Little–Parks oscillations at low temperatures: Gigahertz resonator method

Belkin, A.; Brenner, Matthew; Aref, Thomas; Ku, Jaseung; Bezryadin, Alexey

doi:10.1063/1.3593482

Cited by 14 publications

(19 citation statements)

References 17 publications

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“…In the present work, we study MQT in thin-wire superconducting loops by means of a microwave measurement technique that is capable of detecting individual phase slips [26]. We observe individual phase slips as isolated macroscopic tunneling events.…”

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confidence: 99%

“…Thus, the above constraint on the phase change can be rewritten as ϕ loop ðBÞ ≡ 2ϕ cc þ 2ϕ wire ¼ 2πn. This equation is used to describe Little-Parks (LP) oscillations [28,29] of various types [26,30] that appear when B is varied. The periodicity of these oscillations is related to the fact that whenever the magnetic field is such that 2ϕ cc ðBÞ ¼ 2πk, the family of free-energy minima is identical to the B ¼ 0 case, if the vorticity is redefined as n → ðn AE kÞ, where k is an integer [30].…”

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confidence: 99%

“…1 (see also Ref. [26] for additional technical details on the sample design and the measurement setup). A pair of superconducting nanowires fabricated by molecular templating [19,21] is integrated into the middle of the center conductor (c.c.)…”

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confidence: 99%

“…2. The transmission phase θ S21 ðJÞ is a multivalued function composed of a periodic set of parabolas that are separated by the Little-Parks period, J LP [26]. Each parabola corresponds to a state with particular vorticity.…”

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Formation of Quantum Phase Slip Pairs in Superconducting Nanowires

Belkin

Vakaryuk

et al. 2015

Phys. Rev. X

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Macroscopic quantum tunneling is a fundamental phenomenon of quantum mechanics related to the actively debated topic of quantum-to-classical transition. The ability to realize macroscopic quantum tunneling affects implementation of qubit-based quantum computing schemes and their protection against decoherence. Decoherence in qubits can be reduced by means of topological protection, e.g., by exploiting various parity effects. In particular, paired phase slips can provide such protection for superconducting qubits. Here, we report on the direct observation of quantum paired phase slips in thin-wire superconducting loops. We show that in addition to conventional single phase slips that change the superconducting order parameter phase by 2π, there are quantum transitions that change the phase by 4π. Quantum paired phase slips represent a synchronized occurrence of two macroscopic quantum tunneling events, i.e., cotunneling. We demonstrate the existence of a remarkable regime in which paired phase slips are exponentially more probable than single ones. DOI: 10.1103/PhysRevX.5.021023 Subject Areas: Mesoscopics, Quantum Information, SuperconductivityDecoherence and quantum noise are primary roadblocks for large-scale implementation of quantum computing that in many cases relies on the phenomenon of macroscopic quantum tunneling [1][2][3][4][5]. Decoherence is inherently related to the collapse of macroscopic wave functions caused by various environment-induced interactions. In quantum computers, detrimental effects of decoherence can be eliminated by means of quantum error correction as originally proposed by Shor [6]. An alternative approach was suggested by Kitaev [7], who argued that the use of topologically ordered quantum systems can eliminate the burden of quantum error correction. In such systems, qubits are implemented by topologically distinct states connected by a global operation (such as braiding, in the case of anyons) that cannot be mixed by a local perturbation.Less exotic schemes of topological protection based on various parity effects in superconducting circuits have also been presented [8][9][10][11]. The crucial component of these proposals is a device that discriminates between parity-conserving and parity-violating transitions. Ideally, such a device fully suppresses the latter, thus creating well-separated parity-based sectors in the Hilbert space, which are used as a "grid" for qubit operations.Here, we focus on a multiply-connected device formed by a superconducting loop containing homogeneous superconducting nanowires. Flux states of the loop are described by the winding number (vorticity) of the superconducting phase on a path encircling the loop. Transitions between different winding number states occur through phase slips taking place in the nanowires. Realization of a parityprotected qubit requires suppression of 2π phase slips, which change the winding number by 1, and a significant amplitude of 4π phase slips, which are parity-conserving [12][13][14] events. We term them single phase s...

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confidence: 99%

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confidence: 99%

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Formation of Quantum Phase Slip Pairs in Superconducting Nanowires

Belkin

Vakaryuk

et al. 2015

Phys. Rev. X

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“…An approach that can satisfy the above requirements is to include the Josephson junction into a loop with inductance L or alternatively build an asymmetric SQUID so that one Josephson junction serves as an inductance; see Ref. 22 and 23 for a recent experimental setup. With a magnetic bias, it is possible to add an external flux ϕ ex in the loop that takes the role of the bias current.…”

Section: Measurementmentioning

confidence: 99%

Korshunov instantons in a superconductor at elevated bias current

Otten¹,

Hassler²

2017

Phys. Rev. B

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Even at zero temperature dissipation reduces quantum fluctuations and tends to localize particles. A notable exception is the nonlinear dissipation due to quasiparticle tunneling in a Josephson junction. It is well known that quasiparticle dissipation does not suppress tunneling of the superconducting phase difference between next-nearest metastable phase states even though tunneling to the nearest phase state is suppressed. The reason is that the dissipative action admits an instanton solution, the so-called Korshunov instanton. Here, we analyze this model at elevated bias current I. We find that besides the known regime where the logarithm of the tunneling rate scales as I 2/3there is novel regime with a scaling I 2 . We argue that the increased tunneling rate that derives from the elevated bias current is favorable for an experimental verification of the Korshunov instantons.

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2012

Superconductivity in Nanowires

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Little–Parks oscillations at low temperatures: Gigahertz resonator method

Cited by 14 publications

References 17 publications

Formation of Quantum Phase Slip Pairs in Superconducting Nanowires

Formation of Quantum Phase Slip Pairs in Superconducting Nanowires

Korshunov instantons in a superconductor at elevated bias current

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