Silvia Viola Kusminskiy

Magnon-mediated quantum gates for superconducting qubits

  1. Martijn Dols,
  2. Sanchar Sharma,
  3. Lenos Bechara,
  4. Yaroslav M. Blanter,
  5. Marios Kounalakis,
  6. and Silvia Viola Kusminskiy
We propose a hybrid quantum system consisting of a magnetic particle inductively coupled to two superconducting transmon qubits, where qubit-qubit interactions are mediated via magnons.
We show that the system can be tuned into three different regimes of effective qubit-qubit interactions, namely a transverse (XX+YY), a longitudinal (ZZ) and a non-trivial ZX interaction. In addition, we show that an enhanced coupling can be achieved by employing an ellipsoidal magnet, carrying anisotropic magnetic fluctuations. We propose a scheme for realizing two-qubit gates, and simulate their performance under realistic experimental conditions. We find that iSWAP and CZ gates can be performed in this setup with an average fidelity ≳99% , while an iCNOT gate can be applied with an average fidelity ≳88%. Our proposed hybrid circuit architecture offers an alternative platform for realizing two-qubit gates between superconducting qubits and could be employed for constructing qubit networks using magnons as mediators.
arxiv pdf

Engineering Entangled Coherent States of Magnons and Phonons via a Transmon Qubit

  1. Marios Kounalakis,
  2. Silvia Viola Kusminskiy,
  3. and Yaroslav M. Blanter
We propose a scheme for generating and controlling entangled coherent states (ECS) of magnons, i.e. the quanta of the collective spin excitations in magnetic systems, or phonons in
mechanical resonators. The proposed hybrid circuit architecture comprises a superconducting transmon qubit coupled to a pair of magnonic Yttrium Iron Garnet (YIG) spherical resonators or mechanical beam resonators via flux-mediated interactions. Specifically, the coupling results from the magnetic/mechanical quantum fluctuations modulating the qubit inductor, formed by a superconducting quantum interference device (SQUID). We show that the resulting radiation-pressure interaction of the qubit with each mode, can be employed to generate maximally-entangled states of magnons or phonons. In addition, we numerically demonstrate a protocol for the preparation of magnonic and mechanical Bell states with high fidelity including realistic dissipation mechanisms. Furthermore, we have devised a scheme for reading out the prepared states using standard qubit control and resonator field displacements. Our work demonstrates an alternative platform for quantum information using ECS in hybrid magnonic and mechanical quantum networks.
arxiv pdf