CAVITY OPTOMECHANICS FROM THE MICRO- TO THE MACROSCALE

Transcription

1 CAVITY OPTOMECHANICS FROM THE MICRO- TO THE MACROSCALE Innsbruck, Nov 4 th 6 th, 2013 One of today s major challenges in quantum physics and technology is to reach the same outstanding level of quantum control obtained for cold neutral atoms or ions with fabricated devices. This includes quantum control of matter at or close to macroscopic length- and mass scales. As an emerging field pushing towards this listed goal, cavity optomechanics already shows remarkable experimental and theoretical progress and thereby covers a huge variety of mechanical devices that allow optical control and interfacing with light. While this successful development has profited from the existing methods developed in quantum optics with cold neutral atoms or ions over the years, there is little interplay between these communities at this stage. Progress can evidently be enhanced by bridging the gap between the two communities. To this end, this workshop plans to bring together experts from both areas of research to stimulate the mutual exchange, define future routes towards combining the assets of both fields and to discuss existing approaches. ORGANIZERS (Innsbruck) Claudiu Genes, Helmut Ritsch, and Raimar M. Sandner (Vienna) Nikolai Kiesel and Markus Aspelmeyer Bildunghaus Seehof der AK-Tirol Hungerburg, Gramartstraße Innsbruck, Austria

2 Wireless password: AKSeehof Conference dinner: Tuesday 20:00 The organizers Claudiu Genes Helmut Ritsch Raimar Sandner Nikolai Kiesel Markus Aspelmeyer

3 OVERVIEW TALK MONDAY Nov 4 th 2013 David Vitali (University of Camerino, Italy) André Xuereb (Queen's University Belfast, UK and University of Malta) Collective interactions and phonon dynamics in optomechanical arrays Over the past decade optomechanical technology has proven itself to be a remarkably flexible platform for studying the interaction between light and motion, constructing more sensitive interferometers, and interfacing optical and microwave signals. Recently, interest has surged in the behaviour of optomechanical arrays, where light couples to more than one scatterer. During this talk I shall discuss the idea of transmissive optomechanics with such arrays and explore how this technique lends itself not only to producing very strong interactions between light and motion but also long-ranged switchable interactions between pairs of elements in the array. As an application of these interactions I will look at the possibility to control the dynamics of phonons in the array Florian Marquardt (University of Erlangen, Germany) Optomechanical Arrays as Metamaterials Freestanding photonic crystals ('optomechanical crystals') can support localized vibrational and optical modes. If these defect modes are then arranged in a superlattice, an 'optomechanical array' would be formed. In this talk I will discuss how the bandstructure of such a material can be engineered to realize a variety of effects, such as optomechanical Dirac physics Oriol Romero-Isart (University of Innsbruck, Austria) Quantum magnetomechanics with levitating superconducting microspheres In this talk we will discuss the possibility to bring to the quantum regime the center of mass motion of a magnetically trapped superconducting microsphere close to a quantum circuit. Due to the absence of clamping losses and time-dependent electromagnetic fields, the mechanical motion of micrometer-sized metallic spheres in the Meissner state is predicted to be very well isolated

