arXiv subjects

J. D. Strand

Publications and source records attributed to J. D. Strand.

4 recordsLinked to original sources

arXiv2013

First-order sideband transitions with flux-driven asymmetric transmon qubits

We demonstrate rapid, first-order sideband transitions between a superconducting resonator and a frequency-modulated transmon qubit. The qubit contains a substantial asymmetry between its Josephson junctions leading to a linear portion of the energy band near the resonator frequency. The sideband transitions are driven with a magnetic flux signal of a few hundred MHz coupled to the qubit. This modulates the qubit splitting at a frequency near the detuning between the dressed qubit and resonator frequencies, leading to rates up to 85 MHz for exchanging quanta between the qubit and resonator.

cond-mat.supr-con↗

arXiv2012

Process verification of two-qubit quantum gates by randomized benchmarking

We implement a complete randomized benchmarking protocol on a system of two superconducting qubits. The protocol consists of randomizing over gates in the Clifford group, which experimentally are generated via an improved two-qubit cross-resonance gate implementation and single-qubit unitaries. From this we extract an optimal average error per Clifford of 0.0936. We also perform an interleaved experiment, alternating our optimal two-qubit gate with random two-qubit Clifford gates, to obtain a two-qubit gate error of 0.0653. We compare these values with a two-qubit gate error of ~0.12 obtained from quantum process tomography, which is likely limited by state preparation and measurement errors.

quant-ph↗

arXiv2009

Evidence for the E_2u model of the superconducting order parameter in UPt_3 from Josephson interferometry

We present data on the modulation of the critical current with applied magnetic field in UPt_3-Cu-Pb Josephson junctions and SQUIDs. The junctions were fabricated on polished surfaces of UPt_3 single crystals. The shape of the resulting diffraction patterns provides phase sensitive information on the superconducting order parameter. Our corner junction data show asymmetric patterns with respect to magnetic field, indicating a complex order parameter, and both our junction and SQUID measurements point to a phase shift of Pi, supporting the E_2u representation of the order parameter.

cond-mat.supr-con↗

arXiv2003

Very Low Temperature Tunnelling Spectroscopy in the heavy fermion superconductor PrOs$_4$Sb$_{12}$

We present scanning tunnelling spectroscopy measurements on the heavy fermion superconductor PrOs$_4$Sb$_{12}$. Our results show that the superconducting gap opens over a large part of the Fermi surface. The deviations from isotropic BCS s-wave behavior are discussed in terms of a finite distribution of values of the superconducting gap.

cond-mat.supr-con↗