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:0807.0488 · Physical Review B

Vortex qubit based on an annular Josephson junction containing a microshort

A. N. Price, A. Kemp, D. R. Gulevich, Fedor Vasilievich Kusmartsev, Alexey Vladimirovich Ustinov

Published Jan 8, 2010• 20 citations
arXivHTMLPDF

Abstract

We report theoretical and experimental work on the development of a vortex qubit based on a microshort in an annular Josephson junction. The microshort creates a potential barrier for the vortex, which produces a double-well potential under the application of an in-plane magnetic field; the field strength tunes the barrier height. A one-dimensional model for this system is presented, from which we calculate the vortex-depinning current and attempt frequency as well as the interwell coupling. Implementation of an effective microshort is achieved via a section of insulating barrier that is locally wider in the junction plane. Using a junction with this geometry we demonstrate classical state preparation and readout. The vortex is prepared in a given potential well by sending a series of ``shaker'' bias-current pulses through the junction. Readout is accomplished by measuring the vortex-depinning current.

DOI
10.1103/physrevb.81.014506

Related papers

Development of a Josephson vortex two-state system based on a confocal annular Josephson junction

R. Monaco, J. Mygind, V. P. Koshelets

Abstract We report theoretical and experimental work on the development of a Josephson vortex two-state system based on a confocal annular Josephson tunnel junction (CAJTJ). The key ingredient of this geometrical configuration is a periodically variable width that generates a spatial vortex potential with bistable states. This intrinsic vortex potential can be tuned by an externally applied magnetic field and tilted by a bias current. The two-state system is accurately modeled by a one-dimensional sine-Gordon like equation by means of which one can numerically calculate both the magnetic field needed to set the vortex in a given state as well as the vortex-depinning currents. Experimental data taken at 4.2 K on high-quality Nb/Al–AlO x /Nb CAJTJs with an individual trapped fluxon advocate the presence of a robust and finely tunable double-well potential for which reliable manipulation of the vortex state has been classically demonstrated. The vortex is prepared in a given potential by means of an externally applied magnetic field, while the state readout is accomplished by measuring the vortex-depinning current in a small magnetic field. Our proof of principle experiment convincingly demonstrates that the proposed vortex two-state system based on CAJTJs is robust and workable.

arXiv:1707.01672•Superconductor Science and Technology•Nov 29, 2017•10 citations

Josephson Vortex Qubit: Design, Preparation and Read-Out

A. Kemp, Andreas J. Wallraff, Alexey Vladimirovich Ustinov

The design of a qubit based on a single Josephson vortex trapped in a shaped long Josephson junction is discussed in detail. The vortex potential is formed due to its interaction with an in-plane magnetic field and a bias current applied to the junction. The profile of the potential is calculated using a standard perturbation approach. We examine the dependence of the potential properties on the junction shape and its electrical parameters and discuss the requirements for observing quantum effects in this system. We have developed and experimentally tested methods for the preparation and read-out of vortex states of this qubit in the classical regime.

physica status solidi (b)•Oct 1, 2002•49 citations

Engineering double-well potentials with variable-width annular Josephson tunnel junctions

R. Monaco

Long Josephson tunnel junctions are non-linear transmission lines that allow propagation of current vortices (fluxons) and electromagnetic waves and are used in various applications within superconductive electronics. Recently, the Josephson vortex has been proposed as a new superconducting qubit. We describe a simple method to create a double-well potential for an individual fluxon trapped in a long elliptic annular Josephson tunnel junction characterized by an intrinsic non-uniform width. The distance between the potential wells and the height of the inter-well potential barrier are controlled by the strength of an in-plane magnetic field. The manipulation of the vortex states can be achieved by applying a proper current ramp across the junction. The read-out of the state is accomplished by measuring the vortex depinning current in a small magnetic field. An accurate one-dimensional sine-Gordon model for this strongly non-linear system is presented, from which we calculate the position-dependent fluxon rest-mass, its Hamiltonian density and the corresponding trajectories in the phase space. We examine the dependence of the potential properties on the annulus eccentricity and its electrical parameters and address the requirements for observing quantum-mechanical effects, as discrete energy levels and tunneling, in this two-state system.

arXiv:1606.02494•Journal of Physics Condensed Matter•Sep 8, 2016•16 citations

Josephson vortex coupled to a flux qubit

Kirill G. Fedorov, Anastasia V. Shcherbakova, R. Schäfer +1 more

Experiments towards realizing a readout of superconducting qubits by using ballistic Josephson vortices are reported. We measured the microwave radiation induced by a fluxon moving in an annular Josephson junction. By coupling a flux qubit as a current dipole to the annular junction, we detect periodic variations of the fluxon's oscillation frequency versus magnetic flux through the qubit. We found that the scattering of a fluxon on a current dipole can lead to the acceleration of a fluxon regardless of a dipole polarity. We use the perturbation theory and numerical simulations of the perturbed sine-Gordon equation to analyze our results.

