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arXiv:1805.00201 · ACS Photonics

Purification of Single Photons by Temporal Heralding of Quantum Dot Sources

Hamza A. Abudayyeh, Boaz Lubotzky, Somak Majumder, Jennifer A. Hollingsworth, Ronen Rapaport

Published Jan 24, 2019• 22 citations
arXivHTMLPDF

Abstract

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.

DOI
10.1021/acsphotonics.8b01396

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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.
Quantum light and in particular single photons have become essential resources for a growing number of quantum applications including quantum computing, quantum key distribution and quantum metrology. Solid-state atomlike systems such as semiconductor quantum dots and color defects in crystals have become the hallmark of highly pure single photon emitters in the past two decades. A particular interest has been developed in nanocrystal quantum dots (NQDs) and color centers in diamond as potential compact room-temperature emitters. There are however several challenges that inhibit the use of such sources in current technologies including low photon extraction efficiency, low emission rates and relatively low single photon purities. In this work we will review our efforts in overcoming these technical difficulties using several complementary methods including designing several nanoantenna devices that enhance the directionality and emission rate of the nanoemitter. In addition, we developed several temporal heralding techniques to overcome the hurdle of low single photon purity in NQDs in an effort to produce a highly pure, bright and efficient single photon source on-chip.
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.
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.
A major obstacle to a practical, heralded source of single photons is the fundamental trade-off between high purity and high production rate. To overcome this difficulty, we propose applying sequential spectral and temporal filtering on the signal photons before they are detected for heralding. Based on a multimode theory that takes into account the effect of simultaneous multiple photon-pair emission, we find that these filters can be optimized to yield both high purity and a high production rate. While the optimization conditions vary depending on the underlying photon-pair spectral correlations, all correlation profiles can lead to similarly high performance levels when optimized filters are employed. This suggests that a better strategy for improving the performance of heralded single-photon sources is to adopt an appropriate measurement scheme for the signal photons, rather than tailoring the properties of the photon-pair generation medium.
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