Figure 1
From: Manipulating Frequency-Bin Entangled States in Cold Atoms
Atomic interface for a single-photon frequency-bin entangled state.
A sample of cold atoms loaded into a magneto-optical trap (MOT) and initially pumped to state |1〉 is used as interface. Two continuous strong coupling beams ωcm and ωcp, with the same polarization and Rabi frequency Ωc but different detunings from the excited state |2〉, control the coupling of the frequency entangled state (1) to the interface. The relevant wavepacket of length 
and bandwidth such that 
is double Λ-resonant with the coupling beams (ωm − ωcm = ωp − ωcp) through a nearly-resonant (
) and a far off-resonant (
) (Raman) transition between the two hyperfine electronic ground states |1〉 and |3〉. Under such conditions non-resonantly excited coherences30 can be neglected and control of the entangled state is described by the closed set of coupled equations (2–3). The energy level scheme corresponds to the D2 line in 87Rb (52S1/2 → 52P3/2) with a transition wavelength λ21 = 780.24 nm. Hyperfine ground state dephasing and excited state relaxation rate are γ3 = 2π × 1 kHz and γ2 = 2π × 6 MHz.
