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Quantum technologies

Dieter Meschede's research group
Home Fibre cavity QED People Hannes Pfeifer
People - Fibre cavity QED
Dr. Hannes Pfeifer
Position: Postgraduate student
Field of research: Fibre cavity QED
Institut für Angewandte Physik
Wegelerstr. 8
D-53115 Bonn
Office room: 114
E-mail: This e-mail address is being protected from spam bots, you need JavaScript enabled to view it.
Office: +49 228 73-6580
Fax: +49 228 73-3474
Webpage: https://scholar.google.de/citations?user=RM0iyAgAAAAJ&hl=en&oi=ao


  • H. Ren, T. Shah, H. Pfeifer, C. Brendel, V. Peano, F. Marquardt and O. Painter
    Topological phonon transport in an optomechanical system, arXiv:2009.06174, (2020)arXivBibTeX

    Recent advances in cavity-optomechanics have now made it possible to use light not just as a passive measuring device of mechanical motion, but also to manipulate the motion of mechanical objects down to the level of individual quanta of vibrations (phonons). At the same time, microfabrication techniques have enabled small-scale optomechanical circuits capable of on-chip manipulation of mechanical and optical signals. Building on these developments, theoretical proposals have shown that larger scale optomechanical arrays can be used to modify the propagation of phonons, realizing a form of topologically protected phonon transport. Here, we report the observation of topological phonon transport within a multiscale optomechanical crystal structure consisting of an array of over 800 cavity-optomechanical elements. Using sensitive, spatially resolved optical read-out we detect thermal phonons in a 0.325 - 0.34 GHz band traveling along a topological edge channel, with substantial reduction in backscattering. This represents an important step from the pioneering macroscopic mechanical systems work towards topological phononic systems at the nanoscale, where hypersonic frequency (≳ GHz) acoustic wave circuits consisting of robust delay lines and non-reciprocal elements may be implemented. Owing to the broadband character of the topological channels, the control of the flow of heat-carrying phonons, albeit at cryogenic temperatures, may also be envisioned.

  • C. Saavedra, D. Pandey, W. Alt, H. Pfeifer and D. Meschede
    Tunable Fiber Fabry-Perot Cavities with High Passive Stability, arXiv:2010.02204, (2020)arXivBibTeX

    We present three high finesse tunable monolithic fiber Fabry-Perot cavities (FFPCs) with high passive mechanical stability. The fiber mirrors are fixed inside slotted glass ferrules, which guarantee an inherent alignment of the resonators. An attached piezoelectric element enables fast tuning of the FFPC resonance frequency over the entire free-spectral range for two of the designs. Stable locking of the cavity resonance is achieved for feedback bandwidths as low as 20 mHz, demonstrating the high passive stability. At the other limit, locking bandwidths up to 27 kHz, close to the first mechanical resonance, can be obtained. The root-mean-square frequency fluctuations are suppressed down to ~ 2 % of the cavity linewidth. Over a wide frequency range, the frequency noise is dominated by the thermal noise limit of the system's mechanical resonances. The demonstrated small footprint devices can be used advantageously in a broad range of applications like cavity-based sensing techniques, optical filters or quantum light-matter interfaces.


  • E. Uruñuela, W. Alt, E. Keiler, D. Meschede, D. Pandey, H. Pfeifer and T. Macha
    Ground-State Cooling of a Single Atom in a High-Bandwidth Cavity, Phys. Rev. A 101, 023415 (2020)arXivBibTeXPDF

    We report on vibrational ground-state cooling of a single neutral atom coupled to a high-bandwidth Fabry-Pérot cavity. The cooling process relies on degenerate Raman sideband transitions driven by dipole trap beams, which confine the atoms in three dimensions. We infer a one-dimensional motional ground-state population close to 90% by means of Raman spectroscopy. Moreover, lifetime measurements of a cavity-coupled atom exceeding 40 s imply three-dimensional cooling of the atomic motion, which makes this resource-efficient technique particularly interesting for cavity experiments with limited optical access.

