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Serial-parallel conversion for single photons with heralding sinnals

Takayuki Kiyohara, Ryo Okamoto, Shigeki Takeuchi

Published Dec 25, 2017• 2 citations
OpenAlex

Abstract

We present serial-parallel conversion for a heralded single photon source (heralded SPS). We theoretically show that with the heralding signal, the serial-parallel converter can route a stream of n photons to n different spatial modes more efficiently than is the case without using a heralding signal. We also experimentally demonstrate serial-parallel conversion for two photons generated from a heralded SPS. We achieve a conversion efficiency of 0.533 ± 0.003, which exceeds the maximum achievable efficiency of 0.5 for serial-parallel conversion using unheralded photons, and is double the efficiency (0.25) for that using beamsplitters. When the losses in the optical converter are corrected for, the efficiency of the current set up can be increased up to 0.996 ± 0.00.

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We present serial-parallel conversion for a heralded single photon source (heralded SPS). We theoretically show that with the heralding signal, the serial-parallel converter can route a stream of n photons to n different spatial modes more efficiently than is the case without using a heralding signal. We also experimentally demonstrate serial-parallel conversion for two photons generated from a heralded SPS. We achieve a conversion efficiency of 0.533 \pm 0.003, which exceeds the maximum achievable efficiency of 0.5 for serial-parallel conversion using unheralded photons, and is double the efficiency (0.25) for that using beamsplitters. When the losses in the optical converter are corrected for, the efficiency of the current setup can be increased up to 0.996 \pm 0.006.

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High heralding efficiency single photon source at telecom wavelength

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The generation of high purity single photons and entangled photon pairs is a crucial first step in many quantum optics experiments, including those that require quantum teleportation [1], entanglement swapping [2], and the generation of multi-photon entanglement [3]. The most widely used and established approach for creating photon pairs is spontaneous parametric down conversion (SPDC) - where pump photons undergo a non-linear optical process to create a down-converted photon pair [4]. Traditionally, the generation of high-purity heralded single photons required severe spectral filtering, introducing additional loss. However, through careful engineering of spectral correlations of the down-converted photon pairs one can circumvent the need for filtering and avoid the accompanying reduction in heralding efficiency.

European Quantum Electronics Conference (EQEC)•Jun 21, 2015•1 citation
We present serial-parallel conversion for a heralded single photon source (heralded SPS). We theoretically show that with the heralding signal, the serial-parallel converter can route a stream of n photons to n different spatial modes more efficiently than is the case without using a heralding signal. We also experimentally demonstrate serial-parallel conversion for two photons generated from a heralded SPS. We achieve a conversion efficiency of 0.533 ± 0.003, which exceeds the maximum achievable efficiency of 0.5 for serial-parallel conversion using unheralded photons, and is double the efficiency (0.25) for that using beamsplitters. When the losses in the optical converter are corrected for, the efficiency of the current set up can be increased up to 0.996 ± 0.00.
We present serial-parallel conversion for a heralded single photon source (heralded SPS). We theoretically show that with the heralding signal, the serial-parallel converter can route a stream of n photons to n different spatial modes more efficiently than is the case without using a heralding signal. We also experimentally demonstrate serial-parallel conversion for two photons generated from a heralded SPS. We achieve a conversion efficiency of 0.533 \pm 0.003, which exceeds the maximum achievable efficiency of 0.5 for serial-parallel conversion using unheralded photons, and is double the efficiency (0.25) for that using beamsplitters. When the losses in the optical converter are corrected for, the efficiency of the current setup can be increased up to 0.996 \pm 0.006.
A source to efficiently generate multiple indistinguishable single photons in different spatial modes in parallel (multi-photon parallel state) is indispensable for realizing large-scale photonic quantum circuits. "A naive scheme" may be to use a heralding single photon source with an on-off detector set at each of parallel modes and to select the cases where each mode contains one photon at the same time. However, it is also necessary to suppress the probability of generating more than two photons from a single-photon source. For this requirement, serial-parallel conversion and a multiplexed heralded single photon source (HSPS) have been proposed and demonstrated. In this paper, we propose and demonstrate a novel method to produce a multi-photon parallel state efficiently using multiple HSPSs and an N × N active optical switch. As an advantage over the simple combination of a spatial multiplexed HSPS and a serial-parallel converter, our method, called the "unified integration scheme," can generate a multi-photon parallel state with minimized optical losses in the switch. Using a 2 × 2 active optical switch and a fixed delay, we achieve an enhancement factor of 1.59 ± 0.14, compared with a naive scheme using two HSPSs, and better than the factor of 1.46 using the simple combination scheme. Furthermore, we confirm the reduction of multi-photon events to 62 % of that of the naive scheme.
The non-deterministic nature of photon sources is a key limitation for single-photon quantum processors. Spatial multiplexing overcomes this by enhancing the heralded single-photon yield without enhancing the output noise. Here the intrinsic statistical limit of an individual source is surpassed by spatially multiplexing two monolithic silicon-based correlated photon pair sources in the telecommunications band, demonstrating a 62.4% increase in the heralded single-photon output without an increase in unwanted multipair generation. We further demonstrate the scalability of this scheme by multiplexing photons generated in two waveguides pumped via an integrated coupler with a 63.1% increase in the heralded photon rate. This demonstration paves the way for a scalable architecture for multiplexing many photon sources in a compact integrated platform and achieving efficient two-photon interference, required at the core of optical quantum computing and quantum communication protocols. Photonic quantum technologies will require efficient single-photon sources and spatial multiplexing has been explored as a route to achieve this. Here, the authors present a scheme to integrate several single-photon sources using spatial multiplexing for on-chip applications at telecommunications wavelengths.
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.
We describe two experiments in which photon pairs from a parametric down-conversion source are efficiently coupled into single-mode fibers, and estimation of the heralding efficiency is attempted. One experiment is based on a pulsed pump configuration in a bulk crystal and the other experiment on a CW periodically poled downconverter. The heralding and heralded photons were analyzed spectrally by a monochromator to determine the effect of the correlation between spectral and spatial mode-matching in the heralding efficiency. Moreover, we theoretically model the heralding efficiency of both bulk and periodically poled crystals. Analysis of spatial and spectral mode selection, and their mutual correlation, allows controlled engineering of the spectral and spatial emission modes of PDC single photons.
The generation of high purity single photons and entangled photon pairs is a crucial first step in many quantum optics experiments, including those that require quantum teleportation [1], entanglement swapping [2], and the generation of multi-photon entanglement [3]. The most widely used and established approach for creating photon pairs is spontaneous parametric down conversion (SPDC) - where pump photons undergo a non-linear optical process to create a down-converted photon pair [4]. Traditionally, the generation of high-purity heralded single photons required severe spectral filtering, introducing additional loss. However, through careful engineering of spectral correlations of the down-converted photon pairs one can circumvent the need for filtering and avoid the accompanying reduction in heralding efficiency.