# Latest publications

### Using Bifluxon Tunneling to Protect the Fluxonium Qubit

Waël Ardati, Sébastien Léger, Shelender Kumar, Vishnu N. Suresh, Dorian Nicolas, Cyril Mori, Francesca D’Esposito, Tereza Vakhtel, Olivier Buisson, Quentin Ficheux, Nicolas Roch

Phys. Rev. X 14, 041014 – Published 16 October 2024

A new approach to encoding information in a fluxonium qubit extends its relaxation and coherence times, making this platform a promising candidate for future quantum computing applications. The fluxonium quantum bit, or qubit, consists of a superconducting loop interrupted by a Josephson junction, a thin layer of nonsuperconducting material sandwiched between two superconducting layers. Like all qubits, fluxoniums are easily affected by noise and decoherence, which hampers their ability to store information. Even though this qubit was introduced 10 years ago, we have discovered a new way to operate it that can potentially extend its lifetime. The main idea is to encode the two logical states, 0 and 1, using two different parities of the magnetic flux quanta, or fluxons, that enter the superconducting loop. The ground state corresponds to zero fluxon in the loop, while the first excited states are encoded with an odd fluxon number. As the wave functions of 0 and 1 display minimal overlap, our fluxonium has better protection from relaxation compared to a standard fluxonium with the same 0-1 transition frequency while keeping the same order of protection from dephasing. This encoding of quantum information is enabled by a very large inductance, or superinductance, of 1 μH over a few hundred microns. Despite the challenges in fabricating this circuit, our experiments show impressive stability, with qubits exhibiting long relaxation and coherence times (in the 100-microsecond range). This resilience makes our fluxonium qubit a promising candidate for future quantum computing applications. Additionally, this work demonstrates that large superinductances are a powerful tool in developing robust superconducting qubits, expanding their potential for diverse quantum computing applications.

### Harnessing two-photon dissipation for enhanced quantum measurement and control

A. Marquet, S. Dupouy, U. Réglade, A. Essig, J. Cohen, E. Albertinale, A. Bienfait, T. Peronnin,

S. Jezouin, R. Lescanne, and B. Huard

Phys. Rev. Applied 22, 034053 – Published 23 September 2024

### From nonreciprocal to charge-4e supercurrents in Ge-based Josephson devices

### with tunable harmonic content

##### Axel Leblanc, Chotivut Tangchingchai, Zahra Sadre Momtaz, Elyjah Kiyooka, Jean-Michel Hartmann,

##### Gonzalo Troncoso Fernandez-Bada, Zoltán Scherübl, Boris Brun, Vivien Schmitt, Simon Zihlmann, Romain Maurand,

##### Étienne Dumur, Silvano De Franceschi, and François Lefloch

##### Phys. Rev. Research 6, 033281 – Published 11 September 2024

## S. Messelot et al.

### Direct Measurement of a sin(2𝜑) Current Phase Relation

### in a Graphene Superconducting Quantum Interference Device

##### Simon Messelot, Nicolas Aparicio, Elie de Seze, Eric Eyraud, Johann Coraux, Kenji Watanabe, Takashi Taniguchi, and Julien Renard

##### Phys. Rev. Lett. 133, 106001 – Published 5 September 2024

#####

###### See also the synopsis: A New Nonlinearity for Superconducting Circuits

## H. Chakraborti, C. Gorini, A. Knothe, M.-H. Liu, P. Makk, F. D. Parmentier, D. Perconte, K. Richter, P. Roulleau, B. Sacépé, C. Schönenberger and W. Yang, J. Phys.: Condens. Matter 36 393001 (2024)

## Autoparametric resonance extending the bit-flip time of a cat qubit up to 0.3 s

A. Marquet, A. Essig, J. Cohen, N. Cottet, A. Murani, E. Albertinale, S. Dupouy, A. Bienfait, T. Peronnin, S. Jezouin, R. Lescanne, and B. Huard,

Phys. Rev. X 14, 021019 (2024)

### Near power-law temperature dependence of the superfluid stiffness

### in strongly disordered superconductors

##### Anton V. Khvalyuk, Thibault Charpentier, Nicolas Roch, Benjamin Sacépé, and Mikhail V. Feigel'man

##### Phys. Rev. B 109, 144501 (2024)

### Cyclically Operated Single Microwave Photon Counter with 10−22 W/Hz ̅ ̅ ̅√ sensitivity

L. Balembois, J. Travesedo, L. Pallegoix, A. May, E. Billaud, M. Villiers, D. Estève, D.Vion, P. Bertet, and E. Flurin,

Phys. Rev. Applied 21, 014043 (2024)

Josephson diode effect in Andreev molecules

J.-D. Pillet, S. Annabi, A. Peugeot, H. Riechert, E. Arrighi, J. Griesmar, and L. Bretheau

Phys. Rev. Research 5, 033199 (2023)

One Hundred Second Bit-Flip Time in a Two-Photon Dissipative Oscillator

C. Berdou, A. Murani, U. Réglade, W.C. Smith, M. Villiers, J. Palomo, M. Rosticher, A. Denis, P. Morfin, M. Delbecq, T. Kontos, N. Pankratova, F. Rautschke, T. Peronnin, L.-A. Sellem, P. Rouchon, A. Sarlette, M. Mirrahimi, P. Campagne-Ibarcq, S. Jezouin, R. Lescanne, and Z. Leghtas,

PRX Quantum 4, 020350 (2023)

Stability and decoherence rates of a GKP qubit protected by dissipation

L. A. Sellem, R. Robin, P. Campagne-Ibarcq, and P. Rouchon,

http://www.ifac2023.org/

One hundred second bit-flip time in a two-photon dissipative oscillator

C. Berdou, A. Murani, U. Reglade, W. C. Smith, M. Villiers, J. Palomo, M. Rosticher, A. Denis, P. Morfin, M. Delbecq, T. Kontos, N. Pankratova, F. Rautschke, T. Peronnin, L.-A. Sellem, P. Rouchon, A. Sarlette, M. Mirrahimi, P. Campagne-Ibarcq, S. Jezouin, R. Lescanne, Z. Leghtas, ,

PRX Quantum, 2023, 4 (2), pp.020350

A. Bernard, Y. Peng, A. Kasumov, R. Deblock, M. Ferrier, F. Fortuna, V. T. Volkov, Y. A. Kasumov , Y. Oreg, F. von Oppen, H. Bouchiat, S. Guéron,

Nat. Phys. 19, 358–364 (2023)

Robust suppression of noise propagation in GKP error-correction

C. Siegele and P. Campagne-Ibarcq,

Phys. Rev. A 108, 042427 (2023)

Loss mechanisms in TiN high impedance superconducting microwave circuits,

K. Rafsanjani Amin, C. Ladner, G. Jourdan, S. Hentz, N. Roch, J. Renard,

Appl. Phys. Lett. 120, 164001 (2022)

Magnifying quantum phase fluctuations with Cooper-pair pairing,

W.C. Smith, M. Villiers, A. Marquet, J. Palomo, M.R. Delbecq, T. Kontos, P. Campagne-Ibarcq, B. Doucot and Z. Leghtas,

Phys. Rev. X 12, 021002 (2022)

A gate-tunable graphene Josephson parametric amplifier,

G. Butseraen, A. Ranadive, N. Aparicio, K. Rafsanjani Amin, A. Juyal, M. Esposito, K. Watanabe, T. Taniguchi, N. Roch, F. Lefloch, J. Renard,

Nat. Nanotechnol. 17, 1153–1158 (2022)