We study the correlation properties of single photons carrying orbital angular momentum (OAM) in a Hanbury Brown and Twiss (HBT) type experiment. We have characterized single photon sources obtained by pumping a nonlinear crystal with a laser beam carrying different OAM under same experimental conditions. For heralded twisted single photons carrying OAM, we calculate $g^{(2)}(0)$, a measurable parameter characterizing the quality of a single photon source, and observe an increment with the OAM of the single photon. [1905.01089] Single photon sources with different spatial modes Single photon sources with different spatial modes \name Nijil Lal a,b Anindya Banerji a , Ayan Biswas a,b , Ali Anwar a, † † \dagger and R. P. Singh a CONTACT Nijil Lal. Email: nijil@prl.res.in. a Physical Research Laboratory, Ahmedabad 380009, India; b Indian Institute of Technology, Gandhinagar 382355, India; † † \dagger Currently at Centre for Quantum Technologies, National University of Singapore, 3 Science Drive 2, S117543, Singapore Abstract We study the correlation properties of single photons carrying orbital angular momentum (OAM) in a Hanbury Brown and Twiss (HBT) type experiment. Since the two down converted photons are generated at the same time, detection of one photon heralds the presence of the other ( 7 , 8 ) . Therefore, single photon sources obtained by using this technique are generally called as heralded single photon sources. Optical vortices or Laguerre Gaussian (LG) beams with zero radial index are gaining popularity in implementing various quantum information protocols ( 9 , 10 ) as they provide extra degree of freedom in the form of orbital angular momentum (OAM) ( 11 , 12 ) that can be measured using standard experimental techniques ( 13 , 14 , 15 ) . For an ideal single photon source from which individual photons are emitted one after another as given in Figure 1 a, a photon either gets transmitted (along arm 1 ) at the beam splitter or gets reflected (along arm 2 ). There are no simultaneous incidences at the detectors D 1 subscript 𝐷 1 D_{1} & \& D 2 subscript 𝐷 2 D_{2} when there is no delay between the paths 1 and 2 ( τ = 0 𝜏 0 \tau=0 ). For heralded single photon sources generated by spontaneous parametric down conversion (SPDC), the photon correlation in the HBT experiment has to be done in the signal ( s ) with the conditioned detection of idler( i ) (Figure 1 b). Figure 1: A simplified illustration of HBT experiment for a) an ideal single photon source where photons reaching the beam splitter through the input port will choose any of the paths 1 1 1 or 2 2 2 without resulting in any coincidence detection between the detectors, D 1 subscript 𝐷 1 D_{1} & \& D 2 subscript 𝐷 2 D_{2} and b) a heralded single photon source. Optimizing fiber coupling using fiber collimators, maximum coincidences are achieved between signal and idler arms. The coincident photons are counted using a time to digital converter (ID800 TDC, IDQuantique). The coincidence window for heralding is kept as 410 ps. The detector positions are adjusted such that the relative delay between all three detectors are zero. This is ensured by obtaining maximum two fold coincidences between i 𝑖 i - s 1 subscript 𝑠 1 s_{1} and i 𝑖 i - s 2 subscript 𝑠 2 s_{2} . Figure 2: HBT-like setup to determine the second order correlation for a heralded single photon source. The increment in g ( 2 ) ​ ( 0 ) superscript 𝑔 2 0 g^{(2)}(0) with pump power can be attributed to the fact that the rate of pair production and hence the probability of simultaneous creation of multiple photon pairs are proportional to the pump power ( 27 ) . This results in more than two photons reaching together at the beam splitter leading to coincidences between the two signal arms. A higher g ( 2 ) ​ ( 0 ) superscript 𝑔 2 0 g^{(2)}(0) shows a reduced non-classical behaviour. Hence, it is crucial for quantum optical experiments using heralded single photon sources to be done in the lower pump power regime. Twisted photon OAM, l 0 1 2 3 a)       g ( 2 ) ​ ( 0 ) superscript 𝑔 2 0 g^{(2)}(0) 0.0082 ± plus-or-minus \pm 0.0043 0.015 ± plus-or-minus \pm 0.011 0.030 ± plus-or-minus \pm 0.057 0.045 ± plus-or-minus \pm 0.169 b)       g ( 2 ) ​ ( 0 ) superscript 𝑔 2 0 g^{(2)}(0) 0.0047 ± plus-or-minus \pm 0.0001 0.0094 ± plus-or-minus \pm 0.0003 0.021 ± plus-or-minus \pm 0.001 0.042 ± plus-or-minus \pm 0.002 Table 1: Second order correlation, g ( 2 ) ​ ( 0 ) superscript 𝑔 2 0 g^{(2)}(0) , for a single photon source a) measured directly from three fold coincidences using Equation ( 2 ) and b) accounting only for accidental Photonics 2011 , 3  (2), 161–204. (13) Vaity, P.; Banerji, J.; Singh, R. Measuring the topological charge of an optical vortex by using a tilted convex lens, Phys. Lett. A 2013 , 377  (15), 1154–1156. (14) Prabhakar, S.; Kumar, A.; Banerji, J.; Singh, R. Revealing the order of a vortex through its intensity record, Opt. Lett. 2011 , 36  (22), 4398–4400. (15) Mair, A.; Vaziri, A.; Weihs, G.; Zeilinger, A. Entanglement of the orbital angular momentum states of photons, Nature 2001 , 412  (6844), 313. (16) Kumar, A.; Banerji, J.; Singh, R. Hanbury Brown–Twiss-type experiments with optical vortices and observation of modulated intensity correlation on scattering from rotating ground glass, Phys. Hanbury Brown–Twiss-type experiments with optical vortices and observation of modulated intensity correlation on scattering from rotating ground glass, Phys. Rev. A 2012 , 86  (1), 013825. (22) Mandel, L.; Wolf, E. Optical coherence and quantum optics ; Cambridge university press, 1995. (23) Kimble, H.J.; Dagenais, M.; Mandel, L. Photon antibunching in resonance fluorescence, Phys. Rev. Lett. 1977 , 39  (11), 691. (24) U’Ren, A.B.; Silberhorn, C.; Ball, J.L.; Banaszek, K.; Walmsley, I.A. Characterization of the nonclassical nature of conditionally prepared single photons, Phys. Rev. A 2005 , 72  (2), 021802. (25) Grangier, P.; Roger, G.; Aspect, A.

