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

Abstract

Large-scale quantum networks will employ telecommunication-wavelength photons to exchange quantum information between remote measurement, storage, and processing nodes via fibre-optic channels. Quantum memories compatible with telecommunication-wavelength photons are a key element towards building such a quantum network. Here, we demonstrate the storage and retrieval of heralded 1532 nm-wavelength photons using a solid-state waveguide quantum memory. The heralded photons are derived from a photon-pair source that is based on parametric down-conversion, and our quantum memory is based on a 6 GHz-bandwidth atomic frequency comb prepared using an inhomogeneously broadened absorption line of a cryogenically-cooled erbium-doped lithium niobate waveguide. Using persistent spectral hole burning under varying magnetic fields, we determine that the memory is enabled by population transfer into niobium and lithium nuclear spin levels. Despite limited storage time and efficiency, our demonstration represents an important step towards quantum networks that operate in the telecommunication band and the development of on-chip quantum technology using industry-standard crystals.Many efforts towards future quantum networks [1] have focused on employing photons at wavelengths in the C band (1530-1565 nm) due to the possibility of lowloss transmission using existing fiber-optic telecommunication infrastructure. Local nodes in a quantum network are envisioned to process information using (optical) chips that are comprised of (elementary) quantum computers [1], while the synchronization of information is enabled by quantum memories that store and retrieve quantum information [2]. The latter underpins the operation of quantum repeaters, which promise to transmit quantum information through lossy channels or over intercontinental distances [3].Efforts to realize long-distance quantum communication have been bolstered by the significant progress of researchers to develop of quantum-optical technology [4]. However, much of this work is not compatible with Cband photons without the use of optical frequency conversion [5]. To avoid the conversion step, efforts have focused towards quantum technology that operates in the C-band, which has resulted in the development of efficient photon detectors [6] and single-photon sources [7]. Nonetheless, a C-band quantum memory has turned out to be particularly challenging component to realize and in particular so if it is to be integrated into a solid-state platform such that it is easy to integrate with other photonics components.Significant progress towards quantum memories has been made in the last decade, with most focus on the development of optical, microwave or radio-frequency to matter interfaces [8]. One promising approach to implement quantum memory is based on cryogenicallycooled rare-earth-ion-doped crystals as they often feature long optical and spin coherence times, as well as suitable energy-level structures [9]. Achievements with rare-earth-ion-doped crystals include broadband storage...

Reliable coherent optical memory based on a laser-written waveguide

“…Considering the transmission efficiency of 75 % for other optical elements, insertion loss of the waveguide can be calculated as 4.95 dB. We notice that the insertion loss here is approximately half of that has been achieved in industry-standard waveguides [12][13] [15]. For the ROSE scheme, the preparation & control mode is the same as the spin-wave AFC scheme.…”

“…The first one is using industry-standard Ti indiffusion in LiNbO 3 . High fidelity [10] [11], broadband [12] [13], multiplexed [14] and telecom-wavelength [15] memory as well as integrated processor [16] have been demonstrated. The second one is using focused-ion-beam milling.…”

Persistent atomic frequency comb based on Zeeman sub-levels of an erbium-doped crystal waveguide

“…Details of the waveguide fabrication can be found in Ref. [19]. The waveguide is exposed to magnetic fields up to 5 kG oriented parallel to the c-axis of the crystal.…”

“…More recently, storage of heralded single photons using AFCs in an Er-and Ti-doped LiNbO 3 (Er 3+ :Ti 3+ :LiNbO 3 ) waveguide was achieved by taking advantage of population shelving in superhyperfine levels [19]. However, as before, the efficiency did not exceed the percent level, this time due to remaining absorption in the AFC troughs caused by the complexity of the superhyperfine structure and excitationinduced spin relaxation [19]. In addition, the superhy- After passing a polarization controller (PC), the light creates spectral holes and AFC structures in the erbium-doped lithium niobate waveguide, and furthermore allows probing previously created structures with the help of a photo-detector (PD) and an oscilloscope.…”

Laser-written integrated platform for quantum storage of heralded single photons

“…Rare earth ion doped crystals, already widely known as long-lived and multiplexed optical memories with quantum storage capabilities [6], promise to be excellent systems for the development of on-chip quantum storage devices. The different approaches pursued in this respect include the quantum light storage in Tm 3+ or Er 3+ in LiNbO 3 waveguides [7,8] and the storage with optically controlled retrieval of weak coherent states in a nanophotonic crystal cavity in Nd 3+ :YVO 4 [9]. In these remarkable realizations, the ions used do not offer the possibility of storage at the ground state, thus the storage times are inherently limited by the lifetime of the excited state (further shortened in the case of the nanophotonic crystals by the Purcell enhancement in the cavity).…”