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Phonon Pumping by Modulating the Ultrastrong Vacuum

by Fabrizio Minganti, Alberto Mercurio, Fabio Mauceri, Marco Scigliuzzo, Salvatore Savasta, and Vincenzo Savona

This is not the latest submitted version.

Submission summary

Authors (as registered SciPost users): Alberto Mercurio · Fabrizio Minganti
Submission information
Preprint Link: scipost_202405_00009v1  (pdf)
Date submitted: 2024-05-06 13:41
Submitted by: Minganti, Fabrizio
Submitted to: SciPost Physics
Ontological classification
Academic field: Physics
  • Quantum Physics
Approach: Theoretical


The vacuum (i.e., ground state) of a system in ultrastrong light-matter coupling contains particles that cannot be emitted without any dynamical perturbation, and thus called virtual. We propose a protocol for inducing and observing real mechanical excitations of a mirror enabled by the virtual photons in the ground state of a tripartite system, where a resonant optical cavity is ultrastrongly coupled to a two-level system (qubit) and, at the same time, optomechanically coupled to a mechanical resonator. Real phonons are coherently emitted when the frequency of the two-level system is modulated at a frequency comparable to that of the mechanical resonator and, therefore much lower than the optical frequency. We demonstrate that this hybrid effect is a direct consequence of the virtual photon population in the ground state. Within a classical physics analogy, attaching a weight to a spring only changes its resting position, whereas dynamically modulating the weight makes the system oscillate. In our case, however, the weight is the vacuum itself. We propose and accurately characterize a hybrid superconducting-optomechanical setup based on available state-of-the-art technology, where this effect can be experimentally observed.

Author indications on fulfilling journal expectations

  • Provide a novel and synergetic link between different research areas.
  • Open a new pathway in an existing or a new research direction, with clear potential for multi-pronged follow-up work
  • Detail a groundbreaking theoretical/experimental/computational discovery
  • Present a breakthrough on a previously-identified and long-standing research stumbling block
Current status:
Has been resubmitted

Reports on this Submission

Anonymous Report 2 on 2024-6-7 (Invited Report)


This is a very original and interesting study, which provides insights into an effect generated by modulating the ultrastrong vacuum limit of cavity QED. I strongly recommend it for publication in SciPost, after the authors clarify the issues listed in the report below.


The manuscript is reasonably strong and I do not see major weaknesses. Some minor weak points (relatively easy to fix) are listed below.


Referee Report for the manuscript titled:

Phonon Pumping by Modulating the Ultrastrong Vacuum.

This is a very original and interesting study, which provides insights into an effect generated by modulating the ultrastrong vacuum limit of cavity QED. I strongly recommend it for publication in SciPost, after the authors clarify the following issues:

1. Typically, circuit QED systems are affected by pure dephasing. Why is pure dephasing missing in the dissipative terms?

2. What happens if we use a different qubit (e.g., a Flux qubit)? Would there be any advantage to using a different configuration?

3. The effect is visible according to the authors' simulation and estimation of experimentally achievable parameters. What would make the effect even more visible to allow for an even easier experimental implementation?

4. It would be preferable if the authors consider citing additional references on related effects obtained by modulating the quantum vacuum.

In summary, this is an excellent work, which could be published in SciPost after the authors consider the suggested improvements listed above.

Requested changes

Please see the report, listing requested changes.


Publish (surpasses expectations and criteria for this Journal; among top 10%)

  • validity: top
  • significance: high
  • originality: high
  • clarity: high
  • formatting: excellent
  • grammar: excellent

Anonymous Report 1 on 2024-6-5 (Invited Report)


1 - proposal of a novel effect

2- The proposed effect is quite straightforward and there is no reason to doubt the validity of the predictions. The paper contains an analytical approximation to the phonon number that is validated by full numerical simulations.

3- An experimentally realistic implementation of the predicted effect with superconducting circuits is proposed.

4- The paper is clearly written and easy to follow, even for non-experts in the field. The relevant literature is well cited.

5- The derivations of the model and results are clearly presented in the appendices.


1- the predicted effect is not very large in the proposed superconducting circuit system. Since this is the theoretical and therefore typically idealised estimate, there is some doubt whether this effect is experimentally observable.


By presenting a novel effect by considering a optomechanical system in the strongly coupling regime, the manuscript meets on of the expectations for publication in SciPost.

I therefore recommend the publication of the manuscript.

Requested changes

1- line 264, there is a reference to an equation that is missing

2- line 200-201: in the outlook, it is said that the authors plan to investigate to excited optical excitations by driving the mirrors. To me, it seems that this outlook faces the problem of generating mechanical vibrations that are fast enough to be resonant with the optical modes, a condition that seems not to be facilitated by working in the USC regime. The authors could reconsider whether this outlook is realistic and refer to systems where this resonance condition could be met.


Publish (meets expectations and criteria for this Journal)

  • validity: high
  • significance: good
  • originality: good
  • clarity: high
  • formatting: excellent
  • grammar: excellent

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