Backaction-Driven Transport of Bloch Oscillating Atoms in Ring Cavities

Abstract

We predict that an atomic Bose-Einstein condensate strongly coupled to an intracavity optical lattice can undergo resonant tunneling and directed transport when a constant and uniform bias force is applied. The bias force induces Bloch oscillations, causing amplitude and phase modulation of the lattice which resonantly modifies the site-to-site tunneling. For the right choice of parameters a net atomic current is generated. The transport velocity can be oriented oppositely to the bias force, with its amplitude and direction controlled by the detuning between the pump laser and the cavity. The transport can also be enhanced through imbalanced pumping of the two counter-propagating running wave cavity modes. Our results add to the cold atoms quantum simulation toolbox, with implications for quantum sensing and metrology.PACS numbers: 37.30.+i, 03.75.Lm, 42.50.Pq Periodic potentials play a prominent role in condensed matter systems, and highlight some of the fundamental differences between classical and quantum dynamics: a quantum particle undergoes strong scattering when its de Broglie wavelength satisfies the lattice Bragg condition, and can undergo tunneling through classically forbidden regions between sites. Furthermore, if a constant bias force F is applied a quantum particle is not transported in the direction of the force but instead performs Bloch oscillations with no net displacement at a frequency ω B = F d/ , where d is the lattice period [1]. Indeed, transport of electrons in lattices with an applied DC electric field only occurs as a result of dephasing processes such as scattering from lattice defects.Cold atoms present an especially attractive platform for studies of lattice systems because all of the critical parameters governing the dynamics are tunable in real time. In particular, it is possible to control tunneling and transport by modulating the potential in time. Transport in statistical phase space has been demonstrated in pulsed lattices, realizing the quantum delta-kicked rotor [2] and leading to dynamical localization [3] and chaosassisted tunneling [4]. Directed transport has been observed through ratchet effects in driven dissipative [5] and Hamiltonian lattices [6]. Tunneling control has been achieved through harmonic shaking of lattices without [7][8][9] and with [10, 11] a bias force. It is thus possible to control the superfluid-Mott insulator transition [12,13] and to induce macroscopic delocalization [14] and transport [15] of Bloch oscillating atoms. Recently photonassisted tunneling [16] has been studied in strongly correlated quantum gases [17,18], and artificial vector gauge potentials have been generated [19].What is missing in these schemes is backaction by the atoms upon the electromagnetic fields generating the lattice. Contrast this with the strong backaction effects seen in solids, such as lattice-phonon mediated Cooper pairing and the Meissner effect in superconductors. In principle an optically trapped atomic gas causes refraction of the lattice light, but extremely ...

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