Search

A silicon quantum photonic circuit was proposed and realized for the generation and the dynamic manipulation of telecom-band frequency-degenerate polarization entangled Bell states. Frequency degenerate biphoton states were generated in four silicon waveguides by spontaneous four wave mixing. They were transformed to polarization entangled Bell states through on-chip quantum interference and quantum superposition, and then coupled to optical fibers. The property of polarization entanglement in generated photon pairs was demonstrated by two-photon interference under two non-orthogonal polarization bases. The output state could be dynamically switched between two Bell states, which was demonstrated by the simplified Bell state measurement. The experiment results indicated that the manipulation speed supported a modulation rate of several tens kHz, showing its potential on applications of quantum communication and quantum information processing requiring Bell state encoding and dynamic control.

Dispersive optics quantum key distribution (DO-QKD) based on energy-time entangled photon pairs is an important QKD scheme. In DO-QKD, the arrival time of photons is used in key generation and security analysis, which would be greatly affected by fiber dispersion. In this work, we established a theoretical model of the entanglement-based DO-QKD system, considering the protocol, physical processes (such as fiber transmission and single-photon detection), and the analysis of security tests. Based on this theoretical model, we investigate the influence of chromatic dispersion introduced by transmission fibers on the performance of DO-QKD. By analyzing the benefits and costs of dispersion compensation, the system performance under G.652 and G.655 optical fibers are shown, respectively. The results show that dispersion compensation is unnecessary for DO-QKD systems in campus networks and even metro networks. Whereas, it is still required in DO-QKD systems with longer fiber transmission distances.

For a compact quantum key distribution (QKD) sender for the polarization encoding BB84 protocol, an eavesdropper could take a side-channel attack by measuring the spatial information of photons to infer their polarizations. The possibility of this attack can be reduced by introducing an aperture in the QKD sender, however, the effect of the aperture on the QKD security lacks of quantitative analysis. In this paper, we analyze the mutual information between the actual keys encoded at this QKD sender and the inferred keys at the eavesdropper (Eve), demonstrating the effect of the aperture to eliminate the spatial side-channel information quantitatively. It shows that Eve’s potential on eavesdropping spatial side-channel information is totally dependent on the optical design of the QKD sender, including the source arrangement and the aperture. The height of compact QKD senders with integrated light-emitting diode (LED) arrays could be controlled under several millimeters, showing great potential on applications in portable equipment.

A horizontally slotted photonic crystal nanobeam cavity with an embedded active nanopillar structure is proposed for ultrafast direct modulation. By designing the thicknesses of both the nanobeam and the horizontal slot layer, the quality factor (Q factor) and the mode volume (Vn) of the proposed cavity can be engineered independently. As a result, the spontaneous emission (SpE) rate is enhanced with a small Vn of 2.4 while the SpE rate and the cavity photon lifetime have an optimal Q factor of ∼ 1000. In our simulation, the modulation bandwidth could be enhanced up to 170 GHz with different emission linewidths of the active nanopillar. [ABSTRACT FROM AUTHOR]

The size distribution of Si-nanocrystals (Si-ncs) in evenly annealed SiO is investigated with transmission electron microscopy (TEM), x-ray diffraction (XRD), and Raman scattering. Two groups of Si-ncs with very different most probable diameters are identified, where one is >6nm and the other one is <2 nm. Both of them increase gradually with increasing annealing temperature. Such a phenomenon is observed directly by TEM for samples with larger Si-ncs (>10 nm) and it can be revealed clearly for all samples by Raman spectra with two components (∼500 cm-1 and ∼520 cm-1). The results of XRD show the average effect. The experimental results indicate that the common assumption of Si-nc size distribution with single most probable diameter is not always proper and the possible mechanisms are briefly discussed. [ABSTRACT FROM AUTHOR]