Nonreciprocal devices based on voltage-tunable junctions

  1. Catherine Leroux,
  2. Adrian Parra-Rodriguez,
  3. Ross Shillito,
  4. Agustin Di Paolo,
  5. William D. Oliver,
  6. Charles M. Marcus,
  7. Morten Kjaergaard,
  8. András Gyenis,
  9. and Alexandre Blais
We propose to couple the flux degree of freedom of one mode with the charge degree of freedom of a second mode in a hybrid superconducting-semiconducting architecture. Nonreciprocity
can arise in this architecture in the presence of external static magnetic fields alone. We leverage this property to engineer a passive on-chip gyrator, the fundamental two-port nonreciprocal device which can be used to build other nonreciprocal devices such as circulators. We analytically and numerically investigate how the nonlinearity of the interaction, circuit disorder and parasitic couplings affect the scattering response of the gyrator.

Protected hybrid superconducting qubit in an array of gate-tunable Josephson interferometers

  1. Constantin Schrade,
  2. Charles M. Marcus,
  3. and András Gyenis
We propose a protected qubit based on a modular array of superconducting islands connected by semiconductor Josephson interferometers. The individual interferometers realize effective
cos2ϕ elements that exchange `pairs of Cooper pairs‘ between the superconducting islands when gate-tuned into balance and frustrated by a half flux quantum. If a large capacitor shunts the ends of the array, the circuit forms a protected qubit because its degenerate ground states are robust to offset charge and magnetic field fluctuations for a sizable window around zero offset charge and half flux quantum. This protection window broadens upon increasing the number of interferometers if the individual elements are balanced. We use an effective spin model to describe the system and show that a quantum phase transition point sets the critical flux value at which protection is destroyed.

Destructive Little-Parks Effect in a Full-Shell Nanowire-based Transmon

  1. Deividas Sabonis,
  2. Oscar Erlandsson,
  3. Anders Kringhøj,
  4. Bernard van Heck,
  5. Thorvald W. Larsen,
  6. Ivana Petkovic,
  7. Peter Krogstrup,
  8. Karl D. Petersson,
  9. and Charles M. Marcus
A semiconductor transmon with an epitaxial Al shell fully surrounding an InAs nanowire core is investigated in the low EJ/EC regime. Little-Parks oscillations as a function of fluxalong the hybrid wire axis are destructive, creating lobes of reentrant superconductivity separated by a metallic state at a half-quantum of applied flux. In the first lobe, phase winding around the shell can induce topological superconductivity in the core. Coherent qubit operation is observed in both the zeroth and first lobes. Splitting of parity bands by coherent single-electron coupling across the junction is not resolved beyond line broadening, placing a bound on Majorana coupling, EM/h < 10 MHz, much smaller than the Josephson coupling EJ/h ~ 4.7 GHz.[/expand]

Superconducting Gatemon Qubit based on a Proximitized Two-Dimensional Electron Gas

  1. Lucas Casparis,
  2. Malcolm R. Connolly,
  3. Morten Kjaergaard,
  4. Natalie J. Pearson,
  5. Anders Kringhøj,
  6. Thorvald W. Larsen,
  7. Ferdinand Kuemmeth,
  8. Tiantian Wang,
  9. Candice Thomas,
  10. Sergei Gronin,
  11. Geoffrey C. Gardner,
  12. Michael J. Manfra,
  13. Charles M. Marcus,
  14. and Karl D. Petersson
The coherent tunnelling of Cooper pairs across Josephson junctions (JJs) generates a nonlinear inductance that is used extensively in quantum information processors based on superconducting
circuits, from setting qubit transition frequencies and interqubit coupling strengths, to the gain of parametric amplifiers for quantum-limited readout. The inductance is either set by tailoring the metal-oxide dimensions of single JJs, or magnetically tuned by parallelizing multiple JJs in superconducting quantum interference devices (SQUIDs) with local current-biased flux lines. JJs based on superconductor-semiconductor hybrids represent a tantalizing all-electric alternative. The gatemon is a recently developed transmon variant which employs locally gated nanowire (NW) superconductor-semiconductor JJs for qubit control. Here, we go beyond proof-of-concept and demonstrate that semiconducting channels etched from a wafer-scale two-dimensional electron gas (2DEG) are a suitable platform for building a scalable gatemon-based quantum computer. We show 2DEG gatemons meet the requirements by performing voltage-controlled single qubit rotations and two-qubit swap operations. We measure qubit coherence times up to ~2 us, limited by dielectric loss in the 2DEG host substrate.