We report on the quadrupling of the transition spectrum of an Al/AlO ${}_{x}$ /Al Cooper-pair box (CPB) charge qubit in the $4.0--7.3$ GHz frequency range. The qubit was coupled to a quasilumped-element Al superconducting resonator and measured at a temperature of 25 mK. We obtained good matches between the observed spectrum and the spectra calculated from a model Hamiltonian containing two distinct low-excitation energy two-level systems (TLS) coupled to the CPB. In our model, each TLS has a charge that tunnels between two sites in a local potential and induces a change in the CPB critical current. By fitting the model to the spectrum, we have extracted microscopic parameters of the fluctuators including the well asymmetry, tunneling rate, and a surprisingly large fractional change ( $30%--40%$ ) in the critical current (12 nA). This large change is consistent with a Josephson junction with a nonuniform tunnel barrier containing a few dominant conduction channels and a TLS that modulates one of them.We report on the quadrupling of the transition spectrum of an Al/AlO${}_{x}$/Al Cooper-pair box (CPB) charge qubit in the $4.0--7.3$ GHz frequency range. The qubit was coupled to a quasilumped-element Al superconducting resonator and measured at a temperature of 25 mK. We obtained good matches between the observed spectrum and the spectra calculated from a model Hamiltonian containing two distinct low-excitation energy two-level systems (TLS) coupled to the CPB. In our model, each TLS has a charge that tunnels between two sites in a local potential and induces a change in the CPB critical current. By fitting the model to the spectrum, we have extracted microscopic parameters of the fluctuators including the well asymmetry, tunneling rate, and a surprisingly large fractional change ($30%--40%$) in the critical current (12 nA). This large change is consistent with a Josephson junction with a nonuniform tunnel barrier containing a few dominant conduction channels and a TLS that modulates one of them.

arXiv:1305.3962Physical Review BMay 28, 201318 citations

Two-Level Systems

Ulrich Hohenester

Graduate texts in physicsDec 18, 20190 citations

Two-Level Systems

Brian P. Anderson

SPIE eBooksSep 12, 20190 citations

Atom and photon measurement in cooperative scattering by cold atoms

Tom Bienaimé, M. Petruzzo, D. Bigerni +2 more

In this paper, we study cooperative scattering of low intensity light by a cloud of N two-level systems. We include the incident laser field driving these two-level systems and compute the radiation pressure force on the center of mass of the cloud. This signature is of particular interest for experiments with laser cooled atoms. Including the complex coupling between dipoles in a scalar model for dilute clouds of two-level systems, we obtain expression for cooperative scattering forces taking into account the collective Lamb shift. We also derive the expression of the radiation pressure force on a large cloud of two-level systems from an heuristic approach and show that at lowest driving intensities this force is identical for a product and an entangled state.In this paper, we study cooperative scattering of low intensity light by a cloud of N two-level systems. We include the incident laser field driving these two-level systems and compute the radiation pressure force on the center of mass of the cloud. This signature is of particular interest for experiments with laser cooled atoms. Including the complex coupling between dipoles in a scalar model for dilute clouds of two-level systems, we obtain expression for cooperative scattering forces taking into account the collective Lamb shift. We also derive the expression of the radiation pressure force on a large cloud of two-level systems from an heuristic approach and show that at lowest driving intensities this force is identical for a product and an entangled state.

arXiv:1201.3240Journal of Modern OpticsJul 12, 201168 citations

Controlling cooperativity of a metastable open system coupled weakly to a noisy environment

Victor I. Teslenko, Oleksiy L. Kapitanchuk, Zhao Yang

The notion of cooperativity comprises a specific characteristic of a multipartite system concerning its ability to demonstrate a sigmoidal-type response of varying sensitivities to input stimuli in transitions between states under controlled conditions. From a statistical physics viewpoint, in this work we attempt to describe the cooperativity by the stability of a metastable open system with respect to irreversibility. To treat the evolution of a system weakly coupled to the environment in a kinetic framework, we consider two fluctuating energy levels of different dimensionalities, initial population of one level, reversible transitions of population between the levels, and irreversible depopulation of another level. An average is made over level fluctuations and environment vibrations so that an inter-level transition rate can be obtained accounting for the influences of external control on level position and dimensionality. It is found that the cooperativity of the two-level system is bounded approximately between 0.736 and unity, with the lower bound indicating worsening system stability.The notion of cooperativity comprises a specific characteristic of a multipartite system concerning its ability to demonstrate a sigmoidal-type response of varying sensitivities to input stimuli in transitions between states under controlled conditions. From a statistical physics viewpoint, in this work we attempt to describe the cooperativity by the stability of a metastable open system with respect to irreversibility. To treat the evolution of a system weakly coupled to the environment in a kinetic framework, we consider two fluctuating energy levels of different dimensionalities, initial population of one level, reversible transitions of population between the levels, and irreversible depopulation of another level. An average is made over level fluctuations and environment vibrations so that an inter-level transition rate can be obtained accounting for the influences of external control on level position and dimensionality. It is found that the cooperativity of the two-level system is bounded approximately between 0.736 and unity, with the lower bound indicating worsening system stability.

Chinese Physics BFeb 1, 20157 citations

IN TWO-LEVEL SYSTEMS

N. N. Bogolyubov, A. S. Shumovskiǐ

Jan 1, 19850 citations

We report on the quadrupling of the transition spectrum of an Al/AlO

{}_{x}

/Al Cooper-pair box (CPB) charge qubit in the

4.0--7.3

GHz frequency range. The qubit was coupled to a quasilumped-element Al superconducting resonator and measured at a temperature of 25 mK. We obtained good matches between the observed spectrum and the spectra calculated from a model Hamiltonian containing two distinct low-excitation energy two-level systems (TLS) coupled to the CPB. In our model, each TLS has a charge that tunnels between two sites in a local potential and induces a change in the CPB critical current. By fitting the model to the spectrum, we have extracted microscopic parameters of the fluctuators including the well asymmetry, tunneling rate, and a surprisingly large fractional change (

30%--40%

) in the critical current (12 nA). This large change is consistent with a Josephson junction with a nonuniform tunnel barrier containing a few dominant conduction channels and a TLS that modulates one of them.