Vacuum levitation and motion control on chip.

By isolating from the environment and precisely controlling mesoscopic objects, levitation in vacuum has evolved into a versatile technique that has already benefited diverse scientific directions, from force sensing and thermodynamics to materials science and chemistry. It also holds great promise for advancing the study of quantum mechanics in the unexplored macroscopic regime. However, most current levitation platforms are complex and bulky. Recent efforts in miniaturization of vacuum levitation set-ups have comprised electrostatic and optical traps, but robustness is still a concern for integration into confined settings, such as cryostats or portable devices. Here we show levitation and motion control in high vacuum of a silica nanoparticle at the surface of a hybrid optical-electrostatic chip. By combining fibre-based optical trapping and sensitive position detection with cold damping through planar electrodes, we cool the particle motion to a few hundred phonons. We envisage that our fully integrated platform is the starting point for on-chip devices combining integrated photonics and nanophotonics with precisely engineered electric potentials, enhancing control over the particle motion towards complex state preparation and read-out.

Levitated Optomechanics with Meta-Atoms.

We propose to introduce additional control in levitated optomechanics by trapping a meta-atom, i.e., a subwavelength and high-permittivity dielectric particle supporting Mie resonances. In particular, we theoretically demonstrate that optical levitation and center-of-mass ground-state cooling of silicon nanoparticles in vacuum is not only experimentally feasible but it offers enhanced performance over widely used silica particles in terms of trap frequency, trap depth, and optomechanical coupling rates. Moreover, we show that, by adjusting the detuning of the trapping laser with respect to the particle's resonance, the sign of the polarizability becomes negative, enabling levitation in the minimum of laser intensity, e.g., at the nodes of a standing wave. The latter opens the door to trapping nanoparticles in the optical near-field combining red and blue-detuned frequencies, in analogy to two-level atoms, which is of interest for generating strong coupling to photonic nanostructures and short-distance force sensing.

Ultrathin Tunable Optomechanical Metalens.

Reconfigurable metasurfaces offer great promises to enhance photonics technology by combining integration with improved functionalities. Recently, reconfigurability in otherwise static metasurfaces has been achieved by modifying the electric permittivity of the meta-atoms themselves or their immediate surrounding. Yet, it remains challenging to achieve significant and fast tunability without increasing bulkiness. Here, we demonstrate an ultrathin tunable metalens whose focal distance can be changed through optomechanical control with moderate continuous wave intensities. We achieve fast focal length changes of more than 5% with response time of the order of 10 µs.

Precision Calibration of the Duffing Oscillator with Phase Control.

The Duffing oscillator is a nonlinear extension of the ubiquitous harmonic oscillator and as such plays an outstanding role in science and technology. Experimentally, the system parameters are determined by a measurement of its response to an external excitation. When changing the amplitude or frequency of the external excitation, a sudden jump in the response function reveals the nonlinear dynamics prominently. However, this bistability leaves part of the full response function unobserved, which limits the precise measurement of the system parameters. Here, we exploit the often unknown fact that the response of a Duffing oscillator with nonlinear damping is a unique function of its phase. By actively stabilizing the oscillator's phase we map out the full response function. This phase control allows us to precisely determine the system parameters. Our results are particularly important for characterizing nanoscale resonators, where nonlinear effects are observed readily and which hold great promise for next generation of ultrasensitive force and mass measurements. We demonstrate our approach experimentally with an optically levitated particle in high vacuum.

A Chemical Nanoreactor Based on a Levitated Nanoparticle in Vacuum.

A single levitated nanoparticle is used as a nanoreactor for studying surface chemistry at the nanoscale. Optical levitation under controlled pressure, surrounding gas composition, and humidity provides extreme control over the nanoparticle, including dynamics, charge, and surface chemistry. Using a single nanoparticle avoids ensemble averages and allows studying how the presence of silanol groups at its surface affects the adsorption and desorption of water from the background gas with excellent spatial and temporal resolution. Herein, we demonstrate the potential of this versatile platform by studying the Zhuravlev model in silica particles. In contrast to standard methods, our system allowed the observation of an abrupt and irreversible change in scattering cross section, mass, and mechanical eigenfrequency during the dehydroxylation process, indicating changes in density, refractive index, and volume.

Mechanical Squeezing via Unstable Dynamics in a Microcavity.

