Alexander Balatsky

Laguerre-Gaussian light induction of orbital currents and Kapitza stabilization in superconducting circuits

  1. Hennadii Yerzhakov,
  2. Tien-Tien Yeh,
  3. and Alexander Balatsky
We investigate the effects of a Laguerre-Gaussian (LG) beam on the superconducting state. We show that the vortex angular momentum of a LG beam affects the superconducting state and
induces currents. The induction of the current by light is illustrated on a Josephson loop and SQUID devices. In particular, we establish that coupling a dc SQUID to the AC magnetic flux of a LG beam can stabilize pi phase in the SQUID. This can happen via developing a global or local minimum in the effective potential at pi. In the latter case, this happens via the Kapitza mechanism.
arxiv pdf

Two-tone spectroscopy for the detection of two-level systems in superconducting qubits

  1. Olli Mansikkamäki,
  2. Alexander Tyner,
  3. Alexander Bilmes,
  4. Ilya Drozdov,
  5. and Alexander Balatsky
Two-level systems (TLS) of unclear physical origin are a major contributor to decoherence in superconducting qubits. The interactions of individual TLS with a qubit can be detected
via various spectroscopic methods, most of which have relied on the tunability of the qubit frequency. We propose a novel method that requires only a microwave drive and dispersive readout, and thus also works fixed-frequency qubits. The proposed two-tone spectroscopy involves a microwave pulse of varying frequency and length to excite TLSs of unknown frequencies, followed by a second pulse at the qubit frequency. TLS parameters can be estimated from the qubit population as a function of the first pulse frequency and length.
arxiv pdf