Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

IEEE Transactions on Applied Superconductivity

Coherent Quantum Network of Superconducting Qubits as a Highly Sensitive Detector of Microwave Photons for Searching of Galactic Axions

Claudio D. Gatti, M. Affronte, Alexander G. Balanov, Claudio Bonizzoni, G. Brida, F. Chiarello, Nassim Chikhi, G. Coda, Alessandro D’Elia, Daniele Di Gioacchino, Emanuele Enrico, Ilya Eremin, Mikkel Ejrnaes, E. V. Il’ichev, Luca Fasolo, M. V. Fistul, Alberto Ghirri, Angelo Greco, Carlo Ligi, Grace Maccarone, Alice Meda, Patrick Navez, G. Oelsner, M. Rajteri, A. Rettaroli, B. Ruggiero, Sergey E. Savel'ev, P. Silvestrini, S. Tocci, Alexey Vladimirovich Ustinov, Paolo Vanacore, Alexandre M. Zagoskin, Mikhail Lisitskiy

Published Apr 6, 2023• 4 citations
Publisher

Abstract

We propose a novel approach to detect a low power microwave signal with a frequency of the order of several GHz based on a coherent collective response of quantum states occurring in a superconducting qubits network (SQN). An SQN composes of a large number of superconducting qubits embedded in a low-dissipative superconducting resonator. Our theory predicts that an SQN interacting with the off-resonance microwave radiation, demonstrates the collective alternating current Stark effect that can be measured even in the limit of single photon counting. A design of the layout of three terminals SQN detectors containing 10 flux qubits weakly coupled to a low-dissipative R-resonator and T-transmission line was developed. The samples were fabricated by Al-based technology with Nb resonator. The SQN detector was tested in terms of microwave measurements of scattering parameters and two-tone spectroscopy. A substantial shift of the frequency position of the transmission coefficient drop induced by a second tone pump signal was observed, and this effect clearly manifests a nonlinear multiphoton interaction between the second-tone microwave pump signal and an array of qubits.

DOI
10.1109/tasc.2023.3263807

Related papers

Superconducting Qubit Network as a Single Microwave Photon Detector for Galactic Axion Search

Emanuele Enrico, C. Bonavolontà, G. Brida +13 more

Experimental search of galactic axions requires detection of single photons in the microwave range. We work on a novel approach to detect single microwave photons based on a coherent collective response of quantum states occurring in a superconducting qubit network (SQN) embedded in a lowdissipative superconducting resonator. We propose a two resonators detector configuration with two parallel resonators without common part and with separated input and output terminals. The device consists of a low-dissipative resonator with embedded SQN in which microwave photons arrive (“signal resonator”), and a transmission line for measuring the frequency dependent transmission coefficient demonstrating resonant drops at the qubit frequencies (“readout resonator”). In comparison with T-type three terminal device recently proposed and investigated by us, the device with two resonators with separated input and output terminals doesn't contain common part of both resonators and exclude an unwanted noise from measurement readout circuits to the signal resonator. A layout of two resonators four terminal SQN detectors containing 5 flux qubits weakly coupled to a low-dissipative signal and readout resonator was developed and optimized. The samples were fabricated by Manhattan Al-based technology with Nb resonator circuits. The SQN detector was experimentally tested in terms of microwave measurements of scattering parameters of both resonators, and crosstalk properties. Comparison of experimental data with results of the simulations permits one to conclude that the electromagnetic conditions of the fundamental resonant peak of 8.5 GHz of both resonators aren't affected by the crosstalk phenomenon and their performances provided by the design remain not altered for correct device operation

IEEE Transactions on Applied Superconductivity•Dec 8, 2023•1 citation

Bose condensation and Bogoliubov excitation in resonator-embedded superconducting qubit network

Patrick Navez, Valentina Di Meo, Berardo Ruggiero +12 more

Superconducting qubit networks (SQNs) embedded in a low-dissipative resonator is a promising device allowing one not only to establish the collective quantum dynamics on a macroscopic scale but also to greatly enhance the sensitivity of detectors of microwave photons. A quantum ac Stark effect provided by coupling between an SQN and microwave photons of a resonator, leads to a strong nonlinear interaction between photons. Here, we present a two-tone spectroscopy experiment in which a set of 10 superconducting flux qubits is coupled to the input R- resonator and the output T- transmission line. An external microwave pump field close to the resonance frequency populates macroscopically the resonator mode as a Bose-Einstein condensate, while a second probe beam scans the resonances referred also as Bogoliubov-like excitations. The corresponding excitation frequency measured from the transmission coefficient, |S21(f)| displays an abrupt change of the resonant dip position once the power of the pump field overcomes a critical value Pcr. This sharp shift occurs in a narrow region of pump frequencies, and can be tuned by an applied magnetic field. It is a signature of bistability of the photon number inside the resonator, in agreement with theory.

