Quantum Dynamics in a Camelback Potential of a dc SQUID

Abstract

We investigate a quadratic-quartic anharmonic oscillator formed by a potential well between two potential barriers. We realize this novel potential with a dc SQUID at near-zero current bias and flux bias near half a flux quantum. Escape out of the central well can occur via tunneling through either of the two barriers. We find good agreement with a generalized double-path macroscopic quantum tunneling theory. We also demonstrate an "optimal line" in current and flux bias along which the oscillator, which can be operated as a phase qubit, is insensitive to decoherence due to low-frequency current fluctuations.

Hysteretic Flux Response and Nondegenerate Gain of Flux-Driven Josephson Parametric Amplifiers

“…Note that for j tr = 0 there is no tilt of the potential landscape along the ϕ + -direction. In contrast to other works investigating hysteretic dc-SQUIDs [36][37][38], in our experiments the transport current j tr is negligible at all times, meaning that the possible equilibrium phase differences (ϕ min + , ϕ min − ) of the dc-SQUID are given by the local minima shown in Fig. 3.…”

Quantum dynamics of superconducting nano-circuits: phase qubit, charge qubit and rhombi chains

“…Below we will discuss different quantum properties of a dc SQUID: the two-dimensional effect of MQT escape [2], the quantum measurement procedure and its performance [3,7] and also the coherent oscillations in a multilevel system [6]. We will consider the decoherence processes in this quantum circuit [8] and mention recent results obtained at zero bias current where the half-flux-quantum biased SQUID behaves as a phase qubit [20].…”

“…We demonstrate tunability of the coupling over a large frequency range. Whenever appropriate, we will comment on various sources of decoherence [8,20].…”

Mesoscopic electron transport and atomic gases, a review of Frank W. J. Hekking's scientific work

“…At low microwave power, the dc SQUID corresponds to a phase qubit with only the two first levels involved in the quantum dynamics. This limit is relevant when a zero-biased SQUID with a quartic potential was studied and a Camelback phase qubit demonstrated [62], results obtained in collaboration with Emile Hoskinson and Florent Lecocq at Néel Institute.…”