Storage and Reemission of Heralded Telecommunication-Wavelength Photons Using a Crystal Waveguide

Mohsen Falamarzi Askarani, Marcel.li Grimau Puigibert, Thomas Lutz, Varun B. Verma, Matthew D. Shaw, Sae Woo Nam, Neil Sinclair, Daniel Oblak, and Wolfgang Tittel

Phys. Rev. Applied 11, 054056 – Published 21 May 2019

Abstract

Large-scale fiber-based quantum networks will likely employ telecommunication-wavelength photons of around 1550 nm wavelength to exchange quantum information between remote nodes, and quantum memories, ideally operating at the same wavelength, that allow the transmission distances to be increased, as key elements of a quantum repeater. However, the development of a suitable memory remains an ongoing challenge. Here, we demonstrate the storage and reemission of single heralded 1532-nm-wavelength photons using a crystal waveguide. The photons are emitted from a photon-pair source based on spontaneous parametric down-conversion and the memory is based on an atomic frequency comb of 6 GHz bandwidth, prepared through persistent spectral-hole burning of the inhomogeneously broadened absorption line of a cryogenically cooled erbium-doped lithium niobate waveguide. Despite currently limited storage time and efficiency, this demonstration represents an important step toward quantum networks that operate in the telecommunication band and the development of integrated (on-chip) quantum technology using industry-standard crystals.

Received 8 May 2018
Revised 15 April 2019

DOI:https://doi.org/10.1103/PhysRevApplied.11.054056

Physics Subject Headings (PhySH)

Integrated optics Photonics Quantum communication Quantum information with atoms & light Quantum memories

Rare-earth doped crystals Waveguides

Optical pumping

Quantum Information, Science & TechnologyAtomic, Molecular & Optical

Authors & Affiliations

Mohsen Falamarzi Askarani^1,2,*, Marcel.li Grimau Puigibert^1,3, Thomas Lutz^1,4, Varun B. Verma⁵, Matthew D. Shaw⁶, Sae Woo Nam⁵, Neil Sinclair^1,7, Daniel Oblak¹, and Wolfgang Tittel^1,2

¹Department of Physics & Astronomy and Institute for Quantum Science and Technology, University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada
²QuTech, Delft University of Technology, Delft 2600, Netherlands
³University of Basel, Klingelbergstrasse 82, Basel CH-4056, Switzerland
⁴ETH Zürich, Otto-Stern-Weg 1, Zürich 8093, Switzerland
⁵National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305, USA
⁶Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, California 91109, USA
⁷California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, USA

^*m.falamarziaskarani@tudelft.nl

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Vol. 11, Iss. 5 — May 2019

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Images

Figure 1
(a) The optical depth over a 100-MHz-wide spectral range centered at 1532.05 nm after applying a 19 kG magnetic field. Side holes due to the interaction between the ${Er}^{3 +}$ electronic spin and $^{93} Nb$ , $^{6} Li$ and $^{7} Li$ nuclear spins are visible. The apparent side holes at $\pm 50$ MHz are due to an imperfect frequency sweep. (b) Detuning of $^{7} Li$ and $^{93} Nb$ side holes as a function of the magnetic field. The side holes for $^{6} Li$ are resolved only at the highest field. The uncertainty bars indicate the difference between the detunings of the positive and negative side holes compared to the central hole.
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Figure 2
(a) A 200-MHz-wide section of our 6-GHz-bandwidth AFC. (b) A simplified energy-level diagram of erbium in lithium niobate. An AFC can be created by redistributing—optically pumping through the $^{4} I_{13 / 2}$ excited level—ions between superhyperfine levels of the $^{4} I_{15 / 2}$ ground-state manifold.
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Figure 3
(a) The experimental timing sequence. The sequence is continuously repeated during the experimental run. Switch 2 is closed [and connected to the photodetector (PD)] during the AFC preparation for monitoring the AFC structure and for recording the frequency-dependent optical depth shown in Figs. 1 and 2. The experimental setup consists of two main parts. The part depicted in the top half allows for optical pumping (spectral-hole burning) and AFC generation—it consists of a pump laser, a phase modulator (PM), an acousto-optic modulator (AOM), a polarization controller (PC), optical switches, a circulator, and a PD. The part in the bottom half depicts the heralded single-photon generation and the detection setup—it consists of a pulsed pump laser, second-harmonic generation (SHG), spontaneous parametric down-conversion (SPDC), long-pass filters (LF), Fabry-Perot cavities (FP), superconducting nanowire single-photon detectors (SNSPD), and a time-to-digital converter (TDC). For details of all components, see Appendices C–E.
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Figure 4
The storage and reemission of heralded single photons at telecommunication wavelength. The histogram depicts the time-resolved rate of coincidence detections of heralding 795-nm and heralded 1532-nm photons. The overall acquisition time is 2 min. The time axis is defined relative to the detection of 1532-nm photons that are directly transmitted (not absorbed) by the memory. Stored photons are reemitted after 48 ns and cause the coincidence peak highlighted in red in the enlargement. The number of coincidences in the 500-ps-long window is $18 \pm 4.24$ , clearly exceeding the background of $1.9 \pm 0.45$ per 500 ps window, obtained by averaging coincidences between 44.5 ns and 49.5 ns. The coincidence peaks at $t \approx 2.5$ , 5, 7.5, and 10 ns are due to spurious temporal modes of the pump laser—a consequence of imperfect alignment of the laser cavity—causing additional photon-pair generation by the SPDC crystal. The sequence of coincidence-detection peaks is repeated every 12.5 ns, matching the 80 MHz repetition rate of the pulsed SPDC pump laser. These repeated patterns, often referred to as accidental coincidences, are due to the detection of photons belonging to pairs that have been generated during different laser cycles.
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