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An integrated source of high purity single photon pairs with narrow bandwidths

Kai-Hong Luo, Harald Herrmann, Stephan Krapick, Raimund Ricken, Viktor Quiring, H. Suche, W. Sohler, Christine Silberhorn

Published Jan 1, 2014• 1 citation
Publisher

Abstract

We implemented a compact integrated non-degenerate source which comprises a periodically poled waveguide with highly reflective dielectric mirror coatings to obtain narrowband photon pairs based on type II parametric down-conversion. Our engineered source exploits clustering in the dispersive cavity to restrict the conversion to a predominantly single mode operation with a narrowband linewidth and high spectral purity. The miniaturized monolithic design makes our source a versatile device for various applications in quantum communication and information processing.

DOI
10.1364/cleo_qels.2014.fw3a.3

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We implemented a compact integrated non-degenerate source which comprises a periodically poled waveguide with highly reflective dielectric mirror coatings to obtain narrowband photon pairs based on type II parametric down-conversion. Our engineered source exploits clustering in the dispersive cavity to restrict the conversion to a predominantly single mode operation with a narrowband linewidth and high spectral purity. The miniaturized monolithic design makes our source a versatile device for various applications in quantum communication and information processing.
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 report on an integrated non-degenerate narrowband photon pair source produced at 890 nm and 1320nm via type II parametric down-conversion in a periodically poled waveguide with high-reflective dielectric mirrors deposited on the waveguide end faces. The conversion spectrum consists of three clusters and only 3 to 4 longitudinal modes with about 150 MHz bandwidth in each cluster. The high conversion efficiency in the waveguide, together with the spectral clustering in the double resonator, leads to a high brightness of 3×103 3\times10^3~3×103 pairs/(s⋅\cdot⋅mW⋅\cdot⋅MHz). The compact and rugged monolithic design makes the source a versatile device for various applications in quantum communication.
Efficiently generating photon pairs with high heralding efficiency and high single photon purity that are bandwidth matched to quantum emitters, quantum memories, and other matter-based qubits is critical for quantum networking applications. However, nonlinear optics-based sources require substantial spectral engineering to overcome the orders of magnitude bandwidth mismatch between those sources and qubit systems. A popular solution is cavity-enhanced spontaneous parametric down conversion (SPDC) where the cavity sets the photon bandwidth and simultaneously enhances the spectral brightness of the SPDC. Bulk, free-space configurations are generally required to achieve the MHz-scale bandwidths required to interface with most qubit systems. Replicating these in scalable integrated photonic architectures is an ongoing challenge due to the much higher propagation losses that limit the size and linewidth of chip-based resonators. We show here how an intra-cavity slow light medium, acting as an ultra-narrow filter, would enable narrowband photon pair generation in broadband cavities with high single photon purity and without compromising the heralding efficiency. We show that such metrics can be readily realized in erbium doped thin-film lithium niobate microrings using realistic design parameters.
Photonic quantum technologies require efficient sources of pure single photons. We present a heralded single-photon source based on spontaneous parametric down-conversion in a monolithic cavity optimized for high spectral and spatial purity. The source heralds single photons at a wavelength of 1540 nm and a spectral bandwidth of 168 MHz, with a maximum heralding efficiency of 70% including all transmission and detection losses, while keeping the multi-photon contamination below 3%. The cavity enhancement predominantly generates photons into the central cavity mode, with a theoretical upper bound on the spectral purity of 79.4% arising from nonzero overlap with adjacent cavity modes. Spectral isolation of the central cavity mode with an etalon yields an increased measured spectral purity of (96.2±2.7)%.
Photonic quantum technologies require efficient sources of pure single photons. We present a heralded single-photon source based on spontaneous parametric down-conversion in a monolithic cavity optimized for high spectral and spatial purity. The source heralds single photons at a wavelength of 1540 nm and a spectral bandwidth of 168 MHz, with a maximum heralding efficiency of 70% including all transmission and detection losses, while keeping the multi-photon contamination below 3%. The cavity enhancement predominantly generates photons into the central cavity mode, with a theoretical upper bound on the spectral purity of 79.4% arising from nonzero overlap with adjacent cavity modes. Spectral isolation of the central cavity mode with an etalon yields an increased measured spectral purity of (96.2 ±\pm± 2.7)%.