Session E24: Hybrid/Macroscopic Quantum Systems, Optomechanics, and Interfacing AMO with Solid State/Nano Systems I

Measuring Electromagnetic and Gravitational Responses of Photonic Landau Levels

Topology describes global properties insensitive to local perturbation or manipulation. Mathematical examples include knots in strings, where no manipulation of a closed loop besides cutting it can change its knottedness, and the genus (number of handles) of a closed surface, where no smooth deformation can change its number of handles. Topological materials have recently become a distinct focus in condensed matter physics, appearing famously in the quantum Hall effect and topological insulators.

Synthetic materials in which the constituent particles are photons trapped in an optical resonator offer an exciting platform on which to study topological materials. Recent efforts have realized broad control over the single-photon Hamiltonian, including a strong synthetic magnetic field for photons, and strong photon-photon interactions. In this talk, I will present how a nonplanar resonator can harbor a quantum Hall system in curved space. I will then discuss measurements of three distinct topological indices, offering insight onto their physical meaning and application. We measure the Chern number via real-space local projectors: non-reciprocal products of transmission amplitudes reveal an Aharanov-Bohm phase associated with a non-zero Chern number. Two additional topological invariants, the mean orbital spin and chiral central charge, are encoded in the variation of the local density of states near a singularity of spatial curvature, revealing a complex interplay between geometry and topology. I will conclude with a view towards the experimental introduction of interactions and the role these invariants play in characterizing topological phases of matter.
  

Dynamically Generated Synthetic Electric Fields for Photons

Static synthetic magnetic fields give rise to phenomena including the Lorentz force and the quantum Hall effect even for neutral particles, and they have by now been implemented in a variety of physical systems. Moving towards fully dynamical synthetic gauge fields allows, in addition, for backaction of the particles' motion onto the field. If this results in a time-dependent vector potential, conventional electromagnetism predicts the generation of an electric field. Here, we show how synthetic electric fields for photons arise self-consistently due to the nonlinear dynamics in a driven system. Our analysis is based on optomechanical arrays, where dynamical gauge fields arise naturally from phonon-assisted photon tunneling. We study open, one-dimensional arrays, where synthetic magnetic fields are absent. However, we show that synthetic electric fields can be generated dynamically. The generation of these fields depends on the direction of photon propagation, leading to a novel mechanism for a photon diode, inducing nonlinear unidirectional transport via dynamical synthetic gauge fields.
  

A polarization-selective cavity inside a hollow-core optical fiber

We fabricate and characterize a polarization-selective cavity inside a hollow-core optical fiber by attaching photonic-crystal (PC) membranes acting as metasurface mirrors to the end faces of a segment of such fiber. These slabs are comprised of a thin film of a dielectric material (silicon nitride) perforated with a pattern of holes where the reflective properties are dictated by the type and dimensions of the hole pattern. By breaking the x-y symmetry of the photonic crystal pattern using a rectangular lattice of elliptical holes, the mirrors become polarization-selective, i.e., the mirrors are highly reflective for one linear polarization and almost fully transparent for the orthogonal polarization. The holes of the PC slab allow injection of gasses into the hollow core of the fiber, which would not be possible if the fiber was capped with a dielectric stack mirror. The polarization selectivity is also a unique feature not possible with conventional mirrors.

This novel type of polarization dependent fiber-integrated cavity can enhance quantum optics schemes with atomic ensembles relying on cavity field and single-pass field with the ensemble by choosing the appropriate polarizations of the fields.   

Quantum Noise Free Thermal Noise Measurements of a Fabry-Perot Cavity

As gravitational wave measurements become more sensitive, they will start to be limited by quantum back action noise. Because effects like quantum radiation pressure noise have been previously measured, the next step is to remove these effects from measurement in a process called back action cancellation. Our system, consisting of a Fabry Perot cavity with a microfabricated movable mirror, is used to demonstrate cancellation of quantum back action. We first varify the pressence of this back action by measuring the light in reflection of the cavity. The cancellation is then performed by splitting the transmitted light from the cavity, sending it to two photo detectors, and cross correlating the outputs. By showing that the cross correlated output and previous measurements of thermal noise are the same, we confirm that these quantum effects have been eliminated from the measurement (because thermal noise is the next limiting noise source). These cancellations demonstrate a significant step towards the reduction of quantum radiation pressure noise effects in aLIGO and future generation detectors.   

