Photonic quantum state transfer between a cold atomic gas and a crystal

Abstract

Interfacing fundamentally different quantum systems is key to building future hybrid quantum networks. Such heterogeneous networks offer capabilities superior to those of their homogeneous counterparts, as they merge the individual advantages of disparate quantum nodes in a single network architecture. However, few investigations of optical hybrid interconnections have been carried out, owing to fundamental and technological challenges such as wavelength and bandwidth matching of the interfacing photons. Here we report optical quantum interconnection of two disparate matter quantum systems with photon storage capabilities. We show that a quantum state can be transferred faithfully between a cold atomic ensemble and a rare-earth-doped crystal by means of a single photon at 1,552 nanometre telecommunication wavelength, using cascaded quantum frequency conversion. We demonstrate that quantum correlations between a photon and a single collective spin excitation in the cold atomic ensemble can be transferred to the solid-state system. We also show that single-photon time-bin qubits generated in the cold atomic ensemble can be converted, stored and retrieved from the crystal with a conditional qubit fidelity of more than 85 per cent. Our results open up the prospect of optically connecting quantum nodes with different capabilities and represent an important step towards the realization of large-scale hybrid quantum networks.

Fabrication limits of waveguides in nonlinear crystals and their impact on quantum optics applications

“…Nonlinear optical processes enable complex manipulation of light and have been exploited extensively both in the classical and quantum regime for a wide variety of purposes, e.g. classical single-and multiple-channel frequency conversion [1,2], optical parametric amplification [3], generation of squeezed states and entangled photons [4][5][6], frequency conversion for single-photon detection [7][8][9] and to interface single photons with quantum memories [10][11][12]. Realizing nonlinear processes in integrated waveguides is fundamental in bringing quantum protocols and devices closer to every-day life [13].…”

Characterisation of fabrication inhomogeneities in Ti:LiNbO3 waveguides

“…Such systems are already in use in a myriad of classical applications, for example in second harmonic and sum frequency generation (SHG/SFG) to efficiently produce light in spectral ranges otherwise inaccessible [1][2][3]. More recently these systems are also finding applications in quantum systems, for example in generation and manipulation of quantum states [4][5][6][7][8].…”

Mechanical Tunability of an Ultranarrow Spectral Feature of a Rare-Earth-Doped Crystal via Uniaxial Stress

“…30.Kg Rare-earth ions embedded in a crystalline matrix, at cryogenic temperatures, exhibit optical transitions with excellent coherence properties [1] combined with the ease of use of solid state materials. Such properties can be used for example in classical [2] and quantum [3][4][5][6] information processing schemes, quantum optical memories [7,8], quantum probes of photonic effects [9], and in ultra-high-precision laser stabilisation and spectroscopy [10][11][12]. In these materials, randomly distributed perturbations from the local matrix result in a broad inhomogeneous profile of the ion absorption spectrum, but spectral hole burning techniques can be used to realize narrow spectral features with a resolution only limited by the individual doping ions.…”