New Method Of Highly Sensitive Single-photon Detection

For centuries, scientisits are always trying to understand the nature of light. No matter the "particle theory" supported by Isaac Newton, or "wave theory" introduced by Christiaan Huygens, the nature of light was still not revealed. Until in 1905, inspired by Planck’s theory, a young man named Albert Einstein suggest the concept of "light quantum", which successfully explained the photoelectric effect, and then people started to realize the light may have the wave-particle duality. In reality, the "light quantum" theory introduced by Einstein place a theoretical limit for the achievable sensitivity of any photodetectors-to detect the energy of a "light quantum". In recently years, driven by cutting-edge applications such as optical quantum information technologies, developing high performance single-photon detectors has attracted wide interest and continuous attention from various scientists. Compared with mature single-photon detectors such as photomultiplier tubes and avalanche photodiodes, many new single-photon technologies have been introduced and realized, and they are quite promising to have great impact on demanding applications in the near future.This thesis studies a new type of single-photon detector called quantum dot resonant tunneling diodes (QD-RTDs). The single-photon detection is realized by varying the charging state of a quantum dot with photo-excited carries, and then triggering an addition tunneling current passing through the RTD. Compare with other existing single-photon technologies, the QD-RTD devices stands out with extremely low dark count rates and good detection efficiency. It is also evaluated as a promising single-photon technology with the best reported figures of merit. The contributions and some new work of this thesis is concluded below: 1. Extends the cut-off detection wavelength of present QD-RTD detector from 840nm to at least 1.3μm, by utilizing the optical transition from self-assembled In As quantum dots. Infrared single-photon sensitivity has been demonstrated even at 77 K.Present results reported with QD-RTD devices is using a GaAs layer as photo-absorption layer near quantum dots, therefore the detection wavelength is limited by the bandgap of GaAs (-840 nm), and only photons with energy higher than that gap can be absorbed and detected. This thesis introduces and studies another way of photon absorption. By directly exciting electrons in quantum dots by infrared photons and triggering the resonant tunneling process, we demonstrate the single-photon sensitivity in the infrared.2. Demonstrate the photon-number-resolving capability of the resonant tunneling single-photon detector for the first time.Low noise single-photon detectors that can resolve photon numbers are highly desired in linear quantum computation and long-distance quantum communication. However, up to now, only several single-photon detectors show such an intrinsic photon-number-resolving (PNR) capability. Since the QD-RTD single-photon detector has been invented in 2005, the PNR ability of this detector has never been demonstrated, and was commented by a review paper published in Nature Photonics to be lack of such capability. We study the quantum coupling effect within the device and improved the detection method, thereby giving the first report of such capability.3. An efficient reset operation is introduced by manipulating electronic states in quantum dots, and the dynamic detection range of QD-RTD is at least improved by a factor of two orders.QD-RTD detector has a small active region (<10μm2), typically the detector will be saturated after absorbing several hundreds of photons. Even turn off the incident radiation, the detector will keep in the saturated state for a long time (more than several hours), and cannot recover to initial sensitive state. This thesis studies the saturation mechanism of the detector and introduces a convenient reset technique for this detector. By periodically injecting electrons into the quantum dot, the detector is kept in a well-defined linear response region even under strong illuminations. We have confirmed the dynamic detection range of the detector is extended above 104.