4 from the environment. We will discuss the advantages of using magnetically levitated superconducting microspheres, instead of optically levitated dielectric nanospheres, to prepare large quantum superpositions that can be used to test quantum mechanics in an unprecedented parameter regime Stefan Kuhn (University of Vienna and VCQ, Austria) Cavity cooling of free silicon nanoparticles in high vacuum Laser cooling techniques have given a great boost to the field of atomic physics throughout the last 30 years. Complex molecules and nanoparticles, however, cannot be controlled by these methods due to the lack of addressable cyclic transitions. In order to manipulate their motion, cavity cooling has been proposed more than 15 years ago (1,2) and was recently realised experimentally (3,4). We demonstrate transverse cavity cooling of a silicon nanoparticle while it transits a high finesse optical cavity. Irradiating the back-side of a silicon wafer with a focused pulsed laser beam we produce and launch the nanoparticles under high vacuum conditions. By detecting the scattered light from the particles we can trace their movement in real time and analyse the dynamics of a single particle. Advancing the current techniques will be crucial to enable quantum coherence experiments with nanoparticles. (1) Horak, P., Hechenblaikner, G., Gheri, K. M., Stecher, H. & Ritsch, H. Cavity-induced atom cooling in the strong coupling regime. Phys. Rev. Lett. 79, (1997) (2) Vuletic, V. & Chu, S. Laser cooling of atoms, ions, or molecules by coherent scattering. Phys. Rev. Lett. 84, (2000) (3) Kiesel, N. et al. Cavity cooling of an optically levitated nanoparticle. Proc. Natl. Acad. Sci. USA 110, (2013) (4) Asenbaum, P. et al. Cavity cooling of free silicon nanoparticles in high vacuum. Nat. Commun. doi: /ncomms3743 (accepted) Tristan Briant (Laboratoire Kastler Brossel, ENS, UPMC, CNRS, Paris, France) Cavity Optomechanics with Micro and Nano Resonators The Measurement and Quantum Noise group at Laboratoire Kastler Brossel is one of the very few optomechanics experimental groups with connections to both macroscopic resonators (within the Virgo collaboration) and microresonators with table-top experiments. The development of very high finesse optical cavities together with low-mass micro and nanomirrors opens the way to a new regime in which the dynamical properties of an opto-mechanical system are governed by the radiation pressure exerted by light on mirrors. This opto-mechanical coupling leads to quantum limits in ultra-sensitive interferometric measurements such as gravitational-wave detectors, but also to very efficient laser-cooling mechanisms. This may help to reach the quantum fundamental state of a macroscopic mechanical resonator, by cooling a micromirror down to a temperature unreachable by other conventional techniques.

5 Wolfgang Lechner (Institute for Quantum Optics and Quantum Information and University of Innsbruck, Austria) Resonant Cooling and Non-equilibrium Many- Body Dynamics of Nanospheres in a Cavity The interaction between dielectric particles and an optical mode leads to a classical optical potential and a dissipation mechanism. These two mechanisms can be used to trap and cool nanospheres in optical cavities. I will present a setup with two modes that are chosen such, that the classical potential cancels and only the dissipative part remains. This setup allows one to design dissipation with a linear and resonant cooling regime. In the linear regime, we study the non-equilibirum dynamics of nano-dumbbells. In the resonant regime we propose a setup to cool particles efficiently. This scheme can be enhanced by a time-dependent sweep in the detuning Peter Barker (Department of Physics and Astronomy, University College London, UK) Levitated optomechanics experiments at UCL In this talk I will give an overview and update of levitated optomechanics experiments currently underway at UCL. These include cavity cooling of nanospheres in an electrodynamic trap, the measurement of hot Brownian motion for temperature measurements on the nanoscale [1] and the use of levitated diamond with NV centres for matter-wave interferometry [2]. [1] J. Millen, T. Deesuwan, P. Barker, J. Anders, Nanoscale temperature measurements using nonequilibrium Brownian dynamics of a levitated nanosphere arxiv: [2] M. Scala, M. S. Kim, G. W. Morley, P. F. Barker, S. Bose, Matter Wave Interferometry of a Levitated Thermal Nano-Oscillator Induced and Probed by a Spin, arxiv: Gary A. Steele (Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands) Optomechanics of atomically thin membranes Mechanical membranes consisting of single-crystalline layers of only a few atoms thick have interesting potential as an optomechanical system due to their exceptionally light mass. In this talk, I will present two recent optomechanical experiements we have done with atomically thin membranes. In the first, we use an optical cavity formed naturally below a single layer of MoS 2 deposited over a hole and the substrate below. MoS 2 is a semiconducting analogue of graphene, attractive for industrial applications. Laser reflectometry of the cavity allows us to quickly characterize the mechanical properties of the membranes. We find that MoS 2 membranes at room temperature have quality factors comparable to graphene, and undergo a transition from a

6 bending-dominated plate for thicker layers to a tension-dominated drum behaviour for thin layers. In the second experiment, we couple to motion of a few-layer graphene membrane to microwave photons in a superconducting coplanar waveguide cavity at mk temperatures. Using a d.c. voltage in a dissipatively coupled geometry, we can tune the frequency of the graphene mechanical resonance, the frequency of the superconducting cavity, and the external coupling of the cavity. Using a microwave tone on the mechanical sideband, we observe optomechanically induced transparency and absorption, and use this to calibrate our optomechanical coupling. Our current experiement is approaching the strong coupling limit, suggesting that future experiments with some optimization of the setup should allow us to achieve the quantum ground state of a graphene mechanical resonator.

