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

arXiv:2308.02547

ddd-mon: transmon with strong anharmonicity

Hrishikesh E. Patel, Vedangi Pathak, Oguzhan Can, Andrew C. Potter, Marcel Franz

Published Aug 1, 2023• 0 citations
arXivHTMLPDF

Abstract

We propose a novel qubit architecture based on a planar $c$-axis Josephson junction between a thin flake $d$-wave superconductor ($d$SC), such as a high-$T_c$ cuprate Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$, and a conventional $s$-wave superconductor. When operated in the transmon regime the device -- that we call "$d$-mon" -- becomes insensitive to offset charge fluctuations and, importantly, exhibits at the same time energy level spectrum with strong anharmonicity that is widely tunable through the device geometry and applied magnetic flux. Crucially, unlike previous qubit designs based on $d$-wave superconductors the proposed device operates in a regime where quasiparticles are fully gapped and can be therefore expected to achieve long coherence times.

DOI
10.48550/arxiv.2308.02547

Related papers

d -Mon: A Transmon with Strong Anharmonicity Based on Planar c -Axis Tunneling Junction between d -Wave and s -Wave Superconductors

Hrishikesh E. Patel, Vedangi Pathak, Oguzhan Can +2 more

We propose a novel qubit architecture based on a planar c-axis Josephson junction between a thin flake d-wave superconductor, such as a high-T_{c} cuprate Bi_{2}Sr_{2}CaCu_{2}O_{8+x}, and a conventional s-wave superconductor. When operated in the transmon regime the device-that we call "d mon"-becomes insensitive to offset charge fluctuations and, importantly, exhibits at the same time energy level spectrum with strong anharmonicity that is widely tunable through the device geometry and applied magnetic flux. Crucially, unlike previous qubit designs based on d-wave superconductors the proposed device operates in a regime where quasiparticles are fully gapped and can be therefore expected to achieve long coherence times.

Physical Review Letters•Jan 5, 2024•19 citations

Anomalous magnetic flux via junction twist-angle in a triplet-superconducting transmon qubit

Sebastián Domínguez-Calderón, Harley D. Scammell

Superconducting transmon qubits with strong anharmonicity and insensitivity to offset charge are highly desirable for low-error implementation. In this work we propose a c-axis junction, comprising triplet superconductors, and set at a relative twist angle. Invoking spin-orbit coupling and spin polarization, which are known to occur in the material platform of choice, we examine the resulting transmon Hamiltonian. This junction allows for direct control of the single and double Cooper pair tunneling strength, and most remarkably, an anomalous magnetic flux -- i.e. a phase offset equivalent to magnetic flux, yet in zero magnetic field. Having control over these three parameters -- single and double pair tunneling and anomalous flux -- allows for optimal design of the transmon qubit. Interestingly, in this architecture, the anomalous flux is determined by the twist angle of the junction, thereby offering a novel zero-field functionality. Our key results rely on symmetry arguments, for concreteness we demonstrate the implementation of our concept using a model of moiré graphene-based c-axis junctions.

arXiv:2403.07215•Mar 12, 2024•0 citations

Superconducting Qubit Based on Twisted Cuprate Van der Waals Heterostructures

Valentina Brosco, Giuseppe Serpico, V. M. Vinokur +2 more

Van-der-Waals assembly enables the fabrication of novel Josephson junctions featuring an atomically sharp interface between two exfoliated and relatively twisted Bi_{2}Sr_{2}CaCu_{2}O_{8+x} (Bi2212) flakes. In a range of twist angles around 45°, the junction provides a regime where the interlayer two-Cooper pair tunneling dominates the current-phase relation. Here we propose employing this novel junction to realize a capacitively shunted qubit that we call flowermon. The d-wave nature of the order parameter endows the flowermon with inherent protection against charge-noise-induced relaxation and quasiparticle-induced dissipation. This inherently protected qubit paves the way to a new class of high-coherence hybrid superconducting quantum devices based on unconventional superconductors.

