Coherent interaction of atoms with a beam of light confined in a light cage.

Controlling coherent interaction between optical fields and quantum systems in scalable, integrated platforms is essential for quantum technologies. Miniaturised, warm alkali-vapour cells integrated with on-chip photonic devices represent an attractive system, in particular for delay or storage of a single-photon quantum state. Hollow-core fibres or planar waveguides are widely used to confine light over long distances enhancing light-matter interaction in atomic-vapour cells.

Axial localization and tracking of self-interference nanoparticles by lateral point spread functions.

Sub-diffraction limited localization of fluorescent emitters is a key goal of microscopy imaging. Here, we report that single upconversion nanoparticles, containing multiple emission centres with random orientations, can generate a series of unique, bright and position-sensitive patterns in the spatial domain when placed on top of a mirror. Supported by our numerical simulation, we attribute this effect to the sum of each single emitter's interference with its own mirror image.

Self-Assembly of Plasmonic Nanoantenna-Waveguide Structures for Subdiffractional Chiral Sensing.

Spin-momentum locking is a peculiar effect in the near-field of guided optical or plasmonic modes. It can be utilized to map the spinning or handedness of electromagnetic fields onto the propagation direction. This motivates a method to probe the circular dichroism of an illuminated chiral object.

Real-time nanodiamond thermometry probing in vivo thermogenic responses.

Real-time temperature monitoring inside living organisms provides a direct measure of their biological activities. However, it is challenging to reduce the size of biocompatible thermometers down to submicrometers, despite their potential applications for the thermal imaging of subtissue structures with single-cell resolution. Here, using quantum nanothermometers based on optically accessible electron spins in nanodiamonds, we demonstrate in vivo real-time temperature monitoring inside worms.

Dispersion control in a near-infrared subwavelength resonator with a tailored hyperbolic metamaterial.

We demonstrate experimentally and computationally an intricate cavity size dependence of the anomalous near-infrared mode spectrum of an ordinary optical resonator that is combined with a ZnO:Ga-based hyperbolic metamaterial (HMM). Specifically, we reveal the existence of a resonance in subwavelength-sized cavities and demonstrate control over the first-order cavity mode dispersion. We elaborate that these effects arise due to the HMM combining the mode dispersions of purely metallic and purely dielectric cavity cores into a distinct intermediate regime.

An efficient, tunable, and robust source of narrow-band photon pairs at the Rb D1 line.

We present an efficient and robust source of photons at the Rb D1-line (795 nm) with a narrow bandwidth of δ = 226(1) MHz. The source is based on non-degenerate, cavity-enhanced spontaneous parametric down-conversion in a monolithic optical parametric oscillator far below threshold. The setup allows for efficient coupling to single mode fibers.

Hybrid integrated quantum photonic circuits.

Recent developments in chip-based photonic quantum circuits has radically impacted quantum information processing. However, it is challenging for monolithic photonic platforms to meet the stringent demands of most quantum applications. Hybrid platforms combining different photonic technologies in a single functional unit have great potential to overcome the limitations of monolithic photonic circuits.

Slow and fast single photons from a quantum dot interacting with the excited state hyperfine structure of the Cesium D-line.

Hybrid interfaces between distinct quantum systems play a major role in the implementation of quantum networks. Quantum states have to be stored in memories to synchronize the photon arrival times for entanglement swapping by projective measurements in quantum repeaters or for entanglement purification. Here, we analyze the distortion of a single-photon wave packet propagating through a dispersive and absorptive medium with high spectral resolution.

Silver nanowires with optimized silica coating as versatile plasmonic resonators.

Metal nanoparticles are the most frequently used nanostructures in plasmonics. However, besides nanoparticles, metal nanowires feature several advantages for applications. Their elongation offers a larger interaction volume, their resonances can reach higher quality factors, and their mode structure provides better coupling into integrated hybrid dielectric-plasmonic circuits.

Printed-circuit-board linear Paul trap for manipulating single nano- and microparticles.

Levitation of very small but macroscopic objects is a rapidly developing interrogation technique for nanooptics and optomechanics. Paul traps are one mechanism for levitation of charged particles, which enables interrogation of novel materials or optically active samples in a virtually interaction-free environment, providing a test-bed for completely new experiments. Elementary traps have already been demonstrated for nano- and microparticles as a proof-of-principle for such experiments.

Coupling a Single Nitrogen-Vacancy Center in Nanodiamond to Superparamagnetic Nanoparticles.

Single nitrogen-vacancy (NV) defect centers in diamond have been exploited as single photon sources and spin qubits due to their room-temperature robust quantum light emission and long electron spin coherence times. They were coupled to a manifold of structures, such as optical cavities, plasmonic waveguides, and even injected into living cells to study fundamental interactions of various nature at the nanoscale. Of particular interest are applications of NVs as quantum sensors for local nanomagnetometry.

Mixed basis quantum key distribution with linear optics.

Two-qubit quantum codes have been suggested to obtain better efficiency and higher loss tolerance in quantum key distribution. Here, we propose a two-qubit quantum key distribution protocol based on a mixed basis consisting of two Bell states and two states from the computational basis. All states can be generated from a single entangled photon pair resource by using local operations on only one auxiliary photon.