7 OVERVIEW TALK TUESDAY Nov 5 th, 2013 Andreas Hemmerich (Institut für Laser-Physik, Universität Hamburg, Germany) Peter Domokos (Institute for Solid State Physics and Optics, Wigner Research Centre for Physics,Hungarian Academy of Sciences, Budapest, Hungary) Aurélien Dantan (QUANTOP and Department of Physics and Astronomy, Aarhus University, Denmark) Ion crystals in intracavity optical potentials Cold trapped ions are a near-ideal system for optomechanics investigations, owing to their strong response to optical forces and the high level of control on their internal and external degrees of freedom. In particular, the interaction of Coulomb-interacting particles with steep periodic optical potentials is interesting for investigating structural or dynamical phase transitions, emulating cold solid-state models or enhancing the light-matter coupling in cavity QED experiments. I will present recent experiments on the pinning of few-ions Coulomb crystals in an intracavity optical lattice and some potential applications as well as discuss the prospects for using ion crystals in combination with membrane resonators in hybrid cavity optomechanics experiments Rafael Mottl (Institute for Quantum Electronics, ETH Zürich, Switzerland and Departments of Applied Physics, Physics and E.L. Ginzton Laboratory, Stanford University, US) From cavity optomechanics to the Dicke quantum phase transition with ultracold atoms Coupling motional degrees of freedom of a Bose-Einstein condensate to the field of an optical high-finesse cavity provides a way to realize different optomechanical interactions. Driving the cavity field directly allows the implementation of a 'generic' optomechanical coupling between cavity light field and atoms. Irradiating the atoms however by a transverse laser beam creates a Dicke-type optomechanical coupling. I will show how this second interaction leads to a mode

8 softening of an atomic momentum state and finally to the Dicke quantum phase transition. In our realization, the cavity provides a natural dissipation channel for the light which gives rise to vacuum-induced fluctuations on top of the ground state fluctuations. We observe the systems' dynamics via the cavity output field in real time which reveals the correlations and the spectrum of the enhanced atomic density fluctuations. The observed critical behavior deviates fundamentally from that expected for the closed Dicke model and is in quantitative agreement with open-system calculations for the driven-dissipative system Tracy E. Northup (University of Innsbruck, Austria) Prospects for ion-cavity optomechanics In recent years, an exceptional degree of quantum control has been demonstrated in trapped-ion systems. Moreover, the analogy between cavity QED and the ions' motional degrees of freedom has been central to the field's development. Nevertheless, only a few experiments currently trap ions in optical cavities, and optomechanics with these systems remains largely unexplored. I will give an overview of the state-of-the-art parameter regimes and the experimental tools at hand for engineering light-matter interactions. The focus will be both on identifying potential roles for ion cavity systems as platforms for optomechanics Tatjana Wilk (Max-Planck-Institut für Quantenoptik, Garching, Germany) Parametric feedback cooling of a single atom in an optical cavity An optical cavity can be used as a kind of intensifier to study radiation features of an atom, which are hard to detect in free space, like squeezing [1]. Such experiments make use of strong coupling between atom and cavity mode, which experimentally requires the atom to be well localized in the cavity mode. This can be achieved using feedback on the atomic motion: from intensity variations of a probe beam transmitted through the cavity information about the atomic motion is gained, which is used to synchronously modulate the trapping potential holding the atom, leading to cooling and better localization. Here, we report on efficient parametric feedback cooling of a single atom held in an intra-cavity standing wave dipole trap. In contrast to previous feedback strategies, this scheme cools the fast axial oscillation of the atom as well as the slower radial motion. [1] A.Ourjoumtsev et al., Nature 474, 623 (2011). [2] A. Kubanek et al., Nature 462, 898 (2009). [3] M. Koch et al., Phys. Rev. Lett. 105, (2010).

