Optimal state estimation for cavity optomechanical systems

We demonstrate optimal state estimation for a cavity optomechanical system through Kalman filtering. By taking into account nontrivial experimental noise sources, such as colored laser noise and spurious mechanical modes, we implement a realistic state-space model. This allows us to obtain the conditional system state, i.e., conditioned on previous measurements, with minimal least-square estimation error. We apply this method for estimating the mechanical state, as well as optomechanical correlations both in the weak and strong coupling regime. The application of the Kalman filter is an important next step for achieving real-time optimal (classical and quantum) control of cavity optomechanical systems.Comment: replaced with published version, 5+12 page

Development of a Boston-area 50-km fiber quantum network testbed

Distributing quantum information between remote systems will necessitate the integration of emerging quantum components with existing communication infrastructure. This requires understanding the channel-induced degradations of the transmitted quantum signals, beyond the typical characterization methods for classical communication systems. Here we report on a comprehensive characterization of a Boston-Area Quantum Network (BARQNET) telecom fiber testbed, measuring the time-of-flight, polarization, and phase noise imparted on transmitted signals. We further design and demonstrate a compensation system that is both resilient to these noise sources and compatible with integration of emerging quantum memory components on the deployed link. These results have utility for future work on the BARQNET as well as other quantum network testbeds in development, enabling near-term quantum networking demonstrations and informing what areas of technology development will be most impactful in advancing future system capabilities.Comment: 9 pages, 5 figures + Supplemental Material

Telecom networking with a diamond quantum memory

Practical quantum networks require interfacing quantum memories with existing channels and systems that operate in the telecom band. Here we demonstrate low-noise, bidirectional quantum frequency conversion that enables a solid-state quantum memory to directly interface with telecom-band systems. In particular, we demonstrate conversion of visible-band single photons emitted from a silicon-vacancy (SiV) center in diamond to the telecom O-band, maintaining low noise ($g^2(0)<0.1$) and high indistinguishability ($V=89\pm8\%$). We further demonstrate the utility of this system for quantum networking by converting telecom-band time-bin pulses, sent across a lossy and noisy 50 km deployed fiber link, to the visible band and mapping their quantum states onto a diamond quantum memory with fidelity $\mathcal{F}=87\pm 2.5 \%$. These results demonstrate the viability of SiV quantum memories integrated with telecom-band systems for scalable quantum networking applications.Comment: 9 pages, 5 figures + Supplemental Material

Single Phonon Quantum Optics

Akustische Phononen, die energetischen Eigenzustände von mechanischen Vibrationen, besitzen eine Vielzahl an interessanten Eigenschaften für die Verarbeitung von Quanteninformation. Beispielsweise können sie als langlebige und kompakte Quanteninformationsspeicher eingesetzt werden, oder Quantenzustände zwischen anderweitig inkompatiblen Systemen übertragen. Aufgrund ihrer technischen Relevanz sind hierbei Photonen im optischen Telekommunikations-Frequenzband von besonderem Interesse. Mit Hilfe von künstlich erzeugten optischen und akustischen Resonanzen, können die Photonen mit Phononen mittels Strahlungsdruck interagieren. Jedoch war die Kontrolle einzelner Bewegungsanregungen in mikromechanischen Resonatoren bisher auf den Mikrowellenbereich beschränkt, wohingegen das Ziel einer Manipulation durch Laser unerreicht blieb. In dieser Dissertation beschreibe ich, wie dies experimentell mithilfe von quantenoptischen Protokollen erreicht werden kann. Zunächst wird gezeigt, dass optomechanische Kristalle im Quantenbereich betrieben werden können, indem nichtklassische Photon-Phonon Paare mittels optomechanischer parametrischer Fluoreszenz erzeugt werden. Diese Quantenschnittstelle wird daraufhin verwendet um einzelne Phononen zu charakterisieren, sowie Quantenverschränkung zwischen zwei entfernten mechanischen Oszillatoren zu erzeugen. Die Demonstration dieser klassischen Quantenoptik Experimente mit einzelnen Phononen zeigt, dass mechanische Quanteninformationsspeicher eine vielversprechende Ressource für künftige Quantennetzwerke darstellen.Acoustic phonons, the energy eigenstates of mechanical vibrations, possess a plethora of interesting features for quantum information processing. For example, they can serve as compact quantum memories with long life times, or can transduce quantum states between a variety of otherwise incompatible quantum systems. Particularly interesting among those are infrared photons in the telecommunication wavelength band, due to their widespread use in quantum communication. Using artificial optical and mechanical resonances, they can interact with phonons by radiation pressure. However, controlling individual excitations of motion in micromechanical resonators has thus far been restricted to the domain of microwave radiation, while optical control remained an outstanding goal. In this thesis, I describe how this can be achieved experimentally, employing quantum optics protocols. First, the operation of silicon optomechanical crystals in the quantum regime is demonstrated by creating non-classical photon-phonon pairs through optomechanical down conversion. This quantum interface is subsequently used to characterize heralded single phonons, and to generate quantum entanglement between two remote mechanical oscillators. The realization of these classic quantum optics experiments with single phonons establishes mechanical quantum memories in silicon photonics as a useful resource for future quantum networks