We present a pulsed and integrated, highly non-degenerate parametric down-conversion (PDC) source of heralded single photons at telecom wavelengths, paired with heralding photons around 800 nm. The active PDC section is combined with a passive, integrated wavelength division demultiplexer on-chip, which allows for the spatial separation of signal and idler photons with efficiencies of more than 96.5%, as well as with multi-band reflection and anti-reflection coatings which facilitate low incoupling losses and a pump suppression at the output of the device of more than 99%. Our device is capable of preparing single photons with efficiencies of 60% with a coincidences-to-accidentals ratio exceeding 7400. Likewise, it shows practically no significant background noise compared to continuous wave realizations. For low pump powers, we measure a conditioned second-order correlation function of g (2) = 3.8 × 10 −3 , which proves almost pure single-photon generation. In addition, our source can feature a high brightness of 〈 n pulse 〉 = 0.24 generated photon pairs per pump pulse at pump power levels below 100 μ W. The high quality of the pulsed PDC process in conjunction with the integration of highly efficient passive elements makes our device a promising candidate for future quantum networking applications, where an efficient miniaturization plays a crucial role.
We present a pulsed and integrated, highly non-degenerate parametric down-conversion (PDC) source of heralded single photons at telecom wavelengths, paired with heralding photons around 800 nm. The active PDC section is combined with a passive, integrated wavelength division demultiplexer on-chip, which allows for the spatial separation of signal and idler photons with efficiencies of more than 96.5%, as well as with multi-band reflection and anti-reflection coatings which facilitate low incoupling losses and a pump suppression at the output of the device of more than 99%. Our device is capable of preparing single photons with efficiencies of 60% with a coincidences-to-accidentals ratio exceeding 7400. Likewise, it shows practically no significant background noise compared to continuous wave realizations. For low pump powers, we measure a conditioned second-order correlation function of g (2) = 3.8 × 10 −3 , which proves almost pure single-photon generation. In addition, our source can feature a high brightness of 〈 n pulse 〉 = 0.24 generated photon pairs per pump pulse at pump power levels below 100 μ W. The high quality of the pulsed PDC process in conjunction with the integration of highly efficient passive elements makes our device a promising candidate for future quantum networking applications, where an efficient miniaturization plays a crucial role.
We present a pulsed and integrated, highly non-degenerate parametric downconversion (PDC) source of heralded single photons at telecom wavelengths, paired with heralding photons around 800 nm. The active PDC section is combined with a passive, integrated wavelength division demultiplexer on-chip, which allows for the spatial separation of signal and idler photons with efficiencies of more than 96.5 %, as well as with multi-band reflection and anti-reflection coatings which facilitate low incoupling losses and a pump suppression at the output of the device of more than 99 %. Our device is capable of preparing single photons with efficiencies of 60 % with a coincidences-to-accidentals ratio exceeding 7400. Likewise it shows practically no significant background noise compared to continuous wave realizations. For low pump powers, we measure a conditioned second-order correlation function of g^(2)(0)=0.0038, which proves almost pure single photon generation. In addition, our source can feature a high brightness of <n_pulse>=0.24 generated photon pairs per pump pulse at pump power levels below 100 uW. The high quality of the pulsed PDC process in conjunction with the integration of highly efficient passive elements makes our device a promising candidate for future quantum networking applications, where an efficient miniaturization plays a crucial role.
We report a fibre-integrated heralded single-photon source based on a commercial Zn-indiffused MgO:PPLN ridge waveguide operated in Type-0 degenerate spontaneous parametric down-conversion (SPDC). The device emits a broadband spectrum spanning approximately 70 nm across the telecom C-and L-bands, with an absolute brightness of 9.1×109 pairs/(s mW). After accounting for optical losses, we determine an internal heralding efficiency of 58(5)%. The source maintains high purity, exhibiting a coincidences-to-accidentals ratio exceeding 9×104 and a heralded second-order correlation of gh(2)(0)=(5.53±0.46)×10−4. Low multi-photon noise and broadband emission demonstrate the viability of such platforms for wavelength-multiplexed quantum networking.
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.
