Bose-Einstein Condensation in a Magnetic Lattice
We have realized an array of Bose-Einstein condensates of 87Rb F=1 atoms trapped in a 1D 10 μm-period magnetic lattice close to the surface of an atom chip [5,6]. The grooved structure which generates the magnetic lattice potential is fabricated on a silicon substrate and coated with a perpendicularly magnetized TbGdFeCo film (Fig. 1). The 87Rb atoms are optically pumped into the |F=1, mF=-1> low-field seeking state to minimize losses due to three-body recombination and then evaporatively cooled to ~10 μK in a Z-wire magnetic trap located below the atom chip. Using controlled axial confinement, typically 3x106 F=1 atoms are then loaded from the Z-wire trap into about 100 sites of the magnetic lattice located 8 μm below the chip.
Figure 2 shows part of a reflective absorption image for a periodic array of clouds of 87Rb F=1 atoms trapped in multiple sites of the 1D magnetic lattice. The clouds of atoms are clearly resolved in their individual lattice sites, which allows us to perform site-resolved measurements. Figure 3 presents in-situ radiofrequency (RF) spectra for a single lattice site after the atoms have been evaporatively cooled successively to temperatures below the critical temperature. The RF spectra provide a clear signature for the onset of BEC in the magnetic lattice, exhibiting a pronounced bimodal distribution consisting of a narrow component characteristic of a BEC together with a broad thermal cloud component. Similar bimodal distributions are found for various sites across the magnetic lattice.
The realization of a periodic array of BECs in a magnetic lattice represents a major step towards the implementation of magnetic lattices for quantum simulation of many-body condensed matter phenomena in lattices of complex geometry, such as triangular, honeycomb, Kagome and super-lattices, and sub-micron period.
Sub-Micron Period Magnetic Lattices
We have trapped ultracold 87Rb atoms in a 0.7 micron-period 2D triangular magnetic lattice on an atom chip . The magnetic lattice is created by a lithographically patterned Co/Pd multilayer magnetic film plus bias fields . Rubidium atoms in the |F=1, mF=-1> low-field seeking state are trapped at estimated distances down to about 100 nm from the chip surface and with calculated mean trapping frequencies as high as 800 kHz. The measured lifetimes of the atoms trapped in the magnetic lattice are in the range 0.4 - 1.7 ms, depending on distance from the chip surface. Model calculations suggest the trap lifetimes are currently limited mainly by losses due to surface-induced thermal evaporation following loading of the atoms from the Z-wire trap into the very tight magnetic lattice traps, rather than by fundamental loss processes such as surface interactions, three-body recombination or spin flips due to Johnson magnetic noise. The trapping of atoms in a 0.7 μm-period triangular magnetic lattice represents a significant step towards using magnetic lattices for quantum tunnelling experiments and to simulate condensed matter and many-body phenomena in nontrivial lattice geometries.
Simulating Quantum Spin Models using Rydberg Atoms in a Magnetic Lattice
We have proposed a scheme to simulate lattice spin models based on long-range interacting Rydberg atoms stored in a large-spacing (few μm) magnetic lattice . Each spin is encoded in a collective spin state involving a single nS or (n+1)S Rydberg atom excited from an ensemble of ground-state rubidium atoms prepared via Rydberg blockade. After the excitation laser is switched off, the Rydberg spin states on neighbouring lattice sites interact via general XXZ spin-spin interactions. To read out the collective spin states we propose a single-Rydberg atom triggered avalanche scheme in which the presence of a single Rydberg atom conditionally transfers a large number of ground-state atoms in the trap to an untrapped state which can be detected by standard site-resolved absorption imaging. Such a quantum simulator should allow the study of quantum spin systems in almost arbitrary 1D and 2D configurations. This paves the way towards engineering exotic spin models, such as spin models based on triangular-symmetry lattices which can give rise to frustrated-spin magnetism.