We theoretically show that strong mechanical quantum squeezing in a linear optomechanical system can be rapidly generated through the dynamical instability reached in the far red-detuned and ultrastrong coupling regime. We show that this mechanism, which harnesses unstable multimode quantum dynamics, is particularly suited to levitated optomechanics, and we argue for its feasibility for the case of a levitated nanoparticle coupled to a microcavity via coherent scattering. We predict that for submillimeter-sized cavities the particle motion, initially thermal and well above its ground state, becomes mechanically squeezed by tens of decibels on a microsecond timescale. Our results bring forth optical microcavities in the unresolved sideband regime as powerful mechanical squeezers for levitated nanoparticles, and hence as key tools for quantum-enhanced inertial and force sensing.

Strong optomechanical coupling at room temperature by coherent scattering.

Quantum control of a system requires the manipulation of quantum states faster than any decoherence rate. For mesoscopic systems, this has so far only been reached by few cryogenic systems. An important milestone towards quantum control is the so-called strong coupling regime, which in cavity optomechanics corresponds to an optomechanical coupling strength larger than cavity decay rate and mechanical damping. Here, we demonstrate the strong coupling regime at room temperature between a levitated silica particle and a high finesse optical cavity. Normal mode splitting is achieved by employing coherent scattering, instead of directly driving the cavity. The coupling strength achieved here approaches three times the cavity linewidth, crossing deep into the strong coupling regime. Entering the strong coupling regime is an essential step towards quantum control with mesoscopic objects at room temperature.

Resolved-Sideband Cooling of a Levitated Nanoparticle in the Presence of Laser Phase Noise.

We investigate the influence of laser phase noise heating on resolved sideband cooling in the context of cooling the center-of-mass motion of a levitated nanoparticle in a high-finesse cavity. Although phase noise heating is not a fundamental physical constraint, the regime where it becomes the main limitation in Levitodynamics has so far been unexplored and hence embodies from this point forward the main obstacle in reaching the motional ground state of levitated mesoscopic objects with resolved sideband cooling. We reach minimal center-of-mass temperatures comparable to T_{min}=10 mK at a pressure of p=3×10^{-7} mbar, solely limited by phase noise. Finally we present possible strategies towards motional ground state cooling in the presence of phase noise.

Optimal Feedback Cooling of a Charged Levitated Nanoparticle with Adaptive Control.

We use an optimal control protocol to cool one mode of the center-of-mass motion of an optically levitated nanoparticle. The feedback technique relies on exerting a Coulomb force on a charged particle with a pair of electrodes and follows the control law of a linear quadratic regulator, whose gains are optimized by a machine learning algorithm in under 5 s. With a simpler and more robust setup than optical feedback schemes, we achieve a minimum center-of-mass temperature of 5 mK at 3×10^{-7} mbar and transients 10-600 times faster than cold damping. This cooling technique can be easily extended to 3D cooling and is particularly relevant for studies demanding high repetition rates and force sensing experiments with levitated objects.

Observation of Two-Dimensional Localized Jones-Roberts Solitons in Bose-Einstein Condensates.

Jones-Roberts solitons are the only known class of stable dark solitonic solutions of the nonlinear Schrödinger equation in two and three dimensions. They feature a distinctive elongated elliptical shape that allows them to travel without change of form. By imprinting a triangular phase pattern, we experimentally generate two-dimensional Jones-Roberts solitons in a three-dimensional atomic Bose-Einstein condensate. We monitor their dynamics, observing that this kind of soliton is indeed not affected by dynamic (snaking) or thermodynamic instabilities, that instead make other classes of dark solitons unstable in dimensions higher than one. Our results confirm the prediction that Jones-Roberts solitons are stable solutions of the nonlinear Schrödinger equation and promote them for applications beyond matter wave physics, like energy and information transport in noisy and inhomogeneous environments.

[µ-1,1'-Bis(diphenyl-phosphino)ferro-cene-κP:P']bis-[chloridogold(I)]-chloro-form-hexane (2/2/1).

In the title mixed solvate, [Au(2)Fe(C(17)H(14)P)(2)Cl(2)]·CHCl(3)·0.5CH(3)(CH(2))(4)CH(3), the hexane solvent mol-ecule is disposed about an inversion centre. The Au atoms exist within nearly ideal linear coordination defined by P,Cl-donor sets, and when viewed down the P⋯P axis the Au atoms are gauche to each other. In the crystal structure, the chloro-form solvent mol-ecule is associated with the complex via a C-H⋯Cl contact, and the hexane solvent mol-ecules occupy voids defined by the remaining components of the structure.

