosonic gases. Physical review letters. 2020 Dec 7;125(24):240504. doi: 10.48550/arXiv.2004.01282, 10.1103/PhysRevLett.125.240504
Anders F, Pezzè L, Smerzi A, Klempt C. Phase magnification by two-axis countertwisting for detection-noise robust interferometry. Physical Review A. 2018 Apr;97(4):043813. Epub 2018 Apr 9. doi: 10.1103/PhysRevA.97.043813, 10.15488/3591
Feldmann P, Gessner M, Gabbrielli M, Klempt C, Santos L, Pezzè L et al. Interferometric sensitivity and entanglement by scanning through quantum phase transitions in spinor Bose-Einstein condensates. Physical Review A. 2018 Mar;97(3):032339. Epub 2018 Mar 27. doi: 10.1103/PhysRevA.97.032339, 10.15488/3586
Lange K, Peise J, Lücke B, Gruber T, Sala A, Polls A et al. Creation of entangled atomic states by an analogue of the Dynamical Casimir effect. New journal of physics. 2018 Oct;20(10):103017. Epub 2018 Oct 12. doi: 10.1088/1367-2630/aae116, 10.15488/4888
Lange K, Peise J, Lücke B, Kruse I, Vitagliano G, Apellaniz I et al. Entanglement between two spatially separated atomic modes. Science. 2018 Apr 27;360(6387):416-418. doi: 10.48550/arXiv.1708.02480, 10.1126/science.aao2035
Deuretzbacher F, Becker D, Bjerlin J, Reimann SM, Santos L. Spin-chain model for strongly interacting one-dimensional Bose-Fermi mixtures. Physical Review A. 2017 Apr 21;95(4):043630. doi: 10.1103/PhysRevA.95.043630
Vitagliano G, Apellaniz I, Kleinmann M, Lücke B, Klempt C, Tóth G. Entanglement and extreme spin squeezing of unpolarized states. New Journal of Physics. 2017 Jan 20;19(1):013027. doi: 10.1088/1367-2630/19/1/013027
Kruse I, Lange K, Peise J, Lücke B, Pezzè L, Arlt J et al. Improvement of an Atomic Clock using Squeezed Vacuum. Physical review letters. 2016 Sept 28;117(14):143004. Epub 2016 May 25. doi: 10.1103/PhysRevLett.117.143004, 10.15488/3585
All publications of the Collaborative Research Centre

Project leader

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

Staff

Alexander Idel
Alexander Idel
Fabian Anders
Fabian Anders
Bernd Meyer-Hoppe
Bernd Meyer-Hoppe
Christophe Cassens
Christophe Cassens