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Register a new userDeterministic assembly of a charged quantum dot-micropillar cavity device
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Developing future quantum communication may rely on the ability to engineer cavity-mediated interactions between photons and solid-state artificial atoms, in a deterministic way. Here, we report a set of technological and experimental developments for the deterministic coupling between the optical mode of a micropillar cavity and a quantum dot trion transition. We first identify a charged transition through in-plane magnetic field spectroscopy, and then tune the optical cavity mode to its energy via in-situ lithography. In addition, we design an asymmetric tunneling barrier to allow the optical trapping of the charge, assisted by a quasi-resonant pumping scheme, in order to control its occupation probability. We evaluate the generation of a positively-charged quantum dot through second order auto-correlation measurements of its resonance fluorescence, and the quality of light-matter interaction for these spin-photon interfaces is assessed by measuring the performance of the device as a single-photon source.
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We report on the observation of bright emission of single photons under pulsed resonance fluorescence conditions from a single quantum dot (QD) in a micropillar cavity. The brightness of the QD fluorescence is greatly enhanced via the coupling to the fundamental mode of a micropillar, allowing us to determine a single photon extraction efficiency of $(20.7pm0.8)~%$ per linear polarization basis. This yields an overall extraction efficiency of $(41.4pm1.5)~%$ in our device. We observe the first Rabi-oscillation in a weakly coupled quantum dot-micropillar system under coherent pulsed optical excitation, which enables us to deterministically populate the excited QD state. In this configuration, we probe the single photon statistics of the device yielding $g^{(2)}(0)=0.072pm0.011$ at a QD-cavity detuning of $75~mu$eV.
Giant optical Faraday rotation (GFR) and giant optical circular birefringence (GCB) induced by a single quantum-dot spin in an optical microcavity can be regarded as linear effects in the weak-excitation approximation if the input field lies in the low-power limit [Hu et al, Phys.Rev. B {bf 78}, 085307(2008) and ibid {bf 80}, 205326(2009)]. In this work, we investigate the transition from the weak-excitation approximation moving into the saturation regime comparing a semiclassical approximation with the numerical results from a quantum optics toolbox [S.M. Tan, J. Opt. B {bf 1}, 424 (1999)]. We find that the GFR and GCB around the cavity resonance in the strong coupling regime are input-field independent at intermediate powers and can be well described by the semiclassical approximation. Those associated with the dressed state resonances in the strong coupling regime or merging with the cavity resonance in the Purcell regime are sensitive to input field at intermediate powers, and cannot be well described by the semiclassical approximation due to the quantum dot saturation. As the GFR and GCB around the cavity resonance are relatively immune to the saturation effects, the rapid read out of single electron spins can be carried out with coherent state and other statistically fluctuating light fields. This also shows that high speed quantum entangling gates, robust against input power variations, can be built exploiting these linear effects.
We present a new micromechanical resonator designed for cavity optomechanics. We have used a micropillar geometry to obtain a high-frequency mechanical resonance with a low effective mass and a very high quality factor. We have coated a 60-$mu$m diameter low-loss dielectric mirror on top of the pillar and are planning to use this micromirror as part of a high-finesse Fabry-Perot cavity, to laser cool the resonator down to its quantum ground state and to monitor its quantum position fluctuations by quantum-limited optical interferometry.
Solid state quantum emitters have shown strong potential for applications in quantum information, but spectral inhomogeneity of these emitters poses a significant challenge. We address this issue in a cavity-quantum dot system by demonstrating cavity-stimulated Raman spin flip emission. This process avoids populating the excited state of the emitter and generates a photon that is Raman shifted from the laser and enhanced by the cavity. The emission is spectrally narrow and tunable over a range of at least 125 GHz, which is two orders of magnitude greater than the natural linewidth. We obtain the regime in which the Raman emission is spin-dependent, which couples the photon to a long-lived electron spin qubit. This process can enable an efficient, tunable source of indistinguishable photons and deterministic entanglement of distant spin qubits in a photonic crystal quantum network.
A strong, far-detuned laser can shift the energy levels of an optically active quantum system via the AC Stark effect. We demonstrate that the polarization of the laser results in a spin-selective modification to the energy structure of a charged quantum dot, shifting one spin manifold but not the other. An additional shift occurs due to the Overhauser field of the nuclear spins, which are pumped into a partially polarized state. This mechanism offers a potentially rapid, reversible, and coherent control of the energy structure and polarization selection rules of a charged quantum dot.
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