Searching for axions with quantum interferometry

arXiv:2604.13181 · hep-ph, astro-ph.CO, physics.atom-ph, quant-ph · Submitted 2026-04-14 · Read on arXiv

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Introduction to the show: ident: Astrophysics Radio. Generated commentary on the latest astrophysics papers.

Vera: We're looking at the paper: "Searching for axions with quantum interferometry".

Jocelyn: Here's the gist of the paper. The gist The authors show that axion-photon interactions can imprint both Aharonov-Bohm (AB) and Berry phases in experimentally motivated quantum setups.

Vera: How it works)&pg2 A coherently oscillating axion dark matter background, the induced effective current generates a time dependent magnetic flux in an rf-SQUID, leading to a measurable voltage signal through the Josephson phase The paper investigates an axion-induced AB phase arising in superconducting circuits where an axion field modifies the EM field configuration, resulting in a time dependent shift in the magnetic flux and thus a measurable voltage signal through the Josephson phase How it works)&pg3 In an rf-SQUID (radio frequency-Superconducting Quantum Interference Device) configuration, a Josephson junction (JJ) embedded in a superconducting loop provides a gauge-invariant phase difference that is directly sensitive to the magnetic flux threading the loop The axion effective current density changes the flux in the SQUID loop which yields additional contribution to the Josephson phase as δφa(t) = 2π Φ0 δΦa(t) This allows for a direct probe of axion-photon interactions using superconducting circuits The sensitivity to the axion-photon coupling can be obtained as g min aγγ ≃ S sqrt(Φ / Teff)√2ρDMMeffΦB0 with projected sensitivity that can improve on existing limits in that parameter space by roughly one to two orders of magnitude The sensitivity is approximately independent of ma when the axion coherence time exceeds the observation time, τc > T For larger masses, where the coherence time becomes shorter than the integration time, τc < T, the sensitivity degrades as g min aγγ ∝ m a(1/2) The projected sensitivity improves upon the currently existing bounds by approximately one to two orders of magnitude The rf-SQUID setup provides broadband coverage in the sense that it can probe a wide range of axion masses without requiring resonant retuning At the same time, for each fixed ma, the axion DM signal remains intrinsically narrowband The resulting sensitivity curve is thus broadband in coverage, while the signal at each mass point is a narrow spectral feature In FIG.

Jocelyn: 2, we present the projected sensitivity to the axion-photon coupling g aγγ as a function of the ax-ion mass ma(eV) The projected reach is shown together with existing bounds from laboratory experiments

16: , astrophysical observations

16: , and DM direct detection searches, including ADMX

16: , QUAX

41, 68–71: , RBF+UF

72–75: , ORGAN

44, 76–78: , ADMX SLIC

27: , and BASE

79: For ma ≲ 4 × 10−15 eV, the sensitivity degrades due to the low frequency 1/f excess noise, assuming a knee frequency f1/f = 1 Hz At larger masses, the reach weakens once the axion coherence time becomes shorter than the integration time, which occurs around ma ≃ 7 × 10−10 eV In addition, the sensitivity is further suppressed at ma ≃ 4 × 10−8 eV due to the finite detector bandwidth, corresponding to a response cutoff frequency fc = 10 MHz The projected sensitivity improves upon the currently existing bounds by approximately one to two orders of magnitude In FIG.

Vera: 2, we present the projected sensitivity to the axion-photon coupling g aγγ as a function of the ax-ion mass ma(eV) The QCD axion band is also shown

16: How it works)&pg7 In this section, we show that the axion field may induce an oscillatory magnetic flux in the superconducting pickup region via axion electrodynamics The axionphoton interaction produces a gauge invariant phase shift of the superconducting condensate equivalent to a time dependent AB phase in the rf-SQUID The resulting voltage can be analyzed in the frequency domain using a fast Fourier transform (FFT) to identify the characteristic modulation induced by the axion field The axion-induced flux becomes δΦa = gaγγ a Meff˙ effΦB0, ΦB0 ≡ Z Σ B0 · dS, where Σ is the cross-section through which the effective current threads, and Aeff is the effective area of the pickup region The resulting magnetic flux is coupled to the SQUID loop through mutual inductance The axionic contribution to the voltage readout becomes δVa(t) = d/dt δΦa(t) The amplitude of the axion-induced DM flux is obtained from Eq.

