Re: LU15371 Reversing the temporal envelope of a heralded single photon using a cavity by Bharath Srivathsan, Gurpreet Kaur Gulati, Alessandro Cer\`{e}, et al. Dear Dr. Kurtsiefer, The above manuscript has been reviewed by our referees. We ask you to consider the appended comments from the reports. While we cannot make a definite commitment, the probable course of action if you choose to resubmit is indicated below. ( ) Acceptance, if the editors can judge that all or most of the criticism has been met. (x) Return to the previous referee(s) for review if available. ( ) Submittal to new referee(s) for review. With any resubmittal, please include a summary of changes made and a brief response to all recommendations and criticisms. Yours sincerely, Stojan Rebic Assistant Editor Physical Review Letters Email: prl@aps.org http://journals.aps.org/prl/ IMPORTANT: Editorial "Review Changes" http://journals.aps.org/prl/edannounce/PhysRevLett.111.180001 ---------------------------------------------------------------------- Second Report of Referee A -- LU15371/Srivathsan ---------------------------------------------------------------------- I would like to thank the authors for addressing my concerns with the original manuscript, in particular for clarifying the wider appeal of the technique (I had indeed overlooked the applicability of this scheme in other contexts). This fully addresses my concerns on impact and interest, and overrides my reservations on innovation (although I do look forward to seeing this technique applied explicitly to enhancing coupling to a atom!). Therefore I recommend publication of the revised manuscript in PRL. ---------------------------------------------------------------------- Report of Referee B -- LU15371/Srivathsan ---------------------------------------------------------------------- Srivathsan et al report demonstration of temporal envelop reversal process of heralded single photons using an asymmetric FP cavity: they turn a decaying exponential envelop to a rising exponential envelop. I notice similar results were also reported in a recent work published in PRL [Efficiently Loading a Single Photon into a Single-Sided Fabry-Perot Cavity, C. Liu et al., PRL 113, 133601 (2014)]. The experimental configuration in Fig.1 is nearly identical to that in Fig.4 by C. Liu et al, except C. Liu took backward-wave four-wave mixing. The main result in Fig. 2 is similar to that in Fig.4(e) if C. Liu et al. change the horizontal axis from “t_s-t_as” to “t_as-t_s”. Figure 3 is similar to Fig.4(b). Equation (6) may be equivalent to the loading efficiency defined in (5) in Liu’s work. Of course Liu et al’s work covers more and the envelop conversion, which is the full content of this manuscript, is only part of Liu’s PRL work. Because these two works (Srivathsan et al VS Liu et al) are independent and Liu’s work was published in PRL, I am willing to recommend this work by Srivathsan et al for publication in PRL provided that the authors can address the following issues: 1) The two terms in Eq. (4) (in time domain) is equivalent to the two terms in Eq.(14) of the supplementary material of Liu’s work [PRL 113, 133601 (2014)]. However, the two terms in this work have the same time constants “\tau”, while they are different in Liu’s work. Could the authors comment on this? Or doubly check their Eq. (4)? 2) It is not clear why Eq.(6) represents the mean photon number in the cavity. Similar results was also presented in Ref [17], where the experiment is purely classical. In Ref [17], the result is shown in Fig.2(b) where the peak value at time=0 is nearly 1: Does that mean Ref [17] works with a single photon? It is obvious that Ref [17] uses coherent state of light. I find the mean photon number calculated from Eq.(6) is always <=1 for any input light (even with classical light). Does that really mean the mean photon number is always <=1 for any input light? I think the authors should clarify this issue. 3) The present paper is too simple and some important technical information is missing. For example, how is the cavity designed to match the temporal envelop? I guess the cavity parameters are related to the time constant \tau in Eqs. (4) and (5). But this relation is missing in this paper. The authors may also need provide a quantative analysis of the effect of R2<1. 4) For the photon pair generation experimental setup, the authors do not provide detailed technical information and only refer to Refs. [27] and [16]. However, when I check Refs. [27] and [16], I find the configuration (photon pair generation) of this work (shown in Fig.1) is quite different from those in [27] and [16]. For example, in this work, Fig.1 shows the two pump beams overlaps completely (not mentioned in the text), while in Refs. [27] and [16] they separated by an angle. I suggest the authors provide more information and explains the difference. 5) Does the cavity require stabilization? How? 6) The authors should add a note to the end of the manuscript, such as “Note added. – During the completion of the work, we became aware of similar results reported by Liu et al.” and cite this recent PRL work [PRL 113, 133601 (2014)].