Saturation of two-level systems and charge noise in Josephson junction qubits
نویسندگان
چکیده
We study the charge noise SQ in Josephson qubits produced by fluctuating two-level systems TLSs with electric-dipole moments in the substrate. The TLSs are driven by an alternating electric field of angular frequency and electric field intensity I. It is not widely appreciated that TLS in small qubits can easily be strongly saturated if I Ic, where Ic is the critical electric field intensity. To investigate the effect of saturation on the charge noise, we express the noise spectral density in terms of density-matrix elements. To determine the dependence of the density-matrix elements on the ratio I / Ic, we find the steady-state solution for the density matrix using the Bloch-Redfield differential equations. We then obtain an expression for the spectral density of charge fluctuations as a function of frequency f and the ratio I / Ic. We find 1 / f charge noise at low frequencies, and that the charge noise is white constant at high frequencies. Using a flat density of states, we find that TLS saturation has no effect on the charge noise at either high or low frequencies.
منابع مشابه
Decoherence of a Josephson qubit due to coupling to two-level systems
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 s...
متن کاملDelocalized oxygen as the origin of two-level defects in Josephson junctions.
One of the key problems facing superconducting qubits and other Josephson junction devices is the decohering effects of bistable material defects. Although a variety of phenomenological models exist, the true microscopic origin of these defects remains elusive. For the first time we show that these defects may arise from delocalization of the atomic position of the oxygen in the oxide forming t...
متن کاملDecoherence in josephson phase qubits from junction resonators.
Although Josephson junction qubits show great promise for quantum computing, the origin of dominant decoherence mechanisms remains unknown. Improving the operation of a Josephson junction based phase qubit has revealed microscopic two-level systems or resonators within the tunnel barrier that cause decoherence. We report spectroscopic data that show a level splitting characteristic of coupling ...
متن کامل1/f Flux noise in Josephson phase qubits.
We present a new method to measure 1/f noise in Josephson quantum bits (qubits) that yields low-frequency spectra below 1 Hz. A comparison of the noise taken at positive and negative bias of a phase qubit shows the dominant noise source to be flux noise and not junction critical-current noise, with a magnitude similar to that measured previously in other systems. Theoretical calculations show t...
متن کامل