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:0804.0349 · Journal of the Korean Physical Society

Superconductor-ferromagnet-junction phase qubit

Tae-Wan Noh, H. -S. Sim, Mun Dae Kim

Published Jan 1, 2012• 4 citations
arXivHTMLPDF

Abstract

We propose a scheme for a phase qubit in an SIFIS junction, consisting of bulk superconductors (S), a proximity-induced ferromagnet (F), and insulating barriers (I). The qubit state is constituted by the 0 and the π phase states of the junction, in which the charging energy of the junction leads to a superposition of the two states. The qubit is operated by the gate voltage applied to the ferromagnet and is insensitive to the decoherence sources existing in other superconducting qubits. We discuss a scalable scheme for qubit measurement and tunable two-qubit coupling, and a possible experimental realization.

DOI
10.3938/jkps.60.72

Related papers

Superconducting π Qubit with a Ferromagnetic Josephson Junction

T. Yamashita, K. Tanikawa, Takahashi, S. +1 more

Solid-state qubits have the potential for the large-scale integration and for the flexibility of layout for quantum computing.However, their short decoherence time due to the coupling to the environment remains an important problem to be overcome.We propose a new superconducting qubit which incorporates a spin-electronic device: the qubit consists of a superconducting ring with a ferromagnetic junction which has a metallic contact and a normal Josephson junction with an insulating barrier.Thus, a quantum coherent two-level state is formed without an external magnetic field.This feature and the simple structure of the qubit make it possible to reduce its size leading to a long decoherence time.

•Jan 1, 2005•0 citations

Superconducting π Qubit with a Ferromagnetic Josephson Junction

Tsutomu Yamashita, Kazuo Tanikawa, S. Takahashi +1 more

Solid-state qubits have the potential for the large-scale integration and for the flexibility of layout for quantum computing. However, their short decoherence time due to the coupling to the environment remains an important problem to be overcome. We propose a new superconducting qubit which incorporates a spin-electronic device: the qubit consists of a superconducting ring with a ferromagnetic pi junction which has a metallic contact and a normal Josephson junction with an insulating barrier. Thus, a quantum coherent two-level state is formed without an external magnetic field. This feature and the simple structure of the qubit make it possible to reduce its size leading to a long decoherence time.

arXiv:cond-mat/0410658•Physical Review Letters•Aug 22, 2005•166 citations

Superconducting flux qubit with ferromagnetic Josephson π-junction operating at zero magnetic field

Sunmi Kim, Leonid Victorovich Abdurakhimov, Duong Pham +6 more

Conventional superconducting flux qubits require the application of a precisely tuned magnetic field to set the operation point at half a flux quantum through the qubit loop, which complicates the on-chip integration of this type of device. It has been proposed that by inducing a π-phase shift in the superconducting order parameter using a precisely controlled nanoscale-thickness superconductor/ferromagnet/superconductor Josephson junction, commonly referred to as π-junction, it is possible to realize a flux qubit operating at zero magnetic flux. Here, we report the realization of a zero-flux-biased flux qubit based on three NbN/AlN/NbN Josephson junctions and a NbN/PdNi/NbN ferromagnetic π-junction. The qubit lifetime is in the microsecond range, which we argue is limited by quasiparticle excitations in the metallic ferromagnet layer. Our results pave the way for developing quantum coherent devices, including qubits and sensors, that utilize the interplay between ferromagnetism and superconductivity. Conventional superconducting flux qubits require a finely tuned magnetic field to operate, hindering their on-chip integration. Here, ferromagnetic Josephson junctions with a π-phase shift in the superconducting order parameter allow the realization of a flux qubit operating at zero magnetic field.

arXiv:2401.14597•Communications Materials•Oct 11, 2024•20 citations

Superconductor-ferromagnet-superconductor junctions in flux and phase qubits

N. V. Klenov, Victor K. Kornev, Aleksei Sharafiev +2 more

π-junction qubit based on superconducting quantum interference device ring has been already proposed. In this qubit, a quantum two-level system is spontaneously generated without any bias flux applied. Flux qubit with a single π-junction concerns the large inductance L of the loop, which makes the qubit vulnerable to decoherence caused by magnetic fluctuations in the environment. To overcome this difficulty one can use three-junction π-qubit, comprising three π-junctions in a loop with negligible small inductance or unharmonic two-junction interferometer exploiting non-sinusoidal current-phase relations of the junctions. In the paper we theoretically investigate the macroscopic quantum dynamics of proposed qubits. The measurement process in two types of qubits has been analyzed in the frame of Lindblad equation formalism. Different mechanisms giving a non-sinusoidal CPR in SFS structures are analyzed as well. It is shown, that the largest second harmonic can be obtained for the SFS junction in the "clean" limit with a thin ferromagnet layer at low temperature.

Journal of Physics Conference Series•Jun 1, 2010•1 citation

Two-qubit gate based on a multiterminal double-barrier Josephson junction

Serhii E. Shafranjuk

A multiterminal double-barrier SISIS junction (S and I denote a superconductor and an insulating barrier, respectively) is suggested as a two-qubit gate with tunable intrinsic coupling. Two quantum wells are formed in the vicinities of the left and right SIS subjunctions. This gives two individual qubits, which are intrinsically coupled via the middle S layer due to phase coherence. The interqubit coupling $J$ is tuned by two bias supercurrents ${I}_{1}$ and ${I}_{2}$ across each of the SIS subjunctions independently. Additional coupling is accomplished by transport supercurrents ${I}_{l}^{\mathrm{tr}}$ along adjacent S layers. Using a microscopic model we compute major qubit characteristics and study sources of the intrinsic decoherence. We compute the entanglement of the two-qubit states, leakage and fidelity characteristics versus $J$, and discuss the readout process.

