Publications Project 08 -
Strong Coupling of Remote Ultra-high Q Microresonators

Project Leader: Arno Rauschenbeutel


Chiral quantum optics

P. Lodahl, S. Mahmoodian, S. Stobbe, A. Rauschenbeutel, P. Schneeweiss, J. Volz, H. Pichler, P. Zoller

  Advanced photonic nanostructures are currently revolutionizing the optics and photonics that underpin applications ranging from light technology to quantum-information processing. The strong light confinement in these structures can lock the local polarization of the light to its propagation direction, leading to propagation-direction-dependent emission, scattering and absorption of photons by quantum emitters. The possibility of such a propagation-direction-dependent, or chiral, light–matter interaction is not accounted for in standard quantum optics and its recent discovery brought about the research field of chiral quantum optics. The latter offers fundamentally new functionalities and applications: it enables the assembly of non-reciprocal single-photon devices that can be operated in a quantum superposition of two or more of their operational states and the realization of deterministic spin–photon interfaces. Moreover, engineered directional photonic reservoirs could lead to the development of complex quantum networks that, for example, could simulate novel classes of quantum many-body systems.
 

Published: 2017-01-25
Nature 541, 473–480 (2017)
DOI: 10.1038/nature21037

Press release TU Wien, 2017-01-26

 

Nanophotonic Optical Isolator Controlled by the Internal State of Cold Atoms

C. Sayrin, C. Junge, R. Mitsch, B. Albrecht, D. O'Shea, P. Schneeweiss, J. Volz, A. Rauschenbeutel

  The realization of nanophotonic optical isolators with high optical isolation even at ultralow light levels and low optical losses is an open problem. Here, we employ the link between the local polarization of strongly confined light and its direction of propagation to realize low-loss nonreciprocal transmission through a silica nanofiber at the single-photon level. The direction of the resulting optical isolator is controlled by the spin state of cold atoms.We perform our experiment in two qualitatively different regimes, i.e., with an ensemble of cold atoms where each atom is weakly coupled to the waveguide and with a single atom strongly coupled to the waveguide mode. In both cases, we observe simultaneously high isolation and high forward transmission. The isolator concept constitutes a nanoscale quantum optical analog of microwave ferrite resonance isolators, can be implemented with all kinds of optical waveguides and emitters, and might enable novel integrated optical devices for fiber-based classical and quantum networks.
 

Published: 2015-12-04
Physical Review X 5, 041036 (2015)
DOI: 10.1103/PhysRevX.5.041036

 

Storage of fiber-guided light in a nanofiber-trapped ensemble of cold atoms

C. Sayrin, C. Clausen, B. Albrecht, P. Schneeweiss, A. Rauschenbeutel

  Tapered optical fibers with a nanofiber waist are versatile light–matter interfaces. Of particular interest are laser-cooled atoms trapped in the evanescent field surrounding the optical nanofiber: they exhibit both long ground-state coherence times and efficient coupling to fiber-guided fields. Here, we demonstrate electromagnetically induced transparency, slow light, and the storage of fiber-guided optical pulses in an ensemble of cold atoms trapped in a nanofiber-based optical lattice. We measure group velocities of 50 m/s. Moreover, we store optical pulses at the single-photon level and retrieve them on demand in the fiber after 2 μs with an overall efficiency of 3.0±0.4%. Our results show that nanofiber-based interfaces for cold atoms have great potential for the realization of building blocks for future optical quantum information networks.
 