9 Darrick E. Chang (ICFO - Institut de Ciencies Fotoniques, Barcelona, Spain) Using single atoms coupled to nanophotonic systems as optomechanical elements The rapidly expanding field of optomechanics has revealed rich and unexpected ways in which the interplay between motion and optical response can be utilized. Recently, there have also been increasing efforts to couple cold atoms to nanophotonic systems. In such systems, the tight confinement of optical fields can yield both strong coupling to single atoms and strong forces. Given the close analogies between these two paradigms, an intriguing question is whether optomechanics can teach us new ways to manipulate atoms and their interactions with light. Here, we describe a remarkable example, in which an analogy of the dynamic optical spring effect enables atoms to be trapped by nanoscale quantum vacuum (e.g., Casimir) forces specially engineered through the underlying nanophotonic structure. The strength of nanoscale vacuum forces results in parameter regimes (such as trap depth, spatial confinement, and proximity to dielectric surfaces) an order of magnitude beyond what is possible by conventional atom trapping techniques Jens Eisert (Dahlem Center for Complex Quantum Systems, Freie Universitat Berlin, Germany) Opto-mechanical noise spectroscopy, unconventional decoherence, and Markovianity To exploit the detailed dynamics of a quantum system, it is crucial to obtain both good knowledge and control over its environment. In the first part of the talk, we present a method to reconstruct the relevant properties of the environment, that is, its spectral density, of the center of mass motion of an opto-mechanical oscillator. We observe a clear signature of non-markovian Brownian motion, which is in contrast to the current paradigm to treat the thermal environment of mechanical quantum resonators as fully Markovian. In the second part, we see how in systems allowing for obtaining full tomographic knowledge - such as for superconducting qubits - one can unambiguously detect non-markovianity of a continuous process from a single snapshot in time. If time allows, I will mention in an outlook other present group activities on opto-mechanics, related to employing opto-mechanical systems as thermal machines or issues of quantum synchronisation Tobias Griesser (University of Innsbruck, Austria) Light-Induced Crystallization of Cold Atoms Collective off-resonant scattering of coherent light by a cold gas induces long-range interactions via interference of light scattered by different particles. In a 1D configuration, these interactions

10 grow particularly strong by coupling the particles via an optical nanofiber. Above a threshold pump laser intensity, we predict a phase transition from a homogeneous density to a self-sustained crystalline order. In the dispersive regime, we determine the critical condition for the onset of order as well as the forms of gas density and electric field patterns above threshold. Surprisingly, there can coexist multiple ordered states with distinct appearances.

11 OVERVIEW TALK Wednesday Nov 6 th, 2013 Philipp Treutlein (Department of Physics, University of Basel, Switzerland) Klemens Hammerer (Institut für Theoretische Physik, Leibniz Universität Hannover, Germany) Peter Rabl (Institute of Atomic and Subatomic Physics, TU Wien, Austria) Phonon Cooling and Lasing with Nitrogen-Vacancy Centers in Diamond Diamond has emerged as a promising material for quantum applications, due in part to its optical and mechanical properties and in part to its addressable quantum defects. In this talk I will discuss the deformation potential interactions between nitrogen-vacancy (NV) centers and isolated mechanical modes in diamond nanostructures. I will show that even on a single phonon level, this coupling can lead to significant shifts of the electronic and spin levels of the defect center and could provide a new tool to access and manipulate the quantum state of macroscopic mechanical systems. I will describe applications of this coupling mechanism for actuation (lasing) and ground state cooling of diamond nanoresonators and discuss how phonon mediated interactions between the NV spin states can be used to generate spin squeezed states for magnetometry applications Patrick Maletinsky (Department of Physics, University of Basel, Switzerland) Spin-optomechanics using NV centres in diamond Hybrid optomechanical devices consisting of a nanomechanical oscillator which is coherently coupled to an individual quantum system are highly interesting for studying the crossover from quantum to classical physics and could one day yield novel types of high-performance sensing devices. Here, we report on our efforts towards establishing such a hybrid spin-oscillator system using Nitrogen-Vacancy (NV) centre spins embedded in single crystalline diamond nanomechanical oscillators. Coupling between the two entities is achieved by exploiting crystalline strain, which is induced by the cantilevers vibration. We demonstrate the first experimental evidence for this coupling mechanism by employing static and dynamical displacements of our cantilevers. As a Hallmark for spin-oscillator coupling, we present mechanical-oscillator induced sidebands to the