arXiv:2308.00839•Physical Review Letters•Jan 5, 2024•37 citations

The quartic Blochnium: an anharmonic quasicharge superconducting qubit

Luca Chirolli, Matteo Carrega, Francesco Giazotto

The quasicharge superconducting qubit realizes the dual of the transmon and shows strong robustness to flux and charge fluctuations thanks to a very large inductance closed on a Josephson junction. At the same time, a weak anharmonicity of the spectrum is inherited from the parent transmon, that introduces leakage errors and is prone to frequency crowding in multi-qubit setups. We propose a novel design that employs a quartic superinductor and confers a good degree of anharmonicity to the spectrum. The quartic regime is achieved through a properly designed chain of Josephson junction loops that shows minimal quantum fluctuations without introducing a severe dependence on the external fluxes.

arXiv:2304.10401•Quantum•Dec 4, 2023•3 citations

Tunable anharmonicity in Sn-InAs nanowire transmons beyond the short junction limit

Amrita Purkayastha, Amritesh Sharma, Param J. Patel +11 more

The anharmonicity of a transmon qubit, defined as the difference in energy level spacing, is a key design parameter. In transmons built from hybrid superconductor-semiconductor Josephson elements, the anharmonicity is tunable with gate voltages that control both the Josephson energy and the weak link transparency. In Sn-InAs nanowire transmons, we use two-tone microwave spectroscopy to extract anharmonicity ranging in absolute value from the transmon charging energy $E_c$ to values smaller than $E_c/10$. This behavior contrasts with the predictions of the multi-channel short-junction model, which sets a lower limit on anharmonicity at $E_c/4$. Coherent operation of the qubit is still possible at the point of the lowest anharmonicity. These findings demonstrate the potential of quantum circuits that benefit from widely electrically tunable anharmonicity.

cond-mat.mes-hallCross-listedarXiv:2603.26895•Mar 31, 2026•0 citations

Charge-insensitive qubit design derived from the Cooper pair box

Jens Koch, Terri M. Yu, Jay Gambetta +7 more

Short dephasing times pose one of the main challenges in realizing a quantum computer. Different approaches have been devised to cure this problem for superconducting qubits, a prime example being the operation of such devices at optimal working points, so-called ``sweet spots.'' This latter approach led to significant improvement of ${T}_{2}$ times in Cooper pair box qubits [D. Vion et al., Science 296, 886 (2002)]. Here, we introduce a new type of superconducting qubit called the ``transmon.'' Unlike the charge qubit, the transmon is designed to operate in a regime of significantly increased ratio of Josephson energy and charging energy ${E}_{J}∕{E}_{C}$. The transmon benefits from the fact that its charge dispersion decreases exponentially with ${E}_{J}∕{E}_{C}$, while its loss in anharmonicity is described by a weak power law. As a result, we predict a drastic reduction in sensitivity to charge noise relative to the Cooper pair box and an increase in the qubit-photon coupling, while maintaining sufficient anharmonicity for selective qubit control. Our detailed analysis of the full system shows that this gain is not compromised by increased noise in other known channels.

