In this paper we report recent results on single-photon generation with single InP and CdSe quantum dots. These dots produce single-photons on demand in the visible spectral range 510–690 nm. The emitted photoluminescence was characterized by measuring the autocorrelation function and by performing Fourier spectroscopy on several transitions in the quantum dot. We present the observation and interpretation of carrier trapping and recapture in InP quantum dots which leads to anomalies in the measured correlation functions. Our interpretation is confirmed by numerical simulations based on a rate equation model.
Type-B InP∕GaInP quantum dots are expected to exhibit a type-II electronic structure. Evidence for this is provided by the variation in decay time of the ensemble as a function of excitation power density. Photon correlation measurements were subsequently performed on a single type-B InP∕GaInP quantum dot using a Hanbury-Brown and Twiss setup [Nature 178, 1447 (1956)]. Autocorrelation measurements were carried out under both continuous-wave and pulsed excitation conditions with single-photon emission observed in each case. The continuous-wave measurements display a pronounced antibunching dip at zero time delay while pulsed measurements enable the triggered generation of single photons on demand at a wavelength of approximately 750 nm.
We have studied the photoluminescence correlation from a single InAs/GaAs self-assembled Stranski–Krastanow quantum dot under continuous, as well as under pulsed excitation. Under weak continuous excitation, where the single dot luminescence is due primarily to single exciton recombinations, antibunching is observed in the single dot emission correlation. Under weak pulsed excitation, the number of photons emitted by the quantum dot per pulse is close to one. We present data obtained under both conditions and are able to show that devices based on single quantum dots can be used to generate single photons.
Semiconductor quantum dots (QDs) enable the generation of single and entangled photons, useful for various applications in photonic quantum technologies. Specifically for quantum communication via fiber-optical networks, operation in the telecom C-band centered around 1550
nm is ideal. The direct generation of QD-photons in this spectral range and with high quantum-optical quality, however, remained challenging. Here, we demonstrate the coherent on-demand generation of indistinguishable photons in the telecom C-band from single QD devices consisting of InAs/InP QD-mesa structures heterogeneously integrated with a metallic reflector on a silicon wafer. Using pulsed two-photon resonant excitation of the biexciton-exciton radiative cascade, we observe Rabi rotations up to pulse areas of
4π and a high single-photon purity in terms of
g(2)(0)=0.005(1) and
0.015(1) for exciton and biexciton photons, respectively. Applying two independent experimental methods, based on fitting Rabi rotations in the emission intensity and performing photon cross-correlation measurements, we consistently obtain preparation fidelities at the
π-pulse exceeding 80
%. Finally, performing Hong-Ou-Mandel-type two-photon interference experiments we obtain a photon-indistinguishability of the full photon wave packet of up to
35(3)%, representing a significant advancement in the photon-indistinguishability of single photons emitted directly in the telecom C-band.
We report the realization of the first electrically-driven single photon source. The device is based on a GaAs p-i-n diode containing self-assembled InAs quantum dots embedded within the i-region. Time resolved electroluminescence from the device yields information on the radiative lifetimes of the single quantum dots involved. Applying a continuous current a dip is measured in the second-order correlation function at zero time delay indicating that the luminescence is antibunched. Under pulsed excitation by subnanosecond voltage pulses, strong suppression of multi-photon pulses is achieved with respect to a laser of the same average intensity. The results suggest that conventional semiconductor technology can be used to mass-produce a single photon source for applications in quantum information technology.
We have demonstrated highly pure single-photon emissions from an InAs/InP quantum dot at the wavelength of 1.5 μm. By applying quasi-resonant excitation, one exciton is deterministically generated in an excited state, which then relaxes to the exciton ground state before recombining to emit a single photon. The photon-correlation function of the emission from the exciton ground state exhibits a record g(2)(0) value of (4.4 ± 0.2) × 10−4 measured using high-performance super-conducting single-photon detectors, without any background subtraction. This single-photon source with extremely low multi-photon emission probability paves the way to realize long distance quantum key distribution and low error-rate quantum computation.