Excited state lifetime measurements of ytterbium in indium phosphide

Ingrid de Maat-Gersdorf, T. Gregorkiewicz, C.A.J. Ammerlaan +2 more

Li-Bang Wang, Tuan Dung Nguyen, Martin M. Schauer +1 more

S. K. Borisov, Н.А. Карпов, F. E. Karulin +4 more

Matteo P. Pennacchietti, Mohd Zeeshan, Brady Cunard +6 more

Quantum dots (QDs) embedded inside indium-phosphide (InP) nanowires have the potential to be bright, on-demand sources of perfect polarization-entangled photon pairs fabricated with near-unity yields. However, to date very high degrees of entanglement have not yet been measured from such devices. By performing quantum state tomography with state-of-the-art superconducting nanowire single-photon detectors (SNSPDs) and two-photon resonant excitation of the QD, we show that these sources are indeed capable of producing near-unity entangled photon pairs. We measure a raw peak fidelity of 97.5% +/- 0.8% and a lifetime-weighted fidelity of 0.94% +/- 0.04%. These results conclusively demonstrate that the majority of the degradation from unity-measured entanglement fidelity in earlier studies was not due to spin-spin dephasing from the large 9/2 nuclear spin of indium. These results solidify InP nanowire QDs as a promising platform for future quantum photonics applications.

C.A.J. Ammerlaan, Ingrid de Maat-Gersdorf

In its regular charge state Yb 3+ , the ytterbium impurity in indium-phosphide has the electronic configuration 4f 13 , orbital momentum L = 3 and spin S = 1/2. Ground and excited states with the total spins J = 7/2 and J = 5/2, respectively, are formed by spin-orbit interaction. The EPR spectrum of the centre provides by resolved hyperfine interactions with the isotopes 171 Yb (nuclear spin I = 1/2, natural abundance α = 14%) and 173 Yb (I = 5/2, a = 16%) direct evidence for a one-ytterbium centre in a high-symmetry environment The optical transition between the excited and ground states with an energy around wavenumber σ = 9985 cm -1 (wavelength λ = 1.0015 μm) is easily observed in photoluminescence. A cubic crystal field lifts the eight-fold degeneracy of the ground state 2 F 7/2 into a Γ 6 doublet, a F, doublet and a Γ 8 quartet, whereas the excited state 2 F 5/2 is split into a Γ 7 doublet and a Γ 8 quartet. The ordering of the crystal-field levels is still a matter of discussion, both for the ground and excited spin-orbit multiplets. Several experiments providing information on the ordering will be briefly discussed. These include the luminescence intensity, temperature, hydrostatic stress and magnetic field effects on the optical spectrum, magnetic resonance, together with a crystal-field analysis. A conclusion towards a Γ 7 - Γ 6 - Γ 8 ordering for the ground state multiplet and Γ 7 - Γ 8 for the excited state multiplet, known as the Masterov model, will be drawn.

Chenyu Xu, Jaideep Singh, Jake Zappala +7 more