Low-frequency noise in low 1/f noise dc SQUID’s

Abstract

We demonstrate that the low-frequency noise in our edge junction dc superconducting quantum interference devices, with a basic 1/f flux noise of 2×10−12 Φ20/Hz at 1 Hz, can all be accounted for in terms of junction critical current fluctuations. A novel modulation readout scheme is able to cancel the effect of junction critical current fluctuations and reduce our total noise to 1×10−12 Φ20/Hz at 0.1 Hz, a level that is three times lower than the lowest flux noise ever previously reported at this frequency.

Decoherence of a Josephson qubit due to coupling to two-level systems

“…1/f noise in the critical current of Josephson junctions has been observed experimentally [41,42,43,44]. The microscopic source of this noise is unknown, though it has been suggested that the tunneling of atoms or ions is involved [16].…”

SQUID Concepts and Systems

“…These workers also were able to reduce the 1/f noise in the system using a modified version of the modulation scheme of Foglietti ~&. 39 Although.they need further development, cryogenic digital feedback schemes offer several advantages: they are compact, produce a digitized output for transmission to room temperature, offer wide flux-locked bandwidths, and need not add any noise to the intrinsic noise of the SQUID.…”

“…• An alternate scheme, second harmonic detection (SHAD), has recently been developed by Foglietti et al 39 , and we shall briefly describe it. In Fig.…”

Model for1/fFlux Noise in SQUIDs and Qubits

“…The l/f flux noise S Φ 1/2 (1 Hz) was within a factor of 3 of 10 μΦ 0 Hz -1/2 for Nb-or Pb-based SQUIDs at 4.2 K, even though the loop areas ranged over 6 orders of magnitude; here, Φ denotes magnetic flux and Φ 0 ≡ h/2e is the flux quantum. Subsequently, other authors found rather lower levels of l/f flux noise at 1 Hz and 4.2 K, for example, 0.5 μΦ 0 Hz -1/2 [2] and 0.2 μΦ 0 Hz -1/2 [3]. Wellstood et al [4] reported values of S Φ 1/2 (1 Hz) of (4-10) μΦ 0 Hz -1/2 at temperatures below 0.1 K in 12 Nb, Pb and PbIn devices.…”