Figure 1

A schematic diagram illustrates our experimental setup. A signal field from either a laser or a DLCZ source of conditional single photons at site $A$ is carried by a single-mode fiber to an atomic ensemble at site $B$, where it is resonant on the $|b⟩\leftrightarrow |c⟩$ transition. The signal field is stored, for a duration $T_s$, and subsequently retrieved by time-dependent variation of a control field resonant between levels $|a⟩$ and $|c⟩$. All the light fields responsible for trapping and cooling, as well as the quadrupole magnetic field in the MOT, are shut off during the period of the storage and retrieval process. An externally applied magnetic field created by three pairs of Helmholtz coils (not shown) makes an angle $\theta$ with the signal field wave vector. The inset shows the structure and the initial populations of atomic levels involved. The signal field is measured by detectors D2 and D3, while detector D1 is used in the conditional preparation of single-photon states of the signal field at site $A$.Reuse & Permissions

Figure 2

(a)–(e) The ratio of the number of photoelectric detection events for the retrieved and incident signal fields for various orientations, $\theta =0,\pi /8,\pi /4,3\pi /8,\pi /2$, of the applied magnetic field, and as a function of storage time. The incident signal field is a weak coherent laser pulse. In all cases the control pulse is switched off at $T_s=0$. We observe a series of collapses and revivals at multiples of the half Larmor period of $2.3\mu \mathrm{s}$. The observed damping over several Larmor periods is likely caused by residual magnetic field gradients. The inset in (e) demonstrates the observed substructure within the first Larmor period. (f)–(j) Corresponding theoretical plots of the dark-state polariton number calculated using Eq. (3).Reuse & Permissions

Figure 3

Diamonds show the measured collapse time $T_C$ of the first revival at half the Larmor period as a function of the measured revival time $T_R$, for magnetic field values of 0.8, 0.6, 0.4, and 0.2 G, respectively, and for fixed orientation $\theta =\pi /2$. The line shows the corresponding theoretical prediction $T_C\approx 0.082T_R$ from Eq. (3).Reuse & Permissions

Figure 4

Squares show the measured rate of coincidence detections between D1 and D2, 3, $N_{si}=N_{12}+N_{13}$ as a function of the storage time. Diamonds show the measured level of random coincidences $N_R$. The ratio of squares to diamonds gives $g_{si}$. Uncertainties are based on the statistics of the photoelectric counting events.Reuse & Permissions