We consider two representative problems that deal with the
fluctuator-induced decoherence from two very different
perspectives-microscopic and macroscopic. In the first part, we consider an individual two-level system
inside a Josephson junction shunted by a resistor. If the TLS modulates the Josephson energy and/or is optically
active, it can be Rabi driven by the Josephson oscillation. The Rabi oscillations, in turn, translate into oscillations
of current and voltage which can be detected in noise measurements. This effect provides an option to
fully characterize the TLS inside Josephson junction and to find the TLS's contribution to the decoherence when
the junction is used as a qubit. In the second part, we study the contribution of an ensemble of non-stationary
glassy charge fluctuators on qubit decoherence. Low-temperature dynamics of insulating glasses is dominated
by a macroscopic concentration of tunneling two-level systems. Due to exponentially broad distribution of their
tunneling rates and the finite experimental manipulation timescales, some of the fluctuators are temporarily
stuck in high-energy non-thermal states. We find that at low enough temperatures, non-stationary contribution
due to these slow non-thermal fluctuators can dominate the stationary (thermal) one, and discuss how this effect
can be minimized.
Persistent high-frequency (hf) hopping conductivity near the middles of well developed quantum Hall plateaus has been studied in the Si modulated heterostructures GaAs/Al0.3Ga0.7As, both δ- and modulation doped, under successive infrared irradiation in the 0.8 - 1.44 micron region. The conductivity has been determined by simultaneous measurement of attenuation and velocity of surface acoustic waves. With the increase of the radiation dose the conductivity decreases, whereas the carrier density in the 2D channel grows. There is a threshold of the persistent conductivity from the low energy side located between 0.86 and 0.48 eV. The observed behavior can be attributed to the so-called DX- centers which are localized two-electron states bounded by local lattice distortion. Such states, as known, exist in Si-doped GaAs/AlxGa1-xAs with x ≈ 0.3. We believe that hf hopping is due to tunneling of electron pairs between a two-electron center and its empty neighbor.
Conference Committee Involvement (3)
Noise and Information in Nanoelectronics, Sensors, and Standards III
24 May 2005 | Austin, Texas, United States
Noise and Information in Nanoelectronics, Sensors, and Standards II
26 May 2004 | Maspalomas, Gran Canaria Island, Spain
Noise and Information in Nanoelectronics, Sensors, and Standards
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