Integrated sources of single and entangled photons are currently one of the main topics in the field of integrated quantum optics [1]. Sources at telecom wavelength and compatible with the electronic \nintegrate circuit technology (CMOS) are particularly interesting for their compatibility with the existing fiber network and industrial fabrication processes [2]. As for classical communication, wavelength-division multiplexing (WDM,i.e. the possibility of simultaneously transmitting on the same channel different signals each encoded in a different frequency) could in principle be exploited also for quantum communication for increasing the transmission bit-rate. However, to date only few approaches have been proposed for generating wavelength multiplexing photon pairs in integrated platforms [3,4]. Moreover, until now no integrated photon source managed to achieve at the same time practical requirements such as narrow linewidths (required for quantum memories), compatibility with CMOS technology, multichannel emission, and stable long-term operation [5]. This is due to the fact that narrow linewidths are typically achieved with structures fundamentally incompatible with large-scale integration, while CMOS-compatible devices fail to achieve the high Q-factor required for exhibiting narrow linewidths. Here we report an integrated photon pair source based on a CMOS -compatible micro-ring resonator generating multiple, simultaneous, and independent photon pairs at different wavelengths distributed in a frequency comb, compatible with standard wavelength division multiplexing channels (DWDM, 200 GHz separation) and quantum memories (140 MHz linewidth), covering the full telecommunication band (L+C). We exploit a self-locked pumping scheme allowing an intrinsically stable operation even at the very low pump power levels typically used for photon pair generation. By enclosing the microring in an active external cavity[see Fig. 1(a)], the pump laser includes the microring itself, thus resulting in a passive self-locked pumping mechanism leading to several days of stable operation (compared to only few tens of minutes for standard schemes without active stabilization) [5]. The signal/idler photons are then separated according to their wavelength using a standard commercial DWDM filter, and then characterized by coincidence detection. Clear coincidence peaks [see Fig. 1(b)], with Coincidence to Accidental Ratios higher than 10, are obtained when selecting conjugate frequencies (while no coincidences are observed for non-conjugate signal/idler pair). Finally, Fig. 3(c) reports the measured heralded autocorrelation function, g (2)h, featured by a dip as low as 0.14<0.5, indicating the suitability of our device as heralded single photon source.\n
The practical prospect of quantum communication and information processing relies on sophisticated single-photon pairs, which feature a controllable waveform, narrow spectrum, excellent purity, fiber compatibility, and miniaturized design. For practical realizations, stable, miniaturized, low-cost devices are required. Sources with one or some of the above characteristics have already been demonstrated, but it is quite challenging to obtain a source with all of the described characteristics simultaneously. Here we report on an integrated single-longitudinal-mode, non-degenerate, narrowband photon pair source that exhibits all the requirements needed for quantum applications. The device is composed of a periodically poled, Ti-indiffused, lithium niobate waveguide with high reflective dielectric mirror coatings deposited on the waveguide end-faces. Photon pairs with wavelengths around 890 and 1320 nm are generated via type II phase-matched parametric down-conversion (PDC). Clustering in this dispersive cavity restricts the whole conversion spectrum to one single-longitudinal mode in a single cluster, yielding a narrow bandwidth of only 60 MHz. The high conversion efficiency in the waveguide, together with the spectral clustering in the doubly resonant waveguide, leads to a high brightness of pairs/(s mW MHz). This source exhibits prominent single-longitudinal-mode purity and remarkable temporal shaping capability. In particular, due to temporal broadening, we can observe that the coherence time of the two-photon component of the PDC state is actually longer than that of the single-photon states. The miniaturized monolithic design enables this source to have various fiber communication applications.
We present the design and characterization of a guided-wave, bright, and highly frequency non-degenerate parametric down-conversion (PDC) source in thin-film lithium niobate. The source generates photon pairs with wavelengths of 815 nm and 1550 nm, linking the visible wavelength regime with telecommunication wavelengths. We confirm the high quality of the generated single photons by determining a value for the heralded second-order correlation function as low as g h (2) (0)=(6.7±1.1)⋅10 −3 . Furthermore, we achieve a high spectral brightness of 0.44·10 7 pairss⋅mW⋅GHz which is two orders of magnitude higher than sources based on weakly guiding waveguides. The shape of the PDC spectrum and the strong agreement between the effective and nominal bandwidth highlight our high fabrication quality of periodically poled waveguides. The good agreement between the measured and simulated spectral characteristics of our source demonstrates our excellent understanding of the PDC process. Our result is a valuable step towards practical and scalable quantum communication networks as well as photonic quantum computing.