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Semiconductor double quantum dot micromaser

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Science  16 Jan 2015:
Vol. 347, Issue 6219, pp. 285-287
DOI: 10.1126/science.aaa2501
  • Fig. 1 Double quantum dot micromaser.

    (A) Optical micrograph of the DQD micromaser. Cavity photons are coupled to input and output ports with rates κin and κout. (B) Schematic illustration of the DQD micromaser. Two DQDs are electric-dipole coupled to the microwave cavity. Single-electron tunneling through the DQDs leads to photon emission into the cavity mode. Left (right) DQD detunings εLR) are independently tunable. (C) Scanning electron microscope image of an InAs nanowire DQD. (D) G as a function of εL (measured at frequency fc) with VSD = 2 mV and the right DQD configured in Coulomb blockade. Insets: For εL > 0, electron transport proceeds downhill in energy, resulting in a gain exceeding 7. With εL < 0, an electron will be trapped in the right dot until a photon is absorbed, resulting in cavity loss, G < 1.

  • Fig. 2 Microwave gain induced by single-electron tunneling.

    G as a function of fin with Pin = –120 dBm. The black curve is obtained with both DQDs in Coulomb blockade (in the off/off state). With the left DQD set at a detuning that results in gain (see Fig. 1D) and the right DQD in Coulomb blockade (on/off state), we measure a maximum G ≈ 16. Similarly, in the off/on state, we observe a gain of ≈ 6. Maser action occurs when both DQDs are tuned to produce gain, resulting in G ≈ 1000. (Inset) Data plotted on a linear scale and normalized to the same height.

  • Fig. 3 Maser coherence time.

    Power spectral density S(f) measured in free-running maser mode (on/on state with no cavity drive applied). The maser emission peak width Δf = 34 kHz (FWHM) yields a coherence length lcoh = 2.8 km.

  • Fig. 4 Photon statistics.

    (A) IQ histogram acquired below threshold (off/on configuration). (B) The photon number distribution, pn, extracted from the data in (A) is consistent with a thermal distribution (solid line). A Poisson distribution (dashed line) with Embedded Image = 11.4 is shown for comparison. (C) IQ histogram measured above threshold (on/on configuration). Here the extracted photon number distribution (D) is peaked around n = 8000 and is compared with a Gaussian distribution (dashed line). A small thermal component (solid line) is attributed to charge fluctuations, which shift the device below threshold.

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  • Semiconductor double quantum dot micromaser

    Y.-Y. Liu, J. Stehlik, C. Eichler, M. J. Gullans, J. M. Taylor, J. R. Petta

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