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Interference of Independent, Telecom Wavelength, Heralded Single Photons from PCF and PPLN Based Sources

R. Mcmillan A., Laurent Labonté, Alex S. Clark, B. Bell, W. J. Wadsworth, Olivier Alibart, Sébastien Tanzilli, John Rarity

Published Sep 3, 2012• 0 citations
OpenAlex

Abstract

Heralded single photons with wavelength near 1550nm are expected to be an important resource for future quantum communications applications. Such applications often rely on non-classical Hong Ou Mandel interference (HOMI) that is observed between indistinguishable, pure photon states. While high visibility HOMI is routinely achieved for photons from identically prepared sources, here we observe interference between photons from two dissimilar systems. To generate synchronised indistinguishable photons, two photon sources were pumped with a single 1064nm, picosecond-pulsed fibre laser. In one source the laser pulses generated correlated pairs of photons at 810nm and 1550nm through four-wave mixing in photonic crystal fibre (PCF). In the other, the laser was used to generate second harmonic light at 532nm in a bulk crystal, before being launched into a periodically poled lithium niobate (PPLN) waveguide. This structure was designed to generate signal and idler photons through parametric down-conversion, matched in wavelength to the fibre based source. Idler photons from both sources were input into a fused-fibre coupler in order to measure the HOMI visibility. HOMI with a net visibility of 70% was demonstrated between photons from the two sources (after accounting for the background due to emission of multiple photons from a single source). A visibility of 80% is anticipated for the current sources after further improvement in the purity of the generated states. This result is the first step towards realising a quantum relay system, in which transmitted qubits produced by low loss, fibre-based photon sources interact with photons produced locally on a chip.

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Pure state single photons are at the heart of optical quantum technologies. We have previously reported the generation of photon pairs by four-wave mixing in a single-mode photonic crystal fibre (PCF) and the use of a new birefringent phase matching scheme which results in the generation of narrowband signal photons, around 0.2 nm in bandwidth, and a factorizable photon pair state with no requirement for spectral filtering, leading to increased count rates. Our source is bright, polarized, and tuneable by variable laser wavelength and fibre parameters. Hong-Ou-Mandel (HOM) interference is observed between photons from two of these sources, a requirement for optical quantum information tasks.

Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)•May 1, 2011•0 citations
Heralded single photons with wavelength near 1550nm are expected to be an important resource for future quantum communications applications. Such applications often rely on non-classical Hong Ou Mandel interference (HOMI) that is observed between indistinguishable, pure photon states. While high visibility HOMI is routinely achieved for photons from identically prepared sources, here we observe interference between photons from two dissimilar systems. To generate synchronised indistinguishable photons, two photon sources were pumped with a single 1064nm, picosecond-pulsed fibre laser. In one source the laser pulses generated correlated pairs of photons at 810nm and 1550nm through four-wave mixing in photonic crystal fibre (PCF). In the other, the laser was used to generate second harmonic light at 532nm in a bulk crystal, before being launched into a periodically poled lithium niobate (PPLN) waveguide. This structure was designed to generate signal and idler photons through parametric down-conversion, matched in wavelength to the fibre based source. Idler photons from both sources were input into a fused-fibre coupler in order to measure the HOMI visibility. HOMI with a net visibility of 70% was demonstrated between photons from the two sources (after accounting for the background due to emission of multiple photons from a single source). A visibility of 80% is anticipated for the current sources after further improvement in the purity of the generated states. This result is the first step towards realising a quantum relay system, in which transmitted qubits produced by low loss, fibre-based photon sources interact with photons produced locally on a chip.
The preparation of single photons in a pure quantum state is a subject of great interest in physics, enabling the control of light at an unprecedented level. The ease with which certain degrees of freedom of photon states, such as polarisation, can be manipulated, along with the inherent resilience of photons to decoherence, makes them well suited for use as qubits. Recent rapid developments in the transmission and processing of quantum information, as well as the likely technological impact of potential real-world applications such as quantum cryptography and quantum computation, mean that the demand for high performance single photon sources is likely to increase in the near future. One approach to producing single photon states, which are known to be in a well-defined spatio-temporal mode without destructively measuring them, is to take advantage of nonlinear optics. Nonlinear processes can be used to realise frequency conversion by generating a single, correlated pair of photons from an intense pump laser source. The detection of one of the photons from a pair can then be used to indicate the presence of the other photon in the pair, a procedure known as heralding. This thesis describes the development of a source of heralded single photons at 1550 nm, generated directly in the core of a photonic crystal fibre (PCF). By taking advantage of low loss fibre components for the required spectral filtering of the generated photon state, a heralding fidelity of 52% was achieved. The source was designed to be used with a picosecond pulsed fibre laser, making it relatively low cost and maintenance free. With 148 mW of average pump power a heralded output photon rate of 6.4 × 104 s-1 was observed, demonstrating the brightness of the source. The purity of the generated single photons was established by measuring non-classical interference, with a visibility of 70%, between the photons output from this source and a source based on a PPLN waveguide. The fabrication of a series of birefringent PCFs for the generation of spectrally pure state photons at 1550 nm is also discussed. These PCFs will be useful for incorporation in the next generation of high performance, fibre-based photon sources.
We experimentally demonstrated the Hong-Ou-Mandel (HOM) interference between two photons after visible-to-telecommunication wavelength conversion. In the experiment, we prepared a heralded single photon by using spontaneous parametric down conversion (SPDC) and the other photon from a weak laser source at 780 nm. We converted the wavelength of both photons to the telecommunication wavelength of 1522 nm by using difference-frequency generation in a periodically poled lithium niobate, and then observed the HOM interference between the photons. The observed visibility is $0.76\ifmmode\pm\else\textpm\fi{}0.12$ which clearly shows the nonclassical interference of the two photons. The high-visibility interference is an important step for fiber-based quantum communications of photons generated from visible-photon emitters.
Single photons are at the heart of optical quantum technologies such as quantum cryptography, quantum computing and quantum metrology. In this paper we report on the creation of photon pairs via four-wave-mixing (FWM) in birefringent photonic crystal fibres (PCF). It has recently been suggested that for thoroughly engineering the phase matching condition of a birefringent PCF, photon pairs can by created in an intrinsically pure state and narrow band. This can be achieved for cross-polarized phase matching, where two pump photons in the slow axis are converted into a pair of photons, polarized in the orthogonal fast axis. The aim is to produce such intrinsically pure and narrow-band photons and hence to achieve high non-classical interference visibility without any requirement for spectral filtering. In order to experimentally test the purity of our heralded single photons we performed a Hong-Ou-Mandel experiment using heralded signal photons generated in separate PCF sources.
Quantum information protocols tend to involve more and more entangled photon pairs, for enabling advanced quantum tasks. To compensate for the low success efficiency of these protocols, one can increase the repetition rate of the emitted pairs, up to current telecom standard (40 GHz). In this context, we propose a realization of ultra-fast photon pair sources, intended for either heralded quantum state engineering or entanglement swapping at telecom wave- length. In this paper, we present preliminary results consisting of a two-photon interference experiment using four photons where the achieved raw visibility of the Hong-Ou-Mandel (HOM) dip exceeds 98.6 %. The interfering photons are generated through spontaneous parametric down conversion process (SPDC) in two independent, separate, periodically poled lithium niobate (PPLN) waveguides.
Summary form only given. Recent progress in quantum information processing has highlighted the benefits of integrated optic devices for quantum applications (e.g.[l]). The miniaturization of systems with increased complexity drastically reduces the required space and paves the way for future commercialization.In the past five years, several groups have demonstrated promising approaches to achieve quantum interference and photonic gates on-chip (e.g.[2]). However, in all of these experiments the preparation of the photon pairs has been performed outside the integrated devices employing bulk crystal parametric down-conversion (PDC) sources, while the efficient coupling between these sources and the integrated circuit remains as a bottleneck for the design of systems with increasing complexity. On the other hand remarkable efforts have been devoted to the development of integrated PDC sources for photon pair generation inside channel waveguides [3]. The main benefits of guided-wave PDC processes include high conversion efficiencies and spatial mode control. We combine the prospects of an efficient type-I PDC source based on Titanium-indiffused periodically poled Z-cut Lithium Niobate waveguides (Ti:PPLN) with a passive wavelength division demultiplexing coupler on-chip, shown in Figure 1. The coupler allows for excellent spatial separation generated photon pairs. The non-degenerate decay of pump photons at 532 nm into signal and idler photons provides us with a photon pair at wavelengths of 1575 nm and 800 nm, respectively. Thus low-loss fiber transmission of the prepared states at 1575 nm can be accomplished on the one hand, while on the other hand efficient heralding of conditioned states can be implemented with off-the-shelf silicon-based detectors. The quality and efficiency of our source was improved by the deposition of endface-coatings. This allows for the efficient launching of pump light into the waveguide and it simultaneously provides a close-toperfect transmission of signal and idler at the output of our source, reflecting the pump light by more than 99%. In conditioned coincidence measurements in the picosecond pulsed regime we achieved heralding of single photons with almost no influence of background radiation, expressed by high coincidences-toaccidentals ratios up to CAR > 7400. The preparation exceeded 60% of efficiency in the low pump power regime, accompanied with ultra-low second-order correlation functions of g(2) (0) <; 4.10-3. These figures of merit in conjunction with the integration of active and passive elements make our source a candidate for a basic building block in more complex and miniaturized quantum network realizations in the future.
Pure state single photons are at the heart of optical quantum technologies. We have previously reported the generation of photon pairs by four-wave mixing in a single-mode photonic crystal fibre (PCF) and the use of a new birefringent phase matching scheme which results in the generation of narrowband signal photons, around 0.2 nm in bandwidth, and a factorizable photon pair state with no requirement for spectral filtering, leading to increased count rates. Our source is bright, polarized, and tuneable by variable laser wavelength and fibre parameters. Hong-Ou-Mandel (HOM) interference is observed between photons from two of these sources, a requirement for optical quantum information tasks.