J. Yu

Charge qubits in the ultrastrong coupling regime

  1. J. Yu,
  2. F. A. Cárdenas-López,
  3. C. K. Andersen,
  4. E. Solano,
  5. and A. Parra-Rodriguez
We study the feasibility of reaching the ultrastrong (USC) and deep-strong coupling (DSC) regimes of light-matter interaction, in particular at resonance condition, with a superconducting
charge qubit, also known as Cooper-Pair box (CPB). We show that by shunting the charge qubit with a high-impedance LC-circuit, one can maximally reach both USC and DSC regimes exceeding the classical upper bound |g|≤ωqωr−−−−√/2 between two harmonic systems with frequencies ωq and ωr. In our case, the fundamental model corresponds to an enhanced quantum Rabi model, which contains a displacement field operator that breaks its internal parity symmetry. Furthermore, we consider a multipartite device consisting of two CPBs ultrastrongly coupled to an oscillator as a mediator and study a quantum state transfer protocol between a pair of transmon qubits, all of them subjected to local incoherent noise channels with realistic parameters. This work opens the door for studying light-matter interactions beyond the quantum Rabi model at extreme coupling strengths, providing a new building block for applications within quantum computation and quantum information processing.
arxiv pdf

Superconducting Circuit Architecture for Digital-Analog Quantum Computing

  1. J. Yu,
  2. J. C. Retamal,
  3. M. Sanz,
  4. E. Solano,
  5. and F. Albarrán-Arriagada
We propose a superconducting circuit architecture suitable for digital-analog quantum computing (DAQC) based on an enhanced NISQ family of nearest-neighbor interactions. DAQC makesa smart use of digital steps (single qubit rotations) and analog blocks (parametrized multiqubit operations) to outperform digital quantum computing algorithms. Our design comprises a chain of superconducting charge qubits coupled by superconducting quantum interference devices (SQUIDs). Using magnetic flux control, we can activate/deactivate exchange interactions, double excitation/de-excitations, and others. As a paradigmatic example, we present an efficient simulation of an ℓ×h fermion lattice (with 2<ℓ≤h), using only 2(2ℓ+1)2+24 analog blocks. The proposed architecture design is feasible in current experimental setups for quantum computing with superconducting circuits, opening the door to useful quantum advantage with fewer resources.[/expand]
arxiv pdf