Triggered Single Photons from a Quantum Dot

Abstract

We demonstrate a new method for generating triggered single photons. After a laser pulse generates excitons inside of a single quantum dot, electrostatic interactions between them and the resulting spectral shifts allow a single emitted photon to be isolated. Autocorrelation measurements show a reduction of the two-photon probability to 0.12 times the value for Poisson light. Strong antibunching persists when the emission is saturated. The emitted photons are also polarized.PACS numbers: 42.50. Dv, Photons from classical light sources, which usually consist of a macroscopic number of emitters, follow Poisson statistics or super-Poisson statistics [1]. With a single quantum emitter, however, one can hope to generate a regulated photon stream, containing one and only one photon in a given time interval. Such an "anti-bunched" source would be useful in the new field of quantum cryptography, where security from eavesdropping depends on the ability to produce no more than one photon at a time [2,3].Continuous streams of anti-bunched photons were first observed from single atoms and ions in traps [4,5]. More recently, experiments demonstrating triggered single photons have used single molecules as the emitters, excited optically either by laser pulses [6,7] or through adiabatic following [8].Solid-state sources have potential advantages. Most importantly, they may be conveniently integrated into larger structures, such as distributed-Bragg-reflector (DBR) microcavities [9,10] to make monolithic devices. In addition, most do not suffer from the photo-bleaching effect that severely limits the lifespan of many molecules. The first experimental effort towards a solid-state singlephoton source was based on electrostatic repulsion of single carriers in a semiconductor micropost p-i-n structure [11]. Milli-Kelvin temperatures were required, however, and sufficient collection efficiency to measure the photon autocorrelation function was not obtained. More recently, continuous anti-bunched fluorescence has been seen from color centers in a diamond crystal [12,13] and from CdSe quantum dots [14].Our method to generate triggered single photons involves pulsed optical excitation of a single quantum dot and spectral filtering to remove all but the last emitted photon. Optically active quantum dots confine electrons and holes to small regions so that their energy levels are quantized [15]. If several electrons or holes are placed in the dot at the same time, they will, to a first approximation, occupy single-particle states as allowed by the Pauli exclusion principle. However, electrostatic interactions between the particles cause perturbations in the eigenstates and energies. For example, if two electronhole pairs (excitons) are created (a "biexcitonic" state), the first pair to recombine emits at a slightly lower energy than the second pair, due to a net attractive interaction [16,17]. We exploit this effect to generate single photons not only through regulated absorption, as in the single-molecule experiments, but also through t...

Directed self‐assembly of single quantum dots for telecommunication wavelength optical devices

“…After relaxation, the quantum system is necessarily in its ground state, and can not emit until the next excitation pulse. Antibunched emission, a signature of single photon emission, has been observed in both the InAs/GaAs [10][11][12][13][14] and InAs/InP [15] material systems.…”

“…On demand emission is provided by pulsed excitation, the dwell time determined by the excitation used and the excitation recombination rate. It is the exciton recombination that has been used to demonstrate single photon emission in the InAs/GaAs material system using second-order correlation spectroscopy for both randomly nucleated [10,11,13,14] and site-controlled quantum dots [31,32]. Demonstration of single photon emission from InAs/InP quantum dots [15] has proved more difficult due to the inferior performance with respect to dark counts of single photon InGaAs detectors compared to Si CCD devices.…”

“…Initial studies on dot-cavity systems [11,12,14] used low dot density samples, and large arrays of cavities, relying on statistics in order to find a resonant single dot -cavity system. More recently, deterministic dot-cavity coupling [21] has been achieved by registering the position of pre-selected quantum dots from a randomly nucleated ensemble using various methods [21][22][23] and fabricating tailored microcavities at the dot site.…”

Inversion of exciton level splitting in quantum dots

“…Single InAs quantum dots have attracted escalating interest recently due to their suitability as the basis for photon emission technology for applications in quantum information. Much progress has been made, particularly in the field of single-photon emission devices, [1][2][3] which have been demonstrated with electrical injection, 4 high efficiency, 5 and strong Purcell enhancement of the spontaneous emission rate. [6][7][8][9] It has been proposed that the decay of the biexciton state to the ground state could be used to create pairs of photons 10 entangled by their polarization, 11 due to the superposition of the two alternate decay paths, distinguished by the order in which the spin-up and spin-down excitons recombine.…”

The role of phonons for exciton and biexciton generation in an optically driven quantum dot

“…This compatibility with existing technologies makes QDs attractive candidates for a wide range of applications ranging from optoelectronic devices like QD lasers [1,2,3,4], where the target is an improved performance compared to other laser structures, up to new applications in the fields of quantum cryptography or quantum information processing, where the presence of discrete energy levels is mandatory. Examples of such quantum applications are single-photon sources [5,6,7,8,9,10], sources of entangled photon pairs [11,12,13,14,15,16,17,18], and qubit devices or quantum gates [19,20,21,22,23,24]. The functionality of all these latter applications relies on the preparation of a well-defined quantum state.…”