Charged quantum dot micropillar system for deterministic light-matter interactions

This work was funded by the Future Emerging Technologies (FET) programme within the Seventh Framework Programme for Research of the European Commission, FET-Open, FP7-284743 [project Spin Photon Angular Momentum Transfer for Quantum Enabled Technologies (SPANGL4Q)] and the German Ministry of Education and research (BMBF) and Engineering and Physical Sciences Research Council (EPSRC) [project Solid State Quantum Networks (SSQN)]. J.G.R. is sponsored by the EPSRC fellowship EP/M024458/1.Quantum dots (QDs) are semiconductor nanostructures in which a three-dimensional potential trap produces an electronic quantum confinement, thus mimicking the behavior of single atomic dipole-like transitions. However, unlike atoms, QDs can be incorporated into solid-state photonic devices such as cavities or waveguides that enhance the light-matter interaction. A near unit efficiency light-matter interaction is essential for deterministic, scalable quantum-information (QI) devices. In this limit, a single photon input into the device will undergo a large rotation of the polarization of the light field due to the strong interaction with the QD. In this paper we measure a macroscopic (∼6∘) phase shift of light as a result of the interaction with a negatively charged QD coupled to a low-quality-factor (Q∼290) pillar microcavity. This unexpectedly large rotation angle demonstrates that this simple low-Q-factor design would enable near-deterministic light-matter interactions.Publisher PDFPeer reviewe

Market Power and Collusion on Interconnection Phone Market in Tunisia : What Lessons from International Experiences

We try in this paper to characterize the state of mobile phone market in Tunisia. Our study is based on a survey of foreign experience (Europe) in detecting collusive behavior and a comparison of the critical threshold of collusion between operators in developing countries like Tunisia. The market power is estimated based on the work of Parker Roller (1997) and the assumption of "Balanced Calling Pattern". We use then the model of Friedman (1971) to compare the critical threshold of collusion. We show that the "conduct parameter" measuring the intensity of competition is not null during the period 1993-2011. Results show also that collusion is easier on the Tunisian market that on the Algerian, Jordanian, or Moroccan one

Faecal immunochemical tests (FIT) can help to rule out colorectal cancer in patients presenting in primary care with lower abdominal symptoms:a systematic review conducted to inform new NICE DG30 diagnostic guidance

__Background:__ This study has attempted to assess the effectiveness of quantitative faecal immunochemical tests (FIT) for triage of people presenting with lower abdominal symptoms, where a referral to secondary care for investigation of suspected colorectal cancer (CRC) is being considered, particularly when the 2-week criteria are not met. __Methods:__ We conducted a systematic review following published guidelines for systematic reviews of diagnostic tests. Twenty-one resources were searched up until March 2016. Summary estimates were calculated using a bivariate model or a random-effects logistic regression model. __Results:__ Nine studies are included in this review. One additional study, included in our systematic review, was provided as 'academic in confidence' and cannot be described herein. When FIT was based on a single faecal sample and a cut-off of 10 μg Hb/g faeces, sensitivity estimates indicated that a negative result using either the OC-Sensor or HM-JACKarc may be adequate to rule out nearly all CRC; the summary estimate of sensitivity for the OC-Sensor was 92.1%, based on four studies, and the only study of HM-JACKarc to assess the 10 μg Hb/g faeces cut-off reported a sensitivity of 100%. The corresponding specificity estimates were 85.8% (95% CI 78.3-91.0%) and 76.6%, respectively. When the diagnostic criterion was changed to include lower grades of neoplasia, i.e. the target condition included higher risk adenoma (HRA) as well as CRC, the rule-out performance of both FIT assays was reduced. __Conclusions:__ There is evidence to suggest that triage using FIT at a cut-off around 10 μg Hb/g faeces has the potential to correctly rule out CRC and avoid colonoscopy in 75-80% of symptomatic patients. Systematic review registration: PROSPERO 4201603772