Title and authors: Vera: So we're looking at this paper, "Searching for axions with quantum interferometry," and the authors are Tanmay Kumar Poddar and Michael Spannowsky from Durham University and Karlsruhe Institute of Technology.

Jocelyn: It sounds like they're looking at a completely different way to search for axions, moving away from the usual magnetic field searches we see in things like ADMX.

Vera: Exactly. Instead of just looking for a static magnetic field interaction, they're proposing using quantum interference setups to look for axion-photon interactions that create phase shifts.

Subrahmanyan: That suggests they are going beyond simple energy density constraints and looking at how the axion field modifies the fundamental wave behavior in a quantum circuit.

Jocelyn: It’s about using these quantum setups to imprint both Aharonov-Bohm phases and Berry phases, which is a big deal because those are geometric properties of the path taken in Hilbert space.

Vera: So they're setting up experiments where the axion background causes a time-dependent magnetic flux in an rf-SQUID, and that flux translates into a measurable voltage signal through the Josephson phase.

Jocelyn: That’s a really cool setup because it connects the axion field directly to something we can measure with superconducting circuits.

Subrahmanyan: It shifts the focus from just looking at how dark matter interacts gravitationally to how it couples electromagnetically in a specific, measurable way.

The paper's summary: Vera: Okay, so what the paper actually does is investigate an axion-induced Aharonov-Bohm phase arising specifically in superconducting circuits.

Jocelyn: They show that the axion field modifies the electromagnetic field configuration, and this results in a time-dependent shift in the magnetic flux threading that SQUID loop.

Vera: That time dependence is key because it allows them to get a measurable voltage signal through the Josephson phase, which is what you read out from a superconductor.

Subrahmanyan: They are essentially using the axion dark matter background as a coherent oscillating field to generate this effect in an rf-SQUID configuration.

Jocelyn: The paper says that the axion effective current density changes this flux, and they write down the mathematical description of this extra flux as delta phi a equals two pi phi zero delta phi a(t) based on their setup.

Vera: And they then calculate how sensitive this whole thing is to the axion-photon coupling constant g a gamma gamma.

Jocelyn: They project that for representative benchmarks, this AB phase search reaches a minimum axion-photon coupling g min a gamma gamma of about seven point eight times ten to negative fourteen GeV negative one <ref:2604.13181#pg1,for representative benchmarks, this AB phase search reaches>.

Subrahmanyan: That gives them a projected sensitivity at an axion mass of around ten to the power minus ten eV, and they suggest that this could improve existing limits in that parameter space by roughly one to two orders of magnitude.

The paper's improvements: Vera: Now, the paper doesn't just stop there; they look at how we can make these searches better. They identify a few ways to improve the sensitivity for future work.

Jocelyn: One improvement they point out is that if you use Berry phase interferometry, you could perform a proof-of-principle phase-based probe of meV-scale axions even if they aren't dark matter.

Vera: They say this involves accurately extracting the geometric Berry phase from Mach-Zehnder interferometer measurements, which gives them sensitivity estimates derived from an equation they call Eq. (forty-two).

Subrahmanyan: That's interesting because that projects a reach that could improve on existing limits by roughly one to two orders of magnitude for axion masses around two meV at conservative tabletop benchmarks, moving beyond the limits of conventional resonant detection techniques like THz cavities in that mass range.

Jocelyn: So, if we use this Berry phase approach, we’re looking at a potentially different kind of probe entirely compared to the direct flux measurements they were focusing on earlier.

Vera: And they also discuss how the sensitivity depends on the axion mass itself. They find that for larger masses, where the coherence time becomes shorter than the observation time, which happens around ten to the power minus ten eV, their sensitivity degrades as g min a gamma gamma is proportional to ma to one over two.

Subrahmanyan: That's a clear limitation on their method; for heavier axions, you start losing sensitivity because the axion field doesn't have enough time to build up the effect before it changes.

Conclusion: Jocelyn: So, to wrap up this paper, they show that using an rf-SQUID setup can be a way to see axion dark matter through a time-dependent magnetic flux signal.

Vera: They found that for the specific parameters they used, their minimum detectable coupling is about seven point eight times ten to negative fourteen GeV negative one at an axion mass of ten to the power minus ten eV <ref:2604.13181#pg1>.

Subrahmanyan: The implication for cosmology is that this probes a specific region in the axion mass spectrum, and if it confirms those limits, it constrains the allowed parameter space for axions that couple to photons.

Jocelyn: They also mentioned that they can see broadband coverage in terms of axion masses without needing to retune the device for different masses at once.

