98 research outputs found
Integrated Electronic Transport and Thermometry at milliKelvin Temperatures and in Strong Magnetic Fields
We fabricated a He-3 immersion cell for transport measurements of
semiconductor nanostructures at ultra low temperatures and in strong magnetic
fields. We have a new scheme of field-independent thermometry based on quartz
tuning fork Helium-3 viscometry which monitors the local temperature of the
sample's environment in real time. The operation and measurement circuitry of
the quartz viscometer is described in detail. We provide evidence that the
temperature of two-dimensional electron gas confined to a GaAs quantum well
follows the temperature of the quartz viscometer down to 4mK
Particle-hole Asymmetry of Fractional Quantum Hall States in the Second Landau Level of a Two-dimensional Hole System
We report the first unambiguous observation of a fractional quantum Hall
state in the Landau level of a two-dimensional hole sample at the filling
factor . We identified this state by a quantized Hall resistance and
an activated temperature dependence of the longitudinal resistance and found an
energy gap of 40 mK. To our surprise the particle-hole conjugate state at
filling factor in our sample does not develop down to 6.9 mK. This
observation is contrary to that in electron samples in which the 7/3 state is
typically more stable than the 8/3 state. We present evidence that the
asymmetry between the 7/3 and 8/3 states in our hole sample is due to Landau
level mixing
High Kinetic Inductance Superconducting Nanowire Resonators for Circuit QED in a Magnetic Field
We present superconducting microwave-frequency resonators based on NbTiN
nanowires. The small cross section of the nanowires minimizes vortex
generation, making the resonators resilient to magnetic fields. Measured
intrinsic quality factors exceed in a T in-plane magnetic
field, and in a mT perpendicular magnetic field. Due to
their high characteristic impedance, these resonators are expected to develop
zero-point voltage fluctuations one order of magnitude larger than in standard
coplanar waveguide resonators. These properties make the nanowire resonators
well suited for circuit QED experiments needing strong coupling to quantum
systems with small electric dipole moments and requiring a magnetic field, such
as electrons in single and double quantum dots
Strong spin-photon coupling in silicon
We report the strong coupling of a single electron spin and a single
microwave photon. The electron spin is trapped in a silicon double quantum dot
and the microwave photon is stored in an on-chip high-impedance superconducting
resonator. The electric field component of the cavity photon couples directly
to the charge dipole of the electron in the double dot, and indirectly to the
electron spin, through a strong local magnetic field gradient from a nearby
micromagnet. This result opens the way to the realization of large networks of
quantum dot based spin qubit registers, removing a major roadblock to scalable
quantum computing with spin qubits
Quantitative Analysis of the Disorder Broadening and the Intrinsic Gap for the Fractional Quantum Hall State
We report a reliable method to estimate the disorder broadening parameter
from the scaling of the gaps of the even and major odd denominator fractional
quantum Hall states of the second Landau level. We apply this technique to
several samples of vastly different densities and grown in different MBE
chambers. Excellent agreement is found between the estimated intrinsic and
numerically obtained energy gaps for the fractional quantum Hall
state. Futhermore, we quantify, for the first time, the dependence of the
intrinsic gap at on Landau level mixing.Comment: PRB 84, R121305 (2011
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