Multimode Cavity Optomechanics in superfluid Helium droplets

The “minimal” optomechanical system consists in an optical cavity with a vibrating end mirror. There is, in this case, one optical mode coupled via radiation-pressure force to one mechanical mode [1].
Recently, it was proposed a novel optomechanical system based upon millimeter-size droplets of liquid Helium magnetically levitated in vacuum where the droplet serves both as optical and mechanical resonator [2]. The optical resonances are given by the whispering-gallery modes of light and the mechanical resonances by the vibrational surface modes. These about 10³ resonances ranges from 2π x 23 Hz to 2π x 219 kHz [3].
In this presentation we illustrate the principal unusual characteristics of the multimode dynamics [4] of the optically excited Helium droplet and we present some preliminary results about nonlinear effects.


[1] M. Aspelmeyer, T. J. Kippenberg and F. Marquardt, Rev. Mod. Phys 86, 1391 (2014).
[2] L. Childress et al., Phys. Rev. A 96, 063842 (2017).
[3] A. Aiello, J. Harris and F. Marquardt, arXiv:1809.02640 [physics.optics] (2018).
[4] H. Seok et al., Phys. Rev. A 88, 063850 (2013).   

Towards two spin-mechanical hybrid quantum systems

Hybrid quantum systems combine complimentary phenomena to enable breakthroughs in quantum mechanics, information processing, and simulation - from preparation of non-thermal states of mechanical objects, to quantum buses for long-distance entanglement of qubits. A particular hybrid quantum system with such potential can be achieved by combining the spins with a magnetic mechanical oscillator. Creating such a platform with high cooperativity is both desirable and challenging to implement: we need a large resonator zero-point motion and magnetic field gradient to maximize the coupling, while both the resonator and spin are isolated from the environment.

To address this challenge, we investigate two mechanical resonators, each of which are coupled to a spin: (i) high-Q nanobeam SiN resonators and (ii) levitated mechanical oscillators. In both cases, the small mass results in a large zero-point motion, and the geometry reduces coupling to the environment, thereby minimizing dissipation. For the spin, we use a nearby nitrogen-vacancy (NV) center defect in diamond, which features long coherence times. In this talk, we demonstrate progress towards these hybrid systems, each of which could open doors to unexplored regions of parameter space in the physics of quantum optics.   

Optimized single-shot laser ablation of concave mirror templates on optical fibers

In recent years, techniques have been developed to realize concave mirror templates on the tip of optical fibers. These can be used to define tunable open-access Fabry-Perot microcavities with high finesse. The combination of spectral tunability, high finesse, intrinsic fiber coupling and uniquely small dimensions offered by these optical cavities has led to their widespread adoption in the cavity quantum electrodynamics (CQED) community and to a lesser extent in the optomechanics community.
We realize mirror templates on the tips of optical fibers using a single-shot CO2 laser ablation procedure. We perform a systematic study of the influence of the pulse power, pulse duration, and laser spot size on the radius of curvature, depth, and diameter of the mirror templates. We find that these geometrical characteristics can be tuned to a larger extent than has been previously reported, and notably observe that compound convex-concave shapes can be obtained. This detailed investigation should help further the understanding of the physics of CO2 laser ablation processes and help improve current models. We additionally identify regimes of ablation parameters that lead to mirror templates with favorable geometries for use in cavity quantum electrodynamics and optomechanics.   

Topological phononics at the nanoscale: All-optical excitation and read-out of helical vibrations on a chip

We present the design of and numerical simulations for an on-chip optomechanical device that supports helical vibrations and allows all-optical excitation and read-out thereof. The device is based on a so-called optomechanical crystal, i. e. a nanostructure that supports both mechanical and optical bulk band gaps. The optomechanical crystal of interest is a patterned silicon slab. The pattern of holes has been engineered to give rise to i) topologically distinct domains separated by a domain wall of chosen shape supporting a broadband mechanical helical edge state, ii) high quality factor optical cavities that are localized close to the domain wall and display a good coupling to the helical states. As usual in optomechanics, the optomechanical coupling can be boosted by driving the optical cavities using a laser. This allows the excitation and the high-precision read out of the helical vibrations propagating along the domain wall.   

