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Chemically prepared colloidal semiconductor quantum dots have long been proposed as scalable and color-tunable single emitters in quantum optics, but they have typically suffered from prohibitively incoherent emission. We now demonstrate that individual colloidal lead halide perovskite quantum dots (PQDs) display highly efficient single photon emission with optical coherence times as long as 80 ps, an appreciable fraction of their 210 ps radiative lifetimes. These measurements suggest that PQDs should be explored as building blocks in sources of indistinguishable single photons and entangled photon pairs.Our results present a starting point for the rational design of lead halide perovskite-based quantum emitters with fast emission, wide spectral-tunability, scalable production, and which benefit from the hybrid-integration with nano-photonic components that has been demonstrated for colloidal materials. Tisdale.

Kaplan Responds: In my paper, commented on by Enns and Rangnekar, 2 the existence of bistable solitons was analytically predicted in a highly nonlinear Schrddinger equation for a certain class of nonlinearities. The computer simulation done by Enns and Rangnekar 2 shows that for some particular model of nonlinearity [see Eq. (10) in my paper 1 ], the bistable soliton with db/dP > 0 is stable whereas the bistable soliton with db/dP < 0 is unstable when the two of them collide in a nonlinear medium. As they emphasize, this result supports the hypothetical criterion of stability of these solitons suggested in my paper 1 on which I agree with them. I believe, in fact, that the implication of the simulation 2 goes even further in that it suggests that the soliton with db/dP > 0 (for that particular model of nonlinearity) is stable not only against small perturbation as implied in my paper 1 (see also Kaplan 3 ), but also against such a large perturbation as another soliton. This is a very significant and exciting result. The next point of interest obviously is the collision of two bistable solitons (which carry the same total power) in a medium with such a nonlinearity that for both of them db/dP > 0 [this will require consideration of other models of nonlinearity; see, for example, Eq. (13) and Fig. 1, curve 3 in my paper 1 ]. If such solitons (at least for some models of nonlinearity) survive the collison with their respective powers and momenta unchanged, it will be a clear indication that the bistable solitons are indeed physically realizable. This will be important both for the theory of nonlinear propagation and for applications such as, for example, excitation of bistable soliton pulses in nonlinear optical fibers for communication purposes.One of the comments by Enns and Rangnekar re-

No abstract

We predict that Coulomb explosion of a nanoscale cluster, which is ionized by high-intensity laser radiation and has a naturally occurring spatial density profile, will invariably produce shock waves. In most typical situations, two shocks, a leading and a trailing one, form a shock shell that eventually encompasses the entire cluster. Being the first example of shock waves on the nanometer scale, this phenomenon promises interesting effects and applications, including high-rate nuclear reactions inside each individual cluster.