arXiv:1301.5164•Applied Physics Letters•Apr 1, 2013•17 citations

Tunable qubit based on a molecule of two fractional Josephson vortices

Dennis Manuel Heim, Karl Vogel, W. P. Schleich +3 more

We propose a concept of a qubit based on two coupled fractional vortices pinned at two artificially created $\kappa$ discontinuities of the Josephson phase in a long Josephson junction. Each discontinuity can be created by a pair of tiny current injectors with the current $I_\mathrm{inj}$ applied. We map the dynamics of the system to the dynamics of a single particle in a double-well potential and calculate the effective parameters of this potential. By tuning the discontinuities $\kappa \propto I_\mathrm{inj}$ during the experiment we are able to control the parameters of the effective double-well potential as well as to initialize the fractional vortex molecule to a desired state. The system can be used to study macroscopic quantum phenomena involving tailored vortex matter.

•Aug 30, 2012•0 citations

Josephson vortex quantum bits: Decoherence and entanglement

Ramesh P. Dhungana

In this dissertation work, I investigate the decoherence time of a Josephson vortex qubit (JVQ) and the level of entanglement between two JVQs. A JVQ may be fabricated by embedding two closely spaced microresistors in the insulating layer of a long Josephson junction (LJJ). The phase dynamics of the JVQ may be described by using the perturbed sine-Gordon equation. This sine-Gordon equation is transformed to describe the motion of fluxons in the double-well potential. An oscillation of a fluxon in this double-well potential is mapped onto a quantum two-state system. The coherent oscillation of fluxons in the two-state system decays due to dissipation and noises in the LJJ. To estimate the decoherence time, the two-state system in a noisy environment is described by using the spin-boson Hamiltonian. The time evolution of the system is studied by using the generalized master equation. Finally, I use the experimental parameters for Nb-AlOx-Nb Josephson junction to estimate the decoherence time. The result shows that JVQ has a very long decoherence time (several tens of microseconds) compared to other Josephson qubits. Entanglement between two coupled JVQs is estimated by computing the concurrence. The concurrence depends on the ground-state energy splitting due to the one-fluxon and two-fluxon tunneling between the potential minima of the two coupled JVQs. The tunneling amplitude between the potential minima depends on the junction parameters such as magnetic induction effect S, the separation distance ℓ, and the pinning strength of the microresistors ϵ. The estimation of the concurrence shows that a near perfect entanglement may be achieved by using the experimentally accessible values of the parameters. Also the study shows that the tunneling amplitude of the fluxon between the potential minima of the JVQs may be increased by coupling the junction with a resonant cavity. This characteristic of the junction-cavity coupling may be exploited to control the entanglement between two JVQs.

