Time-frequency Schmidt (TFS) modes of ultrafast quantum states are naturally compatible with high bit-rate integrated quantum communication networks. Thus they offer an attractive alternative for the realization of high dimensional quantum optics. Here, we present a quantum pulse gate based on dispersion-engineered ultrafast frequency conversion in a nonlinear optical waveguide, which is a key element for harnessing the potential of TFS modes. We experimentally retrieve the modal spectral-temporal structure of our device and demonstrate a single-mode operation fidelity of 80%, which is limited by experimental shortcomings. In addition, we retrieve a conversion efficiency of 87.7% with a high signal-to-noise ratio of 8.8 when operating the quantum pulse gate at the single-photon level.

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 antireflection 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 µW. 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.Recent progress in the field of quantum information processing has highlighted the prospects of using integrated optic devices for quantum applications [1][2][3][4][5]. Integrated quantum photonics offers several advantages in comparison with free-space experimental setups with bulk optic components [6]. The miniaturization of systems with increased complexity not only drastically reduces the required space and paves the way for future commercialization, but also enables the implementation of optical networks with a large number of optical modes and an extremely high stability.In 2008 Politi et al [7] demonstrated the first quantum interference and photonic gates onchip, whereas different groups developed sophisticated and integrated experiments with twophoton interference [8,9] or photon entanglement [10,11], controlled qubit operations [12] and the controlled phase shifts in linear optical circuits [5,13]. In 2012, Metcalf et al [14] realized the first three-photon experiment inside a linear optical network, and recent research on boson sampling in an integrated device demonstrates four-photon quantum interference [15].However, in all these experiments the preparation of the photon pairs has actually been performed outside the integrated devices employing traditional bulk crystal parametric downconversion (PDC) sources. The efficient coupling between these sources and the integrated circuit remains a bottleneck for designing 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 [16-23] over the last few decades. The main benefits of...

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The practical prospect of quantum communication and information processing relies on sophisticated single photon pairs which feature 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 above performances have been demonstrated already, but it is quite challenging to have a source with all of the described characteristics simultaneously. Here we report on an integrated singlelongitudinal-mode non-degenerate narrowband photon pair source, which exhibits all 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 nm and 1320 nm are generated via type II phasematched parametric down-conversion. 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 3 × 10 4 pairs/(s•mW•MHz). This source exhibits prominent single-longitudinal-mode purity and remarkable temporal shaping capability. Especially, due to temporal broadening, we can observe that the coherence time of the two-photon component of PDC state is actually longer than the one of the single photon states. The miniaturized monolithic design makes this source have various fiber communication applications.

Hybrid quantum networks rely on efficient interfacing of dissimilar quantum nodes, as elements based on parametric downconversion sources, quantum dots, colour centres or atoms are fundamentally different in their frequencies and bandwidths. Although pulse manipulation has been demonstrated in very different systems, to date no interface exists that provides both an efficient bandwidth compression and a substantial frequency translation at the same time. Here we demonstrate an engineered sum-frequency-conversion process in lithium niobate that achieves both goals. We convert pure photons at telecom wavelengths to the visible range while compressing the bandwidth by a factor of 7.47 under preservation of non-classical photon-number statistics. We achieve internal conversion efficiencies of 61.5%, significantly outperforming spectral filtering for bandwidth compression. Our system thus makes the connection between previously incompatible quantum systems as a step towards usable quantum networks.