Classical clock synchronization for quantum communications using the quantum channel.

We present a time synchronization method for correlation of photon arrival times for quantum communication. The method employs a low-power, low-frequency synchronization beacon that shares the quantum channel and is detected using the same single-photon detectors already present in the quantum communication system. We show experimentally that the system jitter approaches the system resolution limit with negligible impact on the quantum channel in realistic use cases.

Enhancing SPDC brightness using elliptical pump shapes.

We report on the use of elliptical pump spatial modes to increase the observed brightness of spontaneous parametric downconversion in critically phase-matched crystals. Simulations qualitatively predict this improvement, which depends on the eccentricity and orientation of the pump ellipse. We experimentally confirm a factor of two improvement in brightness when compared to the traditional circular-symmetric pump spatial modes.

Manipulation and measurement of quantum states with liquid crystal devices.

We present the use of liquid crystal retarders (LCR) as phase control elements in optical quantum technologies. We show that an entangled photon pair state can be actively controlled using an LCR without introducing state mixing or polarization drifts. Similarly, we demonstrate that the entanglement quality can be conveniently analyzed using liquid crystal polarization retarders.

Experimental entangled photon pair generation using crystals with parallel optical axes.

We present an optical design where polarization-entangled photon pairs are generated within two β-Barium Borate crystals whose optical axes are parallel. This design increases the spatial mode overlap of the emitted photon pairs enhancing single mode collection without the need for additional spatial walk-off compensators. The observed photon pair rate is at least 65 000 pairs/s/mW with a quantum state fidelity of 99.

Fluorescent color centers in laser ablated 4H-SiC nanoparticles.

Nanostructured and bulk silicon carbide (SiC) has recently emerged as a novel platform for quantum nanophotonics due to its harboring of paramagnetic color centers, having immediate applications as a single photon source and spin optical probes. Here, using ultra-short pulsed laser ablation, we fabricated from electron irradiated bulk 4H-SiC, 40-50 nm diameter SiC nanoparticles, fluorescent at 850-950 nm. This photoluminescence is attributed to the silicon vacancy color centers.