We study Polarization Mode Dispersion (PMD) in fiber-based Quantum Key Distribution (QKD) using a broadspectrum polarization-entangled photon source. We analyze wavelength-dependent polarization transformations over 10 km deployed fiber channels, with measurements spanning one year of evolution. By examining the rotation of polarization states on the Poincare sphere and projecting them along a PMD trajectory onto a predefined state within a measurement basis, we derived a simple new formula that accurately links the measurement error probability to finite signal bandwidth and the observed differential group delay (DGD). Finally, we propose strategies to mitigate the PMD effect for entangled-based QKD by optimizing the orientation of the measurement bases and by performing the optimal spectral filtering of the source.
A high-quality heralded single photon source is realized on silicon-on-insulator (SOI) platform. With the help of specially designed ultra-low loss fiber-chip edge couplers, the heralding efficiency of the single photon source system is 56%, after calibrating for a 38% detector efficiency. Compared with the state of the art, this measured heralding efficiency marks a new milestone for integrated, on-chip silicon sources.
We designed and fabricated a -0.64 dB loss hybrid coupling platform for silicon chips. The coupler is also stable enough to maintain within +-0.1 dB coupling fluctuation against 20 um fiber holder movement. This feature allows a constant photon stream over ten days with no active alignment mechanism. Furthermore, the fiber is engineered with centimeterlong small-core fiber spliced on the tip. This minimizes Raman noise and provides high stability compared with other coupling solutions based on ordinary UHNA fibers or lensed fibers.
Nonlocal dispersion compensation facilitated over standard ITU-T G.652/7 telecommunication fiber provides the simplest solution for the preservation of pair-wise timing correlations of broadband spontaneous parametric down converted photons. Its reliance on key parameters such as the relative spectral property of the down converted photons and pump wavelength were studied, providing important insights for an effective use of this scheme. We also raise the benefit of using modern ITU-T G.655 telecommunication fiber to complement this scheme. We preserved the timing correlations of photons distributed over a cumulative distance of 40km to within 60ps, with only 2km of extra G.655 fiber.
To facilitate the implementation of large scale photonic quantum walks, we have developed a polymer waveguide platform capable of robust, polarization insensitive single mode guiding over a broad range of visible and nearinfrared wavelengths. These devices have considerable elasticity, which we exploit to enable tuning of optical behaviour by precise mechanical deformations. In this work, we investigate pairs of beamsplitters arranged as interferometers. These systems demonstrate stable operation over a wide range of phases and reflectivities. We discuss device performance, and present an outlook on flexible polymer chips supporting large, reconfigurable optical circuits.
To enable space-based quantum key distribution proposals the Centre for Quantum Technologies is developing
a source of entangled photons ruggedized to survive deployment in space and greatly miniaturised so that it
conforms to the strict form factor and power requirements of a 1U CubeSat. The Small Photon Entangling
Quantum System is an integrated instrument where the pump, photon pair source and detectors are combined
within a single optical tray and electronics package that is no larger than 10 cm x 10 cm x 3 cm. This footprint
enables the instrument to be placed onboard nanosatellites or the CubeLab structure aboard the International
Space Station. We will discuss the challenges and future prospects of CubeSat-based missions.
The Small Photon Entangling Quantum System is an integrated instrument where the pump, photon pair source and detectors are combined within a single optical tray and electronics package that is no larger than 10cm×10cm×3cm. This footprint enables the instrument to be placed onboard nanosatellites or the CubeLab facility within the International Space Station. The first mission is to understand the different environmental conditions that may affect the operation of an entangled photon source in low Earth orbit. This understanding is crucial for the construction of cost-effective entanglement based experiments that utilize nanosatellite architecture. We will discuss the challenges and lessons we have learned over three years of development and testing of the integrated optical platform and review the perspectives for future advanced experiments.
In this proceedings paper we show describe how a microtool can be assembled, and tracked in three dimensions
such that its full rotational and translational coordinates, q, are recovered. This allows tracking of the motion
of any arbitrary point, d, on the microtool's surface. When the micro-tool is held using multiple optical traps
the motion of such a point investigates the inside of an ellipsoidal volume - we term this a `thermal ellipsoid. We
demonstrate how the shape of this thermal ellipsoid may be controlled by varying the relative trapping power
of the optical traps, and adjusting the angle at which the micro-tool is held relative to the focal plane. Our
experimental results follow the trends derived by Simpson and Hanna.
A Multitouch screen is an obvious choice for a holographic optical tweezers interface, allowing multiple optical traps to be
controlled in real-time. In this paper we describe the user interface used for our original multitouch system and demonstrate
that, for the user tasks performed, the multitouch performs better than a simple point-and-click interface.
Holographic optical tweezers are used to assemble and control probes made from high aspect-ratio CdS and SiO2 nanorods
and SiO2 microspheres. Analysis of the probe position allows for the measurement of forces experienced by the tip in a manner
analogous to existing scanning probe microscopy (SPM) techniques.
CdS nanowires and silica microspheres are manipulated using optical traps into 1D and 2D structures. The bonding occurs through the use of biotin and streptavidin.
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