Physical Review B•Jul 26, 2006•9 citations

Superconducting π qubit with three Josephson junctions

Takashi Yamashita, S. Takahashi, Sadamichi Maekawa

We propose a qubit consisting of a superconducting ring with two zero junctions and one ferromagnetic π junction. In the system, degenerate states appear in the phase space without an external magnetic field because of a competition between the zero and π states. Quantum tunneling between the degenerate states leads to a formation of bonding and antibonding states which are used as a bit. For manipulating the states, only a small magnetic field around zero is required. This feature leads to a large-scale integration and a construction of the smaller-sized qubit which is robust to the decoherence by external noises.

arXiv:cond-mat/0507199•Applied Physics Letters•Mar 24, 2006•42 citations
We propose a scheme for a phase qubit in an SIFIS junction, consisting of bulk superconductors (S), a proximity-induced ferromagnet (F), and insulating barriers (I). The qubit state is constituted by the 0 and the π phase states of the junction, in which the charging energy of the junction leads to a superposition of the two states. The qubit is operated by the gate voltage applied to the ferromagnet and is insensitive to the decoherence sources existing in other superconducting qubits. We discuss a scalable scheme for qubit measurement and tunable two-qubit coupling, and a possible experimental realization.
Solid-state qubits have the potential for the large-scale integration and for the flexibility of layout for quantum computing.However, their short decoherence time due to the coupling to the environment remains an important problem to be overcome.We propose a new superconducting qubit which incorporates a spin-electronic device: the qubit consists of a superconducting ring with a ferromagnetic junction which has a metallic contact and a normal Josephson junction with an insulating barrier.Thus, a quantum coherent two-level state is formed without an external magnetic field.This feature and the simple structure of the qubit make it possible to reduce its size leading to a long decoherence time.
Solid-state qubits have the potential for the large-scale integration and for the flexibility of layout for quantum computing. However, their short decoherence time due to the coupling to the environment remains an important problem to be overcome. We propose a new superconducting qubit which incorporates a spin-electronic device: the qubit consists of a superconducting ring with a ferromagnetic pi junction which has a metallic contact and a normal Josephson junction with an insulating barrier. Thus, a quantum coherent two-level state is formed without an external magnetic field. This feature and the simple structure of the qubit make it possible to reduce its size leading to a long decoherence time.
Conventional superconducting flux qubits require the application of a precisely tuned magnetic field to set the operation point at half a flux quantum through the qubit loop, which complicates the on-chip integration of this type of device. It has been proposed that by inducing a π-phase shift in the superconducting order parameter using a precisely controlled nanoscale-thickness superconductor/ferromagnet/superconductor Josephson junction, commonly referred to as π-junction, it is possible to realize a flux qubit operating at zero magnetic flux. Here, we report the realization of a zero-flux-biased flux qubit based on three NbN/AlN/NbN Josephson junctions and a NbN/PdNi/NbN ferromagnetic π-junction. The qubit lifetime is in the microsecond range, which we argue is limited by quasiparticle excitations in the metallic ferromagnet layer. Our results pave the way for developing quantum coherent devices, including qubits and sensors, that utilize the interplay between ferromagnetism and superconductivity. Conventional superconducting flux qubits require a finely tuned magnetic field to operate, hindering their on-chip integration. Here, ferromagnetic Josephson junctions with a π-phase shift in the superconducting order parameter allow the realization of a flux qubit operating at zero magnetic field.
π-junction qubit based on superconducting quantum interference device ring has been already proposed. In this qubit, a quantum two-level system is spontaneously generated without any bias flux applied. Flux qubit with a single π-junction concerns the large inductance L of the loop, which makes the qubit vulnerable to decoherence caused by magnetic fluctuations in the environment. To overcome this difficulty one can use three-junction π-qubit, comprising three π-junctions in a loop with negligible small inductance or unharmonic two-junction interferometer exploiting non-sinusoidal current-phase relations of the junctions. In the paper we theoretically investigate the macroscopic quantum dynamics of proposed qubits. The measurement process in two types of qubits has been analyzed in the frame of Lindblad equation formalism. Different mechanisms giving a non-sinusoidal CPR in SFS structures are analyzed as well. It is shown, that the largest second harmonic can be obtained for the SFS junction in the "clean" limit with a thin ferromagnet layer at low temperature.
A multiterminal double-barrier SISIS junction (S and I denote a superconductor and an insulating barrier, respectively) is suggested as a two-qubit gate with tunable intrinsic coupling. Two quantum wells are formed in the vicinities of the left and right SIS subjunctions. This gives two individual qubits, which are intrinsically coupled via the middle S layer due to phase coherence. The interqubit coupling JJJ is tuned by two bias supercurrents I1{I}_{1}I1​ and I2{I}_{2}I2​ across each of the SIS subjunctions independently. Additional coupling is accomplished by transport supercurrents Iltr{I}_{l}^{\mathrm{tr}}Iltr​ along adjacent S layers. Using a microscopic model we compute major qubit characteristics and study sources of the intrinsic decoherence. We compute the entanglement of the two-qubit states, leakage and fidelity characteristics versus JJJ, and discuss the readout process.
We propose a qubit consisting of a superconducting ring with two zero junctions and one ferromagnetic π junction. In the system, degenerate states appear in the phase space without an external magnetic field because of a competition between the zero and π states. Quantum tunneling between the degenerate states leads to a formation of bonding and antibonding states which are used as a bit. For manipulating the states, only a small magnetic field around zero is required. This feature leads to a large-scale integration and a construction of the smaller-sized qubit which is robust to the decoherence by external noises.