Published: 2015-04-07
Optics Info Base, Optica, Vol. 2, Issue 4, pp. 353-356
DOI: 10.1364/OPTICA.2.000353

Press release TU Wien, 2015-04-09 [37/2015]

 

Quantum state-controlled directional spontaneous emission of photons into a nanophotonic waveguide

R. Mitsch, C. Sayrin, B. Albrecht, P. Schneeweiss, A. Rauschenbeutel

  The spin of light in subwavelength-diameter waveguides can be orthogonal to the propagation direction of the photons because of the strong transverse confinement. This transverse spin changes sign when the direction of propagation is reversed. Using this effect, we demonstrate the directional spontaneous emission of photons by laser-trapped caesium atoms into an optical nanofibre and control their propagation direction by the excited state of the atomic emitters. In particular, we tune the spontaneous emission into the counterpropagating guided modes from symmetric to strongly asymmetric, where more than 90% of the optical power is launched into one or the other direction. We expect our results to have important implications for research in quantum nanophotonics and for implementations of integrated optical signal processing in the quantum regime.
 

Published: 2014-12-12
nature communications 5, article number 5713
DOI: 10.1038/ncomms6713

 

Exploiting the local polarization of strongly confined light for sub-micrometer-resolution internal state preparation and manipulation of cold atoms

R. Mitsch, C. Sayrin, B. Albrecht, P. Schneeweiss, A. Rauschenbeutel

  A strongly confined light field necessarily exhibits a local polarization that varies on a subwavelength scale. We demonstrate that a single optical mode of this kind can be used to selectively and simultaneously manipulate atomic ensembles that are less than a micron away from each other and equally coupled to the light field. The technique is implemented with an optical nanofiber that provides an evanescent field interface between a strongly guided optical mode and two diametric linear arrays of cesium atoms. Using this single optical mode, the two atomic ensembles can simultaneously be optically pumped to opposite Zeeman states. Moreover, the state-dependent light shifts can be made locally distinct, thereby enabling an independent coherent manipulation of the two ensembles. Our results open a route toward advanced manipulation of atomic samples in nanoscale quantum optics systems.
 

Published: 2014-06-30
Physical Review A 89, 063829
DOI: 10.1103/PhysRevA.89.063829

 

Experimental stress-strain analysis of tapered silica optical fibers with nanofiber waist

S. Holleis, T. Hoinkes, C. Wuttke, P. Schneeweiss, A. Rauschenbeutel

  We experimentally determine tensile force–elongation diagrams of tapered optical fibers with a nanofiber waist. The tapered optical fibers are produced from standard silica optical fibers using a heat and pull process. Both, the force–elongation data and scanning electron microscope images of the rupture points indicate a brittle material. Despite the small waist radii of only a few hundred nanometers, our experimental data can be fully explained by a nonlinear stress–strain model that relies on material properties of macroscopic silica optical fibers. This is an important asset when it comes to designing miniaturized optical elements as one can rely on the well-founded material characteristics of standard optical fibers. Based on this understanding, we demonstrate a simple and non-destructive technique that allows us to determine the waist radius of the tapered optical fiber. We find excellent agreement with independent scanning electron microscope measurements of the waist radius.
 

Published: 2014-04-24
Applied Physics Letters 104, 163109
DOI: 10.1063/1.4873339

 

Back-Scattering Properties of a Waveguide-Coupled Array of Atoms in the Strongly Non-Paraxial Regime

D. Reitz, C. Sayrin, B. Albrecht, I. Mazets, R. Mitsch, P. Schneeweiss, A. Rauschenbeutel

  We investigate experimentally the backscattering properties of an array of atoms that is evanescently coupled to an optical nanofiber in the strongly nonparaxial regime. We observe that the power and the polarization of the backscattered light depend on the nanofiber-guided excitation field in a way that significantly deviates from the predictions of a simple model based on two-level atoms and a scalar waveguide. Even though it has been widely used in previous experimental and theoretical studies of waveguide-coupled quantum emitters, this simple model is thus in general not adequate even for a qualitative description of such systems. We develop an ab initio model that includes the multilevel structure of the atoms and the full vectorial properties of the guided field and find very good agreement with our data.
 

