Semiconductor quantum dot - a quantum light source of multicolor photons with tunable statistics

We investigate the intensity correlation properties of single photons emitted from an optically excited single semiconductor quantum dot. The second order temporal coherence function of the photons emitted at various wavelengths is measured as a function of the excitation power. We show experimentally and theoretically, for the first time, that a quantum dot is not only a source of correlated non-classical monochromatic photons but is also a source of correlated non-classical \emph{multicolor} photons with tunable correlation properties. We found that the emitted photon statistics can be varied by the excitation rate from a sub-Poissonian one, where the photons are temporally antibunched, to super-Poissonian, where they are temporally bunched.Comment: 4 pages, 2 figure

Optical spectroscopy of single quantum dots at tunable positive, neutral and negative charge states

We report on the observation of photoluminescence from positive, neutral and negative charge states of single semiconductor quantum dots. For this purpose we designed a structure enabling optical injection of a controlled unequal number of negative electrons and positive holes into an isolated InGaAs quantum dot embedded in a GaAs matrix. Thereby, we optically produced the charge states -3, -2, -1, 0, +1 and +2. The injected carriers form confined collective 'artificial atoms and molecules' states in the quantum dot. We resolve spectrally and temporally the photoluminescence from an optically excited quantum dot and use it to identify collective states, which contain charge of one type, coupled to few charges of the other type. These states can be viewed as the artificial analog of charged atoms such as H$^{-}$, H$^{-2}$, H$^{-3}$, and charged molecules such as H$_{2}^{+}$ and H$_{3}^{+2}$. Unlike higher dimensionality systems, where negative or positive charging always results in reduction of the emission energy due to electron-hole pair recombination, in our dots, negative charging reduces the emission energy, relative to the charge-neutral case, while positive charging increases it. Pseudopotential model calculations reveal that the enhanced spatial localization of the hole-wavefunction, relative to that of the electron in these dots, is the reason for this effect.Comment: 5 figure

Radiative Lifetimes of Single Excitons in Semiconductor Quantum Dots- Manifestation of the Spatial Coherence Effect

Using time correlated single photon counting combined with temperature dependent diffraction limited confocal photoluminescence spectroscopy we accurately determine, for the first time, the intrinsic radiative lifetime of single excitons confined within semiconductor quantum dots. Their lifetime is one (two) orders of magnitude longer than the intrinsic radiative lifetime of single excitons confined in semiconductor quantum wires (wells) of comparable confining dimensions. We quantitatively explain this long radiative time in terms of the reduced spatial coherence between the confined exciton dipole moment and the radiation electromagnetic field.Comment: 4 pages, 3 figure

Time-resolved spectroscopy of multi-excitonic decay in an InAs quantum dot

The multi-excitonic decay process in a single InAs quantum dot is studied through high-resolution time-resolved spectroscopy. A cascaded emission sequence involving three spectral lines is seen that is described well over a wide range of pump powers by a simple model. The measured biexcitonic decay rate is about 1.5 times the single-exciton decay rate. This ratio suggests the presence of selection rules, as well as a significant effect of the Coulomb interaction on the biexcitonic wavefunction.Comment: one typo fixe

The Grizzly, November 23, 1993

Dr. Davidson to Receive Cottrel Award • U.C.\u27s Questions are Answered • It\u27s Yes to NAFTA • A Dose of Reality • Touch my Flugel! • Exam Schedule • The Way to a Student\u27s Heart is Through His Stomach • Beer: A Historical Precedent? • A Dissatisfied Sanitation Worker Tells Ursinus to Clean Up its Act • Literary Society • Manning Retires as Soccer Coachhttps://digitalcommons.ursinus.edu/grizzlynews/1326/thumbnail.jp

Entangled Photons from Small Quantum Dots

We discuss level schemes of small quantum-dot turnstiles and their applicability in the production of entanglement in two-photon emission. Due to the large energy splitting of the single-electron levels, only one single electron level and one single hole level can be made resonant with the levels in the conduction band and valence band. This results in a model with nine distinct levels, which are split by the Coulomb interactions. We show that the optical selection rules are different for flat and tall cylindrically symmetric dots, and how this affects the quality of the entanglement generated in the decay of the biexciton state. The effect of charge carrier tunneling and of a resonant cavity is included in the model.Comment: 10 pages, 8 figure

The Grizzly, April 6, 1993

Mr. Ursinus, 1993 • ProTheatre\u27s Actors Deliver in Thornwood • Another Weekend of Fighting in Reimert • Changes in Housing Selection • Wismer Renovations • Waco Standoff Continues • Your Chance to Give • Access to the Vault • Congratulations to P.O.D. for Excelling in Blood Drive • Daffodils for Service • Senior Profile: Allen Clowers • Why Can\u27t I Pick my Classes? • Letters to the Editor • Seniors Return, but Bears Fall • Men\u27s LAX Wants to Be Official • Men\u27s Tennis Young and Improvinghttps://digitalcommons.ursinus.edu/grizzlynews/1314/thumbnail.jp

Single Photons on Pseudo-Demand from Stored Parametric Down-Conversion

We describe the results of a parametric down-conversion experiment in which the detection of one photon of a pair causes the other photon to be switched into a storage loop. The stored photon can then be switched out of the loop at a later time chosen by the user, providing a single photon for potential use in a variety of quantum information processing applications. Although the stored single photon is only available at periodic time intervals, those times can be chosen to match the cycle time of a quantum computer by using pulsed down-conversion. The potential use of the storage loop as a photonic quantum memory device is also discussed.Comment: 8 pages, 7 Figs., RevTe

The Lantern Vol. 61, No. 1, December 1993

• In Order to Succeed • Essay • Power of Human Self-Interest: Man vs. Car • In Setterich • Wandering Wanda • Maybe Kitchens • Saltiness • Homecoming • Perfect • Sincerely, Jen • A Midterm and a Paper • Prophet Junkie • Soundless Memo • After Ireland, Part 1https://digitalcommons.ursinus.edu/lantern/1142/thumbnail.jp

The Grizzly, October 12, 1993

The Truth Behind the Conspiracy • U.S. Involvement in Somalia • Homecoming 1993 • Dave Binder: A Tribute to James Taylor • In Other Words • Ursinus College: Altar to the God of Apathy? • Letter to the Editor • Bears Lose Toughhttps://digitalcommons.ursinus.edu/grizzlynews/1321/thumbnail.jp