771 research outputs found
Applications of nonequilibrium Kubo formula to the detection of quantum noise
The Kubo fluctuation-dissipation theorem relates the current fluctuations of
a system in an equilibrium state with the linear AC-conductance. This theorem
holds also out of equilibrium provided that the system is in a stationary state
and that the linear conductance is replaced by the (dynamic) conductance with
respect to the non equilibrium state. We provide a simple proof for that
statement and then apply it in two cases. We first show that in an excess noise
measurement at zero temperature, in which the impedance matching is maintained
while driving a mesoscopic sample out of equilibrium, it is the nonsymmetrized
noise power spectrum which is measured, even if the bare measurement, i.e.
without extracting the excess part of the noise, obtains the symmetrized noise.
As a second application we derive a commutation relation for the two components
of fermionic or bosonic currents which holds in every stationary state and
which is a generalization of the one valid only for bosonic currents. As is
usually the case, such a commutation relation can be used e.g. to derive
Heisenberg uncertainty relationships among these current components.Comment: 10 pages, Invited talk to be given by Y. I. at the SPIE Noise
Conference, Grand Canary, June 2004. Added reference and 2 footnotes,
corrected typo in Eq.
On testing the violation of the Clausius inequality in nanoscale electric circuits
The Clausius inequality, one of the classical formulations of the second law,
was recently found to be violated in the quantum regime. Here this result is
formulated in the context of a mesoscopic or nanoscale linear RLC circuit
interacting with a thermal bath. Previous experiments in this and related
fields are analyzed and possibilities of experimental detection of the
violation are pointed out. It is discussed that recent experiments reached the
range of temperatures, where the effect should be visible, and that a part of
the proposal was already confirmed.Comment: 5 pages revtex 4. No figure
Continuous-variable quantum non-demolishing interaction at a distance
A feasible setup of continuous-variable (CV) quantum non-demolishing (QND)
interaction at a distance is proposed. If two distant experimentalists are able
to locally perform identical QND interactions then the proposed realization
requires only a single quantum channel and classical communication between
them. A possible implementation of the proposed setup in recent quantum optical
laboratories is discussed and an influence of Gaussian noise in the quantum
channel on a quality of the implementation is analyzed. An efficient
realization of the QND interaction at a distance can be a basic step to
possible distributed quantum CV experiments between the distant laboratories.Comment: 5 pages, 2 figure
A low-noise series-array Josephson junction parametric amplifier
We have obtained parametric gain at 19 GHz from a distributed Josephson junction parametric amplifier whose active gain medium consists of a series array of 1000 Josephson junctions embedded in a coplanar waveguide. When cooled to 1.7 K the amplifier provides 16 dB gain in a mode where the internally generated double sideband noise referred to input is 0.5 ± 0.1 K. This noise is consistent with Nyquist noise generated from the losses. An instantaneous bandwidth of 125 MHz has been observed with a peak gain of 12 dB. The 3 dB compression point with a peak gain of 14.6 dB is -90.5 dB and the dynamic range is 38 dB
Position-momentum local realism violation of the Hardy type
We show that it is, in principle, possible to perform local realism violating
experiments of the Hardy type in which only position and momentum measurements
are made on two particles emanating from a common source. In the optical
domain, homodyne detection of the in-phase and out-of-phase amplitude
components of an electromagnetic field is analogous to position and momentum
measurement. Hence, local realism violations of the Hardy type are possible in
optical systems employing only homodyne detection.Comment: 10 pages, no figures, to be published in Physical Review
Witnessing Entanglement with Second-Order Interference
Second-order interference and Hanbury-Brown and Twiss type experiments can
provide an operational framework for the construction of witness operators that
can test classical and nonclassical properties of a Gaussian squeezed state
(GSS), and provide entanglement witness operators to study the separability
properties of correlated Gaussian squeezed sates.Comment: 10 pages, 12 figure
Theory of Microwave Parametric Down Conversion and Squeezing Using Circuit QED
We study theoretically the parametric down conversion and squeezing of
microwaves using cavity quantum electrodynamics of a superconducting Cooper
pair box (CPB) qubit located inside a transmission line resonator. The
non-linear susceptibility \chi_2 describing three-wave mixing can be tuned by
dc gate voltage applied to the CPB and vanishes by symmetry at the charge
degeneracy point. We show that the coherent coupling of different cavity modes
through the qubit can generate a squeezed state. Based on parameters realized
in recent successful circuit QED experiments, squeezing of 95% ~ 13dB below the
vacuum noise level should be readily achievable.Comment: 4 pages, accepted for publication in Phys. Rev. Let
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