Effects of external driving on the coherence time of a Josephson junction qubit in a bath of two level fluctuators

Abstract

We study the effect of external driving on the two level systems (TLSs) assumed to be a major obstacle in increasing the coherence time of solid state Josephson-junction qubits. We find, by use of a Bloch-Redfield approach, that external driving has two major effects on the TLS. The first is increased fluctuations between the two states of the TLS, the significance of this effect compared to thermal fluctuations depend on the energy splitting of the TLS compared to temperature. The second effect is a reduction in the intensity of the noise spectrum at low frequencies, and at the same time an increase in intensity around the renormalized Rabi frequency of the TLS, the driving frequency and at beatings between these two frequencies. Finally we study the ensemble averaged noise spectrum for a typical distribution of TLSs known to give origin to $\propto 1/f$ noise. We find that strong driving leads to reduced noise at low frequencies, and therefore to an increased dephasing time $T_2^Q$ of the qubit. However this effect is exponentially suppressed when the driving frequency is large compared to temperature, as we typically find for Josephson qubits. We suggest that external driving at frequencies much lower than the qubit frequency might be used in order to enhance the the qubit coherence time.

13 pages, 5 figures

References in corpus (8)

• Low-frequency noise as a source of dephasing of a qubit
• Low- and high-frequency noise from coherent two-level systems
• Decoherence in qubits due to low-frequency noise
• Lifetime and Coherence of Two-Level Defects in a Josephson Junction
• Decoupling a Cooper-pair box to enhance the lifetime to 0.2 ms
• Saturation of Two Level Systems and Charge Noise in Josephson Junction Qubits
• Decoherence times of universal two-qubit gates in the presence of broad-band noise
• A Josephson Junction Microscope for Low-frequency Fluctuators

Cited by in corpus (4)

• 1/f noise: implications for solid-state quantum information
• Decoherence of a qubit due to a quantum fluctuator or to a classical telegraph noise
• Spin noise at electron paramagnetic resonance
• Evolution of the inhomogeneously-broadened spin noise spectrum with ac drive