quant-pharXiv:2601.15101•Jan 22, 2026•0 citations

Stepping Closer to Pulsed Single Microwave Photon Detectors for Axions Search

Alessandro D’Elia, A. Rettaroli, S. Tocci +23 more

Axions detection requires the ultimate sensitivity down to the single-photon limit. In the microwave region, this corresponds to energies in the yJ range. This extreme sensitivity has to be combined with an extremely low dark-count rate since the probability of axions conversion into microwave photons is supposed to be very low. To face this complicated task, we followed two promising approaches that both rely on the use of superconducting devices based on the Josephson effect. The first one is to use a single Josephson junction (JJ) as a switching detector (i.e., exploiting the superconducting to normal state transition in the presence of microwave photons). We designed a device composed of a coplanar waveguide terminated on a current-biased JJ. We tested its efficiency to pulsed (pulse duration 10 ns) microwave signals since this configuration is closer to an actual axions search experiment. We show how our device is able to reach detection capability of the order of ten photons with the frequency of 8 GHz. The second approach is based on an intrinsically quantum device formed by two resonators coupled only via a superconducting qubit network. This approach relies on quantum nondemolition measurements of the resonator photons. We show that by injecting radiofrequency power into the resonator, the frequency position of the resonant drop in the transmission coefficient (S21) can be modulated up to 4 MHz. We anticipate that, once optimized, both the devices have the potential to reach single-photon sensitivity.

arXiv:2302.07556•IEEE Transactions on Applied Superconductivity•Nov 4, 2022•16 citations

Quantum dynamics of disordered arrays of interacting superconducting qubits: Signatures of quantum collective states

M. V. Fistul, Oliver Neyenhuys, A. B. Bocaz +2 more

We study theoretically the collective quantum dynamics occurring in various interacting superconducting qubit arrays (SQAs) in the presence of a spread of individual qubit frequencies. The interaction is provided by mutual inductive coupling between adjacent qubits (short-range Ising interaction) or inductive coupling to a low-dissipative resonator (long-range exchange interaction). In the absence of interaction, the Fourier transform of the temporal correlation function of the total polarization ($z$ projection of the total spin), i.e., the dynamic susceptibility $C(\ensuremath{\omega})$, demonstrates a set of sharp small magnitude resonances corresponding to the transitions of individual superconducting qubits. We show that even a weak interaction between qubits can overcome the disorder with a simultaneous formation of the collective excited states. This collective behavior manifests itself by a single large resonance in $C(\ensuremath{\omega})$. In the presence of a weak nonresonant microwave photon field in the low-dissipative resonator, the positions of dominant resonances depend on the number of photons, i.e., the collective ac Stark effect. Coupling of an SQA to the transmission line allows a straightforward experimental access of the collective states in microwave transmission experiments and, at the same time, to employ SQAs as sensitive single-photon detectors.

arXiv:2111.14732•Physical review. B./Physical review. B•Mar 31, 2022•12 citations

Bose-Einstein condensation and collective Bogoliubov excitations of microwave photons in superconducting quantum electrodynamics circuits

Valentina Di Meo, Patrick Navez, B. Ruggiero +13 more

Abstract The seminal phenomenon of the Bose-Einstein condensation has been observed on a large variety of physical platforms, e.g., superfluid helium, fermions with attractive interactions, quasiparticles in solids, and ultracold atomic gases. Recently, the Bose–Einstein condensation of non-interacting photons in an optical microcavity has been confirmed experimentally. Here, we report the experimental observation of Bose-Einstein like condensation and collective Bogoliubov excitations in a low dissipative microwave resonator with embedded superconducting quantum network composed of multiple flux qubits. Under strong coherent pumping the resonator mode becomes macroscopically populated, giving rise to hybridized photon–qubit collective modes. The Bogoliubov-like collective excitations appearing in a response to a nearby-frequency probe tone, accompanied by pronounced bistability and hysteresis in the measured transmission coefficient, provide the first experimental evidence of a Bose–Einstein–like condensate of microwave photons on a superconducting circuit platform. A theoretical framework based on Gross-Pitaevskii formalism and taking into account the ac Stark effect inducing the effective interaction between photons, quantitatively reproduces the experimental observations and identifies the regime of appearance of microwave Bogoliubov excitations. These results establish a proof of principle for exploiting driven collective states in superconducting circuits as a platform for quantum-limited microwave detection and engineered many-body photonic systems for quantum information processing.

