Comment on `Aharonov--Casher-Effect Suppression of Macroscopic Tunneling of Magnetic Flux'

TL;DR

This paper critically examines a proposed device claiming to suppress macroscopic flux tunneling via destructive interference, arguing that the original Hamiltonian used is only valid under specific conditions, thus challenging the generality of the claim.

Contribution

It clarifies the limitations of the Hamiltonian used in the original proposal, showing the suppression effect is not universally valid.

Findings

The Hamiltonian in the original proposal is only valid under certain conditions.

The claimed suppression of flux tunneling is not generally applicable.

The analysis highlights the importance of Hamiltonian validity in quantum device predictions.

Abstract

A recent Letter [1] has proposed a device, consisting of an rf SQUID with the junction replaced by a double one, i.e. a Bloch transistor. For symmetric Josephson couplings, and for specific flux bias and gate voltage applied to the transistor's island, the tunneling of encircled flux between its two local potential minima is claimed to be suppressed completely due to destructive interference. This comment purports to show that this claim in general is not valid. Namely, the very Hamiltonian (1) in [1], from which the effect is derived, describes the circuit only under an additional condition. [1] J.R. Friedman and D.V. Averin, Phys. Rev. Lett._88_, 050403 (2002).