All-optical coherent control of vacuum Rabi oscillations

Journal name:
Nature Photonics
Year published:
Published online


When an atom strongly couples to a cavity, the two systems can coherently exchange a single quantum excitation through the process of vacuum Rabi oscillation. Controlling this process enables precise synthesis of non-classical light, which plays a central role in quantum information and measurement. Although this control has been realized in microwave-frequency devices, it has been difficult to achieve at optical frequencies, which are essential for quantum communication and metrology. Here, we demonstrate coherent control of vacuum Rabi oscillation in an optical frequency device. We use a photonic molecule composed of two coupled nanocavities to simultaneously achieve strong coupling and a cavity-enhanced a.c. Stark shift. The Stark shift tunes a single quantum dot onto resonance with the photonic molecule on picosecond timescales, creating fast coherent transfer of energy between an atomic and photonic excitation. These results enable ultrafast control of light–matter quantum interactions in a nanophotonic device platform.

At a glance


  1. Device design and experimental set-up.
    Figure 1: Device design and experimental set-up.

    a, Schematic of quantum level structure of a cavity–quantum dot system in the presence of a strong off-resonant pulse denoted by the classical Rabi frequency Ω(t). The pulse induces an a.c. Stark shift that optically tunes the quantum dot on-resonance with the cavity. b, Scanning electron microscopy image of the fabricated photonic-crystal molecule composed of two evanescently coupled photonic-crystal cavities (scale bar, 1 µm), together with finite-difference time-domain calculations showing the Ey component of the anti-symmetric (bottom) and symmetric (top) modes of the device. c, Experimental set-up for all performed measurements. BS, beamsplitter; PBS, polarizing beamsplitter; OL, objective lens; HWP, half-wave plate; SMF, single-mode fibre; SPCM, single-photon-counting modules.

  2. Characterization of photonic molecule modes.
    Figure 2: Characterization of photonic molecule modes.

    a, Reflection spectrum of the photonic molecule, recorded at 45 K, showing the two coupled cavity modes (M1 and M2) and the quantum dot (QD). b, Reflection spectrum around mode M1 as a function of temperature. The quantum dot tunes across the cavity mode, exhibiting an anti-crossing.

  3. Stark shift-mediated energy transfer.
    Figure 3: Stark shift-mediated energy transfer.

    a, Cavity spectrum as a function of delay Δτ when the excitation pulse excites the quantum dot resonance. b, Intensity at Δλ = 0, determined from a, as a function of delay Δτ. c, Emission spectrum when the cavity is excited instead of the quantum dot. d, Intensity at Δλ = 0.07 nm (quantum-dot resonance) as a function of delay Δτ using data in c. eh, Numerically calculated results corresponding to the measurements shown in ad, respectively. In f and h, intensities are normalized to the values at Δτ = −100 ps.

  4. Rabi oscillations.
    Figure 4: Rabi oscillations.

    a, Measured reflection spectrum as a function of Stark laser power. b, Emission intensity at cavity resonance (blue squares) and at quantum-dot resonance (green circles), determined from the data in a. c, Calculated spectrum as a function of Stark power. The Stark field is expressed as a classical Rabi frequency with peak amplitude Ω0. d, Calculated emission intensity at cavity resonance (blue squares) and quantum dot (QD) resonance (green circles). Intensities are normalized by their maximum value.

  5. Coherent control of polariton energy transfer.
    Figure 5: Coherent control of polariton energy transfer.

    a, Emission spectrum as a function of delay Δτ when the quantum dot is tuned to resonance with the cavity. b, Emission intensity at the lower and upper polariton resonances as a function of delay between pump and probe. c, Calculated cavity spectrum as a function of delay between the excitation and Stark shift pulses. d, Calculated emission intensity at the lower polariton and upper polariton resonances. In b and d, intensities are normalized to the values at Δτ = −100 ps.


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Author information

  1. These authors contributed equally to this work

    • Ranojoy Bose &
    • Tao Cai


  1. Department of Electrical Engineering and Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742, USA

    • Ranojoy Bose,
    • Tao Cai,
    • Kaushik Roy Choudhury &
    • Edo Waks
  2. Joint Quantum Institute, University of Maryland and National Institute of Standards and Technology, College Park, Maryland 20742, USA

    • Glenn S. Solomon &
    • Edo Waks


E.W. conceived and designed the experiment. R.B. and T.C. designed and fabricated the device, conducted experiments and carried out analysis. K.R.C., E.W., T.C. and R.B. performed theoretical simulations. R.B. and E.W. wrote the manuscript, with input from all authors. G.S.S. grew the quantum-dot wafer. E.W. supervised the work.

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