The contributions of encoding, retention, and recall to the Hebb effect.

The article reports an experiment testing whether the Hebb repetition effect-the gradual improvement of immediate serial recall when the same list is repeated several times-depends on overt recall of the repeated lists. Previous reports which suggest that recall is critical confound the recall manipulation with retention interval. The present experiment orthogonally varies retention interval (0 or 9 s) and whether the list is to be recalled after the retention interval. Hebb repetition learning is assessed in a final test phase. A repetition effect was obtained in all four experimental conditions; it was larger for recalled than non-recalled lists, whereas retention interval had no effect. The results show that encoding is sufficient to generate cumulative long-term learning, which is strengthened by recall. Rehearsal, if it takes place in the retention interval at all, does not have the same effect on long-term learning as overt recall.

Establishment of hapten-specific monoclonal avian IgY by conversion of antibody fragments obtained from combinatorial libraries.

Nowadays, recombinant antibody and phage display technology enable the efficient generation of immunotools and a subsequent manipulation for optimized affinity, specificity or overall performance. Such advantages are of particular interest for haptenic target structures, such as TNT (2,4,6-trinitrotoluene). The toxicity of TNT and its breakdown products makes a reliable and fast detection of low levels in aqueous samples highly important. In the present study, we aimed for the generation of scFvs (single-chain antibody fragments) specific for the TNT-surrogate TNP (2,4,6-trinitrophenyl) and their subsequent production as monoclonal avian IgY immunoglobulins providing improved assay performance. Therefore we subjected a human synthetic scFv library to selection following different strategies. TNP-specific human antibody fragments could be identified, characterized for their primary structure and evaluated for production as soluble scFv in Escherichia coli. Additionally, a murine TNP-specific antibody fragment was obtained from the hybridoma 11B3; however, the prokaryotic expression level was found to be limited. To generate and evaluate immunoglobulin formats with superior characteristics, all recombinant antibody fragments then were converted into two different chimaeric bivalent IgY antibody formats. After expression in mammalian cells, the IgY antibodies were assessed for their reactivity towards TNT. The IgY antibodies generated on the basis of the combinatorial library proved to be useful for detection of TNT, thereby emphasizing the high potential of this approach for the development of detection devices for immunoassay-based techniques.

Strain-specific susceptibility for neurodegeneration in a rat model of autoimmune optic neuritis.

Heterogeneity in clinical disease course and histopathology complicates the treatment of multiple sclerosis. We detected important differences in neurodegeneration in various subtypes of myelin oligodendrocyte glycoprotein (MOG)-induced optic neuritis. Dark Agouti (DA) rats showed a significantly higher survival of retinal ganglion cells in comparison to Brown Norway rats. After surgical transection of the optic nerve neuronal loss was similar in both rat strains. We identified an increased expression of interleukin 1beta and glial cell line-derived neurotrophic factor in DA rats as the possible mechanism of the observed endogenous neuroprotection in MOG-induced optic neuritis.

Human guanylate binding protein-1 is a secreted GTPase present in increased concentrations in the cerebrospinal fluid of patients with bacterial meningitis.

Interferon-gamma-induced GTPases are key to the protective immunity against microbial and viral pathogens. As yet, the cell interior has been regarded as the exclusive residence of these proteins. Here we show that a member of this group, human guanylate binding protein-1 (hGBP-1), is secreted from cells. Secretion occurred in the absence of a leader peptide via a nonclassical, likely ABC transporter-dependent, pathway, was independent of hGBP-1 GTPase activity and isoprenylation, and did not require additional interferon-gamma-induced factors. Interestingly, hGBP-1 was only secreted from endothelial cells but not from any of the nine different cell types tested. Clinically most important was the detection of significantly (P<0.001, Mann-Whitney U-test) increased hGBP-1 concentrations in the cerebrospinal fluid of patients with bacterial meningitis (n=32) as compared to control patients (n=74). In this first report of a secreted GTPase, we demonstrate that secreted hGBP-1 may be a useful surrogate marker for diagnosis of bacterial meningitis.