Generation of Entanglement between Two Two-Level Atoms Coupled to a Microtoroidal Cavity Via Thermal Field

Round 1

Reviewer 1 Report

The paper addresses the modelling of entanglement dynamics between two identical two-level atoms interacting via dipole-dipole interaction and coupled simultaneously to the two WGMs microtoroidal resonator via thermal field. Achivements contribute to the understanding of the relationship between dissipative effects, such as thermal fields, and the overall system parameters. 

This type of results has a potential impacts in quantum computing evolution: in fact, today quantum computers are highly susceptible to the environment and this uncontrollable interaction may result in decoherence, thereby degrading the entanglement and derailing the processing.

Please specify what are the next step you are planning to take in this research.

Please correct dipolo in dipole, in the conclusions sections.

Author Response

Dear Reviewer, The authors thank for you sending the report back review of our manuscript,
"Generation of entanglement between two two-level atoms coupled to a
microtoroidal cavity via thermal field", which we submitted to Quantum
Reports and also thank the reviewers for their time. In this report,
we try to answer all reviewer's questions and present a carefully English
revision on the manuscript. Below follows the reviewer questions and
our answers. Reviewer says: The paper addresses the modelling of entanglement dynamics between two
identical two-level atoms interacting via dipole-dipole interaction and
coupled simultaneously to the two WGMs microtoroidal resonator via thermal
field. Achivements contribute to the understanding of the relationship
between dissipative effects, such as thermal fields, and the overall
system parameters. This type of results has a potential impacts in quantum
computing evolution: in fact, today quantum computers are highly susceptible
to the environment and this uncontrollable interaction may result in
decoherence, thereby degrading the entanglement and derailing the
processing.

(1) Please specify what are the next step you are planning to take in
this research. OUR REPLY: The next step in our work is to the couple, via evanescent waves,
a second microtoroidal cavity, and each one interacting with two two-level
atoms, whose modes are prepared in a thermal state. In this case, our goal
is to transfer an initially prepared entangled state between the two atoms
which are interacting with the first cavity, to the other two atoms that
are interacting with the second cavity. This study, in the initial stage,
is important to understand the effects of noise caused in transmission
and quantum information processing tasks. In the second stage, the proposal
is to work with N coupled cavities. In this case, the main task is to study
such effects over long distances. (2) Please correct dipolo in dipole, in the conclusions sections. OUR REPLY: The authors thank you for your correction of the text in English.

Thank you for your time and consideration. I look forward to your reply. Sincerely, Dr. Emilio Sousa.

Reviewer 2 Report

The authors in this work study the entanglement dynamics (characterized by negativity) of two two-level atoms, both interact with the two counter-propagating whispering gallery modes of a microtoroidal resonator, by designing the specific initial condition: 1) the two atoms are in a given pure entangled state, whose entanglement degree can be preset by the modulation of the relative coefficient of the state; 2) the two resonator modes are in a product state--each in a thermal state, whose average photon number is related to the temperature of the environment; 3) the two resonator modes may couple or may not couple with each other due to the referred ideal and non-ideal cavity regimes. The entanglement dynamics of the two atoms can then be obtained by tailoring the interaction time and by tracing out the degree of freedom of the resonator modes. The studied results show some interesting entanglement phenomena such as two-atom entanglement surviving even at high temperatures. However, some comments need to be addressed by the authors before the paper could be considered for publication.
1. As one of the main interactions involved in the system's Hamiltonian, the coupling between the two resonator modes is referred to as the non-ideal cavity regime, which needs to be importantly clarified for the readers to understand.
2. The temperature is related to the average photon of the thermal field where the resonator modes are in, this can be judged by the average photon number itself defined in Eq. (4), by knowing beforehand the resonator mode frequencies. This point also needs be clarified for understanding easily, because the temperature (thus the average photon number) influences the entanglement greatly throughout the temporal process.
3. There are many unreasonable expressions (or syntax errors) in the text, which need the author to revise and rearrange.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Generation of entanglement between two two-level
atoms coupled to a microtoroidal cavity via thermal
field
Emilio H. S. Sousa* and J. A. Roversi

A study of the generation of entanglement and quantum state transfer is proposed for a system comprising a pair of two-level dipole-dipole interacting atoms coupled to a microtoroidal resonator. In this case, the two atom are individually coupled with the two WGMs (Whispering Gallery Modes) of a microtoroidal resonator through their evanescent fields. We compute the atom-atom entanglement using the negativity for several parameter sets of the system. Two cases are investigated, the ideal and non-ideal cavity regimes, where the latter allows the direct coupling between the WGMs of the resonator.

Results show that entanglement is strongly dependent on the dipole coupling strength and the mean photon number of the thermal field. In this case, we show that, differently from the ideal case (n¯ = 0), via adjusting parameters of the system, the atomic entanglement still survives even at high temperatures, in contrast to schemes based on single mode cavity QED.

I believe the study might result of interest for understanding of dissipative effects, such as thermal fields, for the development of quantum information technologies.

My recommendation is to accept this work in its present form.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors more or less replied to my first and second comments. However, the English of the whole text still needs to be further improved as to meet the high standards of the journal.