•Aug 7, 2026•0 citations

Local sensing with the multilevel ac Stark effect

Andre Schneider, Jochen Braumüller, Lingzhen Guo +5 more

Analyzing weak microwave signals in the GHz regime is a challenging task if the signal level is very low and the photon energy widely undefined. A superconducting qubit can detect signals in the low photon regime, but due to its discrete level structure, it is only sensitive to photons of certain energies. With a multilevel quantum system (qudit) in contrast, the unknown signal frequency and amplitude can be deduced from the higher level ac Stark shift. The measurement accuracy is given by the signal amplitude, its detuning from the discrete qudit energy level structure, and the anharmonicity. We demonstrate an energy sensitivity in the order of ${10}^{\ensuremath{-}3}$ with a measurement range of more than $1\phantom{\rule{0.28em}{0ex}}\mathrm{GHz}$. Here, using a transmon qubit, we experimentally observe shifts in the transition frequencies involving up to three excited levels. These shifts are in good agreement with an analytic circuit model and master equation simulations. For large detunings, we find the shifts to scale linearly with the power of the applied microwave drive. Exploiting the effect, we demonstrated a power meter which makes it possible to characterize the microwave transmission from source to sample.

arXiv:1801.05144•Physical Review A•Jun 22, 2018•35 citations
We propose a novel approach to detect a low power microwave signal with a frequency of the order of several GHz based on a coherent collective response of quantum states occurring in a superconducting qubits network (SQN). An SQN composes of a large number of superconducting qubits embedded in a low-dissipative superconducting resonator. Our theory predicts that an SQN interacting with the off-resonance microwave radiation, demonstrates the collective alternating current Stark effect that can be measured even in the limit of single photon counting. A design of the layout of three terminals SQN detectors containing 10 flux qubits weakly coupled to a low-dissipative R-resonator and T-transmission line was developed. The samples were fabricated by Al-based technology with Nb resonator. The SQN detector was tested in terms of microwave measurements of scattering parameters and two-tone spectroscopy. A substantial shift of the frequency position of the transmission coefficient drop induced by a second tone pump signal was observed, and this effect clearly manifests a nonlinear multiphoton interaction between the second-tone microwave pump signal and an array of qubits.
Experimental search of galactic axions requires detection of single photons in the microwave range. We work on a novel approach to detect single microwave photons based on a coherent collective response of quantum states occurring in a superconducting qubit network (SQN) embedded in a lowdissipative superconducting resonator. We propose a two resonators detector configuration with two parallel resonators without common part and with separated input and output terminals. The device consists of a low-dissipative resonator with embedded SQN in which microwave photons arrive (“signal resonator”), and a transmission line for measuring the frequency dependent transmission coefficient demonstrating resonant drops at the qubit frequencies (“readout resonator”). In comparison with T-type three terminal device recently proposed and investigated by us, the device with two resonators with separated input and output terminals doesn't contain common part of both resonators and exclude an unwanted noise from measurement readout circuits to the signal resonator. A layout of two resonators four terminal SQN detectors containing 5 flux qubits weakly coupled to a low-dissipative signal and readout resonator was developed and optimized. The samples were fabricated by Manhattan Al-based technology with Nb resonator circuits. The SQN detector was experimentally tested in terms of microwave measurements of scattering parameters of both resonators, and crosstalk properties. Comparison of experimental data with results of the simulations permits one to conclude that the electromagnetic conditions of the fundamental resonant peak of 8.5 GHz of both resonators aren't affected by the crosstalk phenomenon and their performances provided by the design remain not altered for correct device operation
Superconducting qubit networks (SQNs) embedded in a low-dissipative resonator is a promising device allowing one not only to establish the collective quantum dynamics on a macroscopic scale but also to greatly enhance the sensitivity of detectors of microwave photons. A quantum ac Stark effect provided by coupling between an SQN and microwave photons of a resonator, leads to a strong nonlinear interaction between photons. Here, we present a two-tone spectroscopy experiment in which a set of 10 superconducting flux qubits is coupled to the input R- resonator and the output T- transmission line. An external microwave pump field close to the resonance frequency populates macroscopically the resonator mode as a Bose-Einstein condensate, while a second probe beam scans the resonances referred also as Bogoliubov-like excitations. The corresponding excitation frequency measured from the transmission coefficient, |S21(f)| displays an abrupt change of the resonant dip position once the power of the pump field overcomes a critical value Pcr. This sharp shift occurs in a narrow region of pump frequencies, and can be tuned by an applied magnetic field. It is a signature of bistability of the photon number inside the resonator, in agreement with theory.
