SuperconductingπQubit with a Ferromagnetic Josephson Junction

Abstract

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 π 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.PACS numbers: 03.67. Lx, 74.50.+r, 74.45.+c, 85.25.Cp The quantum computer is an innovative device in the sense that it would make it possible to solve problems which require unrealistically long computation times on a classical computer [1]. In the quantum computer, the information is stored in a basic element called the qubit, which is a quantum coherent two-level system. The superposition of the two-level state is utilized in the process of quantum computing. For the physical realization of the qubit, various systems have been proposed, e.g., ion traps, nuclear spins, and photons. Among the proposals, solid-state devices have the advantage of large-scale integration and flexibility of layout. On the other hand, a challenging problem for the solid state qubits is the reduction of the decoherence effect, since the solid states qubits in general have a short decoherence time due to their coupling to the environment. In recent years, several qubits based on the Josephson effect have been proposed [2,3,4,5,6,7,8,9,10,11,12,13]. One of the proposals involves a Cooper-pair box type of qubit [2,3,4,5]. In this case, quantum oscillations between the quantum two-level states (Rabi oscillations) have been detected [2,3], and the operation of coupled two qubits has been demonstrated [4,5]. Another example is a flux qubit which uses the superconducting phase. For this proposal, a circuit with a single and relatively large

Magnetic and Transport Properties of Nb/PdNi Bilayers

“…Especially, SFS JJs have great advantages for manipulating a spin degree of freedom in Josephson-junction-based electronics, for example, JJ-based qubits [7]. In SFS JJs, -Josephson junction ( -JJs) behaviors have been predicted due to exchange field-induced oscillations of the superconducting order parameter over the coherence length in the ferromagnetic layer (see Fig.…”

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

“…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] .…”

Ferromagnetic 0–π Josephson junctions

“…The presented SIFS technology allows us to construct 0, π and 0-π JJs with comparable j 0 c and j π c in a single fabrication run. Such JJs may be used to construct classical and quantum devices such as oscillators, memory cells, π flux qubits [22,23] or semifluxon based qubits [24].…”