Resonant Coupling of a Bose-Einstein Condensate to a Micromechanical Oscillator

Abstract

We report experiments in which the vibrations of a micromechanical oscillator are coupled to the motion of Bose-condensed atoms in a trap. The interaction relies on surface forces experienced by the atoms at about one micrometer distance from the mechanical structure. We observe resonant coupling to several well-resolved mechanical modes of the condensate. Coupling via surface forces does not require magnets, electrodes, or mirrors on the oscillator and could thus be employed to couple atoms to molecular-scale oscillators such as carbon nanotubes.PACS numbers: 37.10. Gh, 37.90.+j, 34.35.+a, 3.75.Kk, 3.75.Nt, 85.85.+j Ultracold atoms can be trapped and coherently manipulated close to a surface using chip-based magnetic microtraps ("atom chips") [1]. This opens the possibility of studying interactions between atoms and on-chip solid-state systems such as micro-and nanostructured mechanical oscillators [2, 3]. Such resonators have attracted much attention e.g. due to the extreme force sensitivity [2] down to the single spin level [4] and the novel manipulation techniques demonstrated in cavity optomechanics [3]. The question is raised whether the sophisticated toolbox for coherent manipulation of the quantum state of atoms could be employed to read out, cool, and coherently manipulate the oscillators' state. Several theoretical proposals have considered the coupling of micro-and nanomechanical oscillators to atoms [5][6][7][8][9], ions [10][11][12], and molecules [13]. They show that sufficiently strong and coherent coupling would enable studies of atom-oscillator entanglement, quantum state transfer, and quantum control of mechanical force sensors. In most scenarios, the coupling relies on local field gradients, calling for very close approach of the atoms to the oscillator. In this respect, ground-state neutral atoms stand out because preparation [14] and coherent manipulation [15] at micrometer distance from a solid surface has already been demonstrated on atom chips. While the intrinsically weak coupling of neutral atoms to the environment enables long coherence times, it makes coupling to solid-state degrees of freedom non-trivial. So far, only first steps have been made to investigate coupling mechanisms experimentally. Recently [16], atoms in a vapor cell were magnetically coupled to a mechanical oscillator. There, thermal motion of the atoms limits the interaction time and the control over the coupling.In our experiment, we use a Bose-Einstein condensate (BEC) of 87 Rb atoms [17] as a sensitive local probe for oscillations of a micromechanical cantilever. Benefiting from its small spatial extent (< 300 nm) and high positioning reproducibility (< 6 nm) in a magnetic microtrap, we place the BEC at about one micrometer distance from the surface of the cantilever. At such small distance, the magnetic trapping potential U m is substantially modified by the surface potential U s = U CP +U ad . It consists of the Casimir-Polder (CP) potential U CP [14, 18, 19] and an additional potential U ad due to surface...

Evaporative cooling of cold atoms at surfaces

“…There is potential to use such systems as quantum memory devices [13][14][15], precision measurement devices [16][17][18][19] and even rewritable electronic systems [20]. More recently, there have been proposals to use cold atoms to cool nanoscaled solid objects [21,22]; ion cooling using neutral atoms has already been demonstrated [23,24].…”

Quantum-measurement backaction from a Bose-Einstein condensate coupled to a mechanical oscillator

“…The robust and scalable infrastructure provided by micro-and nanoelectromechanical systems, coupled with the high-precision-measurement capability of quantum gases [5][6][7][8], makes them an attractive combination for sensitive force measurements, as well as for a quantitative study of dissipation and decoherence processes at the quantum-classical interface. As a result, there are ongoing experimental [9,10] and theoretical [11][12][13][14][15] efforts toward coupling mechanical systems to atomic ensembles.…”

Effects of classical stochastic webs on the quantum dynamics of cold atomic gases in a moving optical lattice

“…Delicate control potentials of this form could therefore be used for precise, nondestructive, quantum state preparation and coherent evolution. Our results also suggest different directions for experimental studies of BECs coupled to an oscillating cantilever or membrane [12]. In particular, stochastic webs may be created and used to control atom clouds by coupling the atoms, via the atom-surface Casimir-Polder attraction, to mechanical standing waves along the nearby solid-state oscillator.…”

“…Conversely, studies of the interactions of ultracold atoms with real crystal lattices, for example semiconductor surfaces, have highlighted the strong Casimir-Polder attraction of atoms to a surface that is approximately 1 μm away and have shown how that attraction can facilitate interaction between atomic gases and condensed matter [9][10][11]. For example, the Casimir-Polder attraction has been used to couple BECs in a harmonic trap to a vibrating SiN cantilever whose mean position is of the order of 1 μm away from the trap center [12]. Dynamical perturbations have also been applied to BECs by using oscillating OLs [13][14][15] and by exploiting Feshbach resonances to create a periodic driving term [16].…”