  • T. Macha, E. Uruñuela, W. Alt, M. Ammenwerth, D. Pandey, H. Pfeifer and D. Meschede
    Non-adiabatic Storage of Short Light Pulses in an Atom-Cavity System, Phys. Rev. A 101, 053406 (2020)arXivBibTeXPDF

    We demonstrate the storage of 5 ns light pulses in a single rubidium atom coupled to a fiber-based optical resonator. Our storage protocol addresses a regime beyond the conventional adiabatic limit and approaches the theoretical bandwidth limit. We extract the optimal control laser pulse properties from a numerical simulation of our system and measure storage efficiencies of (8.1±1.1)%, in close agreement with the maximum expected efficiency. Such well-controlled and high-bandwidth atom-photon interfaces are key components for future hybrid quantum networks.

  • H. Ren, M. H. Matheny, G. S. MacCabe, J. Luo, H. Pfeifer, M. Mirhosseini and O. Painter
    Two-Dimensional Optomechanical Crystal Cavity with High Quantum Cooperativity, Nature Communications 11, 3373 (2020)arXivBibTeX

    Optomechanical systems offer new opportunities in quantum information processing and quantum sensing. Many solid-state quantum devices operate at millikelvin temperatures -- however, it has proven challenging to operate nanoscale optomechanical devices at these ultralow temperatures due to their limited thermal conductance and parasitic optical absorption. Here, we demonstrate a two-dimensional optomechanical crystal resonator capable of achieving large cooperativity C and small effective bath occupancy nb,  resulting in a quantum cooperativity Ceff = C/nb = 1.3 > 1 under continuous-wave optical driving. This is realized using a two-dimensional phononic bandgap structure to host the optomechanical cavity, simultaneously isolating the acoustic mode of interest in the bandgap while allowing heat to be removed by phonon modes outside of the bandgap. This achievement paves the way for a variety of applications requiring quantum-coherent optomechanical interactions, such as transducers capable of bi-directional conversion of quantum states between microwave frequency superconducting quantum circuits and optical photons in a fiber optic network.

  • J. Graf, H. Pfeifer, F. Marquardt and S. V. Kusminskiy
    Cavity optomagnonics with magnetic textures: Coupling a magnetic vortex to light, Physical Review B 98 (24), 241406 (2018)arXivBibTeX

    Optomagnonic systems, where light couples coherently to collective excitations in magnetically ordered solids, are currently of high interest due to their potential for quantum information processing platforms at the nanoscale. Efforts so far, both at the experimental and theoretical level, have focused on systems with a homogeneous magnetic background. A unique feature in optomagnonics is, however, the possibility of coupling light to spin excitations on top of magnetic textures. We propose a cavity-optomagnonic system with a nonhomogeneous magnetic ground state, namely, a vortex in a magnetic microdisk. In particular, we study the coupling between optical whispering gallery modes to magnon modes localized at the vortex. We show that the optomagnonic coupling has a rich spatial structure and that it can be tuned by an externally applied magnetic field. Our results predict cooperativities at maximum photon density of the order of C102 by proper engineering of these structures.

  • M. Kalaee, T. K. Paraiso, H. Pfeifer and O. Painter
    Design of a quasi-2D photonic crystal optomechanical cavity with tunable, large x²-coupling, Optics express 24 (19), 21308-21328 (2016)arXivBibTeX

    We present the optical and mechanical design of a mechanically compliant quasi-two-dimensional photonic crystal cavity formed from thin-film silicon in which a pair of linear nanoscale slots are used to create two coupled high-Q optical resonances. The optical cavity supermodes, whose frequencies are designed to lie in the 1500 nm wavelength band, are shown to interact strongly with mechanical resonances of the structure whose frequencies range from a few MHz to a few GHz. Depending upon the symmetry of the mechanical modes and the symmetry of the slot sizes, we show that the optomechanical coupling between the optical supermodes can be either linear or quadratic in the mechanical displacement amplitude. Tuning of the nanoscale slot size is also shown to adjust the magnitude and sign of the cavity supermode splitting 2J, enabling near-resonant motional scattering between the two optical supermodes and greatly enhancing the x2-coupling strength. Specifically, for the fundamental flexural mode of the central nanobeam of the structure at 10 MHz the per-phonon linear cross-mode coupling rate is calculated to be ~g+-/2π = 1 MHz corresponding to a per-phonon x2-coupling rate of ~g'/2π = 1 kHz for a mode splitting 2J/2π = 1 GHz which is greater than the radiation-limited supermode linewidths.

