Cross-talk in superconducting qubit lattices with tunable couplers – comparing transmon and fluxonium architectures

  1. F. Lange,
  2. L. Heunisch,
  3. H. Fehske,
  4. D. P. DiVincenzo,
  5. and M. J. Hartmann
Cross-talk between qubits is one of the main challenges for scaling superconducting quantum processors. Here, we use the density-matrix renormalization-group to numerically analyze
lattices of superconducting qubits from a perspective of many-body localization. Specifically, we compare different architectures that include tunable couplers designed to decouple qubits in the idle state, and calculate the residual ZZ interactions as well as the inverse participation ratio in the computational basis states. For transmon qubits outside of the straddling regime, the results confirm that tunable C-shunt flux couplers are significantly more efficient in mitigating the ZZ interactions than tunable transmons. A recently proposed fluxonium architecture with tunable transmon couplers is demonstrated to also maintain its strong suppression of the ZZ interactions in larger systems, while having a higher inverse participation ratio in the computational basis states than lattices of transmon qubits. Our results thus suggest that fluxonium architectures may feature lower cross talk than transmon lattices when designed to achieve similar gate speeds and fidelities.

Canonical Circuit Quantization with Non-Reciprocal Devices

  1. A. Parra-Rodriguez,
  2. I. L. Egusquiza,
  3. D. P. DiVincenzo,
  4. and E. Solano
Non-reciprocal devices effectively mimic the breaking of time-reversal symmetry for the subspace of dynamical variables that it couples, and they can be used to create chiral information
processing networks. We study how to systematically include ideal gyrators and circulators into Lagrangian and Hamiltonian descriptions of lumped-element electrical networks. The proposed theory is of wide applicability in general non-reciprocal networks on the quantum regime. We apply it to useful and pedagogical examples of circuits containing Josephson junctions and non-reciprocal ideal elements described by admittance matrices, and compare it with the more involved treatment of circuits based on non-reciprocal devices characterized by impedance and/or scattering matrices. Finally, we discuss the dual quantization of circuits containing phase-slip junctions and non-reciprocal devices.

Dispersive Qubit Measurement by Interferometry with Parametric Amplifiers

  1. Sh. Barzanjeh,
  2. D. P. DiVincenzo,
  3. and B. M. Terhal
We perform a detailed analysis of how an amplifier-based interferometer can be used to enhance the quality of a dispersive qubit measurement, such as one performed on a superconducting
transmon qubit, using homodyne detection on an amplified microwave signal. Our modeling makes a realistic assessment of what is possible in current circuit-QED experiments; in particular, we take into account the frequency-dependence of the qubit-induced phase shift for short microwaves pulses. We compare the possible signal-to-noise ratios obtainable with (single-mode) SU(1,1) interferometers with the current coherent measurement and find a considerable reduction in measurement error probability in an experimentally-accessible range of parameters.