arXiv subjects

Tamas Geszti

Publications and source records attributed to Tamas Geszti.

4 recordsLinked to original sources

arXiv2010

Post-selected weak measurement beyond the weak value

Closed expressions are derived for the quantum measurement statistics of pre-and postselected gaussian particle beams. The weakness of the pre-selection step is shown to compete with the non-orthogonality of post-selection in a transparent way. The approach is shown to be useful in analyzing post-selection-based signal amplification, allowing measurements to be extended far beyond the range of validity of the well-known Aharonov-Albert-Vaidman limit.

quant-ph↗

arXiv2008

Theory of a double-dot charge detector

A double quantum dot charge detector, with one dot Coulomb coupled to the electron to be detected and the other modulated by a time-dependent plunger voltage, is analyzed in a minimal model. The signal and noise of the detector are calculated by a standard master equation and MacDonald formula technique. We find a dip in the noise spectrum at the double Rabi frequency of the double dot, defining the bandwidth available for detecting charges in motion.

cond-mat.mes-hall↗

arXiv2007

Simple theory of the measured current through quantum dots

A simple theory of the detected current I(t) flowing through charge qubits -- quantum dots -- is proposed in terms of standard continuous measurement theory. Applied to a double dot, our formalism easily confirms previous results on quantum Zeno effect, driven by growing ammeter performance gamma. Due to the transparent formalism, we can calculate the exact fluctuation spectrum S(omega) of the detected current, containing a significant Lorentzian peak near the Rabi frequency of the double dot.

cond-mat.mes-hall↗

arXiv2004

Gravitational self-localization in quantum measurement

Within Newton-Schrödinger quantum mechanics which allows gravitational self-interaction, it is shown that a no-split no-collapse measurement scenario is possible. A macroscopic pointer moves at low acceleration, controlled by the Ehrenfest-averaged force acting on it. That makes classicality self-sustaining, resolves Everett's paradox, and outlines a way to spontaneous emergence of quantum randomness. Numerical estimates indicate that enhanced short-range gravitational forces are needed for the scenario to work. The scheme fails to explain quantum nonlocality, including two-detector anticorrelations, which points towards the need of a nonlocal modification of the Newton-Schrödinger coupling scheme.

quant-ph↗