Miroslav Grajcar

Josephson Traveling Wave Parametric Amplifiers with Plasma oscillation phase-matching

  1. Emil Rizvanov,
  2. Samuel Kern,
  3. Pavol Neilinger,
  4. and Miroslav Grajcar
High gain and large bandwidth of traveling-wave parametric amplifier exploiting the nonlinearity of Josephson Junctions can be achieved by fulfilling the so-called phase-matching condition.
This condition is usually addressed by placing resonant structures along the waveguide or by periodic modulations of its parameters, creating gaps in the waveguide’s dispersion. Here, we propose to employ the Josephson junctions, which constitute the centerline of the amplifier, as resonant elements for phase matching. By numerical simulations in JoSIM (and WRspice) software, we show that Josephson plasma oscillations can be utilized to create wavevector mismatch sufficient for phase matching as well as to prevent the conversion of the pump energy to higher harmonics. The proposed TWPA design has a gain of 15 dB and a 3.5 GHz bandwidth, which is comparable to the state-of-the-art TWPAs.
arxiv pdf

Simulating long-distance entanglement in quantum spin chains by superconducting flux qubits

  1. Stefano Zippilli,
  2. Miroslav Grajcar,
  3. Evgeni Il'ichev,
  4. and Fabrizio Illuminati
We investigate the performance of superconducting flux qubits for the adiabatic quantum simulation of long distance entanglement (LDE), namely a finite ground-state entanglement between
the end spins of an open quantum spin chain. As such, LDE can be considered an elementary precursor of edge modes and topological order. We discuss two possible implementations which simulate open chains with uniform bulk and weak end bonds, either with Ising or with XX nearest-neighbor interactions. In both cases we discuss a suitable protocol for the adiabatic preparation of the ground state in the physical regimes featuring LDE. In the first case the adiabatic manipulation and the Ising interactions are realized using dc-currents, while in the second case microwaves fields are used to control the smoothness of the transformation and to realize the effective XX interactions. We demonstrate the adiabatic preparation of the end-to-end entanglement in chains of four qubits with realistic parameters and on a relatively fast time scale.
arxiv pdf