The study of frequency‐dependent intrinsic dissipation in a highly transparent Josephson junction by means of quantum‐bit (qubit) spectroscopy is proposed. The spectral density of the effective dissipative bath may contain significant contributions from Andreev bound states coupled to fluctuations of the Josephson phase. Varying either the bias current applied to the junction or magnetic flux through a superconducting ring in the radiofrequency superconducting quantum interference device (rf‐SQUID) setup, one can tune the level splitting value close to the bottom of the Josephson potential well. Monitoring the qubit energy relaxation time one can probe the spectral density of the effective dissipative bath and unambiguously identify the contribution emerging from Andreev levels.The study of frequency‐dependent intrinsic dissipation in a highly transparent Josephson junction by means of quantum‐bit (qubit) spectroscopy is proposed. The spectral density of the effective dissipative bath may contain significant contributions from Andreev bound states coupled to fluctuations of the Josephson phase. Varying either the bias current applied to the junction or magnetic flux through a superconducting ring in the radiofrequency superconducting quantum interference device (rf‐SQUID) setup, one can tune the level splitting value close to the bottom of the Josephson potential well. Monitoring the qubit energy relaxation time one can probe the spectral density of the effective dissipative bath and unambiguously identify the contribution emerging from Andreev levels.

arXiv:1810.00750physica status solidi (RRL) - Rapid Research LettersAug 24, 20182 citations

Decoherence in Josephson vortex quantum bits: Long-Josephson-junction approach to a two-state system

Ju H. Kim, Ramesh P. Dhungana, Kee-Su Park

We investigated decoherence of a Josephson vortex quantum bit (qubit) in dissipative and noisy environment. As the Josephson vortex qubit (JVQ) is fabricated by using a long Josephson junction (LJJ), we use the perturbed sine-Gordon equation to describe the phase dynamics representing a two-state system and estimate the effects of quasiparticle dissipation and weakly fluctuating critical and bias currents on the relaxation time ${T}_{1}$ and on the dephasing time ${T}_{\ensuremath{\phi}}$. We show that the critical current fluctuation does not contribute to dephasing of the qubit in the lowest order approximation. Modeling the weak current variation from magnetic field fluctuations in the LJJ by using the Gaussian colored noise with long correlation time, we show that the coherence time ${T}_{2}$ is limited by the low frequency current noise at very low temperatures. Also, we show that a ultra-long coherence time may be obtained from the JVQ by using experimentally accessible value of physical parameters.We investigated decoherence of a Josephson vortex quantum bit (qubit) in dissipative and noisy environment. As the Josephson vortex qubit (JVQ) is fabricated by using a long Josephson junction (LJJ), we use the perturbed sine-Gordon equation to describe the phase dynamics representing a two-state system and estimate the effects of quasiparticle dissipation and weakly fluctuating critical and bias currents on the relaxation time ${T}_{1}$ and on the dephasing time ${T}_{\ensuremath{\phi}}$. We show that the critical current fluctuation does not contribute to dephasing of the qubit in the lowest order approximation. Modeling the weak current variation from magnetic field fluctuations in the LJJ by using the Gaussian colored noise with long correlation time, we show that the coherence time ${T}_{2}$ is limited by the low frequency current noise at very low temperatures. Also, we show that a ultra-long coherence time may be obtained from the JVQ by using experimentally accessible value of physical parameters.

Physical Review BJun 6, 200621 citations

Decoherence in Josephson Qubits

R. McDermott

Bulletin of the American Physical SocietyMar 14, 20060 citations

Bistable Josephson cell as a single microwave photon sensor

D. S. Pashin, M. V. Bastrakova

The dissipative dynamics of a bistable Josephson cell in a transmission line resonator in a weakly dissipative regime was studied theoretically and numerically. The bistable cell consists of a quantronium qubit and a nonlinear bifurcation amplifier. Under the rotating wave approximation, the problem of the system evolution in a boson thermostat is reduced to the Pauli equation. Using the master equation, we have numerically studied the dissipative dynamics of the system. It was shown that the nonlinear bifurcation amplifier can determine the qubit states and the system can be used as a detector of single microwave photons.The dissipative dynamics of a bistable Josephson cell in a transmission line resonator in a weakly dissipative regime was studied theoretically and numerically. The bistable cell consists of a quantronium qubit and a nonlinear bifurcation amplifier. Under the rotating wave approximation, the problem of the system evolution in a boson thermostat is reduced to the Pauli equation. Using the master equation, we have numerically studied the dissipative dynamics of the system. It was shown that the nonlinear bifurcation amplifier can determine the qubit states and the system can be used as a detector of single microwave photons.

International Journal of Quantum InformationJan 24, 20201 citation

{T}_{1}

and on the dephasing time ${T}_{\ensuremath{\phi}}$. We show that the critical current fluctuation does not contribute to dephasing of the qubit in the lowest order approximation. Modeling the weak current variation from magnetic field fluctuations in the LJJ by using the Gaussian colored noise with long correlation time, we show that the coherence time

{T}_{2}

is limited by the low frequency current noise at very low temperatures. Also, we show that a ultra-long coherence time may be obtained from the JVQ by using experimentally accessible value of physical parameters.