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:1408.3574 · Europhysics Letters (EPL)

Strain designed Josephson π -junction qubits with topological insulators

Colin Benjamin

Published Jun 1, 2015• 7 citations
arXivHTMLPDF

Abstract

A Josephson qubit is designed via the application of a tensile strain to a topological insulator surface sandwiched between two s -wave superconductors. The strain applied leads to a shift in the Dirac point without changing the pre-existing conducting states, on the surface of a topological insulator. The strain applied can be tuned to form a π -junction in such a structure. Combining two such junctions in a ring architecture leads to the ground state of the ring being in a doubly degenerate state —the "0" and "1" states of a qubit. A qubit designed this way is quite easily controlled via the tunable strain applied. We report on the conditions necessary to design such a qubit. Finally the operating time of a single-qubit phase gate is derived.

DOI
10.1209/0295-5075/110/50003

Related papers

Design aspects of superconducting-phase quantum bits

G. Blatter, V. B. Geshkenbeǐn, L. B. Ioffe

A superconducting-phase quantum bit (qubit) involves three or more Josephson junctions combined into a superconducting loop and defines one of the promising solid-state device implementations for quantum computing. Recently, so called $\ensuremath{\pi}$ junctions, Josephson junctions with a ground state characterized by a \ensuremath{\pi}-phase shift across, have attracted much attention. We show how to make use of such $\ensuremath{\pi}$ junctions in the construction of superconducting phase qubits and discuss the advantage over conventional designs based on magnetically frustrated loops. Starting from a basic five-junction loop with one $\ensuremath{\pi}$ junction, we show how to construct effective junctions with degenerate minima characterized by phase shifts 0 and $\ensuremath{\pi}$ and superconducting-phase switches. These elements are then combined into a superconducting-phase qubit which operates exclusively with switches, thus avoiding permanent contact with the environment through external biasing. The resulting superconducting-phase qubits can be understood as the macroscopic analog of the ``quiet'' s-wave--d-wave--s-wave Josephson-junction qubits introduced by Ioffe et al. [Nature (London) 398, 679 (1999)].

Physical review. B, Condensed matter•Apr 11, 2001•181 citations

Graphene Josephson Qubit

Colin Benjamin, Jiannis K. Pachos

We propose to combine the advantages of graphene, such as easy tunability and long coherence times, with Josephson physics to manufacture qubits. If these qubits are built around a 0 and $\pi$ junction they can be controlled by an external flux. Alternatively, a d-wave Josephson junction can itself be tuned via a gate voltage to create superpositions between macroscopically degenerate states. We show that ferromagnets are not required for realizing $\pi$ junction in graphene, thus considerably simplifying its physical implementation. We demonstrate how one qubit gates, such as arbitrary phase rotations and the exchange gate, can be implemented.

arXiv:0808.1979•Bulletin of the American Physical Society•Aug 14, 2008•0 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-junction phase qubit

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

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.

arXiv:0804.0349•Journal of the Korean Physical Society•Jan 1, 2012•4 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 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
A Josephson qubit is designed via the application of a tensile strain to a topological insulator surface sandwiched between two s -wave superconductors. The strain applied leads to a shift in the Dirac point without changing the pre-existing conducting states, on the surface of a topological insulator. The strain applied can be tuned to form a π -junction in such a structure. Combining two such junctions in a ring architecture leads to the ground state of the ring being in a doubly degenerate state —the "0" and "1" states of a qubit. A qubit designed this way is quite easily controlled via the tunable strain applied. We report on the conditions necessary to design such a qubit. Finally the operating time of a single-qubit phase gate is derived.
A superconducting-phase quantum bit (qubit) involves three or more Josephson junctions combined into a superconducting loop and defines one of the promising solid-state device implementations for quantum computing. Recently, so called $\ensuremath{\pi}$ junctions, Josephson junctions with a ground state characterized by a \ensuremath{\pi}-phase shift across, have attracted much attention. We show how to make use of such $\ensuremath{\pi}$ junctions in the construction of superconducting phase qubits and discuss the advantage over conventional designs based on magnetically frustrated loops. Starting from a basic five-junction loop with one $\ensuremath{\pi}$ junction, we show how to construct effective junctions with degenerate minima characterized by phase shifts 0 and $\ensuremath{\pi}$ and superconducting-phase switches. These elements are then combined into a superconducting-phase qubit which operates exclusively with switches, thus avoiding permanent contact with the environment through external biasing. The resulting superconducting-phase qubits can be understood as the macroscopic analog of the ``quiet'' s-wave--d-wave--s-wave Josephson-junction qubits introduced by Ioffe et al. [Nature (London) 398, 679 (1999)].
We propose to combine the advantages of graphene, such as easy tunability and long coherence times, with Josephson physics to manufacture qubits. If these qubits are built around a 0 and π\piπ junction they can be controlled by an external flux. Alternatively, a d-wave Josephson junction can itself be tuned via a gate voltage to create superpositions between macroscopically degenerate states. We show that ferromagnets are not required for realizing π\piπ junction in graphene, thus considerably simplifying its physical implementation. We demonstrate how one qubit gates, such as arbitrary phase rotations and the exchange gate, can be implemented.
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.
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 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.
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.