  • H. Pfeifer, T. Paraïso, L. Zang and O. Painter
    Design of tunable GHz-frequency optomechanical crystal resonators, Optics express 24 (11), 11407-11419 (2016)arXivBibTeX

    We present a silicon optomechanical nanobeam design with a dynamically tunable acoustic mode at 10.2 GHz. The resonance frequency can be shifted by 90 kHz/V^2 with an on-chip capacitor that was optimized to exert forces up to 1 µN at 10 V operation voltage. Optical resonance frequencies around 190 THz with Q-factors up to 2.2 × 10^6 place the structure in the well-resolved sideband regime with vacuum optomechanical coupling rates up to g_0/2π = 353 kHz. Tuning can be used, for instance, to overcome variation in the device-to-device acoustic resonance frequency due to fabrication errors, paving the way for optomechanical circuits consisting of arrays of optomechanical cavities.

  • T. K. Paraïso, M. Kalaee, L. Zang, H. Pfeifer, F. Marquardt and O. Painter
    Position-squared coupling in a tunable photonic crystal optomechanical cavity, Physical Review X 5 (4), 041024 (2015)arXivBibTeX

    We present the design, fabrication, and characterization of a planar silicon photonic crystal cavity in which large position-squared optomechanical coupling is realized. The device consists of a double-slotted photonic crystal structure in which motion of a central beam mode couples to two high-Q optical modes localized around each slot. Electrostatic tuning of the structure is used to controllably hybridize the optical modes into supermodes that couple in a quadratic fashion to the motion of the beam. From independent measurements of the anticrossing of the optical modes and of the dynamic optical spring effect, a position-squared vacuum coupling rate as large as ˜g/2π=245Hz is inferred between the optical supermodes and the fundamental in-plane mechanical resonance of the structure at ωm/2π=8.7MHz, which in displacement units corresponds to a coupling coefficient of g/2π=1THz/nm2. For larger supermode splittings, selective excitation of the individual optical supermodes is used to demonstrate optical trapping of the mechanical resonator with measured ˜g/2π=46Hz.

  • D. Ploss, A. Kriesch, H. Pfeifer, P. Banzer and U. Peschel
    Generation and subwavelength focusing of longitudinal magnetic fields in a metallized fiber tip, Optics express 22 (11), 13744-13754 (2014)arXivBibTeX

    We demonstrate experimentally and numerically that in fiber tips as they are used in NSOMs azimuthally polarized electrical fields (|E_azi|^2 / |E_tot|^2 ≈55% ± 5% for λ_0 = 1550 nm), respectively subwavelength confined (FWHM ≈450 nm ≈λ_0/3.5) magnetic fields, are generated for a certain tip aperture diameter (d = 1.4 μm). We attribute the generation of this field distribution in metal-coated fiber tips to symmetry breaking in the bend and subsequent plasmonic mode filtering in the truncated conical taper.

  • A. Kriesch, S. P. Burgos, D. Ploss, H. Pfeifer, H. A. Atwater and U. Peschel
    Functional plasmonic nanocircuits with low insertion and propagation losses, Nano letters 13 (9), 4539-4545 (2013)arXivBibTeX

    We experimentally demonstrate plasmonic nanocircuits operating as subdiffraction directional couplers optically excited with high efficiency from free-space using optical Yagi-Uda style antennas at λ0 = 1550 nm. The optical Yagi-Uda style antennas are designed to feed channel plasmon waveguides with high efficiency (45% in coupling, 60% total emission), narrow angular directivity (<40°), and low insertion loss. SPP channel waveguides exhibit propagation lengths as large as 34 μm with adiabatically tuned confinement and are integrated with ultracompact (5 × 10 μm2), highly dispersive directional couplers, which enable 30 dB discrimination over Δλ = 200 nm with only 0.3 dB device loss.

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