Coupling of Josephson current qubits using a connecting loop

Kim, Mun Dae; Hong, Jongbae

doi:10.1103/physrevb.70.184525

Cited by 21 publications

(27 citation statements)

References 14 publications

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“…Hence the effective potential in Eq. ( 12 ) becomes which describes the inductive energies of three loops with geometric inductance and the Josephson junction energies 25 , 31 , 32 , complying with the intuitive picture.…”

Section: Resultsmentioning

confidence: 74%

“…The precise fluxoid quantization condition of superconducting loop reads with being the average velocity of Cooper pairs, the Cooper pair charge, and the Cooper pair mass 24 , 25 . The total magnetic flux threading the loop is the sum of the external and the induced flux .…”

Section: Resultsmentioning

confidence: 99%

“…The induced flux, , consists of contributions from three conducting lines, and , where and are the geometric inductance of the three-Josephson junction loop and a branch, respectively, and the inductance of one third of the loop contributes to the induced flux. Further, we introduce the kinetic inductances and 25 , 28 , 29 , and then the induced fluxes become , , and to represent the boundary conditions as In the system of Fig. 1 a three Josephson junctions with compose a trijunction which satisfies the periodic boundary condition with an integer .…”

Section: Resultsmentioning

confidence: 99%

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Circulator function in a Josephson junction circuit and braiding of Majorana zero modes

Kim

2021

Sci Rep

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We propose a scheme for the circulator function in a superconducting circuit consisting of a three-Josephson junction loop and a trijunction. In this study we obtain the exact Lagrangian of the system by deriving the effective potential from the fundamental boundary conditions. We subsequently show that we can selectively choose the direction of current flowing through the branches connected at the trijunction, which performs a circulator function. Further, we use this circulator function for a non-Abelian braiding of Majorana zero modes (MZMs). In the branches of the system we introduce pairs of MZMs which interact with each other through the phases of trijunction. The circulator function determines the phases of the trijunction and thus the coupling between the MZMs to gives rise to the braiding operation. We modify the system so that MZMs might be coupled to the external ones to perform qubit operations in a scalable design.

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Section: Resultsmentioning

confidence: 74%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Circulator function in a Josephson junction circuit and braiding of Majorana zero modes

Kim

2021

Sci Rep

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“…Several schemes for tunable qubit-qubit coupling have been proposed [40][41][42][43][44][45][46][47][48] following the original proposal by Makhlin et al [32]. We fabricated the design Fig.…”

Section: Tuneable Flux Qubit Couplingmentioning

confidence: 99%

Weak continuous measurements of multiqubits systems

Il’ichev

Ploeg

Grajcar

et al. 2009

Quantum Inf Process

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In this review we summarize our recent experiments on the investigation on superconducting qubits. Instead of strong projective measurement used by other groups in their first pioneering experiments we have proposed and realized a weak continuous readout which belongs to the class of quantum non-demolition measurements. Moreover, our scheme enables to measure a superconducting qubit at the so called sweet (or magic) point where a qubit is in a superposition of two classical states and its sensitivity to external noise is minimized. In this scheme, which is widely used nowadays, the superconducting oscillator coupled to superconducting qubit is used as a detector of the qubit's state. Such system is analogue to a system of a single atom interacting with photons in a cavity, which allows to study quantum electrodynamics in artificial macroscopic systems. Pushing this analogy we demonstrate Sisyphus cooling and amplification caused by energy exchange between an oscillator and a flux qubit. Using the Sisyphus effect we show consistency between the adiabatic weak continuous measurement in the ground state and the spectroscopic measurement. This allows us to characterize the more complicated system of coupled qubits by making use of the same method. We have realized and studied fixed ferromagnetic, antiferromagnetic as well as tunable qubit-qubit coupling. We argue that ground state measurements can be used for characterization of entangled states in coupled flux qubits. E. Il'ichev (B) · 123 134 E. Il'ichev et al.

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“…Especially, we use a phase coupling by introducing a connecting wire between the two qubit loops (see Fig. 1) [10] because the phase coupling gives more controllable parameters than the inductive coupling with respect for the manipulation of qubit states [11]. It is shown that the Josephson junction in the connecting superconducting wires plays a role of controller in determining exchange interactions between the two qubits.…”

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confidence: 99%

Realizable spin models and entanglement dynamics in superconducting flux qubit systems

Shi

Cho

et al. 2008

Phys. Rev. B

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Realizable spin models are investigated in a two superconducting flux qubit system. It is shown that a specific adjustment of system parameters in the two flux qubit system makes it possible to realize an artificial two-spin system that cannot be found naturally. For the artificial two-spin systems, time evolution of a prepared quantum state is discussed to quantify quantum entanglement dynamics. The concurrence and fidelity as a function of time are shown to reveal a characteristic entanglement dynamics of the artificial spin systems. It is found that the unentangled input state can evolute to be a maximally entangled output state periodically due to the exchange interactions induced by two-qubit flipping tunneling processes while single-qubit flipping tunneling processes plays a role of magnetic fields for the artificial spins. [6,7,8]. Moreover, such realizations of artificial spin systems make possible to observe entangled states of two qubits [1,2,4,5]. Indeed, for the time evolution of states in the experiments of charge [1] and phase qubits [4], a partial entanglement has been observed. An experiment of a capacitively coupled two phase qubits [5] shows that higher fidelity for the entanglement exhibits in an excited level. The higher fidelity is caused by two-qubit tunneling processes [9] between two qubit states, i.e., flipping both qubits. Such a two-qubit tunneling processes contributes exchange interactions between the two artificial spins.

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Coupling of Josephson current qubits using a connecting loop

Cited by 21 publications

References 14 publications

Circulator function in a Josephson junction circuit and braiding of Majorana zero modes

Circulator function in a Josephson junction circuit and braiding of Majorana zero modes

Weak continuous measurements of multiqubits systems

Realizable spin models and entanglement dynamics in superconducting flux qubit systems

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