Research ArticlePHYSICS

Fast, noise-free memory for photon synchronization at room temperature

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Science Advances  12 Jan 2018:
Vol. 4, no. 1, eaap8598
DOI: 10.1126/sciadv.aap8598
  • Fig. 1 FLAME scheme.

    (A) A ladder-level structure comprising purely orbital transitions (the surface colors display the phase structure of the orbitals 5s, 5p, and 5d) is achieved by optical pumping (purple) of the nuclear and electronic spins (green arrows) to the maximally polarized state. Nonzero detuning Δ from the intermediate level can be introduced. (B) To keep the ladder within the maximally polarized subspace, the counter-propagating signal and control beams are circularly polarized using quarter-wave plates (QWP; polarizations shown by green arrows). The collimated optical pump beams enter the cell at a small angular deviation. After storage and retrieval, a polarizing beam-splitter (PBS) picks out the signal. Scattered control light and spontaneous emission are filtered out spectrally by laser-line (LL) filters and spatially by a single-mode fiber coupled to the photodetector. (C) The parameters governing the synchronization capability of the memory are pulse duration τp, memory lifetime τs, retrieval efficiency η, and noise ν.

  • Fig. 2 FLAME operation for different storage times t, off resonance (left) and on resonance (right).

    (A and D) Typical pulse sequence, presented for t = 40 ns. The incoming pulse is shown for reference. (B and E) Traces from the single-photon counter for different storage times (colors). The blackened areas mark the portion of the leaked signal. (C and F) Decay of memory efficiency with t. Continuous optical pumping [yellow symbols in (C)] demonstrates the vanishing of beating for a fully polarized ensemble (while introducing more noise). Gray area in (F) marks the delay of the signal because of the reduced group velocity while the control pulse is on.

  • Fig. 3 Efficiency and noise dependence on control power (bottom axis) or control Rabi frequency Ω (top axis).

    (A) Memory efficiency for t = 40 ns. (B) Total photons in the collection window absent an incoming signal (shaded areas are 1σ statistical uncertainty). Note that the collection window is larger by 45% in the Δ = 0 case (for accommodating the wider retrieved signal). The arrows mark the operating powers of Fig. 2.

  • Fig. 4 Projected performance of reported quantum memories for synchronizing six heralded single-photon sources: High production rate and low noise (top-right quarter) are desired.

    The vertical dotted line marks the value 10−3 used as the success probability of the sources (thus indicating their intrinsic noise-to-signal ratio). The labels present the group, year, and memory protocol. AFC, full atomic frequency comb; EIT, EIT storage; GEM, gradient echo memory; Raman, far-detuned Raman storage; SL, storage loop. The calculation takes the source repetition rate as the minimum between Embedded Image and 50 GHz, the latter estimating the current limit of the required feed-forward electronics. Source data, references, and additional details are provided in section S3.

  • Fig. 5 Experimental setup.

    EOAM, electro-optic amplitude modulator; EOPM, electro-optic phase modulator; Glan, Glan-laser polarizer; HWP, half-wave plate; LIA, lock-in amplifier; PD, photodetector; SPCM, single-photon counting module.

  • Table 1 Memory parameters extracted from the measurements using the fit function of Eq. 1.

    Uncertainties in parentheses are 1σ SD.

    τs (ns)η0 (%)Embedded Image (ns)t0 (ns)AB
    Off-resonance86(2)25.1(8)101(12)−1.0(3)0.160(9)0.006(9)
    On-resonance82(1)17.1(3)337(43)9.2(6)0.032(4)0.007(4)

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/1/eaap8598/DC1

    section S1. Atomic level scheme

    section S2. Noise sources

    section S3. Source data and performance analysis of different quantum optical memories

    fig. S1. Rubidium level scheme.

    fig. S2. External efficiency as a function of storage time t, with the optical pumping continuously on (yellow) or switched off before storage (red), or with no pumping at all (blue).

    table S1. Memory parameters used for compiling Fig. 4.

    table S2. Memory parameters used for compiling Fig. 4 (cont.).

    References (3044)

  • Supplementary Materials

    This PDF file includes:

    • section S1. Atomic level scheme
    • section S2. Noise sources
    • section S3. Source data and performance analysis of different quantum optical memories
    • fig. S1. Rubidium level scheme.
    • fig. S2. External efficiency as a function of storage time t, with the optical pumping continuously on (yellow) or switched off before storage (red), or with no pumping at all (blue).
    • table S1. Memory parameters used for compiling Fig. 4.
    • table S2. Memory parameters used for compiling Fig. 4 (cont.).
    • References (30–44)

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