Resolving Zeeman splitting in quantum dot ensembles

This letter presents a technique for the investigation of the fine structure and spin properties of quantum dot (QD) ensembles, allowing measurement of QD parameters previously accessible only from studies of individual QDs. We show how ∼μeV splittings can be deduced from information contained in the shape of the ensemble polarization spectra and demonstrate the effectiveness of this technique by measuring Zeeman splittings, g-factors, and sensitivity to QD fine structure effects

Influence of p-doping on the temperature dependence of In As/GaAs quantum dot excited state radiative lifetime

The radiative lifetime of the excited state transition of undoped and p-doped InAs/GaAs quantum dots(QDs) is estimated from measurements of time-integrated and time-resolved luminescence from both ground and excited states. The radiative lifetime of the undoped QDs increases from 500 ps at 10 K to almost 3 ns at room temperature, consistent with a Boltzmann redistribution of holes over the available energy states. The rate of increase can be suppressed by a factor of ∼2 by p-doping the QDs to maintain a hole population in the lowest confined dot states to high temperatures

Quantum modulation of a coherent state wavepacket with a single electron spin

The interaction of quantum objects lies at the heart of fundamental quantum physics and is key to a wide range of quantum information technologies. Photon-quantum-emitter interactions are among the most widely studied. Two-qubit interactions are generally simplified into two quantum objects in static well-defined states . In this work we explore a fundamentally new dynamic type of spin-photon interaction. We demonstrate modulation of a coherent narrowband wavepacket with another truly quantum object, a quantum dot with ground state spin degree of freedom. What results is a quantum modulation of the wavepacket phase (either 0 or {\pi} but no values in between), a new quantum state of light that cannot be described classically.Comment: Supplementary Information available on reques

Design principles for > 90 % efficiency and > 99 % indistinguishability broadband quantum dot cavities

Quantum dots have the potential to be one of the brightest deterministic single photon sources with high end applications in quantum computing and cluster state generation. In this work, we re-examine the design of plain micropillars by meticulously examining the structural effects of the decay into leaky channels beyond an atom-like cavity estimation. We show that precise control of the side losses with the diameter and avoidance of propagating Bloch modes in the distributed Bragg reflectors can result in easy-to-manufacture broadband ( Q≈750–2500) micropillars, allowing for broad optical coherent control pulses necessary for high single photon purity ( >99.2%–99.99% achievable) while simultaneously demonstrating extremely high efficiency out the top (90.5%–96.4%). We also demonstrate that such cavities naturally decouple from the phonon sideband, with the phonon sideband reducing by a factor of 5–33 allowing us to predict that the photons should show 98.5%–99.8% indistinguishability without the need for filtering

Perfect Chirality with Imperfect Polarization

Unidirectional (chiral) emission of light from a circular dipole emitter into a waveguide is only possible at points of perfect circular polarization (C points), with elliptical polarizations yielding a lower directional contrast. However, there is no need to restrict engineered systems to circular dipoles, and with an appropriate choice of dipole unidirectional emission is possible for any elliptical polarization. Using elliptical dipoles, rather than circular, typically increases the size of the area suitable for chiral interactions (in an exemplary mode by a factor ∼30), while simultaneously increasing coupling efficiencies. We propose illustrative schemes to engineer the necessary elliptical transitions in both atomic systems and quantum dots

Persistent template effect in InAs/GaAs quantum dot bilayers

The dependence of the optical properties of InAs/GaAs quantum dot(QD) bilayers on seed layer growth temperature and second layer InAs coverage is investigated. As the seed layer growth temperature is increased, a low density of large QDs is obtained. This results in a concomitant increase in dot size in the second layer, which extends their emission wavelength, reaching a saturation value of around 1400 nm at room temperature for GaAs-capped bilayers. Capping the second dot layer with InGaAs results in a further extension of the emission wavelength, to 1515 nm at room temperature with a narrow linewidth of 22 meV. Addition of more InAs to high density bilayers does not result in a significant extension of emission wavelength as most additional material migrates to coalesced InAs islands but, in contrast to single layers, a substantial population of regular QDs remains