Probability Of Single-photon Emission Research Articles

Correlation between Single-Photon Emission and Size of Cesium Lead Bromide Perovskite Nanocrystals.

Emission photon statistics of semiconductor nanocrystal quantum dots (QDs), including lead halide perovskite nanocrystals (PNCs), are important fundamental and practical optical properties. Single QDs exhibit high-probability single-photon emission owing to the efficient Auger recombination between generated excitons. Because the recombination rate depends on QD size, single-photon emission probability should be size-dependent. Previous studies have researched QDs smaller than their exciton Bohr diameters (twice the Bohr radius of excitons). Here, we investigated the relationship between the single-photon emission behavior and size of CsPbBr3 PNCs to elucidate their size threshold. Simultaneous single-nanocrystal spectroscopy and atomic force microscopy observations on single PNCs with approximately 5-25 nm edge length showed that those smaller than approximately 10 nm, which had size-dependent photoluminescence (PL) spectral shifts, exhibited high-probability single-photon emissions, which decreased linearly with PNC volume. Novel single-photon emission, size, and PL peak correlations of PNCs are important for understanding the relationship between single-photon emission and quantum confinement.

Spin Effects in the Emission of a Photon by a Two-Dimensional Hydrogen-Like Atom

It is shown that the result of calculation of the probability of single-photon emission by a two-dimensional hydrogen-like atom can depend on the choice of the spin operator. Specifically, if it is chosen to be the projection operator of the spin onto the plane of motion, then the result, as expected, agrees with the classical theory of emission of a three-dimensional atom, as was demonstrated by the author in one of his previous works. If, however, it is chosen as the projection operator onto the perpendicular to the plane of motion, the result does not agree with the classical theory. This puts in doubt the results presented in [S. H. Guo, X. L. Yang, F. T. Chan, Phys. Rev. A, 43, No. 3, 1197 (1991)].

Characteristics of a Two-Dimensional Hydrogen-like Atom

Using the customary and well-known representation of the radiation probability of a hydrogen-like atom in the three-dimensional case, a general expression for the probability of single-photon emission of a twodimensional atom has been obtained along with an expression for the particular case of the transition from the first excited state to the ground state, in the latter case in comparison with corresponding expressions for the three-dimensional atom and the one-dimensional atom. Arguments are presented in support of the claim that this method of calculation gives a value of the probability that is identical to the value given by exact methods of QED extended to the subspace {0, 1, 2}. Relativistic corrections ~ (Zα)4 to the usual Schrodinger value of the energy (~ (Zα)2) are also discussed.

Two-Dimensional Hydrogen-like Atom: Photon Emission and Relativistic Energy Corrections

Using the well-known solution Ψ S of the Schrodinger equation for an electron in the field of a nucleus (Ze) in polar coordinates, via which the spin-state-dependent Dirac spinor Ψ± obtained here is expressed, and by extending the QED methods to subspace {0; 1, 2}, we have calculated the probability of single-photon emission by a two-dimensional hydrogen-like atom with allowance made for the polarization and spin states. Relativistic energy corrections ∼(Zα)4 to the energy value have also been found. We show that the so-called contact interaction typical of a three-dimensional hydrogen-like atom also takes place in the twodimensional case, while the ordinary three-dimensional spin–orbit interaction is absent altogether.

Phonon-assisted control of the single-photon spectral characteristics in a semiconductor quantum dot using a single laser pulse

We theoretically demonstrate the phonon-assisted control of the single-photon spectral characteristics such as central frequency and linewidth in a semiconductor quantum dot coupled to a pillar microcavity using a single laser pulse as both excitation and control. We derive the relevant optical Bloch equations from the suitable polaron master equation for taking into account the effects of phonons accurately. We show that with the appropriately chosen parameters of the exciting laser pulse (pump pulse) and cavity, the central frequency and linewidth of the single photon can be controlled simply by controlling the frequency and pulse width of the exciting laser pulse, respectively. Subsequently, we show that these are essentially the phonon-induced processes which ensure that the probability of single-photon emission does not change significantly with the variation of the frequency and pulse width of the exciting laser pulse. Furthermore, we demonstrate that the polarization of the single photon can also be controlled by adjusting the polarization of the pump pulse.

Active temporal and spatial multiplexing of photons

The maturation of many photonic technologies from individual components to next-generation system-level circuits will require exceptional active control of complex states of light. A prime example is in quantum photonic technology: while single-photon processes are often probabilistic, it has been shown in theory that rapid and adaptive feedforward operations are sufficient to enable scalability. Here, we use simple “off-the-shelf” optical components to demonstrate active multiplexing—adaptive rerouting to single modes—of eight single-photon “bins” from a heralded source. Unlike other possible implementations, which can be costly in terms of resources or temporal delays, our new configuration exploits the benefits of both time and space degrees of freedom, enabling a significant increase in the single-photon emission probability. This approach is likely to be employed in future near-deterministic photon multiplexers with expected improvements in integrated quantum photonic technology.

