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arXiv:1007.4798 · Physical Review A

Experimental generation of single photons via active multiplexing

Xiao‐Song Ma, Stefan Zotter, Johannes Kofler, Thomas D. Jennewein, Anton Zeilinger

Published Apr 13, 2011• 211 citations
arXivHTMLPDF

Abstract

An on-demand single-photon source is a fundamental building block in quantum science and technology. We experimentally demonstrate the proof of concept for a scheme to generate on-demand single photons via actively multiplexing several heralded photons probabilistically produced from pulsed spontaneous parametric down-conversions (SPDCs). By utilizing a four-photon-pair source, an active feed-forward technique, and an ultrafast single-photon router, we show a fourfold enhancement of the output photon rate. Simultaneously, we maintain the quality of the output single-photon states, confirmed by correlation measurements. We also experimentally verify, via Hong-Ou-Mandel interference, that the router does not affect the indistinguishability of the single photons. Furthermore, we give numerical simulations, which indicate that photons based on multiplexing of four SPDC sources can outperform the heralding based on highly advanced photon-number-resolving detectors. Our results show a route for on-demand single-photon generation and the practical realization of scalable linear optical quantum-information processing.

DOI
10.1103/physreva.83.043814

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An on-demand single-photon source is a fundamental building block in quantum science and technology. We experimentally demonstrate the proof of concept for a scheme to generate on-demand single photons via actively multiplexing several heralded photons probabilistically produced from pulsed spontaneous parametric down-conversions (SPDCs). By utilizing a four-photon-pair source, an active feed-forward technique, and an ultrafast single-photon router, we show a fourfold enhancement of the output photon rate. Simultaneously, we maintain the quality of the output single-photon states, confirmed by correlation measurements. We also experimentally verify, via Hong-Ou-Mandel interference, that the router does not affect the indistinguishability of the single photons. Furthermore, we give numerical simulations, which indicate that photons based on multiplexing of four SPDC sources can outperform the heralding based on highly advanced photon-number-resolving detectors. Our results show a route for on-demand single-photon generation and the practical realization of scalable linear optical quantum-information processing.
It is a fundamental challenge in quantum optics to deterministically generate indistinguishable single photons through non-deterministic nonlinear optical processes, due to the intrinsic coupling of single- and multi-photon-generation probabilities in these processes. Actively multiplexing photons generated in many temporal modes can decouple these probabilities, but key issues are to minimize resource requirements to allow scalability, and to ensure indistinguishability of the generated photons. Here we demonstrate the multiplexing of photons from four temporal modes solely using fibre-integrated optics and off-the-shelf electronic components. We show a 100% enhancement to the single-photon output probability without introducing additional multi-photon noise. Photon indistinguishability is confirmed by a fourfold Hong-Ou-Mandel quantum interference with a 91 ± 16% visibility after subtracting multi-photon noise due to high pump power. Our demonstration paves the way for scalable multiplexing of many non-deterministic photon sources to a single near-deterministic source, which will be of benefit to future quantum photonic technologies.
Photons have proven to be excellent carriers of quantum information, and play essential roles in numerous quantum information processing (QIP) applications. In particular, heralded single- photon sources 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 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% 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 should enable larger scale optical QIP systems than ever realized.
Generating N single photons simultaneously is a formidable challenge due to the lack of deterministic single photon sources. Recent work [New J. Phys. 19, 063013 (2017] has proposed a relative multiplexing scheme that can enhance the N single photons probability with a minimum of active switching resources. We experimentally demonstrate relative temporal multiplexing on two photon sources with a 90% additional enhancement over the standard temporal multiplexing scheme demonstrated previously. 88 ± 11% visibility of Hong-Ou-Mandel quantum interference verifies the indistinguishability of the heralded single photons after the synchronization. This proof-of-principle demonstration points out the potential significance of the relative multiplexing scheme for large-scale photonic quantum information processing.
We present the status of our work implementing a single photon on-demand source based on a multiplexed arrangement of parametric downconverters. An array of downconverters with multiplexed outputs makes it possible to create light pulses with increased probability of containing a single photon, while suppressing the probability of producing more than one photon. This is crucial for quantum cryptographic applications. Our current setup implements the scheme in a greatly simplified manner that produces photons along with a measure of the likelihood that the light pulse emitted is just a single photon. This implementation uses a virtual array of downconverters and an array of staggered length optical fibers allowing a single detector to measure a herald photon output by a series of downconverters. This single detector arrangement is a great savings considering the cost of such detectors. The timing of the herald tells us which path the herald took, which in turn, provides information on the single vs. multiphoton probabilities. So far, our work shows that the individual correlated photon peaks are clearly resolvable with our 2.4 ns delay line steps and the 1 ns full width half maximum (FWHM) of the correlated photon peaks, and that we can observe four correlated photon peaks simultaneously, a requirement to fully implement our scheme. Our current efforts are to increase the brightness and utility of the system for incorporation into a quantum communication testbed.
Scalable quantum photonic technologies require the simultaneous production of highly indistinguishable multi-photon states with high probability. This need may be met, and the output probability significantly increased by multiplexed sources, which channel numerous low-probability heralded single-photon sources into a specified output mode using time or spatial multiplexing. However, conventional methods merely replicate these multiplexing units when scaled to multiple output modes, which is fundamentally inefficient because it discards many valid multi-photon events. To address this, we propose and experimentally demonstrate a novel multiplexing source architecture based on a multi-input/multi-output switching network, which can utilize combinatorial photon events. A super-exponential enhancement in multi-port single-photon creation is revealed by theoretical analysis, which significantly reduces the number of heralded single-photon sources needed. We demonstrate multiplexing with two output ports, supported by four integrated heralded single-photon sources. Our strategy has a generation probability of 1.60 times that of conventional methods and 2.58 times that of implementations without multiplexing. This multi-port multiplexed method opens a new avenue for establishing a solid foundation for advanced multi-photon quantum interference and large-scale quantum information processing.
Heralded spontaneous parametric down-conversion (SPDC) has become the mainstay for single-photon-state preparation in present-day photonics experiments. Because they are heralded, in principle one knows when a single photon has been prepared. However, the heralding efficiencies in experimentally realistic SPDC sources are typically very low. To overcome this, multiplexing techniques have been proposed which employ a bank of SPDC sources in parallel and route successfully heralded photons to the output, thereby effectively boosting the heralding efficiency. However, running a large bank of independent SPDC sources is costly and requires complex switching. We analyze a multiplexing technique based on time-bin encoding that allows the heralding efficiency of just a single SPDC source to be increased. The scheme is simple and experimentally viable using present-day technology. We analyze the operation of the scheme in terms of experimentally realistic considerations, such as losses, detector inefficiency, and pump power.