Figure 1

(a) Preparation of atom-photon entanglement in ${}^{87}\mathrm{Rb}$. The excited hyperfine level with $F^{\prime }=0$ can decay to three possible ground states with the magnetic quantum numbers $m_F=-1$, 0, or 1, by spontaneously emitting a ${\sigma }^{+}$, $\pi$, or ${\sigma }^{-}$ polarized photon, respectively. If the light is collected along the quantization axis, $\pi$-polarized photons are suppressed. Thus, an effective $\Lambda$ configuration is obtained which allows the preparation of a maximally entangled state between the photon polarization and the orientation of the atomic magnetic moment. (b) Scheme of the experimental setup. The dipole trap light ($\lambda =856\mathrm{nm}$, $P=30\mathrm{mW}$) is focused by a microscope objective ($\mathrm{NA}=0.38$) to a waist of $3.5\mu \mathrm{m}$. The photon from the spontaneous decay is collected with the same objective, separated from the trapping beam by a dichroic mirror, and coupled into a single mode optical fiber guiding it to the polarization analyzer. The analyzer consists of a rotable half- and quarter-wave plate, a polarizing beam splitter (PBS), and two avalanche photodiodes (APD) for single photon detection. Triggered by the detection of the photon in either ${\mathrm{APD}}_1$ or ${\mathrm{APD}}_2$, the atomic state is analyzed using a STIRAP light field whose polarization defines the atomic measurement basis.Reuse & Permissions

Figure 2

Experimental procedure for the atomic state detection. To analyze the atomic state, a two-photon STIRAP-process state selectively transfers a superposition of the states $|m_F=-1⟩$ and $|m_F=+1⟩$ to the $F=2$ hyperfine level. To read out the atomic qubit, a hyperfine-level selective detection pulse is applied before standard fluorescence detection.Reuse & Permissions

Figure 3

Probability of detecting the atom in the ground level $F=1$ (after the STIRAP pulse) conditioned on the detection of the photon in detector ${\mathrm{APD}}_1$ (-●-) or ${\mathrm{APD}}_2$ (-○-) as the linear polarization of the photonic qubit is rotated by an angle $\beta$. (a) The atomic qubit is measured in ${\widehat{\sigma }}_x$ and (b) in ${\widehat{\sigma }}_y$, whereas the photonic qubit is projected onto the states $1/\sqrt{2}(|{\sigma }^{+}⟩\pm e^{2i\beta }|{\sigma }^{-}⟩)$.Reuse & Permissions

Figure 4

(a) Graphical representation of the real part of the measured density matrix of the entangled atom-photon state. The fidelity (overlap with the expected state $|{\Psi }^{+}⟩$) from this measurement is $\mathcal{F}=0.87\pm 0.01$. Insets (b) and (c) show the single particle density matrices for the atom and photon state, respectively, indicating that the single particles when observed on their own are found in a completely mixed state.Reuse & Permissions