Microscopic origin of critical current fluctuations in large, small, and ultra-small area Josephson junctions

Faoro, Lara; Ioffe, L. B.

doi:10.1103/physrevb.75.132505

Cited by 36 publications

(36 citation statements)

References 25 publications

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“…(11), we show in Fig. (3) that the magnetisation obtained from the energy minimization does indeed behave like M ∝ (α − α c ) 1 2 close to the transition. The magnetisation data are again in good agreement with the QMC and SPSA results [16,17].…”

Section: Magnetization and Coherencementioning

confidence: 99%

“…The physics of quantum systems in contact with environmental degrees of freedom plays a fundamental role in many areas of physics, chemsitry and biology, including systems as diverse as solid state quantum computers [1,2], quantum impurities [3], and photosynthetic biomolecules [4][5][6][7][8]. A key theoretical model for the study of system-environment interactions is the spin-boson model (SBM), which consists of a two-level system (TLS) that is linearly coupled to an 'environment' of harmonic oscillators [9,10].…”

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confidence: 99%

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Generalized Polaron Ansatz for the Ground State of the Sub-Ohmic Spin-Boson Model: An Analytic Theory of the Localization Transition

et al. 2011

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The sub-ohmic spin-boson model is known to possess a novel quantum phase transition at zero temperature between a localised and delocalised phase. We present here an analytical theory based on a variational ansatz for the ground state, which describes a continuous localization transition with mean-field exponents for 0 < s < 0.5. Our results for the critical properties show good quantitiative agreement with previous numerical results, and we present a detailed description of all the spin observables as the system passes through the transition. Analysing the ansatz itself, we give an intuitive microscopic description of the transition in terms of the changing correlations between the system and bath, and show that it is always accompanied by a divergence of the lowfrequency boson occupations. The possible relevance of this divergence for some numerical approaches to this problem is discussed and illustrated by looking at the ground state obtained using density matrix renormalisation group methods.The physics of quantum systems in contact with environmental degrees of freedom plays a fundamental role in many areas of physics, chemsitry and biology, including systems as diverse as solid state quantum computers[1, 2], quantum impurities [3], and photosynthetic biomolecules [4][5][6][7][8]. A key theoretical model for the study of system-environment interactions is the spin-boson model (SBM), which consists of a two-level system (TLS) that is linearly coupled to an 'environment' of harmonic oscillators [9,10]. Although this model has been studied extensively, there are still many open problems in SBM physics, most notably those concerning the quantum phase transition (QPT) between delocalised and localised phases that exists in the SBM when the oscillators are characterised by sub-Ohmic spectral densities.The standard quantum-classical mapping predicts that the sub-ohmic SBM should be equivalent to a classical Ising spin chain with long-range interactions, and predicts a continuous magnetic transition with mean-field critical exponents for 0 < s < 0.5. In Ref.[11], a continuous transition in the sub-Ohmic SBM was observed using the numerical renormalisation group (NRG) technique for all values of 0 < s < 1, but the critical properties of the transition were found to be non-mean-field for 0 < s < 0.5. It was suggested that this implied a breakdown of the classical to quantum mapping, and some subsequent work in this and other systems has supported this claim [12,13]. However, it is now believed that the nonmean-field results found by NRG in 0 < s < 0.5 are incorrect, and arise from the truncation of the number of states N b used to describe each oscillator in the Wilson chain [14,15]. Recent studies of the sub-Ohmic QPT using quantum monte carlo (QMC) [16], sparse polynomial space approach (SPSA) [17], and an extended coherent state technique have indeed found mean-field critical exponents for 0 < s < 0.5 [18].In this article we propose a variational ansatz for the ground state of the sub-Ohmic SBM for 0 < s < 0.5 whi...

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Section: Magnetization and Coherencementioning

confidence: 99%

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confidence: 99%

Generalized Polaron Ansatz for the Ground State of the Sub-Ohmic Spin-Boson Model: An Analytic Theory of the Localization Transition

et al. 2011

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“…4,5 Several microscopic models of TLFs have been proposed. [6][7][8][9] It was suggested 4,10 that in charge qubits the relaxation is due to charge fluctuators which are simultaneously responsible for the 1 / f charge noise. 11 On the other hand, the flux noise might also be due to a large number of paramagnetic impurities.…”

Section: Introductionmentioning

confidence: 99%

Relaxation of Josephson qubits due to strong coupling to two-level systems

2009

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We investigate the energy relaxation ͑T 1 ͒ process of a qubit coupled to a bath of dissipative two-level fluctuators ͑TLFs͒. We consider the fluctuators strongly coupled to the qubit both in the limit of spectrally sparse single TLFs as well as in the limit of spectrally dense TLFs. We conclude that the avoided level crossings, usually attributed to very strongly coupled single TLFs, could also be caused by many weakly coupled spectrally dense fluctuators.

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“…In this case two-level defects could be formed by Andreev bound states 20 or Kondo impurities. 21,22 Since the form of the potential in the qubit circuit depends on the strength of the critical current, a modulation of I C will always result in a direct change in the level splitting in the circuit. Since we do not observe signatures of longitudinal coupling in our experiments ͑as has also been shown in flux qubits 10 ͒, we rule out this coupling mechanism and assume the TLS to be a charged defect.…”

Section: Introductionmentioning

confidence: 99%

Multiphoton spectroscopy of a hybrid quantum system

et al. 2010

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We report on experimental multiphoton spectroscopy of a hybrid quantum system consisting of a superconducting phase qubit coherently coupled to an intrinsic two-level system ͑TLS͒. We directly probe hybridized states of the combined qubit-TLS system in the strongly interacting regime, where both the qubit-TLS coupling and the driving cannot be considered as weak perturbations. This regime is described by a theoretical model which incorporates anharmonic corrections, multiphoton processes and decoherence. We present a detailed comparison between experiment and theory and find excellent agreement over a wide range of parameters.

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Microscopic origin of critical current fluctuations in large, small, and ultra-small area Josephson junctions

Cited by 36 publications

References 25 publications

Generalized Polaron Ansatz for the Ground State of the Sub-Ohmic Spin-Boson Model: An Analytic Theory of the Localization Transition

Generalized Polaron Ansatz for the Ground State of the Sub-Ohmic Spin-Boson Model: An Analytic Theory of the Localization Transition

Relaxation of Josephson qubits due to strong coupling to two-level systems

Multiphoton spectroscopy of a hybrid quantum system

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