Stacked Josephson junctions in view of macroscopic quantum experiments

Granata, C.; Corato, V.; Monaco, A.; Ruggiero, B.; Russo, M.; Silvestrini, P.

doi:10.1063/1.1391238

Cited by 21 publications

(6 citation statements)

References 14 publications

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“…L 12 , the mutual inductance between the two rings, could be controlled experimentally by a further device with Josephson junctions [20] and switched off for convenience in performing other operations.…”

Section: A Two Variablesmentioning

confidence: 99%

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Adiabatic evolution of a coupled-qubit Hamiltonian

et al. 2003

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We present a general method for studying coupled qubits driven by adiabatically changing external parameters. Extended calculations are provided for a two-bit Hamiltonian whose eigenstates can be used as logical states for a quantum CNOT gate. From a numerical analysis of the stationary Schroedinger equation we find a set of parameters suitable for representing CNOT, while from a time-dependent study the conditions for adiabatic evolution are determined. Specializing to a concrete physical system involving SQUIDs, we determine reasonable parameters for experimental purposes. The dissipation for SQUIDs is discussed by fitting experimental data. The low dissipation obtained supports the idea that adiabatic operations could be performed on a time scale shorter than the decoherence time.

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Section: A Two Variablesmentioning

confidence: 99%

“…The technology to control this coupling may need to be developed, but could be reasonably provided by stacked junctions [20], or small doublejunctions loop [19], interrupting the coupling transformers. The coupling is then controlled by external current signals.…”

Section: B System Designmentioning

confidence: 99%

Adiabatic evolution of a coupled-qubit Hamiltonian

et al. 2003

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“…2e is the flux quantum, h is the Planck's constant, and c is the light velocity) manipulation of I c allows one to control the B x field. In the experiment[17] I c = 0 (and B x = 0) for I inj ≈ 2.5 mA. Using the electrical signals instead of the localized magnetic fluxes for conrolling the B x field would allow one to speed up the quantum computer operations and to simplify the design.…”

mentioning

confidence: 99%

“…At the same time, the fast independent control of magnetic fluxes through the different SQUIDs with the distance ∼ 1 µm between them and the switching time ∼ 1 ns represents a challenge to the present-day technology. As an alternative, the B x field can be manipulated by using recently proposed [17] Nb/AlO x Nb-Al/AlO x /Nb stacked Josephson junctions instead of SQUIDs. In the double Josephson junction device, injection current I inj (of the order of several mA) in the control junction induces variation of the Josephson critical current I c (of the order of several µA).…”

Section: Introductionmentioning

confidence: 99%

Quantum logic operations and creation of entanglement in a scalable superconducting quantum computer with long-range constant interaction between qubits

et al. 2005

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We consider a one-dimensional chain of many superconducting quantum interference devices (SQUIDs), serving as charge qubits. Each SQUID is coupled to its nearest neighbors through constant capacitances. We study the quantum logic operations and implementation of entanglement in this system. Arrays with two and three qubits are considered in detail. We show that the creation of entanglement with an arbitrary number of qubits can be implemented, without systematic errors, even when the coupling between qubits is not small. A relatively large coupling constant allows one to increase the clock speed of the quantum computer. We analytically and numerically demonstrate the creation of the entanglement for this case, which can be a good test for the experimental implementation of a relatively simple quantum protocol with many qubits. We discuss a possible application of our approach for implementing universal quantum logic for more complex algorithms by decreasing the coupling constant and, correspondingly, decreasing the clock speed.The errors introduced by the long-range interaction for the universal logic gates are estimated analytically and calculated numerically. Our results can be useful for experimental implementation of quantum algorithms using controlled magnetic fluxes and gate voltages applied to the SQUIDs. The algorithms discussed in this paper can be implemented using already existing technologies in superconducting systems with constant inter-qubit coupling.

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“…Such a device is also designable including meanderlike filtering stages 15 or with a switchable on-off flux transformer. 16 In Fig. 1 the picture of a SQUID device is shown.…”

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confidence: 99%

Measurement of the effective dissipation in an rf SQUID system

et al. 2003

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We present an experimental study of the effective dissipation of a fully integrated Nb/AlO x /Nb Josephson device consisting of a rf superconducting quantum interference device ͑SQUID͒ coupled to a readout system based on a dc SQUID sensor. In the classical regime data on the decay rate from the metastable flux states of rf SQUID are reported. The low dissipation level and the good insulation of the probe from the external noise are encouraging in view of building a macroscopic quantum device.

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Stacked Josephson junctions in view of macroscopic quantum experiments

Cited by 21 publications

References 14 publications

Adiabatic evolution of a coupled-qubit Hamiltonian

Adiabatic evolution of a coupled-qubit Hamiltonian

Quantum logic operations and creation of entanglement in a scalable superconducting quantum computer with long-range constant interaction between qubits

Measurement of the effective dissipation in an rf SQUID system

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