Dynamical Spin Polarization of Excess Quasiparticles in Superconductors

Meyer, Jacques; Houzet, Manuel; Nazarov, Yuli V.

doi:10.1103/physrevlett.125.097006

Cited by 4 publications

(5 citation statements)

References 37 publications

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“…Also thickness variations [46] and unpaired surface spins [47] due to native oxide [48] may induce ∆-variations. Quasiparticles can be trapped at these suppressed ∆ regions [49,50], preventing recombination events and resulting in a background number of trapped quasiparticles, N t . At low temperatures, N qp (Eq.…”

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confidence: 99%

Strong reduction of quasiparticle fluctuations in a superconductor due to decoupling of the quasiparticle number and lifetime

et al. 2021

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We measure temperature-dependent quasiparticle fluctuations in a small Al volume, embedded in a NbTiN superconducting microwave resonator. The resonator design allows for readout close to equilibrium. By placing the Al film on a membrane, we enhance the fluctuation level and separate quasiparticle effects from phonon effects. When lowering the temperature, the recombination time saturates and the fluctuation level reduces by a factor ∼100. From this we deduce that the number of free quasiparticles is still thermal. Therefore, the theoretical, inverse relation between the quasiparticle number and recombination time is invalid in this experiment. This is consistent with quasiparticle trapping, where on-trap recombination limits the observed quasiparticle lifetime.

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confidence: 99%

Strong reduction of quasiparticle fluctuations in a superconductor due to decoupling of the quasiparticle number and lifetime

et al. 2021

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“…To conclude, the length scale l ϕ for the mesoscopic phase coherence of the superconducting quasiparticles was phenomenologically introduced in our description. The effect offers the possibility to directly probe quantum coherence of the superconducting quasiparticle states, and to bridge with the physics of quasiparticle poisoning [6][7][8][9][10][11][12][13], in connection with the tremendous interest in the superconducting circuits of quantum engineering. It seems that future experiments could be a guideline towards further progress in understanding this complex physics.…”

Section: Discussionmentioning

confidence: 99%

“…Superconductivity is a platform for fundamental studies of large-scale quantum systems [1][2][3][4] and for assembling quantum processors [5]. Superconducting quasiparticles can generally propagate over the entire sample and quasiparticle poisoning [6][7][8][9][10][11][12][13] turns out to severely limit the range of quantum mechanical coherence in superconductors. Superconducting devices with three or more terminals could naturally be used for fundamental studies of coherent quasiparticle propagation.…”

Section: Introductionmentioning

confidence: 99%

Ultralong-distance quantum correlations in three-terminal Josephson junctions

Mélin

2021

Phys. Rev. B

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In these studies, the distance between the contacts is limited by the zero-energy superconducting coherence length. Here, we demonstrate nonlocality and quantum correlations in voltage-biased three-terminal Josephson junctions over the ultralong distance that exceeds the superconducting coherence length by orders of magnitude. The effect relies on the interplay between the time-periodic Floquet-Josephson dynamics, Cooper pair splitting, and long-range coupling similar to the two-terminal Tomasch effect. We find crossover between the "Floquet-Andreev quartets" (if the spatial separation is smaller than the superconducting coherence length) and the "ultralong-distance Floquet-Tomasch clusters of Cooper pairs" if the separation exceeds the superconducting coherence length, possibly reaching the same 30 μm as in the Tomasch experiments. The effect can be detected with DC-transport and zero-frequency quantum current-noise cross-correlation experiments, and it can be used for fundamental studies of superconducting quasiparticle quantum coherence in the circuits of quantum engineering.

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“…It is expected that the considered ultralong-distance Floquet-Tomasch signal will be above detection threshold, given the large signal in Tomasch experiment [77][78][79] In our description, the length scale l ϕ for coherence of the BCS quasiparticles was phenomenologically introduced. The ultralong-distance Floquet-Tomasch effect offers the perspective of directly probing quantum coherence of the quasiparticle states in superconductors, and to bridge with the physics of quasiparticle poisoning [6][7][8][9][10][11][12][13] , in connection with the tremendous interest in the superconducting circuits of quantum engineering.…”

Section: Methodsmentioning

confidence: 99%

“…Superconductivity is dedicated platform for fundamental studies of large-scale quantum systems [1][2][3][4] and for assembling quantum processors 5 . Superconducting quasiparticles can generally propagate over the entire sample and quasiparticle poisoning [6][7][8][9][10][11][12][13] turns out to severely limit the range of quantum mechanical coherence in superconductors. Superconducting devices with more than three terminals could naturally be used for fundamental studies of coherent quasiparticle propagation.…”

Section: Introductionmentioning

confidence: 99%

Ultralong-distance quantum correlations in three-terminal Josephson junctions

Mélin

2021

Preprint

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In the paper, we address nonlocality and quantum correlations in three-terminal Josephson junctions, where the BCS superconductors S a , S b and S c are voltage-biased at (V a ,V b ,V c ) = (V, −V, 0) and V is a significant fraction of the gap. The constituting two-terminal S a -dot-S c and S c -dot-S b are connected at arbitrary distance R 0 on the grounded S c . The proposed interpretation of the numerical experiments relies on the interplay between the time-periodic Floquet-Josephson dynamics, Cooper pair splitting and the long-range Tomasch effect. We find cross-over between the "Floquet-Andreev quartets" (if R 0 ξ 0 is smaller than the superconducting coherence length), and the "ultralong-distance Floquet-Tomasch clusters of Cooper pairs" if R 0 l ϕ , where l ϕ ξ 0 is the mesoscopic coherence length of the BCS quasiparticles. Analytical theory is presented for the simplest cluster at voltage eV > ∆/2, i.e. the ultralong-distance Floquet-Tomasch octets, where ∆ is the superconducting gap. The range of the effect is conjectured to be the same as in the Tomasch experiment, i.e. the junctions can be remotely separated by the mesoscopic R 0 ≈ 30 µm which is orders of magnitude larger than the zero-energy BCS coherence length ξ 0 . Our results go beyond the paradigm of classical synchronization in the macroscopic Josephson circuits. The effect can be detected with dc-transport and zero-frequency quantum current-noise cross-correlation experiments, and it can be used for fundamental studies of superconducting quasiparticle quantum coherence in the circuits of quantum engineering.

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Dynamical Spin Polarization of Excess Quasiparticles in Superconductors

Cited by 4 publications

References 37 publications

Strong reduction of quasiparticle fluctuations in a superconductor due to decoupling of the quasiparticle number and lifetime

Strong reduction of quasiparticle fluctuations in a superconductor due to decoupling of the quasiparticle number and lifetime

Ultralong-distance quantum correlations in three-terminal Josephson junctions

Ultralong-distance quantum correlations in three-terminal Josephson junctions

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