The development of quantum-enhanced technologies requires single-photon sources, as well as methods for their characterization and verification. Here, we describe a methodology for measuring the correlation function of a single-photon source using an experimental setup that comprises a laser-excited fluorescence microscope equipped with a Hanbury Brown–Twiss intensity interferometer as one of the detection systems. Measurements of the response function of the device and the reference samples are performed. The second-order autocorrelation function of the exciton state of GaAs quantum dots in AlGaAs nanowires is obtained and reveals a single-photon emission.

Abstract Exciton creation and annihilation by charges are crucial processes for technologies relying on charge-exciton-photon conversion. Improvement of organic light sources or dye-sensitized solar cells requires methods to address exciton dynamics at the molecular scale. Near-field techniques have been instrumental for this purpose; however, characterizing exciton recombination with molecular resolution remained a challenge. Here, we study exciton dynamics by using scanning tunnelling microscopy to inject current with sub-molecular precision and Hanbury Brown–Twiss interferometry to measure photon correlations in the far-field electroluminescence. Controlled injection allows us to generate excitons in solid C 60 and let them interact with charges during their lifetime. We demonstrate electrically driven single-photon emission from localized structural defects and determine exciton lifetimes in the picosecond range. Monitoring lifetime shortening and luminescence saturation for increasing carrier injection rates provides access to charge-exciton annihilation dynamics. Our approach introduces a unique way to study single quasi-particle dynamics on the ultimate molecular scale.

Tin-vacancy (Sn−V) color centers were created in diamond via ion implantation and subsequent high-temperature annealing up to 2100 °C at 7.7 GPa. The first-principles calculation suggested that a large atom of tin can be incorporated into a diamond lattice with a split-vacancy configuration, in which a tin atom sits on an interstitial site with two neighboring vacancies. The Sn−V center showed a sharp zero phonon line at 619 nm at room temperature. This line split into four peaks at cryogenic temperatures, with a larger ground state splitting (∼850 GHz) than that of color centers based on other group-IV elements, i.e., silicon-vacancy (Si−V) and germanium-vacancy (Ge−V) centers. The excited state lifetime was estimated, via Hanbury Brown–Twiss interferometry measurements on single Sn−V quantum emitters, to be ∼5 ns. The order of the experimentally obtained optical transition energies, compared with those of Si−V and Ge−V centers, was in good agreement with the theoretical calculations.

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, g 2 τ , 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 g 2 0 = 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.

An outstanding goal in quantum optics and scalable photonic quantum technology is to develop a source that each time emits one and only one entangled photon pair with simultaneously high entanglement fidelity, extraction efficiency, and photon indistinguishability. By coherent two-photon excitation of a single InGaAs quantum dot coupled to a circular Bragg grating bullseye cavity with broadband high Purcell factor up to 11.3, we generate entangled photon pairs with a state fidelity of 0.90(1), pair generation rate of 0.59(1), pair extraction efficiency of 0.62(6), and photon indistinguishability of 0.90(1) simultaneously. Our work will open up many applications in high-efficiency multi-photon experiments and solid-state quantum repeaters.

We propose and provide experimental evidence in support of a theory for the remote preparation of a complex spatial state of a single photon. An entangled two-photon source was obtained by spontaneous parametric down-conversion, and a double slit was placed in the path of the signal photon as a scattering object. The signal photon was detected after proper spatial filtering so that the idler photon was prepared in the corresponding single-photon state. By using a two-photon coincidence measurement, we obtained the Radon transform, at several longitudinal distances, of the single-photon Wigner distribution function modified by the double slit. The experimental results are consistent with the idler photon being in a pure state. An inverse Radon transformation can, in principle, be applied to the measured data to reconstruct the modified single-photon Wigner function, which is a complete representation of the amplitude and phase structure of the scattering object.