Atomtronics

Abstract: 1. Introduction 2. Statistical physics of condensed matter: basic concepts 3. Ultracold gases in optical lattices: Basic concepts 4. Quantum simulators of condensed matter 5. Bose Hubbard models: Methods of treatment 6. Fermi and Fermi-Bose Hubbard models: Methods of treatment 7. Ultracold spinor atomic gases 8. Ultracold dipolar gases 9. Disordered ultracold atomic gases 10. Frustrated models in cold atom systems 11. Ultracold atomic gases in " gauge fields 12. Many body physics from a quantum information perspective 13. Quantum information with lattice gases 14. Detection of quantum systems realised with ultracold atoms 15. Summary and future perspectives Bibliography

Abstract: There is a pressing need for robust and straightforward methods to create potentials for trapping Bose?Einstein condensates (BECs) that are simultaneously dynamic, fully arbitrary and sufficiently stable to not heat the ultracold gas. We show here how to accomplish these goals, using a rapidly moving laser beam that 'paints' a time-averaged optical dipole potential in which we create BECs in a variety of geometries, including toroids, ring lattices and square lattices. Matter wave interference patterns confirm that the trapped gas is a condensate. As a simple illustration of dynamics, we show that the technique can transform a toroidal condensate into a ring lattice and back into a toroid. The technique is general and should work with any sufficiently polarizable low-energy particles.

Abstract: Hysteresis is observed between circulation states in an ‘atomtronic’ circuit formed from a ring of superfluid Bose–Einstein condensate obstructed by a rotating weak link (a region of low atomic density), and may prove as crucial in future atomtronic devices as it has done in electronic devices. Hysteresis, a phenomenon by which the physical properties of a system depend strongly on the history of the applied perturbation, is widely exploited in electronic circuits including hard disk drives and flux-gate magnetometers and is essential to the function of radio-frequency SQUIDs (superconducting quantum interference devices). Hysteresis is also fundamental to superfluidity and has been predicted to occur in superfluid atomic-gases, such as Bose–Einstein condensates (BECs). Gretchen Campbell and colleagues now report the first direct detection of hysteresis between quantized circulation states in a circuit formed from a ring of superfluid BEC obstructed by a rotating weak link. The presence of hysteresis in this system is of importance in the emerging field of 'atomtronics', in which ultracold atoms have a role analogous to that of the electrons in electronics. Controlled hysteresis in atomtronic circuits may prove to be a crucial feature for the development of practical devices. Atomtronics1,2 is an emerging interdisciplinary field that seeks to develop new functional methods by creating devices and circuits where ultracold atoms, often superfluids, have a role analogous to that of electrons in electronics. Hysteresis is widely used in electronic circuits—it is routinely observed in superconducting circuits3 and is essential in radio-frequency superconducting quantum interference devices4. Furthermore, it is as fundamental to superfluidity5 (and superconductivity) as quantized persistent currents6,7,8, critical velocity9,10,11,12,13,14 and Josephson effects15,16. Nevertheless, despite multiple theoretical predictions5,17,18,19, hysteresis has not been previously observed in any superfluid, atomic-gas Bose–Einstein condensate. Here we directly detect hysteresis between quantized circulation states in an atomtronic circuit formed from a ring of superfluid Bose–Einstein condensate obstructed by a rotating weak link (a region of low atomic density). This contrasts with previous experiments on superfluid liquid helium where hysteresis was observed directly in systems in which the quantization of flow could not be observed20, and indirectly in systems that showed quantized flow21,22. Our techniques allow us to tune the size of the hysteresis loop and to consider the fundamental excitations that accompany hysteresis. The results suggest that the relevant excitations involved in hysteresis are vortices, and indicate that dissipation has an important role in the dynamics. Controlled hysteresis in atomtronic circuits may prove to be a crucial feature for the development of practical devices, just as it has in electronic circuits such as memories, digital noise filters (for example Schmitt triggers) and magnetometers (for example superconducting quantum interference devices).

Abstract: Atomtronics focuses on atom analogs of electronic materials, devices, and circuits. A strongly interacting ultracold Bose gas in a lattice potential is analogous to electrons in solid-state crystalline media. As a consequence of the gapped many-body energy spectrum, cold atoms in a lattice exhibit insulatorlike or conductorlike properties. $P$-type and $N$-type material analogs are created by introducing impurity sites into the lattice. Current through an atomtronic wire is generated by connecting the wire to an atomtronic battery which maintains the two contacts at different chemical potentials. The design of an atomtronic diode with a strongly asymmetric current-voltage curve exploits the existence of superfluid and insulating regimes in the phase diagram. The atom analog of a bipolar junction transistor exhibits large negative gain. Our results provide the building blocks for more advanced atomtronic devices and circuits such as amplifiers, oscillators, and fundamental logic gates.