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Optics Express

Efficient frequency downconversion at the single photon level from the red spectral range to the telecommunications C-band

Sebastian Zaske, Andreas Lenhard, Christoph Becher

Published Jun 17, 2011• 93 citations
Publisher

Abstract

We report on single photon frequency downconversion from the red part of the spectrum (738 nm) to the telecommunications C-band. By mixing attenuated laser pulses with an average photon number per pulse < 1 with a strong continuous light field at 1403 nm in a periodically poled Zn:LiNbO3 ridge waveguide an internal conversion efficiency of ∼ 73% is achieved. We further investigate the noise properties of the process by measuring the output spectrum. Our results indicate that by narrow spectral filtering a quantum interface should be feasible which bridges the wavelength gap between quantum emitters like color centers in diamond emitting in the red part of the spectrum and low-loss fiber-optic telecommunications wavelengths.

DOI
10.1364/oe.19.012825

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We report on single photon frequency downconversion from the red part of the spectrum (738 nm) to the telecommunications C-band. By mixing attenuated laser pulses with an average photon number per pulse < 1 with a strong continuous light field at 1403 nm in a periodically poled Zn:LiNbO3 ridge waveguide an internal conversion efficiency of ∼ 73% is achieved. We further investigate the noise properties of the process by measuring the output spectrum. Our results indicate that by narrow spectral filtering a quantum interface should be feasible which bridges the wavelength gap between quantum emitters like color centers in diamond emitting in the red part of the spectrum and low-loss fiber-optic telecommunications wavelengths.
We demonstrate a low-noise frequency down-conversion of photons at 637 nm to the telecommunication band at 1587 nm by the difference frequency generation in a periodically-poled lithium niobate. An internal conversion efficiency of the converter is estimated to be 0.44 at the maximum which is achieved by a pump power of 0.43 W, whereas a rate of internal background photons caused by the strong cw pump laser is estimated to be 9 kHz/mW within a bandwidth of about 1 nm. By using the experimental values related to the intrinsic property of the converter, and using the intensity correlation and the average photon number of a 637 nm input light pulse, we derive the intensity correlation of a converted telecom light pulse. Then we discuss feasibility of a single-photon frequency conversion to the telecommunication band for a long-distance quantum communication based on NV centers in diamond.
Single-photon sources based on quantum dots have been shown to exhibit almost ideal properties such as high brightness and purity in terms of clear anti-bunching as well as high two-photon interference visibilities of the emitted photons, making them promising candidates for different quantum information applications such as quantum computing, quantum communication and quantum teleportation. However, as most single-photon sources also quantum dots typically emit light at wavelengths of electronic transitions within the visible or the near infrared range. In order to establish quantum networks with remote building blocks, low-loss single photons at telecom wavelengths are preferable, though. Despite recent progress on emitters of telecom-photons, the most efficient single-photon sources still work at shorter wavelengths. On that matter, quantum frequency down-conversion, being a nonlinear optical process, has been used in recent years to alter the wavelength of single photons to the telecom wavelength range while conserving their nonclassical properties. Characteristics such as lifetime, first-order coherence, anti-bunching and entanglement have been shown to be conserved or even improved due to background suppression during the conversion process, while the conservation of indistinguishability was yet to be shown. Here we present our experimental results on quantum frequency down-conversion of single photons emitted by an InAs/GaAs quantum dot at 903.6 nm following a pulsed excitation of a p-shell exciton at 884 nm. The emitted fluorescence photons are mixed with a strong pump-field at 2155 nm inside a periodically poled lithium niobate ridge waveguide and converted to 1557 nm. Common issues of a large background due to Raman-scattered pump-light photons spectrally overlapping with the converted single photons could largely be avoided, as the pump-wavelength was chosen to be fairly longer than the target wavelength. Additional narrowband spectral filtering at the telecom regime as a result of the small conversion bandwidth and using a high-performance fiber-Bragg-grating solely left the detector dark counts as the only noise source in our setup. Therefore, we could achieve conversion efficiencies of more than 20 %. In order to test the indistinguishability, sequentially emitted photons were fed into a Mach-Zehnder interferometer and spatially as well as temporally overlapped at the output beam splitter. Cross-correlation measurements between both output-ports of the beam splitter exhibit two-photon interference contrasts of more than 40 % prior to and after the down-conversion step. Accordingly, we demonstrate that the process of quantum frequency conversion preserves photon indistinguishability and can be used to establish a versatile source of indistinguishable single photons at the telecom C-Band. Furthermore our scheme allows for converting photons in a wavelength band from 900 nm to 910 nm to the same telecom target wavelength. This enables us to test indistinguishability of frequency-converted photons, originally stemming from different sources with dinstinguishable wavelengths.
The silicon-vacancy center in diamond holds great promise as a qubit for quantum communication networks. However, since the optical transitions are located within the visible red spectral region, quantum frequency conversion to low-loss telecommunication wavelengths becomes a necessity for its use in long-range, fiber-linked networks. This work presents a highly efficient, low-noise quantum frequency conversion device for photons emitted by a silicon-vacancy (SiV) center in diamond to the telecom C-band. By using a two-stage difference-frequency mixing scheme SPDC noise is circumvented and Raman noise is minimized, resulting in a very low noise rate of 10.4±0.710.4 \pm 0.710.4±0.7 photons per second as well as an overall device efficiency of 35.6 %35.6\, \%35.6%. By converting single photons from SiV centers we demonstrate the preservation of photon statistics upon conversion.
Interconnected quantum devices are the building blocks of quantum networks, where state transduction plays a central role. The frequency conversion of photons into the telecommunication C-band is decisive in taking advantage of current low-loss transmission lines. Here, we report the difference frequency conversion of 637.2 nm fluorescent light from a cluster of NV centers in diamond to tunable wavelengths between 1559.0 nm and 1564.9 nm. In order to avoid detrimental noise from spontaneous emissions, we use a two-step conversion device based on a single-pumped periodically poled lithium niobate waveguide. We observed a total external (internal) conversion efficiency of 3.0 ± 0.1 (20.5 ± 0.8) % with a noise rate of 2.4 ± 0.8 (16 ± 5) cps/GHz.
We present a novel device for the efficient, low-noise down-conversion of low-power light from the red visible spectrum. It can be applied to interface electronic spin-qubits in nitrogen-vacancy centers in diamond to the telecommunication wavelengths and thus offers the possibility to implement large-scale quantum networks in existing fiber infrastructure. In comparison to state-of-the-art frequency converters for this application, the device presented here generates an overall noise rate, which is one order of magnitude better than current record values. Simultaneously, an internal conversion efficiency of 50 % was measured. Furthermore, the converter serves as a feasibility demonstration of a general concept for the down-conversion of light from the sub-micron spectral range to telecommunication wavelengths.
Frequency upconversion for single photons at telecom wavelengths is important to simultaneously meet the different wavelength requirements for long-distance communications and quantum memories in a quantum nodal network. It also enables the detection for the telecom "flying qubit" photons with silicon-based efficient single-photon detectors with low dark count (DC) rates. Here, we demonstrate the frequency upconversion of attenuated single photons, using a low-loss titanium-indiffused periodically poled lithium niobate waveguide, pumped with a readily available erbium-doped fiber amplifier in the L-band. Internal and conversion efficiencies up to 84.4% and 49.9% have been achieved, respectively. The DC rates are suppressed down to 44 kHz at 13.9% end-to-end quantum efficiency (including full conversion and detection), enabled by our long-wavelength pump configuration and narrow 3.5-GHz bandpass filtering.