The influence of phonon bath on the control of single photon**Project supported by the Fundamental Research Funds for the Central Universities of Central South University, China (Grant No. 2014zzts145).

The influence of vacuum fluctuation and phonon bath on the probability of single photon emission are both considered in the two-level system model theoretically; by using the master equations and generating function method we get the analytical expression of the second-order fluorescence correlation function, probability of single photon emission, and Mandel’s Q parameter. The results manifest that the coupling between the phonon bath and single photon source destroys the superposition state induced by the square laser pulse, the Rabi oscillation damped rapidly with the increasing of temperature. Theoretically, when the structure parameter of arsenide quantum dots α scaled to 0.1 times of the sample, the critical coherence-temperature will rise up to hundreds of Kelvin, which means a step forward to the realization of coherent control of single photon source at room temperature.

Phonon-induced effects on exciton dynamics and photon emission from a semiconductor quantum dot microcavity: phonon coherent state representation

A microscopic theory to study the combined dynamics of a quantum dot exciton coupled to a single cavity mode as well as acoustic phonons is presented. By considering the phonon subsystem in the coherent state representation, the phonon’s impact on the emitted photons is investigated. The single photon emission probability and phonon effects on this quantity are studied. On the other hand, we illustrate that while a quantum dot interacts with a single cavity mode, the collapse and revival phenomenon will occur. It is demonstrated that acoustic phonons have a pronounced impact on the collapse and revival of the quantum dot exciton. Our finding reveals that at elevated temperatures the phonon interaction decreases the Rabi frequency. Moreover, the cavity mode possesses non-classical features such as sub-Poissonian statistics.

Coherent Control of Single-Photon Absorption and Reemission in a Two-Level Atomic Ensemble

We demonstrate coherent control of single-photon absorption and reemission in a two-level cold atomic ensemble. This is achieved by interfering the incident single-photon wave packet with the emission (or scattering) wave. For a photon with an exponential growth waveform with a time constant equal to the excited-state lifetime, we observe that the single-photon emission probability during the absorption can be suppressed due to the perfect destructive interference. After the incident photon waveform is switched off, the absorbed photon is then reemitted to the same spatial mode as that of the incident photon with an efficiency of 20%. For a photon with an exponential decay waveform with the same time constant, both the absorption and reemission occur within the waveform duration. Our experimental results suggest that the absorption and emission of a single photon in a two-level atomic ensemble may possibly be manipulated by shaping its waveform in the time domain.

Single-photon emission from a single nanoparticle consisting of a single conjugated polymer chain

Single-photon behavior in the emission from a single nanoparticle consisting of a single poly[2-methoxy-5-(2′-ethylhexyloxy)- p-phenylene vinylene] (MEH-PPV, molecular weight: 2,600,000 amu) chain has been investigated. Photon correlation measurements of a number of single nanoparticles revealed that the probability of single-photon emission from the single nanoparticles clearly increases, compared with that of single chains embedded in host polymer matrices, poly(methyl methacrylate) (PMMA) and polystyrene (PS). The result suggested that even a single MEH-PPV chain with high molecular weight, which does not exhibit single-photon emission in PMMA and PS, is forced to exhibit single-photon emission by adopting “compact” chain conformation like nanoparticle. Efficient exciton migration and exciton annihilation processes in the compact chain conformation most probably result in the efficient single-photon emission from the single nanoparticle. The present results indicate that multi-quantum systems consisting of a large number of chromophores, such as the MEH-PPV, can be made to behave as single-photon sources by appropriately controlling their size.

Influence of molecular weight and conformation on single-photon emission from isolated conjugated polymer chains

The influence of molecular weight (MW) and chain conformation on single-photon emission from isolated chains of poly[2-methoxy,5-(2′-ethylhexyloxy)-p-phenylene-vinylene] have been investigated. The probability of single-photon emission clearly increased with decreasing MW, and when the polymer chains adopted the “collapsed” conformation, this probability was larger than for the “extended” conformation. Even single polymer chains of high MW behaved as single-photon sources by adopting the collapsed conformation. These results indicate that multi-quantum systems consisting of a large number of chromophores can be made to behave as single-photon sources by appropriately controlling their size.

Efficiency of single photon emission in three-level system of semiconductor quantum dots with pulsed excitation

The statistic characteristics of single photon emission in single semiconductor quantum dot with pulse excitation have been investigated.With rotating-wave approximation,we deduce the dynamics equations including second-order correlation function from the master equations of the populations and discuss the correlation function of photon emission from the exciton combination under different input pulse areas.There will appear an apparant split peak around zero time delay under strong excitation.For short pulse width,the probability of single photon emission p and the efficiency of single photon emission η oscillate as the excitation intensity increases.It is revealed that high efficient single photon emissions can be realized in this system when excited with input pulse area about π and short pulse width.