•Jan 1, 2009•0 citations
We report theoretical and experimental work on the development of a vortex qubit based on a microshort in an annular Josephson junction. The microshort creates a potential barrier for the vortex, which produces a double-well potential under the application of an in-plane magnetic field; the field strength tunes the barrier height. A one-dimensional model for this system is presented, from which we calculate the vortex-depinning current and attempt frequency as well as the interwell coupling. Implementation of an effective microshort is achieved via a section of insulating barrier that is locally wider in the junction plane. Using a junction with this geometry we demonstrate classical state preparation and readout. The vortex is prepared in a given potential well by sending a series of ``shaker'' bias-current pulses through the junction. Readout is accomplished by measuring the vortex-depinning current.
Abstract We report theoretical and experimental work on the development of a Josephson vortex two-state system based on a confocal annular Josephson tunnel junction (CAJTJ). The key ingredient of this geometrical configuration is a periodically variable width that generates a spatial vortex potential with bistable states. This intrinsic vortex potential can be tuned by an externally applied magnetic field and tilted by a bias current. The two-state system is accurately modeled by a one-dimensional sine-Gordon like equation by means of which one can numerically calculate both the magnetic field needed to set the vortex in a given state as well as the vortex-depinning currents. Experimental data taken at 4.2 K on high-quality Nb/Al–AlO x /Nb CAJTJs with an individual trapped fluxon advocate the presence of a robust and finely tunable double-well potential for which reliable manipulation of the vortex state has been classically demonstrated. The vortex is prepared in a given potential by means of an externally applied magnetic field, while the state readout is accomplished by measuring the vortex-depinning current in a small magnetic field. Our proof of principle experiment convincingly demonstrates that the proposed vortex two-state system based on CAJTJs is robust and workable.
The design of a qubit based on a single Josephson vortex trapped in a shaped long Josephson junction is discussed in detail. The vortex potential is formed due to its interaction with an in-plane magnetic field and a bias current applied to the junction. The profile of the potential is calculated using a standard perturbation approach. We examine the dependence of the potential properties on the junction shape and its electrical parameters and discuss the requirements for observing quantum effects in this system. We have developed and experimentally tested methods for the preparation and read-out of vortex states of this qubit in the classical regime.
Long Josephson tunnel junctions are non-linear transmission lines that allow propagation of current vortices (fluxons) and electromagnetic waves and are used in various applications within superconductive electronics. Recently, the Josephson vortex has been proposed as a new superconducting qubit. We describe a simple method to create a double-well potential for an individual fluxon trapped in a long elliptic annular Josephson tunnel junction characterized by an intrinsic non-uniform width. The distance between the potential wells and the height of the inter-well potential barrier are controlled by the strength of an in-plane magnetic field. The manipulation of the vortex states can be achieved by applying a proper current ramp across the junction. The read-out of the state is accomplished by measuring the vortex depinning current in a small magnetic field. An accurate one-dimensional sine-Gordon model for this strongly non-linear system is presented, from which we calculate the position-dependent fluxon rest-mass, its Hamiltonian density and the corresponding trajectories in the phase space. We examine the dependence of the potential properties on the annulus eccentricity and its electrical parameters and address the requirements for observing quantum-mechanical effects, as discrete energy levels and tunneling, in this two-state system.
Experiments towards realizing a readout of superconducting qubits by using ballistic Josephson vortices are reported. We measured the microwave radiation induced by a fluxon moving in an annular Josephson junction. By coupling a flux qubit as a current dipole to the annular junction, we detect periodic variations of the fluxon's oscillation frequency versus magnetic flux through the qubit. We found that the scattering of a fluxon on a current dipole can lead to the acceleration of a fluxon regardless of a dipole polarity. We use the perturbation theory and numerical simulations of the perturbed sine-Gordon equation to analyze our results.
We propose a concept of a qubit based on two coupled fractional vortices pinned at two artificially created κ\kappaκ discontinuities of the Josephson phase in a long Josephson junction. Each discontinuity can be created by a pair of tiny current injectors with the current IinjI_\mathrm{inj}Iinj​ applied. We map the dynamics of the system to the dynamics of a single particle in a double-well potential and calculate the effective parameters of this potential. By tuning the discontinuities κ∝Iinj\kappa \propto I_\mathrm{inj}κ∝Iinj​ during the experiment we are able to control the parameters of the effective double-well potential as well as to initialize the fractional vortex molecule to a desired state. The system can be used to study macroscopic quantum phenomena involving tailored vortex matter.
In this dissertation work, I investigate the decoherence time of a Josephson vortex qubit (JVQ) and the level of entanglement between two JVQs. A JVQ may be fabricated by embedding two closely spaced microresistors in the insulating layer of a long Josephson junction (LJJ). The phase dynamics of the JVQ may be described by using the perturbed sine-Gordon equation. This sine-Gordon equation is transformed to describe the motion of fluxons in the double-well potential. An oscillation of a fluxon in this double-well potential is mapped onto a quantum two-state system. The coherent oscillation of fluxons in the two-state system decays due to dissipation and noises in the LJJ. To estimate the decoherence time, the two-state system in a noisy environment is described by using the spin-boson Hamiltonian. The time evolution of the system is studied by using the generalized master equation. Finally, I use the experimental parameters for Nb-AlOx-Nb Josephson junction to estimate the decoherence time. The result shows that JVQ has a very long decoherence time (several tens of microseconds) compared to other Josephson qubits. Entanglement between two coupled JVQs is estimated by computing the concurrence. The concurrence depends on the ground-state energy splitting due to the one-fluxon and two-fluxon tunneling between the potential minima of the two coupled JVQs. The tunneling amplitude between the potential minima depends on the junction parameters such as magnetic induction effect S, the separation distance ℓ, and the pinning strength of the microresistors ϵ. The estimation of the concurrence shows that a near perfect entanglement may be achieved by using the experimentally accessible values of the parameters. Also the study shows that the tunneling amplitude of the fluxon between the potential minima of the JVQs may be increased by coupling the junction with a resonant cavity. This characteristic of the junction-cavity coupling may be exploited to control the entanglement between two JVQs.