Photons have proven to be excellent carriers of quantum information, and play essential roles in numerous quantum information processing (QIP) applications [1][2][3][4]. In particular, heralded singlephoton sources [5] via spontaneous parametric-down conversion (SPDC) have been a key technology for demonstrating small-scale QIP, yet their low generation efficiency is a critical limitation for further scaling up optical QIP technology. In order to efficiently overcome the probabilistic nature of SPDC, here we demonstrate time multiplexing [6][7][8][9][10] for up to 30 time slots of a periodically pumped heralded single-photon source, using a switchable low-loss optical storage cavity. We observe a maximum single-photon probability of 38.6±0.4% in periodic output time windows, corresponding to ∼6 times enhancement over a non-multiplexed source, but with no increase in the contribution of unwanted multi-photon events. Combining this time-multiplexing technique with a heralded source producing pure single-photon states [11][12][13] should enable larger scale optical QIP systems than ever realized.Realizing and scaling up optical QIP systems requires on-demand preparation of quantum states of light such as single-photon and definite multi-photon states. Single atoms, ions, and solid-state single-emitter sources such as colorcenters in diamond and semiconductor quantum dots can generate true single-photon states, and especially solid-state systems have great potential for integration. However, while high indistinguishability [14,15] and somewhat high (50-80%) collection efficiency [16] have been reported in different single-emitter systems, achieving both simultaneously remains a challenge. Moreover, most single-emitter sources generate single photons with narrow bandwidths (5-100 MHz) that may be unsuitable for pursuing high-speed applications (e.g., a 5-MHz bandwidth source can produce non-overlapping single-photon gaussian wavepackets-of duration 90 ns-at a maximum rate of ∼10 MHz).SPDC is another approach that has been conventionally and widely used for generating entangled photon pairs, multi-photon entangled states, and small-scale quantum algorithms [4]. A photon pair generated via SPDC can also be used for generating a "heralded" single-photon state; detecting one of the photons "heralds" the presence of the other. Moreover, current technology has realized photons with very high coupling efficiency into single-mode optical fibers [17,18] and controlled two-photon spectral shape [11,12]. However, the photon-pair generation process via SPDC is probabilistic: one cannot obtain a photon pair or a heralded single photon on demand. Unfortunately, indefinitely increasing the mean number of photon pairs per pump pulse p also increases the likelihood of unwanted k-photon pairs (∼p k ) by higher-order processes. To overcome the probabilistic nature of photon-pair generation, time-multiplexing techniques were first proposed and demonstrated by Pittman, Jacobs, and Franson [6] in 2002. The method was since extended and t...

We describe an experimental demonstration of a novel three-photon N00N state generation scheme using a single source of photons based on spontaneous parametric down-conversion (SPDC). The three-photon entangled state is generated when a photon is subtracted from a double pair of photons and detected by a heralding counter. Interference fringes measured with an emulated three-photon detector reveal the three-photon de Broglie wavelength and exhibit visibility > 70% without background subtraction.

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The primary objective of this study was to determine the presence of unregulated organic chemicals in reclaimed water using complementary targeted and broad spectrum approaches. Eleven of 12 targeted human pharmaceuticals, antioxidants, and plasticizers, and 27 tentatively identified non-target organic chemicals, were present in secondary effluent entering tertiary treatment trains at a wastewater treatment plant and two water reclamation facilities. The removal of these compounds by three different tertiary treatment trains was investigated: coagulantassisted granular media filtration (California Title-22 water, 22 CCR § §60301-60357; Barclay [2006]), lime clarification/reverse osmosis (lime/ RO), and microfiltration-reverse osmosis (MF/RO). Carbamazepine, clofibric acid, gemfibrozil, ibuprofen, p-toluenesulfonamide, caffeine, butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), and N-butyl benzenesulfonamide (N-BBSA) were present at low to high nanogram-perliter levels in Title 22 water. The lime/RO product waters contained lower concentrations of clofibric acid, ibuprofen, caffeine, BHA, and N-BBSA (,10 to 71 ng/L) than their Title 22 counterparts. The MF/RO treatment reduced concentrations to levels below their detection limits, although BHT was present in MF/RO product water from one facility. The presence of the target analytes in two surface waters used as raw drinking water sources and a recharged groundwater was also examined. Surface waters used as raw drinking water sources contained caffeine, BHA, BHT, and N-BBSA, while recharged groundwater contained BHT, BHA, and N-BBSA. Nontarget compounds in recharged groundwater appeared to be attenuated with increased residence time in the aquifer. Water Environ. Res., 79, 156 (2007).