Photon correlations for colloidal nanocrystals and their clusters

Abstract

Images of semiconductor 'dot in rods' and their small clusters are studied by measuring the second-order correlation function with a spatially resolving ICCD camera. This measurement allows one to distinguish between a single dot and a cluster and, to a certain extent, to estimate the number of dots in a cluster. A more advanced measurement is proposed, based on higher-order correlations, enabling more accurate determination of the number of dots in a small cluster. , and a noticeable probability of two-photon emission, are still one of the most promising types of singlephoton emitters as they can be operated at room temperature and can be synthesized relatively easily. Especially promising are dot-in-rods (DR) [10], which have a higher probability of single-photon emission, show reduced blinking [11], and emit single photons with a high degree of polarization [12]. DRs can also merge into clusters. A cluster of DRs is not a single-photon emitter but it can be used for quantum information purposes since it still emits nonclassical light. In this work we perform measurements that allow one to distinguish between a single DR and a cluster. As a criterion, we use Glauber's second-order correlation function (CF) and the brightness of emission. Another method of distinguishing between a single DR and a cluster is defocused microscope technique [12], based on the dipole-like angular distribution of the DR emission; however, this method only allows one to recognize clusters consisting of differently oriented DRs. As an extension of our correlation measurement, we propose the study of higher-order correlation functions. Such a measurement will allow one to resolve the number of DRs in a cluster and also observe nonclassical behavior of its emission.For our experiment we used an intensified CCD (ICCD) camera. This device is equivalent to an array of single-photon detectors and can be used for spatially resolved measurements of Glauber's CFs. Alternatively, the pixels can be used for photon-number, rather than spatial, resolution, so that higher-order CFs can be measured. The ICCD camera can be used in either analog or photon-counting mode. In the photon-counting mode, used in our experiment, a certain level of the dimensionless readout signal S (proportional to the integral electric charge acquired in a pixel) is chosen as a threshold, and any signal exceeding this value is interpreted as a single-photon event in a corresponding pixel. If the threshold S th is taken too high, the resulting quantum efficiency becomes low, which fortunately does not affect the normalized CF measured in our experiment [13]. If the threshold is too low, the noise is increased.

Multiphoton nonclassical light from clusters of single-photon emitters

“…After subtracting the background noise, the integral output signal obtained for these clusters varies from 1.7×10 5 to 1.1×10 6 analog-to-digital conversion units of the camera (figure 2(c)). As demonstrated in [8], this parameter can be used as an indicator of the number m of DRs in a cluster. This, together with the measured value g (2) =0.413±0.009 for the smallest cluster, allows us to conclude that the clusters contain from m=1.7±0.2 to m=14±2 DRs 7 .…”

“…The radiation from the chosen cluster is selected by an iris aperture I and sent, by removing the FM M, through a multimode fiber into the Hanbury Brown-Twiss (HBT) setup using two avalanche photodiodes (APDs) and time multiplexing [30,31]. (Note that, although the ICCD camera in single-photon regime can be used for the HBT measurement [8], its low quantum efficiency [32] does not allow detection of multiphoton events within a reasonable acquisition time.) The time multiplexing scheme contains a 60 m fiber loop (figure 1), so that each of the APDs can receive photons in one of the two time slots, separated by 300 ns.…”

“…For such a cluster, the number of photons will not significantly exceed the number of emitters, which suggests applications in quantum key distribution (QKD) [9] and quantum metrology [10], where a limit on the maximal number of the photons is highly relevant. Recently, it has been predicted that even a large number of realistic single-photon emitters can produce nonclassical light [8,11]. Importantly, this way of obtaining multiphoton quantum states does not require postselection or heralding, unlike methods based on nonlinear optical effects.…”

Detection of non-classical space-time correlations with a novel type of single-photon camera

“…Using SPDC radiation, the quantum efficiency of an ICCD camera was calibrated [7] by means of a fit to the measured correlation functions. Recently, an ICCD camera was also used for spatially resolved characterization of single-photon emitters and their clusters [8]. A huge disadvantage of ICCD cameras (and even more in the case of EMCCDs) for correlation measurements and therefore coincident detection is the necessity for a long measurement time.…”

Single-photon emitters based on NIR color centers in diamond coupled with solid immersion lenses

“…[1][2][3][4][5][6][7] Diamond is a promising platform for the development of single-photon emitters, due to a remarkable variety of luminescent defects 8,9 with appealing emission properties combined with the broad spectral transparency of the hosting crystal structure. The negatively charged nitrogen-vacancy (NVÀ) complex had a prominent role in the development of the¯rst diamond-based single-photon emitters [10][11][12] due to its abundance, quantum e±ciency and well understood electronic transition structure.…”