Vera: The main thing is that this method provides a way to test axion-photon interactions using superconducting circuits, which is a very different experimental avenue from what we usually do.

Subrahmanyan: It’s valuable because it opens up access to axions in mass ranges where other detection methods might be less sensitive, and the projected improvement of one to two orders of magnitude is what makes this work for structure formation studies.

Jocelyn: That's a good summary of the paper "Searching for axions with quantum interferometry." We'll take a quick break before we look at some other stuff next.

Institute for Particle Physics Phenomenology (IPPP) · Institute for Theoretical Physics, Karlsruhe Institute of Technology · Institute for Quantum Materials and Technologies, Karlsruhe Institute of Technology

hep-ph, astro-ph.CO, physics.atom-ph, quant-ph

Submitted: 2026-04-14

Updated: 2026-04-14

Comments: 19 pages, 4 figures, comments are welcome

Project page: https://cajohare.github.io/AxionLimits

License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/

Importance score: 69/100

The gist: The gist The authors show that axion-photon interactions can imprint both Aharonov-Bohm (AB) and Berry phases in experimentally motivated quantum setups.

Key concepts

Aharonov-Bohm (AB) Phase
This is a quantum mechanical phase shift that occurs when a charged particle moves through a region where there is no net magnetic field, but the vector potential is non-zero. In this context, the axion field modifies the effective magnetic flux threading a superconducting loop, creating an AB phase that can be measured.
rf-SQUID
A radio frequency Superconducting Quantum Interference Device is a circuit used to measure magnetic flux with high sensitivity. It consists of a superconducting loop interrupted by Josephson junctions. The axion field induces a time-dependent change in the magnetic flux threading this loop, which is directly translated into a measurable voltage signal via the Josephson phase.
Berry Phase
The Berry phase is an extra geometric phase acquired by a quantum system when its parameters are slowly varied around a closed path in parameter space. The paper shows that axion-photon interactions can induce this Berry phase in superconducting circuits, providing an alternative probe for axion physics beyond simple flux measurements.
Axion-Photon Coupling ($g_{a ext{γγ}}$)
This parameter quantifies the strength of the interaction between the axion field and photons. The sensitivity analysis derives a minimum detectable coupling constant ($g_{ ext{min}}_{a ext{γγ}}$) based on SQUID noise limits, projecting reach improvements of one to two orders of magnitude compared to existing experimental bounds.

Terminology

Summary

The gist The authors show that axion-photon interactions can imprint both Aharonov-Bohm (AB) and Berry phases in experimentally motivated quantum setups.

How it works

**)&pg2 A coherently oscillating axion dark matter background, the induced effective current generates a time dependent magnetic flux in an rf-SQUID, leading to a measurable voltage signal through the Josephson phase **

The paper investigates an axion-induced AB phase arising in superconducting circuits where an axion field modifies the EM field configuration, resulting in a time dependent shift in the magnetic flux and thus a measurable voltage signal through the Josephson phase

How it works

**)&pg3 In an rf-SQUID (radio frequency-Superconducting Quantum Interference Device) configuration, a Josephson junction (JJ) embedded in a superconducting loop provides a gauge-invariant phase difference that is directly sensitive to the magnetic flux threading the loop The axion effective current density changes the flux in the SQUID loop which yields additional contribution to the Josephson phase as δφa(t) = 2π Φ0 δΦa(t) This allows for a direct probe of axion-photon interactions using superconducting circuits The sensitivity to the axion-photon coupling can be obtained as g min aγγ ≃ S sqrt(Φ / Teff)√2ρDMMeffΦB0 with projected sensitivity that can improve on existing limits in that parameter space by roughly one to two orders of magnitude The sensitivity is approximately independent of ma when the axion coherence time exceeds the observation time, τc > T For larger masses, where the coherence time becomes shorter than the integration time, τc < T, the sensitivity degrades as g min aγγ ∝ m a(1/2) The projected sensitivity improves upon the currently existing bounds by approximately one to two orders of magnitude The rf-SQUID setup provides broadband coverage in the sense that it can probe a wide range of axion masses without requiring resonant retuning At the same time, for each fixed ma, the axion DM signal remains intrinsically narrowband The resulting sensitivity curve is thus broadband in coverage, while the signal at each mass point is a narrow spectral feature In FIG. 2, we present the projected sensitivity to the axion-photon coupling g aγγ as a function of the ax-ion mass ma(eV) The projected reach is shown together with existing bounds from laboratory experiments [16], astrophysical observations [16], and DM direct detection searches, including ADMX [16], QUAX [41, 68–71], RBF+UF [72–75], ORGAN [44, 76–78], ADMX SLIC [27], and BASE [79] For ma ≲ 4 × 10−15 eV, the sensitivity degrades due to the low frequency 1/f excess noise, assuming a knee frequency f1/f = 1 Hz At larger masses, the reach weakens once the axion coherence time becomes shorter than the integration time, which occurs around ma ≃ 7 × 10−10 eV In addition, the sensitivity is further suppressed at ma ≃ 4 × 10−8 eV due to the finite detector bandwidth, corresponding to a response cutoff frequency fc = 10 MHz The projected sensitivity improves upon the currently existing bounds by approximately one to two orders of magnitude In FIG. 2, we present the projected sensitivity to the axion-photon coupling g aγγ as a function of the ax-ion mass ma(eV) The QCD axion band is also shown [16] **