Limitations of Particle-Based Spasers.

We present a semiclassical analytic model for spherical core-shell surface plasmon lasers. Within this model, we drop the widely used one-mode approximations in favor of fully electromagnetic Mie theory. This allows for incorporation of realistic gain relaxation rates that so far are massively underestimated.

A realistic fabrication and design concept for quantum gates based on single emitters integrated in plasmonic-dielectric waveguide structures.

Tremendous enhancement of light-matter interaction in plasmonic-dielectric hybrid devices allows for non-linearities at the level of single emitters and few photons, such as single photon transistors. However, constructing integrated components for such devices is technologically extremely challenging. We tackle this task by lithographically fabricating an on-chip plasmonic waveguide-structure connected to far-field in- and out-coupling ports via low-loss dielectric waveguides.

Micro-concave waveguide antenna for high photon extraction from nitrogen vacancy centers in nanodiamond.

The negatively charged nitrogen-vacancy colour center (NV(-) center) in nanodiamond is an excellent single photon source due to its stable photon generation in ambient conditions, optically addressable nuclear spin state, high quantum yield and its availability in nanometer sized crystals. In order to make practical devices using nanodiamond, highly efficient and directional emission of single photons in well-defined modes, either collimated into free space or waveguides are essential. This is a Herculean task as the photoluminescence of the NV centers is associated with two orthogonal dipoles arranged in a plane perpendicular to the NV defect symmetry axis.

Miniaturized Bragg-grating couplers for SiN-photonic crystal slabs.

We report on an experimental and theoretical investigation of an integrated Bragg-like grating coupler for near-vertical scattering of light from photonic crystal waveguides with an ultra-small footprint of a few lattice constants only. Using frequency-resolved measurements, we find the directional properties of the scattered radiation and prove that the coupler shows a good performance over the complete photonic bandgap. The results compare well to analytical considerations regarding 1d-scattering phenomena as well as to FDTD simulations.

Highly efficient coupling of nanolight emitters to a ultra-wide tunable nanofibre cavity.

Solid-state microcavities combining ultra-small mode volume, wide-range resonance frequency tuning, as well as lossless coupling to a single mode fibre are integral tools for nanophotonics and quantum networks. We developed an integrated system providing all of these three indispensable properties. It consists of a nanofibre Bragg cavity (NFBC) with the mode volume of under 1 μm(3) and repeatable tuning capability over more than 20 nm at visible wavelengths.

Investigation of Line Width Narrowing and Spectral Jumps of Single Stable Defect Centers in ZnO at Cryogenic Temperature.

Finding new solid state defect centers in novel host materials is crucial for realizing integrated hybrid quantum photonic devices. We present a preparation method for defect centers with photostable bright single photon emission in zinc oxide, a material with promising properties in terms of processability, availability, and applications. A detailed optical study reveals a complex dynamic of intensity fluctuations at room temperature.

On-demand electrostatic coupling of individual precharacterized nano- and microparticles in a segmented Paul trap.

We present a novel versatile method for one-by-one coupling of single nano- and microparticles. The particles are levitated in a segmented linear Paul trap, which is ideal for fast particle characterization and assembly of two or more preselected particles by electrostatic attraction. The final compound particles remain in the trap or can be deposited on other structures.

Broadband linear high-voltage amplifier for radio frequency ion traps.

We developed a linear high-voltage amplifier for small capacitive loads consisting of a high-voltage power supply and a transistor amplifier. With this cost-effective circuit including only standard parts sinusoidal signals with a few volts can be amplified to 1.7 kVpp over a usable frequency range at large-signal response spanning four orders of magnitude from 20 Hz to 100 kHz under a load of 10 pF.

Numerical analysis of efficient light extraction with an elliptical solid immersion lens.

We introduce and analyze a design concept based on nonspherical solid immersion lens (SIL) geometry. We find via finite difference time domain (FDTD) simulations that elliptical solid immersion lenses (eSILs) exhibit a notably improved emission directionality compared to the standard SIL design. Large light-collection efficiencies are achieved even for small numerical apertures (NAs).

Scanning single quantum emitter fluorescence lifetime imaging: quantitative analysis of the local density of photonic states.

Their intrinsic properties render single quantum systems as ideal tools for quantum enhanced sensing and microscopy. As an additional benefit, their size is typically on an atomic scale that enables sensing with very high spatial resolution. Here, we report on utilizing a single nitrogen vacancy center in nanodiamond for performing three-dimensional scanning-probe fluorescence lifetime imaging microscopy.

Thermo-optical response of photonic crystal cavities operating in the visible spectral range.

In this paper we study thermo-optical effects in gallium phosphite photonic crystal cavities in the visible range. By measuring the shift of narrow resonances, we derive the temperature dependency of the local refractive index of gallium phosphide in an attoliter volume over a temperature range between 5 and 300 K at a wavelength of about 605 nm. Additionally, the potential of photonic crystal cavities for thermo-optical switching of visible light is investigated.