Rapid single-flux quantum logic using π-shifters

Ustinov, A. V.; Kaplunenko, V. K.

doi:10.1063/1.1604964

Cited by 125 publications

(96 citation statements)

References 11 publications

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“…That result has been confirmed by numerous groups since the initial discovery, using a wide variety of weak and strong ferromagnetic materials [3][4][5][6][7][8][9] . There have been several proposals to use π-junctions as new components in either classical or quantum information processing circuits [10][11][12][13][14][15][16] .…”

Section: Introductionmentioning

confidence: 99%

Critical current oscillations of elliptical Josephson junctions with single-domain ferromagnetic layers

Glick

Khasawneh

Niedzielski

et al. 2017

Journal of Applied Physics

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Josephson junctions containing ferromagnetic layers are of considerable interest for the development of practical cryogenic memory and superconducting qubits. Such junctions exhibit a ground-state phase shift of π for certain ranges of ferromagnetic layer thickness. We present studies of Nb based micron-scale ellipticallyshaped Josephson junctions containing ferromagnetic barriers of Ni 81 Fe 19 or Ni 65 Fe 15 Co 20 . By applying an external magnetic field, the critical current of the junctions are found to follow characteristic Fraunhofer patterns, and display sharp switching behavior suggestive of single-domain magnets. The high quality of the Fraunhofer patterns enables us to extract the maximum value of the critical current even when the peak is shifted significantly outside the range of the data due to the magnetic moment of the ferromagnetic layer. The maximum value of the critical current oscillates as a function of the ferromagnetic barrier thickness, indicating transitions in the phase difference across the junction between values of zero and π. We compare the data to previous work and to models of the 0-π transitions based on existing theories.

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Section: Introductionmentioning

confidence: 99%

Critical current oscillations of elliptical Josephson junctions with single-domain ferromagnetic layers

Glick

Khasawneh

Niedzielski

et al. 2017

Journal of Applied Physics

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“…For example, a Josephson junction containing a ferromagnetic material can exhibit an intrinsic phase shift of π in its ground state for certain thicknesses of the material 1 . Such 'π-junctions' were first realized experimentally in 2001 (refs 2,3), and have been proposed as circuit elements for both high-speed classical superconducting computing and for quantum computing [4][5][6][7][8][9][10] . Here we demonstrate experimentally that the phase state of a Josephson junction containing two ferromagnetic layers can be toggled between 0 and π by changing the relative orientation of the two magnetizations.…”

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confidence: 99%

Controllable 0–π Josephson junctions containing a ferromagnetic spin valve

et al. 2016

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“…In these junctions the sign of the critical current and, therefore, the phase µ (0 or π) in the ground state, depends on the thickness d F of the ferromagnetic layer and on temperature T [9]. π JJs may substantially improve parameters of various classical and quantum electronic circuits [10,11,12,13,14,15]. To use π JJs not only as a "phase battery", but also as an active (switching) element in various circuits it is important to have a rather high characteristic voltage V c (defined e.g.…”

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confidence: 99%

0−πJosephson Tunnel Junctions with Ferromagnetic Barrier

Weides¹,

et al. 2006

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We fabricated high quality Nb/Al 2 O 3 /Ni 0.6 Cu 0.4 /Nb superconductor-insulator-ferromagnet-superconductor Josephson tunnel junctions. Using a ferromagnetic layer with a step-like thickness, we obtain a 0-π junction, with equal lengths and critical currents of 0 and π parts. The ground state of our 330 µm (1.3λ J ) long junction corresponds to a spontaneous vortex of supercurrent pinned at the 0-π step and carrying ∼ 6.7% of the magnetic flux quantum Φ 0 . The dependence of the critical current on the applied magnetic field shows a clear minimum in the vicinity of zero field. PACS numbers: 74.50.+r, In his classical paper[1] Brian Josephson predicted that the supercurrent through a Josephson junction (JJ) is given by I s = I c sin(µ). Here, µ is the Josephson phase (the difference of phases of the quantum mechanical wave functions describing the superconducting condensate in the electrodes), and I c > 0 is the critical current (maximum supercurrent that one can pass through the JJ). When one passes no current (I s = 0), the Josephson phase µ = 0 corresponds to the minimum of energy (ground state). The solution µ = π corresponds to the energy maximum and is unstable. Later it was suggested that using a ferromagnetic barrier one can realize JJs where. Such junctions obviously have µ = π in the ground state and, therefore, are called π JJs. The solution µ = 0 corresponds to the energy maximum and is unstable.π JJs were recently realized using superconductor-ferromagnet-superconductor (SFS) [3,4,5,6], superconductorinsulator-ferromagnet-superconductor (SIFS) [7] and other [8] technologies. In these junctions the sign of the critical current and, therefore, the phase µ (0 or π) in the ground state, depends on the thickness d F of the ferromagnetic layer and on temperature T [9]. π JJs may substantially improve parameters of various classical and quantum electronic circuits [10,11,12,13,14,15]. To use π JJs not only as a "phase battery", but also as an active (switching) element in various circuits it is important to have a rather high characteristic voltage V c (defined e.g. as V at I = 1.2I c ) and low damping. For example, for classical single flux quantum logic circuits V c defines the speed of operation. For qubits the value of a quasi-particle resistance R qp at V = 0 should be high enough since it defines the decoherence time of the circuits. Both high values of R qp and V c can be achieved by using tunnel SIFS JJs rather than SFS JJs. The dissipation in SIFS JJs decreases exponentially at low temperatures [16], thus, making SIFS technology an appropriate candidate for creating low decoherence quantum circuits, e.g., π qubits. [13,14,15].Actually, the most interesting situation is when one half of the JJ (x < 0) behaves as a 0 JJ, and the other half (x > 0) as a π JJ (a 0-π JJ) [17]: In the symmetric case (equal critical currents and lengths of 0 and π parts) the ground state of such a 0-π JJ corresponds to a spontaneously formed vortex of supercurrent circulating around the 0-π boundary, generating magnetic...

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Rapid single-flux quantum logic using π-shifters

Cited by 125 publications

References 11 publications

Critical current oscillations of elliptical Josephson junctions with single-domain ferromagnetic layers

Critical current oscillations of elliptical Josephson junctions with single-domain ferromagnetic layers

Controllable 0–π Josephson junctions containing a ferromagnetic spin valve

0−πJosephson Tunnel Junctions with Ferromagnetic Barrier

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