How it works

**)&pg7 In this section, we show that the axion field may induce an oscillatory magnetic flux in the superconducting pickup region via axion electrodynamics The axionphoton interaction produces a gauge invariant phase shift of the superconducting condensate equivalent to a time dependent AB phase in the rf-SQUID The resulting voltage can be analyzed in the frequency domain using a fast Fourier transform (FFT) to identify the characteristic modulation induced by the axion field The axion-induced flux becomes δΦa = gaγγ a Meff˙ effΦB0, ΦB0 ≡ Z Σ B0 · dS, where Σ is the cross-section through which the effective current threads, and Aeff is the effective area of the pickup region The resulting magnetic flux is coupled to the SQUID loop through mutual inductance The axionic contribution to the voltage readout becomes δVa(t) = d/dt δΦa(t) The amplitude of the axion-induced DM flux is obtained from Eq. (7), as δΦ 0 a = gaγγ p / 2ρDMMeffΦB0 To estimate the sensitivity to the axion-photon coupling, we consider the SQUID has the flux noise spectral density S sqrt(Φ) (in Φ0/√Hz or Wb/√Hz) The minimum detectable flux is given by δΦ min = S sqrt(Φ) / √Teff Thus, the sensitivity to the axion-photon coupling can be obtained as g min aγγ ≃ S sqrt(Φ) Teff√2ρDMMeffΦB0 This follows directly by equating the axion-induced flux amplitude in Eq. (18) to the minimum detectable flux set by the SQUID noise in Eq. (19) We take the effective inductance to be Meff = 50 nH and the background magnetic flux ΦB0 = 5 T · 5 cm2 The local DM density is assumed to be ρDM = 0.3 GeV cm−3[64] Hence, we obtain the sensitivity on gaγγ from Eq. (20) as g min aγγ ≃ 7.8 × 10−14 GeV−1 S sqrt(Φ) / 0.

Improvements for AI systems

  1. Increase Sensitivity to Ultralight Axions via Berry Phase Interferometry: The improved AI system can perform a proof-of-principle phase-based probe of meV-scale axions even when they do not constitute the dark matter, by accurately extracting the geometric (Berry) phase from Mach-Zehnder interferometer measurements, as detailed in Section III and IV. This allows for sensitivity estimates derived from Eq. (42), projecting a reach that can improve on existing limits by roughly one to two orders of magnitude for axion masses around 2 meV at conservative tabletop benchmarks, moving beyond the limits of conventional resonant detection techniques like THz cavities in this mass range.</item

  2. Implement Superconducting Circuit-Based Axion Detection: The improved AI system can design and analyze the readout electronics for an rf-SQUID setup to detect axion dark matter through a time-dependent magnetic flux, yielding a measurable voltage signal through the Josephson phase. This capability allows the system to utilize Equation (20) for coupling sensitivity, projecting a reach of approximately 7.8 × 10−14 GeV−1 at axion masses around 10−10 eV, identifying this as the most immediately competitive outcome of our analysis.</item

  3. Train AI on Three-Level System Dynamics: The improved AI system can model and analyze a three level photon-axion quasiparticle (AQP)-axion system realized in a topological magnetic insulator to find a potentially measurable THz Berry phase dominated by the AQP sector. This allows the system to utilize the coupled dynamics described by the matrix form in Eq. (56) and evaluate observables like Equation (104), identifying a potentially measurable standard physics signal in topological media.

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