Demonstration of controlled-NOT quantum gates on a pair of superconducting quantum bits

Plantenberg, J. H.; Groot, P. C. de; Harmans, C.J.P.M.; Mooij, J. E.

doi:10.1038/nature05896

Cited by 342 publications

(304 citation statements)

References 16 publications

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“…[42][43][44][45][46][47][48][49][50]. In these works the basic parameters of qubits and coupling constants have been measured and also some relaxation characteristics of coupled qubits have been studied.…”

Section: Introductionmentioning

confidence: 99%

“…In these works the basic parameters of qubits and coupling constants have been measured and also some relaxation characteristics of coupled qubits have been studied. Rabi-spectroscopy of two coupled qubits both experimentally and theoretically have been investigated in publications 44,45,47,49,50 . Recently different schemes of controlled coupling between two or more qubits have been proposed 48,[51][52][53] .…”

Section: Introductionmentioning

confidence: 99%

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Amplitude spectroscopy of two coupled qubits

2012

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We study the effect of a time-dependent driving field with a large amplitude on a system composed of two coupled qubits (two-level systems). Using the rotating wave approximation (RWA) makes it possible to find simple conditions for resonant excitation of the four-level system. We find that the resonance conditions include the coupling strength between the qubits. Numerical simulations confirm the qualitative conclusions following from the RWA. To reveal the peculiarities of resonant transitions caused by the quasi-level motion and crossing in a periodic driving field, we use Floquet states, which determine the precise intermediate states of the system. Calculating the quasi-energy states of the multi-level system makes it possible to find the transition probabilities and build interference patterns for the transition probabilities. The interference patterns demonstrate the possibility of obtaining various pieces of information about the qubits, since the positions of transition-probability maxima depend on various system parameters, including the coupling strength between the qubits.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Amplitude spectroscopy of two coupled qubits

2012

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“…Superconducting qubits utilize charge [5][6][7] or flux [8] degrees of freedom, or energy levels quantization in a single current-biased Josephson junction [9,10]. Inter-qubit coupling [15][16][17][18][19][20] and also quantum logic gates [21][22][23] have been reported later. Further progress in the field slowed down due to obvious decoherence issues that are still to be overcome in order to implement a working quantum computer.…”

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confidence: 99%

Josephson charge qubits: a brief review

Pashkin

Astafiev

Yamamoto

et al. 2009

Quantum Inf Process

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The field of solid-state quantum computation is expanding rapidly initiated by our original charge qubit demonstrations. Various types of solid-state qubits are being studied, and their coherent properties are improving. The goal of this review is to summarize achievements on Josephson charge qubits. We cover the results obtained in our joint group of NEC Nano Electronics Research Laboratories and RIKEN Advanced Science Institute, also referring to the works done by other groups. Starting from a short introduction, we describe the principle of the Josephson charge qubit, its manipulation and readout. We proceed with coupling of two charge qubits and implementation of a logic gate. We also discuss decoherence issues. Finally, we show how a charge qubit can be used as an artificial atom coupled to a resonator to demonstrate lasing action.

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“…Indeed, the entanglements between two charges, 7 phase, 8,9 and flux qubits 10,11 have been reported. While the timely evolving states in the experiments of charge qubits 7 exhibit a partial entanglement, the excited level ͑eigenstate͒ of capacitively coupled two phase qubits 9 shows higher fidelity for the entanglement.…”

mentioning

confidence: 99%

“…As a macroscopic quantum system, superconducting qubit systems have been investigated intensively in experiments because their system parameters can be controlled to manipulate quantum states coherently. Indeed, the entanglements between two charges, 7 phase, 8,9 and flux qubits 10,11 have been reported. While the timely evolving states in the experiments of charge qubits 7 exhibit a partial entanglement, the excited level ͑eigenstate͒ of capacitively coupled two phase qubits 9 shows higher fidelity for the entanglement.…”

mentioning

confidence: 99%

Macroscopic Greenberger-Horne-Zeilinger andWstates in flux qubits

Kim

Cho

2008

Phys. Rev. B

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We investigate two types of genuine three-qubit entanglement, known as the Greenberger-Horne-Zeilinger ͑GHZ͒ and W states, in a macroscopic quantum system. Superconducting flux qubits are theoretically considered in order to generate such states. A phase coupling is proposed to offer enough strength of interactions between qubits. While an excited state can be the W state, the GHZ state is formed at the ground state of the three flux qubits. The GHZ and W states are shown to be robust against external flux fluctuations for feasible experimental realizations. As a macroscopic quantum system, superconducting qubit systems have been investigated intensively in experiments because their system parameters can be controlled to manipulate quantum states coherently. Indeed, the entanglements between two charges, 7 phase, 8,9 and flux qubits 10,11 have been reported. While the timely evolving states in the experiments of charge qubits 7 exhibit a partial entanglement, the excited level ͑eigenstate͒ of capacitively coupled two phase qubits 9 shows higher fidelity for the entanglement. The experiments in Ref. 10 show a possibility that two flux qubits can be entangled by a macroscopic quantum tunneling between two-qubit states, flipping both qubits. Actually, the higher fidelity in the capacitively coupled two phase qubits is caused by the two-qubit tunneling processes. 9 In a very recent study, the two-qubit tunneling process was theoretically shown to play an important role in generating the Bell states, maximally entangled, in the ground and excited states. 12 For multipartite entanglements in superconducting qubit systems, there have been few studies. To produce the GHZ state in three charge qubits, only a way of doing a local qubit operation via time evolutions was suggested. 13 As one of the possible directions to produce such multipartite entanglements, then it is natural to ask how to create the W state as well as the GHZ state in the eigenstates of superconducting three-qubit systems. Here, we consider three flux qubits. Normally, the interaction strength between inductively coupled flux qubits 14 is not so strong that the controllable range of interaction is not sufficiently wide. To control a wide range of interaction strengths in the qubits, we use the phase-coupling scheme [15][16][17][18][19] for three qubit ͓see Fig. 1͑a͔͒ which enables one to generate the GHZ and W states and to keep them robust against external flux fluctuations for feasible experimental realizations.We start with the model shown in Fig. 1͑a͒. The Hamiltonian is written by Ĥ = 1 2 P i T M ij −1 P j + U eff ͑ˆ͒, where The periodic boundary conditions involved in the qubit loops and the connecting loops can be written aswhere q = a, b, and c is qubit index and r, s, and n q integers. Here, f q ϵ ⌽ q / ⌽ 0 with external flux ⌽ q and the superconducting unit flux quantum ⌽ 0 = h / 2e. Two independent conditions in Eqs. ͑2͒ and ͑3͒ are the boundary conditions for connecting loops. For simplicity, we consider E J2 = E J3 = E J and C 2 = C 3 = C,...

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Demonstration of controlled-NOT quantum gates on a pair of superconducting quantum bits

Cited by 342 publications

References 16 publications

Amplitude spectroscopy of two coupled qubits

Amplitude spectroscopy of two coupled qubits

Josephson charge qubits: a brief review

Macroscopic Greenberger-Horne-Zeilinger andWstates in flux qubits

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