Published: 2014-03-28
Physical Review A 89, 031804(R)
DOI: 10.1103/PhysRevA.89.031804

 

Nanofiber-based trap created by combining fictitious and real magnetic fields

P. Schneeweiss, F.L. Kien, A. Rauschenbeutel

  We propose a trap for cold neutral atoms using a fictitious magnetic field induced by a nanofiber-guided light field in conjunction with an external magnetic bias field. In close analogy to magnetic side-guide wire traps realized with currentcarrying wires, a trapping potential can be formed when applying a homogeneous magnetic bias field perpendicular to the fiber axis. We discuss this scheme in
detail for laser-cooled cesium atoms and find trap depths and trap frequencies comparable to the two-color nanofiber-based trapping scheme but with one order of magnitude lower power of the trapping laser field. Moreover, the proposed scheme allows one to bring the atoms closer to the nanofiber surface, thereby enabling efficient optical interfacing of the atoms with additional light fields. Specifically, optical depths per atom, σ0/Aeff, of more than 0.4 are predicted, making this system eligible for nanofiber-based nonlinear and quantum optics experiments.
 

Published: 2014-01-13
New Journal of Physics 16, 013014
DOI: 10.1088/1367-2630/16/1/013014

 

Negative azimuthal force of a nanofiber-guided light on a particle

F.L. Kien, A. Rauschenbeutel

  We calculate the force of a quasicircularly polarized guided light field of a nanofiber on a dielectric spherical particle. We show that the orbital parts of the axial and azimuthal components of the Poynting vector are always positive, while the spin parts can be either positive or negative. We find that, for appropriate values of the size parameter of the particle, the azimuthal component of the force is directed oppositely to the circulation direction of the energy flow around the nanofiber. The occurrence of such a negative azimuthal force indicates that the particle undergoes a negative torque.
 

Published: 2013-12-27
Physical Review A 88, 063845
DOI: 10.1103/PhysRevA.88.063845

 

State-dependent potentials in a nanofiber-based two-color trap for cold atoms

F.L. Kien, P. Schneeweiss, A. Rauschenbeutel

  We analyze the ac Stark shift of a cesium atom interacting with far-off-resonance guided light fields in the nanofiber-based two-color optical dipole trap realized by Vetsch et al. [Phys. Rev. Lett. 104, 203603 (2010)]. Particular emphasis is given to the fictitious magnetic field produced by the vector polarizability of the atom in conjunction with the ellipticity of the polarization of the trapping fields. Taking into account the ac Stark shift, the atomic hyperfine interaction, and a magnetic interaction, we solve the stationary Schr¨odinger equation at a fixed point in space and find Zeeman-state-dependent trapping potentials. In analogy to the dynamics in
magnetic traps, a local degeneracy of these state-dependent trapping potentials can cause spin flips and should thus be avoided.We show that this is possible using an external magnetic field. Depending on the direction of this external magnetic field, the resulting trapping configuration can still exhibit state-dependent displacement of the potential minima. In this case, we find nonzero Franck-Condon factors between motional states of the potentials for different hyperfine-structure levels and propose the possibility of microwave cooling in a nanofiber-based two-color trap.
 

Published: 2013-09-24
Physical Review A 88, 033840
DOI: 10.1103/PhysRevA.88.033840

 

Quantum dynamics of an atom orbiting around an optical nanofiber

F.L. Kien, K. Hakuta, D. Reitz, P. Schneeweiss, A. Rauschenbeutel

  We propose a platform for the investigation of quantum wave-packet dynamics, offering a complementary approach to existing theoretical models and experimental systems. It relies on laser-cooled neutral atoms which orbit around an optical nanofiber in an optical potential produced by a red-detuned guided light field. We show that the atomic center-of-mass motion exhibits genuine quantum effects like collapse and revival of the atomic wave packet. As distinctive advantages, our approach features a tunable dispersion relation as well as straightforward readout for the wave-packet dynamics and can be implemented using existing quantum optics techniques.
 

Published: 2013-06-07
Physical Review A 87, 063607
DOI: 10.1103/PhysRevA.87.063607

 

 

 

 

 

 

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