Quantum Dot Single Photon Sources Research Articles

Publisher's Note: Multiple time scale blinking in InAs quantum dot single-photon sources [Phys. Rev. B89, 161303(R) (2014)

Publisher's Note: Multiple time scale blinking in InAs quantum dot single-photon sources [Phys. Rev. B<b>89</b>, 161303(R) (2014)

Multiple time scale blinking in InAs quantum dot single-photon sources

We use photon correlation measurements to study blinking in single, epitaxially grown self-assembled InAs quantum dots situated in circular Bragg grating and microdisk cavities. The normalized second-order correlation function ${g}^{(2)}(\ensuremath{\tau})$ is studied across 11 orders of magnitude in time, and shows signatures of blinking over time scales ranging from tens of nanoseconds to tens of milliseconds. The ${g}^{(2)}(\ensuremath{\tau})$ data is fit to a multilevel system rate equation model that includes multiple nonradiating (dark) states, from which radiative quantum yields significantly less than 1 are obtained. This behavior is observed even in situations for which a direct histogramming analysis of the emission time-trace data produces inconclusive results.

Free space quantum key distribution over 500 meters using electrically driven quantum dot single-photon sources—a proof of principle experiment

Highly efficient single-photon sources (SPS) can increase the secure key rate of quantum key distribution (QKD) systems compared to conventional attenuated laser systems. Here we report on a free space QKD test using an electrically driven quantum dot single-photon source (QD SPS) that does not require a separate laser setup for optical pumping and thus allows for a simple and compact SPS QKD system. We describe its implementation in our 500 m free space QKD system in downtown Munich. Emulating a BB84 protocol operating at a repetition rate of 125 MHz, we could achieve sifted key rates of 5–17 kHz with error ratios of 6–9% and -values of 0.39–0.76.

A quantum dot single photon source driven by resonant electrical injection

We present a demonstration of single photon emission from an entirely electrically driven resonant injection quantum dot device. We selectively measure the emission from a single dot in the ensemble by tuning the applied bias so as to induce resonant tunneling into the dot. Direct injection of carriers into the dot leads to a suppression of background light, allowing us to demonstrate single photon emission from a single dot with no spectral filtering. We study the effects limiting the linewidths of photons emitted from the device.

Improving the performance of bright quantum dot single photon sources using temporal filtering via amplitude modulation.

Single epitaxially-grown semiconductor quantum dots have great potential as single photon sources for photonic quantum technologies, though in practice devices often exhibit nonideal behavior. Here, we demonstrate that amplitude modulation can improve the performance of quantum-dot-based sources. Starting with a bright source consisting of a single quantum dot in a fiber-coupled microdisk cavity, we use synchronized amplitude modulation to temporally filter the emitted light. We observe that the single photon purity, temporal overlap between successive emission events, and indistinguishability can be greatly improved with this technique. As this method can be applied to any triggered single photon source, independent of geometry and after device fabrication, it is a flexible approach to improve the performance of systems based on single solid-state quantum emitters, which often suffer from excess dephasing and multi-photon background emission.

Electrically driven quantum dot single-photon source at 2 GHz excitation repetition rate with ultra-low emission time jitter

The influence of the bias voltage on emission properties of a red emitting InP/GaInP quantum dot based single-photon source was investigated. Under pulsed electrical excitation, we can influence the band bending of the p-i-n diode with the applied bias voltage and thus the charge carrier escape by quantum tunneling. This leads to control over the non-radiative decay channel and allows carrier escape times as low as 40 ps, effectively reducing the time jitter of the photon emission. We realized high excitation repetition rates of up to 2 GHz while autocorrelation measurements with g(2)(0)-values of 0.27 attest dominant single-photon emission.

Quantum key distribution using quantum dot single-photon emitting diodes in the red and near infrared spectral range

We report on in-lab free space quantum key distribution (QKD) experiments over 40 cm distance using highly efficient electrically driven quantum dot single-photon sources emitting in the red as well as near-infrared spectral range. In the case of infrared emitting devices, we achieve sifted key rates of 27.2 kbit s−1 (35.4 kbit s−1) at a quantum bit error rate (QBER) of 3.9% (3.8%) and a g(2)(0) value of 0.35 (0.49) at moderate (high) excitation. The red emitting diodes generate sifted keys at a rate of 95.0 kbit s−1 at a QBER of 4.1% and a g(2)(0) value of 0.49. This first successful proof of principle QKD experiment based on electrically operated semiconductor single-photon sources can be considered as a major step toward practical and efficient quantum cryptography scenarios.

