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Quantum Dots and Nanostructures: Growth, Characterization, and Modeling

Impact of a time gate to the purity of single photons emitted from colloidal quantum dots

Toshiyuki Ihara, Shigehito Miki, Toshiki Yamada, Hirotaka Terai

Published Mar 4, 2019• 2 citations
Publisher

Abstract

Colloidal quantum dots (CQDs) are attractive material for single-photon sources (SPSs) that can be utilized at room temperature. In this work, we performed simultaneous measurements of photoluminescence (PL) decay curve and second-order photon correlation, g(2), on single CQDs to study the purity of their single photons, which is determined by the value of g(2)at the time origin. We demonstrate that the single-photon purity can be improved through time-gated g(2) analysis, where a part of the PL signal is excluded by applying a temporal filter to the PL decay curve. We show that by using a superconducting nanowire single-photon detector, it is possible to observe highly-purified single photons that exhibited g(2) at the time origin ranging from 0.01 to 0.02.

DOI
10.1117/12.2507334

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Colloidal quantum dots (CQDs) are attractive material for single-photon sources (SPSs) that can be utilized at room temperature. In this work, we performed simultaneous measurements of photoluminescence (PL) decay curve and second-order photon correlation, g(2), on single CQDs to study the purity of their single photons, which is determined by the value of g(2)at the time origin. We demonstrate that the single-photon purity can be improved through time-gated g(2) analysis, where a part of the PL signal is excluded by applying a temporal filter to the PL decay curve. We show that by using a superconducting nanowire single-photon detector, it is possible to observe highly-purified single photons that exhibited g(2) at the time origin ranging from 0.01 to 0.02.
Abstract The realization of high-quality quantum emitters that can operate at room temperature is important for accelerating the application of quantum technologies, such as quantum communication, quantum information processing, and quantum metrology. In this work, we study the photon-antibunching properties on room-temperature emission from individual colloidal quantum dots (CQDs) using superconducting-nanowire single-photon detectors and temporal filtering of the photoluminescence decay curve. We find that high single-photon purities and high photon-generation rates can be simultaneously achieved by removing the signals originating from the sequential two-photon emission of biexcitons created by multiple excitation pulses. We successfully demonstrate that the ultrahigh performance of the room-temperature single-photon sources showing g(2)(0) ≪ 10−2 can be confirmed by the ultralow-dark-count detection of the temporally purified single photons. These findings provide strong evidence for the attractiveness of CQDs as candidates for high-quality room-temperature quantum light sources.
Efficient, high rate photon sources with high single-photon purity are essential ingredients for quantum technologies. Single-photon sources based on solid state emitters such as quantum dots are very advantageous for integrated photonic circuits, but they can suffer from a high two-photon emission probability, which in cases of noncryogenic environment cannot be spectrally filtered. Here we propose two temporal purification-by-heralding methods for using a two-photon emission process to yield highly pure and efficient single-photon emission, bypassing the inherent problem of spectrally overlapping biphoton emission at elevated temperatures. We experimentally emulate their feasibility on the emission from a single nanocrystal quantum dot at room temperature, exhibiting single-photon purities exceeding 99.5%, without a significant loss of single-photon efficiency. By utilizing these methods with commercially available components, nanocrystal quantum dots can be made realistic high-quality room-temperature sources for single photons. These approaches can also be applied for any indeterministic source of spectrally broadband photon pairs.
Single-photon sources with photon antibunching characteristics are essential for quantum information technologies. This paper investigates the potential of quaternary-alloy CdTeSeS colloidal core quantum dots (cQDs) as compact, room-temperature, and fiber-integrated single-photon sources. Single-photon emission from CdTeSeS cQDs was verified by measuring the second-order correlation function, g2τ, using a Hanbury-Brown and Twiss setup. A novel method to determine zero-time delay through afterpulsing analysis is presented. The results demonstrate strong photon antibunching with g20=0.13, confirming that the photoemission from the CdTeSeS cQDs function as a single-photon source. This work highlights the potential of CdTeSeS cQDs as reliable and efficient single-photon sources for practical use in fiber-based quantum information technologies.
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)g^{(2)}g(2)(0), is less than 0.260$\pm0.024fortemperaturesupto100K.At120K,0.024 for temperatures up to 100 K. At 120 K,0.024fortemperaturesupto100K.At120K,g^{(2)}(0)increasestoabout0.471,whichisslightlylessthanthesecond−orderintensitycorrelationexpectedfromtwoindependentsingleemitters.Inaddition,wecharacterizetheperformanceofasuperconductingsinglephotondetector(SSPD)basedonananopatternedniobiumnitridewirethatexhibits68(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(0)increasestoabout0.471,whichisslightlylessthanthesecond−orderintensitycorrelationexpectedfromtwoindependentsingleemitters.Inaddition,wecharacterizetheperformanceofasuperconductingsinglephotondetector(SSPD)basedonananopatternedniobiumnitridewirethatexhibits68\pm3−pstimingjitterandlessthan100−Hzdarkcountratewithadetectionefficiency(DE)ofupto23-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 13−pstimingjitterandlessthan100−Hzdarkcountratewithadetectionefficiency(DE)ofupto2\mumandtheGaussiantemporalresponseofthissuperconductingdetectorpresentclearadvantagesovertheconventionaldetectortechnologies.WealsousethisdetectortocharacterizetheemissionfromasingleInGaAsQDembeddedinamicropillarcavity,measuringaspontaneousemissionlifetimeof370psandam 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 amandtheGaussiantemporalresponseofthissuperconductingdetectorpresentclearadvantagesovertheconventionaldetectortechnologies.WealsousethisdetectortocharacterizetheemissionfromasingleInGaAsQDembeddedinamicropillarcavity,measuringaspontaneousemissionlifetimeof370psandag^{(2)}(0)of0.24(0) of 0.24(0)of0.24\pm$0.03.
Superconducting Nanowire Single-Photon Detectors (SNSPDs) are well known for their single-photon sensitivity, low jitter, and high efficiency. Their dynamic range is generally limited either to zero or one (no photon, or a photon absorbed), and if single-photon sensitivity is needed in the vicinity of a strong light pulse, a counteraction like gating needs to be deployed. In such a scheme, we aim at the fastest possible transition time which is helpful to increase sensitivity, to temporally filter any strong laser excitation, and further suppress dark counts. Here, we present our work of time-gated SNSPDs where the detection current can be switched on- and off to allow the detector not to be saturated. We start our discussion by introducing the simplest gating scheme based on a square wave resulting in switch-off-switching transition times of ≈50ns. Then we present a new method to improve this relatively slow transition time to the sub-nanosecond range. Latest measurements of efficiency recovery and jitter are presented, and we show that a 1550nm light pulse with 100’000 photons within 500ns, applied right before the on-transition of the SNSPD, does not yet affect the performance in the on-state.