We theoretically study the coupling of Bose-Einstein condensed atoms to the mechanical oscillations of a nanoscale cantilever with a magnetic tip. This is an experimentally viable hybrid quantum system which allows one to explore the interface of quantum optics and condensed matter physics. We propose an experiment where easily detectable atomic spin-flips are induced by the cantilever motion. This can be used to probe thermal oscillations of the cantilever with the atoms. At low cantilever temperatures, as realized in recent experiments, the backaction of the atoms onto the cantilever is significant and the system represents a mechanical analog of cavity quantum electrodynamics. With high but realistic cantilever quality factors, the strong coupling regime can be reached, either with single atoms or collectively with Bose-Einstein condensates. We discuss an implementation on an atom chip. Quantum optics and condensed matter physics show a strong convergence. On the one hand, quantum optical systems, most notably neutral atoms in optical lattices, have been used to experimentally investigate concepts of condensed matter physics such as Bloch oscillations and Fermi surfaces [1]. On the other hand, micro-and nanostructured condensed matter systems enter a regime described by concepts of quantum optics, as exemplified by circuit cavity quantum electrodynamics [2], laser-cooling of mechanical resonators [3], and measurement backaction effects in cryogenic mechanical resonators [4]. A new exciting possibility beyond this successful conceptual interaction is to physically couple a quantum optical system to a condensed matter system. Such a hybrid quantum system can be used to study fundamental questions of decoherence at the transition between quantum and classical physics and has possible applications in precision measurement [5] and quantum information processing [6].Atom chips [7] are ideally suited for the implementation of hybrid quantum systems. Neutral atoms can be positioned with nanometer precision [8] and trapped at distances below 1 µm from the chip surface [9]. Coherent control of internal [10] and motional [11] states of atoms in chip traps is a reality. Atom-surface interactions are sufficiently understood [7] so that undesired effects can be mitigated by choice of materials and fabrication techniques. This is an advantage over systems such as ions or polar molecules on a chip, which have recently been considered in this context [6,12]. A first milestone is to realize a controlled interaction between atoms and a nanodevice on the chip surface.In this paper, we investigate magnetic coupling between the spin of atoms in a Bose-Einstein condensate (BEC) [13] and a single vibrational mode of a nanomechanical resonator [14] on an atom chip. We find that the BEC can be used as a sensitive quantum probe which allows one to detect the thermal motion of the resonator at room temperature. At lower resonator temperatures, the backaction of the atoms onto the resonator is significant and the coupled system realizes ...

We have realized a hybrid optomechanical system by coupling ultracold atoms to a micromechanical membrane. The atoms are trapped in an optical lattice, which is formed by retroreflection of a laser beam from the membrane surface. In this setup, the lattice laser light mediates an optomechanical coupling between membrane vibrations and atomic center-of-mass motion. We observe both the effect of the membrane vibrations onto the atoms as well as the backaction of the atomic motion onto the membrane. By coupling the membrane to laser-cooled atoms, we engineer the dissipation rate of the membrane. Our observations agree quantitatively with a simple model.

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...