Wavelength Tunable Quantum Dot Single-Photon Source with a Side Gate

We demonstrate photon antibunching from a wavelength controlled quantum dot single-photon source with a side gate. The photoluminescence peaks from the quantum dots embedded in the side-gate structure are clearly identified as a neutral exciton and a neutral biexciton by the studies of excitation-power dependence, polarization dependence, and photon correlation. The neutral exciton energy is controlled by the side gate via the quantum confined Stark effect. Measurement of the second-order autocorrelation function indicates g(2)(0) = 0.07 at 0 V, 0.14 at 0.8 V, and 0.24 at 0.9 V. The results show g(2)(0)s are below the 0.5 limit necessary for classification as a single photon source even under applied gate voltage. We also show a biexciton-exciton cascade which can be used to create entangled photon pairs.

Fast quantum dot single photon source triggered at telecommunications wavelength

We demonstrate a quantum dot single photon source at 900 nm triggered at 100 MHz by a continuous wave telecommunications wavelength laser followed by an electro-optic modulator. The quantum dot is excited by on-chip-generated second harmonic radiation, resonantly enhanced by a GaAs photonic crystal cavity surrounding the InAs quantum dot. Our result suggests a path toward the realization of telecommunications wavelength-compatible quantum dot single photon sources with speeds exceeding 1 GHz.

Highly efficient single-photon emission from single quantum dots within a two-dimensional photonic band-gap

We report highly efficient single-photon generation from InGaAs self-assembled quantum dots emitting within a two-dimensional photonic band-gap. A strongly suppressed multiphoton probability is obtained for single quantum dots in bulk GaAs and those emitting into the photonic band-gap. In the latter case, photoluminescence saturation spectroscopy is employed to measure a $\ensuremath{\sim}16$ times enhancement of the average photon extraction efficiency, when compared to quantum dots in bulk GaAs. For quantum dots in the photonic crystal, we measure directly the external quantum efficiencies up to 25%, much higher than for dots on the same sample without a tailored photonic environment. The results show that efficient quantum dot single-photon sources can be realized, without the need for complex nanopositioning techniques.

Single-photon source characterization with twin infrared-sensitive superconducting single-photon detectors

We report on the high fidelity characterization, via spontaneous emission lifetime and g(2)(τ) measurements, of a cavity-coupled quantum dot single-photon source at 902nm using a pair of nanowire-based superconducting single-photon detectors (SSPDs). We analyze the suitability of the twin SSPD scheme reported here for the characterization of single-photon sources at telecommunications wavelengths (1310 and 1550nm).

Electrically driven quantum dot single photon source

AbstractWe report on a miniature solid state emitter structure, which allows electrical pumping of only one single InAs quantum dot (QD) grown in the Stranski‐Krastanow mode. The emitter demonstrates a strongly monochromatic polarized emission of a single QD exciton. Correlation measurements of the emitted photons show a clear antibunching behavior. The structure is thus attractive for practical implementation as effective single photon source for quantum cryptography. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

High Q whispering gallery modes in GaAs/AlAs pillar microcavities

We report the observation of whispering gallery modes (WGM) in high quality GaAs/AlAs pillar microcavities defined by electron-beam lithography and electron cyclotron resonance reactive ion etching. Photoluminescence experiments, conducted using InAs quantum dots as an internal probe, reveal a remarkably simple WGM spectrum, consisting of a single series of TE modes. For diameters ranging from 3 to 4 mum, Q-factors in excess of 15 000 were measured, allowing for WGM lasing. Noticeably, sub-micron diameter micropillars also display high Qs (~ 1000), close to the limit set by intrinsic radiative losses. These results open the way to the development of original microlasers and improved quantum-dot single photon sources.

