Biomedical subjects

Y Imry

Publications and source records attributed to Y Imry.

At least 19 recordsLinked to original sources

PubMed2006

Quantum noise minimization in transistor amplifiers.

General quantum restrictions on the noise performance of linear transistor amplifiers are used to identify the region in parameter space where the quantum-limited performance is achievable and to construct a practical procedure for approaching it experimentally using only the knowledge of directly measurable quantities: the gain, (differential) conductance, and the output noise. A specific example of resonant barrier transistors is discussed.

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PubMed2004

Generalized constraints on quantum amplification.

We derive quantum constraints on the minimal amount of noise added in linear amplification involving input or output signals whose component operators do not necessarily have c-number commutators, as is the case for fermion currents. This is a generalization of constraints derived for the amplification of bosonic fields whose components possess c-number commutators.

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PubMed2003

Persistent currents in interacting Aharonov-Bohm interferometers and their enhancement by acoustic radiation.

We consider an Aharonov-Bohm interferometer, connected to two electronic reservoirs, with a quantum dot embedded on one of its arms. We find a general expression for the persistent current at steady state, valid for the case where the electronic system is free of interactions except on the dot. The result is used to derive the modification in the persistent current brought about by coupling the quantum dot to a phonon source. The magnitude of the persistent current is found to be enhanced in an appropriate range of the intensity of the acoustic source.

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PubMed2003

Enhanced sensitivity of the transmission phase of a quantum dot to Kondo correlations.

The strong sensitivity of the transmission phase through a quantum dot embedded into one arm of a two-wave Aharonov-Bohm interferometer to the Kondo effect is explained. The enhancement takes place because of the buildup of the exchange scattering on the dot due to Kondo correlations even much above T(K). The enhanced exchange competes with the potential scattering, which is always weak. Both cases of the Anderson impurity model and a multilevel quantum dot are considered. In the latter case in addition to the description of peculiar phase behavior a mechanism leading to ferromagnetic Kondo coupling in quantum dots is proposed.

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PubMed2003

Magnetic response of disordered metallic rings: large contribution of far levels.

We calculate the orbital linear magnetic response of disordered metallic rings to an Aharonov-Bohm flux using the BCS model for attractive electron-electron interaction. The contribution of all levels including those up to a high energy cutoff results in a much larger value than previously obtained using the local interaction model. The possible relevance of our results to the resolution of the discrepancy between the experimental and theoretical values for the ensemble-averaged persistent currents in these systems is discussed.

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PubMed2002

Broken unitarity and phase measurements in Aharonov-Bohm interferometers.

Aharonov-Bohm mesoscopic solid-state interferometers yield a conductance which contains a term cos(phi+beta), where phi relates to the magnetic flux. Experiments with a quantum dot on one of the interfering paths aim to relate beta to the dot's intrinsic Friedel transmission phase alpha(1). For closed systems, which conserve the electron current (unitarity), the Onsager relation requires that beta = 0 or pi. For open systems, we show that in general beta depends on the details of the broken unitarity. Although it gives information on the resonances of the dot, beta is generally not equal to alpha(1). A direct relation between beta and alpha(1) requires specific ways of opening the system, which are discussed.

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PubMed2001

Shot-noise in transport and beam experiments.

Consider two Fermi gases with the same average currents: a transport gas, as in solid-state experiments where the chemical potentials of terminal 1 is mu+eV and of terminal 2 and 3 is mu, and a beam, i.e., electrons entering only from terminal 1 having energies between mu and mu+eV. By expressing the current noise as a sum over single-particle transitions we show that the temporal current fluctuations are very different: The beam is noisier due to allowed single-particle transitions into empty states below mu. Surprisingly, the correlations between terminals 2 and 3 are the same.

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PubMed2000

Towards an explanation of the mesoscopic double-slit experiment: A new model for charging of a quantum Dot

For a quantum dot (QD) in the intermediate regime between integrable and fully chaotic, the widths of single-particle levels naturally differ by orders of magnitude. In particular, the width of one strongly coupled level may be larger than the spacing between other, very narrow, levels. In this case many consecutive Coulomb blockade peaks are due to occupation of the same broad level. Between the peaks the electron jumps from this level to one of the narrow levels, and the transmission through the dot at the next resonance essentially repeats that at the previous one. This offers a natural explanation to the recently observed behavior of the transmission phase in an interferometer with a QD.

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PubMed1995