Ultrafast switching of photonic entanglement

To deploy and operate a quantum network which utilizes existing telecommunications infrastructure, it is necessary to be able to route entangled photons at high speeds, with minimal loss and signal-band noise, and---most importantly---without disturbing the photons' quantum state. Here we present a switch which fulfills these requirements and characterize its performance at the single photon level; it exhibits a 200-ps switching window, a 120:1 contrast ratio, 1.5 dB loss, and induces no measurable degradation in the switched photons' entangled-state fidelity (< 0.002). Furthermore, because this type of switch couples the temporal and spatial degrees of freedom, it provides an important new tool with which to encode multiple-qubit states in a single photon. As a proof-of-principle demonstration of this capability, we demultiplex a single quantum channel from a dual-channel, time-division-multiplexed entangled photon stream, effectively performing a controlled-bit-flip on a two-qubit subspace of a five-qubit, two-photon state

All-optical switching of photonic entanglement

Future quantum optical networks will require the ability to route entangled photons at high speeds, with minimal loss and added in-band noise, and---most importantly---without disturbing the photons' quantum state. Here we present an all-optical switch which fulfills these requirements and characterize its performance at the single photon level. It exhibits a 200-ps switching window, 120:1 contrast, 1.5-dB loss, and induces no measurable degradation in the switched photons' entangled-state fidelity (< 0.002). As a proof-of-principle demonstration of its capability, we use the switch to demultiplex a single quantum channel from a dual-channel, time-division-multiplexed entangled photon stream. Furthermore, because this type of switch couples the temporal and spatial degrees of freedom, it provides an important new tool with which to encode multiple-qubit quantum states on a single photon

Madagascar: Transitions in health care

Before actually visiting the country, the author theorized that as the health care system is being transformed from traditional to modern health care in the country of Madagascar, the traditional aspect of health care needs to be heavily incorporated in the transition. In this way, efficacy could be maximized and the cultural practices could be protected. After traveling to Madagascar in 2011 to conduct research as part of her study abroad program, the author found she had had underestimated the extent to which biomedicine was already present in the country. As she visited and interviewed traditional healers, toured biomedical hospitals, and lived in solidarity with Malagasy families, she learned that the problem was not that biomedicine had not yet been introduced, but that most Malagasy families do not have access to or cannot afford clean drinking water, let alone prescription medication or biomedical services. She quickly learned that the opposite of her proposed thesis seemed to be the case in Madagascar

Loophole-free Bell test based on local precertification of photon's presence

A loophole-free violation of Bell inequalities is of fundamental importance for demonstrating quantum nonlocality and long-distance device-independent secure communication. However, transmission losses represent a fundamental limitation for photonic loophole-free Bell tests. A local precertification of the presence of the photons immediately before the local measurements may solve this problem. We show that local precertification is feasible by integrating three current technologies: (i) enhanced single-photon down-conversion to locally create a flag photon, (ii) nanowire-based superconducting single-photon detectors for a fast flag detection, and (iii) superconducting transition-edge sensors to close the detection loophole. We carry out a precise space-time analysis of the proposed scheme, showing its viability and feasibility.Comment: REVTeX4, 7 Pages, 1 figur

A pulsed Sagnac source of narrowband polarization-entangled photons

We demonstrate pulsed operation of a bidirectionally pumped polarization Sagnac interferometric down-conversion source and its generation of narrowband, high-visibility polarization-entangled photons. Driven by a narrowband, mode-locked pump at 390.35 nm, the phase-stable Sagnac source with a type-II phase-matched periodically poled KTiOPO$_4$ crystal is capable of producing 0.01 entangled pair per pulse in a 0.15-nm bandwidth centered at 780.7 nm with 1 mW of average pump power at a repetition rate of 31.1 MHz. We have achieved a mean photon-pair generation rate of as high as 0.7 pair per pulse, at which multi-pair events dominate and significantly reduce the two-photon quantum-interference visibility. For low generation probability $\alpha$, the reduced visibility $V=1-\alpha$ is independent of the throughput efficiency and of the polarization analysis basis, which can be utilized to yield an accurate estimate of the generation rate $\alpha$. At low $\alpha$ we have characterized the source entanglement quality in three different ways: average quantum-interference visibility of 99%, the Clauser-Horne-Shimony-Holt $S$ parameter of $2.739 \pm 0.119$, and quantum state tomography with 98.85% singlet-state fidelity. The narrowband pulsed Sagnac source of entangled photons is suitable for use in quantum information processing applications such as free-space quantum key distribution.Comment: 10 pages, 6 figures, accepted for publication in Phys. Rev.

Heralding Single Photons Without Spectral Factorability

Recent efforts to produce single photons via heralding have relied on creating spectrally factorable two-photon states in order to achieve both high purity and high production rate. Through a careful multimode analysis, we find, however, that spectral factorability is not necessary. Utilizing single-mode detection, a similar or better performance can be achieved with non-factorable states. This conclusion rides on the fact that even when using a broadband filter, a single-mode measurement can still be realized, as long as the coherence time of the triggering photons exceeds the measurement window of the on/off detector.Comment: 7 pages, 5 figure