Axions detection requires the ultimate sensitivity down to the single-photon limit. In the microwave region, this corresponds to energies in the yJ range. This extreme sensitivity has to be combined with an extremely low dark-count rate since the probability of axions conversion into microwave photons is supposed to be very low. To face this complicated task, we followed two promising approaches that both rely on the use of superconducting devices based on the Josephson effect. The first one is to use a single Josephson junction (JJ) as a switching detector (i.e., exploiting the superconducting to normal state transition in the presence of microwave photons). We designed a device composed of a coplanar waveguide terminated on a current-biased JJ. We tested its efficiency to pulsed (pulse duration 10 ns) microwave signals since this configuration is closer to an actual axions search experiment. We show how our device is able to reach detection capability of the order of ten photons with the frequency of 8 GHz. The second approach is based on an intrinsically quantum device formed by two resonators coupled only via a superconducting qubit network. This approach relies on quantum nondemolition measurements of the resonator photons. We show that by injecting radiofrequency power into the resonator, the frequency position of the resonant drop in the transmission coefficient (S21) can be modulated up to 4 MHz. We anticipate that, once optimized, both the devices have the potential to reach single-photon sensitivity.
We study theoretically the collective quantum dynamics occurring in various interacting superconducting qubit arrays (SQAs) in the presence of a spread of individual qubit frequencies. The interaction is provided by mutual inductive coupling between adjacent qubits (short-range Ising interaction) or inductive coupling to a low-dissipative resonator (long-range exchange interaction). In the absence of interaction, the Fourier transform of the temporal correlation function of the total polarization (zzz projection of the total spin), i.e., the dynamic susceptibility $C(\ensuremath{\omega})$, demonstrates a set of sharp small magnitude resonances corresponding to the transitions of individual superconducting qubits. We show that even a weak interaction between qubits can overcome the disorder with a simultaneous formation of the collective excited states. This collective behavior manifests itself by a single large resonance in $C(\ensuremath{\omega})$. In the presence of a weak nonresonant microwave photon field in the low-dissipative resonator, the positions of dominant resonances depend on the number of photons, i.e., the collective ac Stark effect. Coupling of an SQA to the transmission line allows a straightforward experimental access of the collective states in microwave transmission experiments and, at the same time, to employ SQAs as sensitive single-photon detectors.
Abstract The seminal phenomenon of the Bose-Einstein condensation has been observed on a large variety of physical platforms, e.g., superfluid helium, fermions with attractive interactions, quasiparticles in solids, and ultracold atomic gases. Recently, the Bose–Einstein condensation of non-interacting photons in an optical microcavity has been confirmed experimentally. Here, we report the experimental observation of Bose-Einstein like condensation and collective Bogoliubov excitations in a low dissipative microwave resonator with embedded superconducting quantum network composed of multiple flux qubits. Under strong coherent pumping the resonator mode becomes macroscopically populated, giving rise to hybridized photon–qubit collective modes. The Bogoliubov-like collective excitations appearing in a response to a nearby-frequency probe tone, accompanied by pronounced bistability and hysteresis in the measured transmission coefficient, provide the first experimental evidence of a Bose–Einstein–like condensate of microwave photons on a superconducting circuit platform. A theoretical framework based on Gross-Pitaevskii formalism and taking into account the ac Stark effect inducing the effective interaction between photons, quantitatively reproduces the experimental observations and identifies the regime of appearance of microwave Bogoliubov excitations. These results establish a proof of principle for exploiting driven collective states in superconducting circuits as a platform for quantum-limited microwave detection and engineered many-body photonic systems for quantum information processing.
Analyzing weak microwave signals in the GHz regime is a challenging task if the signal level is very low and the photon energy widely undefined. A superconducting qubit can detect signals in the low photon regime, but due to its discrete level structure, it is only sensitive to photons of certain energies. With a multilevel quantum system (qudit) in contrast, the unknown signal frequency and amplitude can be deduced from the higher level ac Stark shift. The measurement accuracy is given by the signal amplitude, its detuning from the discrete qudit energy level structure, and the anharmonicity. We demonstrate an energy sensitivity in the order of ${10}^{\ensuremath{-}3}$ with a measurement range of more than 1GHz1\phantom{\rule{0.28em}{0ex}}\mathrm{GHz}1GHz. Here, using a transmon qubit, we experimentally observe shifts in the transition frequencies involving up to three excited levels. These shifts are in good agreement with an analytic circuit model and master equation simulations. For large detunings, we find the shifts to scale linearly with the power of the applied microwave drive. Exploiting the effect, we demonstrated a power meter which makes it possible to characterize the microwave transmission from source to sample.