Joaquin Minguzzi

Sub-MHz SWAP spectroscopy of two-level systems in superconducting qubits

  1. Joaquin Minguzzi,
  2. John Clai Owens,
  3. Oskar Painter,
  4. Matthew H. Matheny,
  5. and Loren J. Swenson
An outstanding challenge in superconducting quantum circuits is mitigating loss from two-level system (TLS) defects. SWAP spectroscopy with flux-tunable qubits can detect individual
TLSs, but the Rabi chevrons that signal coherent exchange have been observed only for the most strongly coupled defects. Here, we introduce a sequence with fast flux pulses only at state preparation and readout, switched off during the energy-relaxation delay for finer frequency resolution and longer interaction times. We detect Rabi chevrons at swap rates as low as 0.1 MHz, an order of magnitude lower than previously reported. In the dressed-state picture, we fit the coherent swap oscillations to extract the TLS energy-relaxation time. These Rabi chevrons reveal coherent TLSs with a median energy-relaxation time of 10 microseconds, at coupling strengths previously associated with incoherent TLSs. The swap coherence times exceed the qubit T2* limited by flux noise, indicating that the dressed gap protects them from low-frequency 1/f noise.
arxiv pdf

Improving the lifetime of aluminum-based superconducting qubits through atomic layer etching and deposition

  1. Neha Mahuli,
  2. Joaquin Minguzzi,
  3. Jiansong Gao,
  4. Rachel Resnick,
  5. Sandra Diez,
  6. Cosmic Raj,
  7. Guillaume Marcaud,
  8. Matthew Hunt,
  9. Loren Swenson,
  10. Jefferson Rose,
  11. Oskar Painter,
  12. and Ignace Jarrige
We present a dry surface treatment combining atomic layer etching and deposition (ALE and ALD) to mitigate dielectric loss in fully fabricated superconducting quantum devices formed
from aluminum thin films on silicon. The treatment, performed as a final processing step prior to device packaging, starts by conformally removing the native metal oxide and fabrication residues from the exposed surfaces through ALE before \textit{in situ} encapsulating the metal surfaces with a thin dielectric layer using ALD. We measure a two-fold reduction in loss attributed to two-level system (TLS) absorption in treated aluminum-based resonators and planar transmon qubits. Treated transmons with compact capacitor plates and gaps achieve median Q and T1 values of 3.69±0.42×106 and 196±22~μs, respectively. These improvements were found to be sustained over several months. We discuss how the combination of ALE and ALD reverses fabrication-induced surface damages to significantly and durably improve device performance via a reduction of the TLS defect density in the capacitive elements.
arxiv pdf