Probing dynamics of an electron-spin ensemble via a superconducting resonator

We study spin relaxation and diffusion in an electron-spin ensemble of nitrogen impurities in diamond at low temperature (0.25-1.2 K) and polarizing magnetic field (80-300 mT). Measurements exploit mode- and temperature-dependent coupling of hyperfine-split sub-ensembles to the resonator. Temperature-independent spin linewidth and relaxation time suggest that spin diffusion limits spin relaxation. Depolarization of one sub-ensemble by resonant pumping of another indicates fast cross-relaxation compared to spin diffusion, with implications on use of sub-ensembles as independent quantum memories.Comment: 5 pages, 5 figures, and Supplementary Information (2 figures

Josephson φ_0-junction in nanowire quantum dots

The Josephson effect describes supercurrent flowing through a junction connecting two superconducting leads by a thin barrier. This current is driven by a superconducting phase difference ϕ between the leads. In the presence of chiral and time-reversal symmetry of the Cooper pair tunnelling process2, the current is strictly zero when ϕ vanishes. Only if these underlying symmetries are broken can the supercurrent for ϕ = 0 be finite. This corresponds to a ground state of the junction being offset by a phase ϕ_0, different from 0 or π. Here, we report such a Josephson ϕ0-junction based on a nanowire quantum dot. We use a quantum interferometer device to investigate phase offsets and demonstrate that ϕ_0 can be controlled by electrostatic gating. Our results may have far-reaching implications for superconducting flux- and phase-defined quantum bits as well as for exploring topological superconductivity in quantum dot systems

Josephson ϕ0-junction in nanowire quantum dots

International audienceThe Josephson effect describes supercurrent flowing througha junction connecting two superconducting leads by a thinbarrier1. This current is driven by a superconducting phasedifferenceφbetween the leads. In the presence of chiral andtime-reversal symmetry of the Cooper pair tunnelling process2,the current is strictly zero whenφvanishes. Only if theseunderlying symmetries are broken can the supercurrent forφ=0 be finite3–5. This corresponds to a ground state of thejunction being offset by a phaseφ0, different from 0 orπ.Here, we report such a Josephsonφ0-junction based on ananowire quantum dot. We use a quantum interferometerdevice to investigate phase offsets and demonstrate thatφ0can be controlled by electrostatic gating. Our results mayhave far-reaching implications for superconducting flux- andphase-defined quantum bits as well as for exploring topologicalsuperconductivity in quantum dot systems

Josephson φ0-junction in nanowire quantum dots

\u3cp\u3eThe Josephson effect describes supercurrent flowing through a junction connecting two superconducting leads by a thin barrier. This current is driven by a superconducting phase difference φbetween the leads. In the presence of chiral and time-reversal symmetry of the Cooper pair tunnelling process, the current is strictly zero when φvanishes. Only if these underlying symmetries are broken can the supercurrent for φ= 0 be finite. This corresponds to a ground state of the junction being offset by a phase φ0, different from 0 or π. Here, we report such a Josephson φ0 -junction based on a nanowire quantum dot. We use a quantum interferometer device to investigate phase offsets and demonstrate that φ0 can be controlled by electrostatic gating. Our results may have far-reaching implications for superconducting flux- and phase-defined quantum bits as well as for exploring topological superconductivity in quantum dot systems.\u3c/p\u3

Erratum: Josephson φ0-junction in nanowire quantum dots (vol 12, pg 568, 2016)

In the version of this Letter originally published ref. 34 was not updated and should have read: Gingrich, E. C. et al. Controllable 0-π Josephson junctions containing a ferromagnetic spin valve. Nature Phys. 12, 564–567 (2016). This has now been corrected in the online versions of the Letter

Erratum: Josephson φ0-junction in nanowire quantum dots (vol 12, pg 568, 2016)

In the version of this Letter originally published ref. 34 was not updated and should have read: Gingrich, E. C. et al. Controllable 0-π Josephson junctions containing a ferromagnetic spin valve. Nature Phys. 12, 564–567 (2016). This has now been corrected in the online versions of the Letter

Formation and electronic properties of InSb nanocrosses

Signatures of Majorana fermions have recently been reported from measurements on hybrid superconductor–semiconductor nanowire devices. Majorana fermions are predicted to obey special quantum statistics, known as non-Abelian statistics. To probe this requires an exchange operation, in which two Majorana fermions are moved around one another, which requires at least a simple network of nanowires. Here, we report on the synthesis and electrical characterization of crosses of InSb nanowires. The InSb wires grow horizontally on flexible vertical stems, allowing nearby wires to meet and merge. In this way, near-planar single-crystalline nanocrosses are created, which can be measured by four electrical contacts. Our transport measurements show that the favourable properties of the InSb nanowire devices—high carrier mobility and the ability to induce superconductivity—are preserved in the cross devices. Our nanocrosses thus represent a promising system for the exchange of Majorana fermions

Andreev spectrum of a Josephson junction with spin-split superconductors

The Andreev bound states and charge transport in a Josephson junction between two superconductors with intrinsic exchange fields are studied. We find that for a parallel configuration of the exchange fields in the superconductors the discrete spectrum consists of two pairs of spin-split states. The Josephson current in this case is mainly carried by bound states. In contrast, for the antiparallel configuration we find that there is no spin-splitting of the bound states and that for phase differences smaller than a certain critical value there are no bound states at all. Hence the supercurrent is only carried by states in the continuous part of the spectrum. Our predictions can be tested by performing a tunneling spectroscopy of a weak link between two spin-split superconductors