12 NV's electron spin resonance. Our results demonstrate first essential steps towards studying the quantum-dynamics of hybrid spin-oscillator systems, such as spin-based sideband cooling of a mechanical oscillator or the recently proposed generation of spin-squeezing in nanomechanical oscillators Mika Sillanpää (O V Lounasmaa Laboratory and Department of Applied Physics, Aalto University, Finland) Optomechanics with Josephson junction cavities One of the next challenges in optomechanics is to increase the single-quantum coupling strength to exceed the cavity dissipation rate. Motivated by this goal, we present a new design of the circuit optomechanical experiment, where the on-chip microwave cavity includes a Josephson charge qubit. This creates an effective cavity whose frequency is tunable by charge. The cavity is coupled to a micromechanical resonator whose motion is visible as charge, and hence affects the cavity frequency. We thereby obtain a radiation pressure interaction between the mechanical resonator and cavity. This way we were able to boost the coupling in the setup by six orders of magnitude up to (2 \pi) 1.5 MHz Eva M. Weig (Department of Physics, University of Konstanz, Germany) Coherent control and TLS-mediated damping of SiN nanoresonators Nanomechanical systems based on strongly prestressed silicon nitride (SiN) nanostrings are receiving considerable interest for their large mechanical quality factors exceeding several 100,000 at room temperature for the eigenfrequency range of 10 MHz. To realize the potential of these high Q resonators for applications in nano-electro- as well as nano-optomechanics, suitable control techniques are required. Here I will discuss recent progress in coherently controlling the dynamics of two strongly coupled modes of such a resonator by means of electromagnetic pulse techniques. The system can be described as a classical two-level system, adopting the well-known Bloch sphere picture. Analogous to the coherent control of two-level systems in atoms, spin ensembles or quantum bits, full Bloch sphere control is achieved by a combination of Rabi, Ramsey and Hahn echo experiments. Furthermore, our experiments enable deep insights into decoherence of nanomechanical vibration, which we find to be entirely limited by energy relaxation. Temperaturedependent damping measurements between 7 and 350 K suggest that, in turn, energy relaxation is limited by three-particle scattering with two-level defect systems (TLS) in the amorphous silicon nitride. This clearly opens up the perspective of enhancing the coherence of nanomechanical systems by engineering lower defect materials.

13 Paolo Tombesi (University of Camerino, Italy) Continuous Variables Quantum Relays with Cavity Opto-mechanics The continuous variables (CV) teleportation protocol is shown to be realizable at telecom wavelength by entangling two distant devices. These devices, one at Alice site and the other at Bob station, exploit the steady state entanglement generated by two optical beams at 1550 nm and 810 nm because of their interaction with a mechanical resonator in a Fabry-Perot cavity. The 810 nm light beams exiting the two devices are sent to Charlie who performs a swapping protocol entangling the two 1550 nm beams, realizing a steady state CV relay. An unknown coherent state is given to Alice who teleports it to Bob with very high fidelity using the standard CV protocol Mauro Paternostro (School of mathematics and physics, Queen's University Belfast, UK) Quantum feedback control of mechanical squeezing and work I will discuss a simple feedback control mechanism for the squeezing of a quantum harmonic oscillator embodied by the phononic mode of a mechanical oscillator. I will show how, when assuming appropriate working conditions, a simple adiabatic approach is able to induce mechanical squeezing. I will then go beyond the limitations of such a specific working point and demonstrate the possibility to induce stationary squeezing by using frequent repeated measurements and re-initialisation of the state of a simple two-level system ancilla that interacts with the oscillator. Finally, I will introduce the concept of work probability distribution following a quantum process and illustrate an optomechanical pathway for its experimental inference.

14 Monday Tuesday Wednesday S1 9:00 10:00: Overview (Vitali/Vitali) Coffee break 10:30 11:00: Xuereb 11:00 11:30: Marquardt 11:30 12:00: Romero-Isart S3 9:00 10:00: Overview (Hemmerich/Domokos) Coffee break 10:30 11:00: Dantan 11:00 11:30: Mottl 11:30 12:00: Northup S5 9:00 10:00: Overview (Treutlein/Hammerer) Coffee break 10:30 11:00: Rabl 11:00 11:30: Maletinsky 11:30 12:00: Sillanpää Lunch Break / Roundtable Discussions/ Informal Meetings S2 14:00 14:30: Kuhn S4 14:00 14:30: Wilk 14:30 15:00: Briant 14:30 15:00: Chang 15:00 15:30: Lechner 15:00 15:30: Eisert Coffee break 15:30 16:00: Griesser S6 14:00 14:30: Weig 14:30 15:00: Tombesi 15:00 15:30: Paternostro Coffee break 16:00 16:30: Barker 16:30 17:00: Steele 16:00 17:30: Future trends (plenary discussions) Poster Session 1 Workshop Dinner Poster Session 2