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

Abstract

Noise and decoherence are major obstacles to the implementation of Josephson junction qubits in quantum computing. Recent experiments suggest that two level systems (TLS) in the oxide tunnel barrier are a source of decoherence. We explore two decoherence mechanisms in which these two level systems lead to the decay of Rabi oscillations that result when Josephson junction qubits are subjected to strong microwave driving. (A) We consider a Josephson qubit coupled resonantly to a two level system, i.e., the qubit and TLS have equal energy splittings. As a result of this resonant interaction, the occupation probability of the excited state of the qubit exhibits beating.

Lifetime and Coherence of Two-Level Defects in a Josephson Junction

“…(1). We approximate the deformation potential by ¼ A is the extracted dipole size, we get % 1 eV, consistent with defects in other dielectrics [3]. Since the dielectric layer thickness is much smaller than the relevant phonon wavelength, the speed of sound in Eq.…”

“…Two-level defects in amorphous insulators are of fundamental interest due to their impact on many low temperature properties, such as heat conductivity [1] and the generation of 1=f noise [2,3]. On the practical side, these effects limit the operation of solid state devices, for example, amplifiers [4] and CCD detectors [5], and increase the dielectric loss of insulators [6].…”

Materials in superconducting quantum bits

“…39 There are two primary ways by which a TLS in the tunnel barrier can interact with the qubit. 40 In the fi rst scenario, the dipole moment of the TLS couples directly to the voltage across the junction. 41 When the TLS and qubit are in resonance, charge fl uctuations in the former drive phase oscillations in the latter, and the two quantum systems become coupled.…”

Electromagnetically induced transparency in superconducting quantum circuits: Effects of decoherence, tunneling, and multilevel crosstalk

“…The present work carries the spirit of previous investigations in which additional degrees of freedom (beyond two-level models) were required to explain quantitatively experimental Rabi oscillations in SQCs. Examples of these works include resonant tunneling across the barrier [31], diagonal dipole matrix elements [32], and coupling to additional degrees of freedom outside the SQC, such as micro-resonators [27,33]. Just as EIT is sensitive to decoherence, it will be similarly sensitive to effects beyond the idealized three-level model.…”