arXiv:cond-mat/0703002•Physical Review A•Oct 12, 2007•3,350 citations
We propose a novel qubit architecture based on a planar ccc-axis Josephson junction between a thin flake ddd-wave superconductor (dddSC), such as a high-TcT_cTc​ cuprate Bi2_22​Sr2_22​CaCu2_22​O8+x_{8+x}8+x​, and a conventional sss-wave superconductor. When operated in the transmon regime the device -- that we call "ddd-mon" -- becomes insensitive to offset charge fluctuations and, importantly, exhibits at the same time energy level spectrum with strong anharmonicity that is widely tunable through the device geometry and applied magnetic flux. Crucially, unlike previous qubit designs based on ddd-wave superconductors the proposed device operates in a regime where quasiparticles are fully gapped and can be therefore expected to achieve long coherence times.
We propose a novel qubit architecture based on a planar c-axis Josephson junction between a thin flake d-wave superconductor, such as a high-T_{c} cuprate Bi_{2}Sr_{2}CaCu_{2}O_{8+x}, and a conventional s-wave superconductor. When operated in the transmon regime the device-that we call "d mon"-becomes insensitive to offset charge fluctuations and, importantly, exhibits at the same time energy level spectrum with strong anharmonicity that is widely tunable through the device geometry and applied magnetic flux. Crucially, unlike previous qubit designs based on d-wave superconductors the proposed device operates in a regime where quasiparticles are fully gapped and can be therefore expected to achieve long coherence times.
Superconducting transmon qubits with strong anharmonicity and insensitivity to offset charge are highly desirable for low-error implementation. In this work we propose a c-axis junction, comprising triplet superconductors, and set at a relative twist angle. Invoking spin-orbit coupling and spin polarization, which are known to occur in the material platform of choice, we examine the resulting transmon Hamiltonian. This junction allows for direct control of the single and double Cooper pair tunneling strength, and most remarkably, an anomalous magnetic flux -- i.e. a phase offset equivalent to magnetic flux, yet in zero magnetic field. Having control over these three parameters -- single and double pair tunneling and anomalous flux -- allows for optimal design of the transmon qubit. Interestingly, in this architecture, the anomalous flux is determined by the twist angle of the junction, thereby offering a novel zero-field functionality. Our key results rely on symmetry arguments, for concreteness we demonstrate the implementation of our concept using a model of moiré graphene-based c-axis junctions.
Van-der-Waals assembly enables the fabrication of novel Josephson junctions featuring an atomically sharp interface between two exfoliated and relatively twisted Bi_{2}Sr_{2}CaCu_{2}O_{8+x} (Bi2212) flakes. In a range of twist angles around 45°, the junction provides a regime where the interlayer two-Cooper pair tunneling dominates the current-phase relation. Here we propose employing this novel junction to realize a capacitively shunted qubit that we call flowermon. The d-wave nature of the order parameter endows the flowermon with inherent protection against charge-noise-induced relaxation and quasiparticle-induced dissipation. This inherently protected qubit paves the way to a new class of high-coherence hybrid superconducting quantum devices based on unconventional superconductors.
The quasicharge superconducting qubit realizes the dual of the transmon and shows strong robustness to flux and charge fluctuations thanks to a very large inductance closed on a Josephson junction. At the same time, a weak anharmonicity of the spectrum is inherited from the parent transmon, that introduces leakage errors and is prone to frequency crowding in multi-qubit setups. We propose a novel design that employs a quartic superinductor and confers a good degree of anharmonicity to the spectrum. The quartic regime is achieved through a properly designed chain of Josephson junction loops that shows minimal quantum fluctuations without introducing a severe dependence on the external fluxes.
The anharmonicity of a transmon qubit, defined as the difference in energy level spacing, is a key design parameter. In transmons built from hybrid superconductor-semiconductor Josephson elements, the anharmonicity is tunable with gate voltages that control both the Josephson energy and the weak link transparency. In Sn-InAs nanowire transmons, we use two-tone microwave spectroscopy to extract anharmonicity ranging in absolute value from the transmon charging energy EcE_cEc​ to values smaller than Ec/10E_c/10Ec​/10. This behavior contrasts with the predictions of the multi-channel short-junction model, which sets a lower limit on anharmonicity at Ec/4E_c/4Ec​/4. Coherent operation of the qubit is still possible at the point of the lowest anharmonicity. These findings demonstrate the potential of quantum circuits that benefit from widely electrically tunable anharmonicity.
Short dephasing times pose one of the main challenges in realizing a quantum computer. Different approaches have been devised to cure this problem for superconducting qubits, a prime example being the operation of such devices at optimal working points, so-called ``sweet spots.'' This latter approach led to significant improvement of T2{T}_{2}T2​ times in Cooper pair box qubits [D. Vion et al., Science 296, 886 (2002)]. Here, we introduce a new type of superconducting qubit called the ``transmon.'' Unlike the charge qubit, the transmon is designed to operate in a regime of significantly increased ratio of Josephson energy and charging energy EJ∕EC{E}_{J}∕{E}_{C}EJ​∕EC​. The transmon benefits from the fact that its charge dispersion decreases exponentially with EJ∕EC{E}_{J}∕{E}_{C}EJ​∕EC​, while its loss in anharmonicity is described by a weak power law. As a result, we predict a drastic reduction in sensitivity to charge noise relative to the Cooper pair box and an increase in the qubit-photon coupling, while maintaining sufficient anharmonicity for selective qubit control. Our detailed analysis of the full system shows that this gain is not compromised by increased noise in other known channels.