arXiv subjects

B. Yurke

Publications and source records attributed to B. Yurke.

7 recordsLinked to original sources

arXiv2006

High fidelity transfer of an arbitrary quantum state between harmonic oscillators

It is shown that by switching a specific time-dependent interaction between a harmonic oscillator and a transmission line (a waveguide, an optical fiber, etc.) the quantum state of the oscillator can be transferred into that of another oscillator coupled to the distant other end of the line, with a fidelity that is independent of the initial state of both oscillators. For a transfer time $T$, the fidelity approaches 1 exponentially in $γT$ where $γ$ is a characteristic damping rate. Hence, a good fidelity is achieved even for a transfer time of a few damping times. Some implementations are discussed.

quant-ph↗

arXiv2006

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.

cond-mat.other↗

arXiv2004

Heisenberg constraints on mesoscopic and molecular amplifiers

Heisenberg uncertainty relations for current components impose constraints on the performance of linear amplifiers. Here we derive such constraints for amplifiers in which the input signal modulates a bias current in order to produce an amplified output. These amplifiers include transistors, macroscopic, mesoscopic, or molecular, operated as linear amplifiers.

cond-mat.mes-hall↗

arXiv2004

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 posses c-number commutators.

cond-mat.mes-hall↗

arXiv2004

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.

cond-mat.mes-hall↗

arXiv2002

What quantity is measured in an excess noise experiment?

Consider a measurement in which the current coming out of a mesoscopic sample is filtered around a given frequency, amplified, measured and squared. Then this process is repeated many times and the results are averaged. Often, two such measurements are performed on the same system in and out of equilibrium (the nonequilibrium state can be obtained by a variety of methods, e.g., by applying a DC voltage or electromagnetic radiation to the sample). The excess noise is defined as the difference in the noise between these two measurements. We find that this excess noise is given by the excess of the non-symmetrized power-spectrum of the current-noise. This result holds for a rather general class of experimental setups.

cond-mat.mes-hall↗

arXiv1996

Experimental Measurement of the Persistence Exponent of the Planar Ising Model

Using a twisted nematic liquid crystal system exhibiting planar Ising model dynamics, we have measured the scaling exponent $θ$ which characterizes the time evolution, $p(t) \sim t^{-θ}$, of the probability p(t) that the local order parameter has not switched its state by the time t. For 0.4 seconds to 200 seconds following the phase quench, the system exhibits scaling behavior and, measured over this interval, $θ= 0.19 \pm 0.031$, in good agreement with theoretical analysis and numerical simulations.

cond-mat.soft↗