Quantum optical frequency up-conversion for polarisation entangled qubits: towards interconnected quantum information devices

Abstract

Realising a global quantum network requires combining individual strengths of different quantum systems to perform universal tasks, notably using flying and stationary qubits. However, transferring coherently quantum information between different systems is challenging as they usually feature different properties, notably in terms of operation wavelength and wavepacket. To circumvent this problem for quantum photonics systems, we demonstrate a polarisation-preserving quantum frequency conversion device in which telecom wavelength photons are converted to the near infrared, at which a variety of quantum memories operate. Our device is essentially free of noise which we demonstrate through near perfect single photon state transfer tomography and observation of high-fidelity entanglement after conversion. In addition, our guided-wave setup is robust, compact, and easily adaptable to other wavelengths. This approach therefore represents a major building block towards advantageously connecting quantum information systems based on light and matter.

Indistinguishable photons from a trapped-ion quantum network node

“…In order to prove that the up-conversion coupling/propagation efficiency of 70(5)% is dominated by coupling, we performed a separate measurement with adjusted 1550 beam diameter before the wavguide incoupler and achieved 82(3)% efficiency calculated as the ratio of the number of photons at 854 nm wavelength right after the waveguide to the number of 1550 nm photons right before the waveguide. Note, that the external and internal up-conversion efficiencies reported here are higher than the ones achieved in similar systems before [38,39]. , showing: the ≈ 4 Gauss DC magnetic field (quantisation axis) generated by rings of permanent magnets and the circularly-polarized Raman laser for generating 854 nm cavity photons.…”

Indistinguishable photons from a trapped-ion quantum network node

“…In order to prove that the up-conversion coupling/propagation efficiency of 70(5)% is dominated by coupling, we performed a separate measurement with adjusted 1550 beam diameter before the wavguide incoupler and achieved 82(3)% efficiency calculated as the ratio of the number of photons at 854 nm wavelength right after the waveguide to the number of 1550 nm photons right before the waveguide. Note, that the external and internal up-conversion efficiencies reported here are higher than the ones achieved in similar systems before [38,39]. For the experiment without photon conversion, point A and A', as well as the points B' and B directly are fiber connected , such that the vertical photon only has to pass the 3 km fiber spool (Corning SMF-28 Ultra).…”

A universal, plug-and-play synchronisation scheme for practical quantum networks

“…In the context of digital society, quantum networks promise to combine highly efficient data processing with ultra-secure data exchanges [1][2][3]. This vision has motivated the development of crucial constituents including quantum memories [4,5], coherent interfaces between different systems [6][7][8][9], and optical quantum communication links based on quantum teleportation over long fibre connections [10][11][12][13]. Nevertheless, the development of operational quantum networks remains hindered by the lack of practical synchronisation methods that allow the different building blocks to work together under high timing accuracy.…”