Quantum Dot Single Photon Sources Studied with Superconducting Single Photon Detectors

We report the observation of photon antibunching from a single, self-assembled InGaAs quantum dot (QD) at temperatures up to 135 K. The second-order intensity correlation, g(2)(0), is less than 0.260 plusmn 0.024 for temperatures up to 100 K. At 120 K, g(2) (0) increases to about 0.471, which is slightly less than the second-order intensity correlation expected from two independent single emitters. In addition, we characterize the performance of a superconducting single photon detector (SSPD) based on a nanopatterned niobium nitride wire that exhibits 68 plusmn 3-ps timing jitter and less than 100-Hz dark count rate with a detection efficiency (DE) of up to 2% at 902 nm. This detector is used to measure spontaneous emission lifetimes of semiconductor quantum wells (QWs) emitting light at wavelengths of 935 and 1245 nm. The sensitivity to wavelengths longer than 1 mum and the Gaussian temporal response of this superconducting detector present clear advantages over the conventional detector technologies. We also use this detector to characterize the emission from a single InGaAs QD embedded in a micropillar cavity, measuring a spontaneous emission lifetime of 370 ps and a g(2)(0) of 0.24 plusmn 0.03

Polarization control of quantum dot single-photon sources via a dipole-dependent Purcell effect

We study single photon emission from excitons confined in single InAs quantum dots in elliptical pillar microcavities, demonstrating a polarization dependence of the Purcell effect. The enhancement of the radiative decay rate and emission intensity differs for the two components of the exciton doublet, suggesting each exciton state corresponds to a well-defined dipole direction in the sample plane. This allows the linear polarization of the single photon source to be selected between orthogonal directions by tuning the exciton emission energy between different polarization modes of the cavity.

Erratum: Quantum-dot single-photon sources: Prospects for applications in linear optics quantum-information processing [Phys. Rev. A69, 032305 (2004)

Erratum: Quantum-dot single-photon sources: Prospects for applications in linear optics quantum-information processing [Phys. Rev. A<b>69</b>, 032305 (2004)

Quantum-dot single-photon sources: Prospects for applications in linear optics quantum-information processing

An optical source that produces single photon pulses on demand has potential applications in linear optics quantum computation, provided that stringent requirements on indistinguishability and collection efficiency of the generated photons are met. We show that these are conflicting requirements for anharmonic emitters that are incoherently pumped via reservoirs. As a model for a coherently pumped single photon source, we consider cavity-assisted spin-flip Raman transitions in a single charged quantum dot embedded in a microcavity. We demonstrate that using such a source, arbitrarily high collection efficiency and indistinguishability of the generated photons can be obtained simultaneously with increased cavity coupling. We analyze the role of errors that arise from distinguishability of the single photon pulses in linear optics quantum gates by relating the gate fidelity to the strength of the two-photon interference dip in photon cross-correlation measurements. We find that performing controlled phase operations with error < 1% requires nano-cavities with Purcell factors F_P >= 40 in the absence of dephasing, without necessitating the strong coupling limit.

Quantum teleportation with a quantum dot single photon source.

We report the experimental demonstration of a quantum teleportation protocol with a semiconductor single photon source. Two qubits, a target and an ancilla, each defined by a single photon occupying two optical modes (dual-rail qubit), were generated independently by the single photon source. Upon measurement of two modes from different qubits and postselection, the state of the two remaining modes was found to reproduce the state of the target qubit. In particular, the coherence between the target qubit modes was transferred to the output modes to a large extent. The observed fidelity is 80%, in agreement with the residual distinguishability between consecutive photons from the source. An improved version of this teleportation scheme using more ancillas is the building block of the recent Knill, Laflamme, and Milburn proposal for efficient linear optics quantum computation.

Entanglement formation and violation of Bell's inequality with a semiconductor single photon source.

We report the generation of polarization-entangled photons, using a quantum dot single photon source, linear optics, and photodetectors. Two photons created independently are observed to violate Bell's inequality. The density matrix describing the polarization state of the postselected photon pairs is reconstructed and agrees well with a simple model predicting the quality of entanglement from the known parameters of the single photon source. Our scheme provides a method to create no more than one entangled photon pair per cycle after postselection, a feature useful to enhance quantum cryptography protocols based on shared entanglement.