1. Trapping Ultracold Atoms in a Sub-Micron Period Triangular Magnetic Lattice
Y. Wang, T. Tran, P. Surendran, I. Herrera, A. Balcytis, D. Nissen, M. Albrecht, A. Sidorov and P. Hannaford
Physical Review A 96, 013630 (2017)
2. Simulating quantum spin models using Rydberg-excited atomic ensembles in magnetic microtrap arrays
Shannon Whitlock, Alexander Glaetzle, Peter Hannaford
Journal of Physics B: Atomic, Molecular and Optical Physics, 50, 074001 (2017)
3. Magnetic lattices for ultracold atoms and degenerate quantum gases
Yibo Wang, Prince Surendran, Smitha Jose, Tien Tran, Ivan Herrera, Shannon Whitlock, Russell McLean, Andrei Sidorov, Peter Hannaford
Science Bulletin 61, 1097-1106 (2016)
4. Sub-micron period lattice structures of magnetic microtraps for ultracold atoms on an atom chip
I. Herrera, Y. Wang, P. Michaux, D. Nissen, P. Surendran, S. Juodkazis, S. Whitlock, R.J. McLean, A. Sidorov, M. Albrecht and P. Hannaford
J. Phys. D: Appl. Phys. 48, 115002 (2015) arXiv:1410.0528
5. Radiofrequency spectroscopy of a linear array of Bose-Einstein condensates in a magnetic lattice.
P. Surendran, S. Jose, Y. Wang, I. Herrera, H. Hu, X. Liu, S. Whitlock, R. McLean, A. Sidorov, P. Hannaford
Phys. Rev. A 91, 023605 (2015)
6. Periodic array of Bose-Einstein condensates in a magnetic lattice.
S. Jose, P. Surendran, Y. Wang, I. Herrera, L. Krzemien, S. Whitlock, R. McLean, A. Sidorov and P. Hannaford
Phys. Rev. A 89, 051602(R) (2014)
7. Analysis of a simple square magnetic lattice for ultracold atoms
Saeed Ghanbari, Ahmed Abdalrahman, Andrei Sidorov and Peter Hannaford
J. Phys. B: Atomic, Molecular and Optical Physics 47, 115301 (2014)
8. From magnetic mirrors to atom chips
A. Sidorov and P. Hannaford
in Atom Chips (Eds. J. Reichel and V. Vuletic) Wiley-VCH Chapter 1, pp. 3-31 (2011)
9. Effect of projection velocity and temperature on the reflection of ultracold atoms from a periodic
one-dimensional corrugated magnetic potential
Mandip Singh and Peter Hannaford
Physical Review A 82, 013416 (2010)
10. Asymmetrical two-dimensional magnetic lattices for ultracold atoms
A. Abdelrahman, M. Vasiliev, K. Alameh and P. Hannaford
Physical Review A 82, 012320 (2010)
11. Superfluid to Mott insulator quantum phase transition in a 2D permanent magnetic lattice
S. Ghanbari, P. B. Blakie, P. Hannaford and T. D Kieu
Eur. Phys. J. B 70 305-310 (2009)
12. Adiabatically induced coherent Josephson oscillations of ultracold atoms in an asymmetric two-dimensional magnetic lattice
A. Abdelrahman, P. Hannaford and K. Alameh
Optics Express 17, 24358-70 (2009)
13. Dynamics of reflection of ultracold atoms from a periodic one-dimensional magnetic lattice potential
M. Singh, R. McLean, A. Sidorov and P. Hannaford
Phys. Rev. A 79, 053407 (2009)
14. One dimensional lattice of permanent magnetic microtraps for ultracold atoms on an atom chip
M. Singh, M. Volk, A. Akulshin, A. Sidorov, R. McLean and P. Hannaford
J. Phys. B: At. Mol. Opt. Phys. 41, 065301 (2008)
15. A class of permanent magnetic lattices for ultracold atoms
S. Ghanbari, T. D. Kieu and P. Hannaford
J. Phys. B: At. Mol. Opt. Phys. 40, 1283 (2007)
16. Permanent magnetic lattices for ultracold atoms and quantum degenerate gases
S. Ghanbari, T.D Kieu, A. Sidorov and P. Hannaford
J. Phys. B: At. Mol. Opt. Phys. 39, 847 (2006)
17. Perpendicularly magnetized grooved GdTbFeCo microstructures for atom optics.
J.Y. Wang, S. Whitlock, F. Scharnberg, D.S. Gough, A.I. Sidorov, R.J. McLean and P. Hannaford
J. Phys. D: Appl. Phys. 38, 4015-4020 (2005).