Michael K. Koch

Bio: Michael K. Koch is an academic researcher from University of Ulm. The author has co-authored 1 publications.

Integrated magnetometry platform with stackable waveguide-assisted detection channels for sensing arrays

Abstract: The negatively charged nitrogen vacancy (N-V−) center in diamond has shown great success in nanoscale, high-sensitivity magnetometry. Efficient fluorescence detection is crucial for improving the sensitivity. Furthermore, integrated devices enable practicable sensors. Here, we present an integrated architecture which allows us to create N-V− centers a few nanometers below the diamond surface, and at the same time covering the entire mode field of femtosecond-laser-written type-II waveguides. We experimentally verify the coupling efficiency, showcase the detection of magnetic resonance signals through the waveguides and perform proof-of-principle experiments in magnetic field and temperature sensing. The sensing task can be operated via the waveguide without direct light illumination through the sample, which is important for magnetometry in biological systems that are sensitive to light. In the future, our approach will enable the development of two-dimensional sensing arrays facilitating spatially and temporally correlated magnetometry.

Quantum technologies in diamond enabled by laser processing

Abstract: Integrated photonic circuits promise to be foundational for applications in quantum information and sensing technologies, through their ability to confine and manipulate light. A key role in such technologies may be played by spin-active quantum emitters, which can be used to store quantum information or as sensitive probes of the local environment. A leading candidate is the negatively charged nitrogen vacancy (NV−) diamond color center, whose ground spin state can be optically read out, exhibiting long (≈1 ms) coherence times at room temperature. These properties have driven research toward the integration of photonic circuits in the bulk of diamond with the development of techniques allowing fabrication of optical waveguides. In particular, femtosecond laser writing has emerged as a powerful technique, capable of writing light guiding structures with 3D configurations as well as creating NV complexes. In this Perspective, the physical mechanisms behind laser fabrication in diamond will be reviewed. The properties of waveguides, single- and ensemble-NV centers, will be analyzed, together with the possibility to combine such structures in integrated photonic devices, which can find direct application in quantum information and sensing.

Laser-written vapor cells for chip-scale atomic sensing and spectroscopy

Abstract: We report the fabrication of alkali-metal vapor cells using femtosecond laser machining. This laser-written vapor-cell (LWVC) technology allows arbitrarily-shaped 3D interior volumes and has potential for integration with photonic structures and optical components. We use non-evaporable getters both to dispense rubidium and to absorb buffer gas. This enables us to produce cells with sub-atmospheric buffer gas pressures without vacuum apparatus. We demonstrate sub-Doppler saturated absorption spectroscopy and single beam optical magnetometry with a single LWVC. The LWVC technology may find application in miniaturized atomic quantum sensors and frequency references.

Super-Poissonian Light Statistics from Individual Silicon Vacancy Centers Coupled to a Laser-Written Diamond Waveguide

Abstract: Modifying light fields at the single-photon level is a key challenge for upcoming quantum technologies and can be realized in a scalable manner through integrated quantum photonics. Laser-written diamond photonics offers 3D fabrication capabilities and large mode-field diameters matched to fiber optic technology, though limiting the cooperativity at the single-emitter level. To realize large coupling efficiencies, we combine excitation of single shallow-implanted silicon vacancy centers via high numerical aperture optics with detection assisted by laser-written type-II waveguides. We demonstrate single-emitter extinction measurements with a cooperativity of 0.0050 and a relative beta factor of 13%. The transmission of resonant photons reveals single-photon subtraction from a quasi-coherent field resulting in super-Poissonian light statistics. Our architecture enables light field engineering in an integrated design on the single quantum level although the intrinsic cooperativity is low. Laser-written structures can be fabricated in three dimensions and with a natural connectivity to optical fiber arrays.

Fabrication and Characterization of Femtosecond Laser Written Low Loss Depressed Cladding Waveguides in Diamond

Abstract: Femtosecond laser writing was employed to fabricate and characterize circular, depressed cladding waveguides in diamond with different dimensions and writing parameters, resulting in waveguides with propagation loss as low as 2.05 dB/cm at 633 nm.

On-Chip Quantum Devices Enabled by Shallow-Implanted Vacancy Centers in Laser-Written Waveguides in Diamond

Abstract: We present a quantum device platform enabled by shallow implanted vacancy centers in the front facet of laser-written waveguides in diamond. Two proof-of-principle experiments highlight the potential for quantum sensing and single photon light-field engineering.