Magnon heralding in cavity optomagnonics

Cavity optomagnonics is an emergent field where photons couple to elementary magnetic excitations in solid state systems. For optical photons, the coupling is parametric and the magnetic material is both the optical cavity and the host of the magnetic excitations (magnons). These systems are promising for integration in hybrid quantum platforms. In this context, we propose a magnon heralding protocol to generate a magnon Fock state by detecting a cavity photon. We analyze the constraints imposed by the magnonic decay rate and by the strength of the optomagnonic coupling. We show that the detrimental thermal effects can be overcome by initially actively cooling the magnon mode. We discuss the feasibility of the proposed protocol for state of the art YIG cavity optomagnonic systems.   

Faddeev-Kulish Asymptotic States in Cold Atom Quantum Physisorption on 2D Materials

Theories with long-range interactions like QED or perturbative gravity exhibit severe infrared divergences in their scattering rates due to the emission of infinitely many soft quanta. Remarkably, a low-energy condensed matter analogue of this infamous infrared problem in QED is realized in a hybrid system of cold atoms coupled to a vibrating elastic membrane. We focus on the atom-phonon coupling of the vibrating membrane and provide procedures to address the infrared divergences. Our methods include non-perturbative techniques that can be broadly categorized into two schemes: (1) inclusion of emission of infinitely many soft-phonons and (2) dressing of asymptotic states which is similar in essence to the Faddeev-Kulish treatment of the infrared divergences in QED. We provide results for both the schemes in the spirit of the well-known exact solution of the independent boson model and discuss the validity of the results corresponding to the different scales of the infrared. In particular, we present the results of our resummation procedures for the physisorption rate of cold atomic hydrogen as function of membrane sizes and temperature.



  

Cavity Superconductor-Polaritons

Following the success of realizing exciton-polariton condensates in cavities, we examine the hybridization of cavity photons with the closest analog of excitons within a superconductor, states called Bardasis-Schrieffer modes. Though these modes do not typically couple linearly to light, one can engineer a coupling with an externally imposed supercurrent, leading to the formation of hybridized Bardasis-Schrieffer-polariton states, which we obtain both as poles of the bosonic Green's function and through the derivation of an effective Hamiltonian picture for the model. These new excitations have nontrivial overlap with both the original photon states and d-wave superconducting fluctuations. We conjecture that their condensation could produce a finite d-wave component of the superconducting order parameter -- an s±id superconducting state.   

Cavity superconductor Higgs-polaritons

Motivated by the dramatic success of cavity exciton-polariton physics we consider the formation of a polariton from cavity photons and the amplitude mode of a disordered superconductor. Enabled by the recently predicted and observed supercurrent-induced coupling between these excitations we find that signficant hybridization between cavity photons and Higgs excitations in a quasi-2D superconductor can occur. We analyze the character and damping of the hybrid modes.
  

Investigating Light-Matter Interactions Through the Coupling of Single Emitters to Bowtie Nanoantennas

Metallic nanoparticles, which confine light into very small volumes and greatly enhance fields, have many exceptional and tunable optical properties. Nanodimers known as bowtie nanoantennas are known to have strong field enhancements and confinement to the gap between the triangles. However, due to intrinsic ohmic losses, obtaining strong coupling between an emitter and the cavity remains an issue. In this study, to elucidate the effects of the nanometric positioning of the emitter, we employ super-resolution single-molecule fluorescence techniques to study the effects of detuning, polarization, orientation, nanometer gap size, and adhesion layer have on the fluorescence properties of the dye, as well as the trapping dynamics of the system. A clear set of optimal parameters has been found, aided by finite element simulations, hinting towards obtaining the maximal coupling for single emitters in this geometry.