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arXiv:1907.10355 · Physical Review Applied

Pure Single Photons From Scalable Frequency Multiplexing

T. Hiemstra, T.F. Parker, P. Humphreys, J. Tiedau, M. Beck, M. Karpiński, B.J. Smith, A. Eckstein, W.S. Kolthammer, Ian A. Walmsley

Published Jul 17, 2020• 32 citations
arXivHTMLPDF

Abstract

We demonstrate multiphoton interference using a resource-efficient frequency multiplexing scheme, suitable for quantum information applications that demand multiple indistinguishable and pure single photons. In our source, frequency-correlated photon pairs are generated over a wide range of frequencies by pulsed parametric down conversion. Indistinguishable single photons of a predetermined frequency are prepared using frequency-resolved detection of one photon to control an electro-optic frequency shift applied to its partner. Measured photon statistics show multiplexing increases the probability of delivering a single photon, without a corresponding increase to multiphoton events. Interference of consecutive outputs is used to bound the modal purity and demonstrate the nonclassical nature of the emitted light.

DOI
10.1103/physrevapplied.14.014052

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We demonstrate multiphoton interference using a resource-efficient frequency multiplexing scheme, suitable for quantum information applications that demand multiple indistinguishable and pure single photons. In our source, frequency-correlated photon pairs are generated over a wide range of frequencies by pulsed parametric down conversion. Indistinguishable single photons of a predetermined frequency are prepared using frequency-resolved detection of one photon to control an electro-optic frequency shift applied to its partner. Measured photon statistics show multiplexing increases the probability of delivering a single photon, without a corresponding increase to multiphoton events. Interference of consecutive outputs is used to bound the modal purity and demonstrate the nonclassical nature of the emitted light.
Summary form only given. Here we demonstrate a novel frequency-multiplexed scheme in which the number of physical components is independent of the number of heralded sources to be combined. In particular, we use one nonlinear interaction, one heralding wavelength-resolving detector, and one electro-optic phase modulator (Fig. 1a). A pulsed spontaneous PDC source generates frequency-correlated photon pairs (Fig. 1b). We use a time-of-flight singlephoton spectrometer [4] to measure a heralding photon with 0.09 nm resolution. Feed-forward control with an electro-optic serrodyne modulator [5] shifts the heralded photon to the desired output frequency (Fig. 1c).
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.
We present an experimental demonstration of heralded single photons prepared in pure quantum states from a parametric down-conversion source. It is shown that, through controlling the modal structure of the photon pair emission, one can generate pairs in factorable states and thence eliminate the need for spectral filters in multiple-source interference schemes. Indistinguishable heralded photons were generated in two independent spectrally engineered sources and Hong-Ou-Mandel interference observed between them without spectral filters. The measured visibility of 94.4% sets a minimum bound on the mean photon purity.
Abstract Parametric single-photon sources are well suited for large-scale quantum networks due to their potential for photonic integration. Active multiplexing of photons can overcome the intrinsically probabilistic nature of these sources, resulting in near-deterministic operation. However, previous implementations using spatial and temporal multiplexing scale unfavorably due to rapidly increasing switching losses. Here, we break this limitation via frequency multiplexing in which switching losses remain fixed irrespective of the number of multiplexed modes. We use low-noise optical frequency conversion for efficient frequency switching and demonstrate multiplexing of three modes. We achieve a generation rate of 4.6 × 104 photons per second with an ultra-low g(2)(0) = 0.07 indicating high single-photon purity. Our scalable, all-fiber multiplexing system has a total loss of just 1.3 dB, such that the 4.8 dB multiplexing enhancement markedly overcomes switching loss. Our approach offers a promising path to creating a deterministic photon source on an integrated chip-based platform.
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.
The cascade-emitted biphotons generated from alkali metal atomic ensembles are an excellent entanglement resource which enables long-distance quantum communication. The communication of quantum information between distant locations can be realized by utilizing the low-loss telecom bandwidth in the upper transition of the cascaded photons in a fiber-based quantum network. Meanwhile, the infrared photon from the lower transition of this highly directional and frequency-correlated biphoton can be created using the four-wave mixing process and can be stored locally as a collective spin wave. Here, we theoretically investigate the frequency entanglement of this biphoton and propose two approaches to remove the two photons' mutual correlations in frequency spaces. The first approach applies an optical cavity which modulates the biphoton spectrum into a more symmetric and narrow spectral function by multiplexing multiple atomic ensembles with phase compensation. The purity of the single photons reaches up to 0.999, and the entanglement entropy SSS of the biphoton is reduced to 0.006, which is 200 times smaller than the one without multiplexing. The other approach employs a symmetric pumping of the laser fields in two atomic ensembles, which leads to a moderate reduction of $S\ensuremath{\sim}0.3$ when nondiscrimination detection devices are used for both photons. An extremely low frequency entanglement implies an almost indistinguishable single-photon source, which offers a potential resource for photonic quantum emulation and computation.